Research ArticleDensity Functional Theory of Mild Steel Corrosion inAcidic Media Using Dyes as Inhibitor Adsorption ontoFe(110) from Gas Phase
R S Oguike A M Kolo A M Shibdawa and H A Gyenna
Material Science Research Laboratory Department of Chemistry Abubakar Tafawa Balewa University BauchiPMB 0248 Bauchi Nigeria
Correspondence should be addressed to R S Oguike oguikeraphaelyahoocom
Received 15 January 2013 Accepted 13 March 2013
Academic Editors T Bligaard J G Han and B-T Liu
Copyright copy 2013 R S Oguike et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
Quantum chemical calculations based on density functional theory (DFT)methods were performed on indigo blue (IB) methyleneblue (MB) and crystal violet (CV) molecules as inhibitors for iron corrosion in acid media DFT calculations were performedon the molecular structures to describe electronic parameters which are associated with inhibition efficiency such as the 119864Homovalues minus4981 eV minus4518 eV and minus3872 eV which increased in the order IB gtMB gt CV while 119864LUMO values were minus373 eV minus363 eVand minus287 eV for IB MB and CV respectively Quench molecular dynamics simulations performed at metalvacuum interfacewere applied to find the equilibrium adsorption configurations and calculate the minima interaction energy between inhibitormolecules and iron surface Fe(110) The theoretical order of inhibition efficiency of these dye molecules had a linear relationshipwith experimentally observed inhibition efficiency on iron corrosion in acid media The electronic structures as well as reactivityelucidate parameters which could be practical in designing novel high-efficiency cheap and eco-friendly inhibitors by quantitativestructure-activity relationship (QSAR) method
1 Introduction
A dye is a coloured substance that has an affinity to thesubstrate to which it is being applied Dyes are obtainedfrom animal vegetable or mineral origin and appear to becoloured because they absorb somewavelengths of lightDyesare in our ancient science and effects of dyes are known inthemedical industry textile industry and cellulose industriesand in recent times as corrosion inhibitors of metals bothin acidic and alkaline aggressive environments as redoxindicator in analytical chemistry photosensitizer used tocreate singlet oxygen when exposed to both oxygen and lightto examine RNA or DNA gel electrophoresis and also in anumber of different staining procedures such asWrightrsquos stainand Jennerrsquos stain [1ndash5]The corrosion inhibition characteris-tics of dye are attributed to adsorption of the dye molecule onthemetal surface hence reducing the surface area susceptibleto attacks by the corrosive media This might be by algebraicblocking of active sites on the metal surface or by polarizingthe individual metal atoms to which they are adsorbed
thereby influencing the intrinsic reactivity of the metal [6]Many researchers report that the inhibition effect mainlydepends on some physicochemical and electronic propertiesof the organic inhibitor which relate to its functional groupssteric effects electronic density of donor atoms orbitalcharacter of donating electrons and so on The concept ofassessing the efficiency of a corrosion inhibitor with the helpof computational chemistry is to search for compounds withdesired properties using chemical intuition and experienceinto a mathematically quantified (development of efficientalgorithms) and computerized form [7ndash15]
Quantum chemical methods have already proven to bevery useful in determining the molecular structure aswell as elucidating the electronic structure and reactivitywhich could be practical in designing novel high-efficiencyinhibitors by quantitative structure-activity relationship(QSAR) method [16ndash19] These DFT-based quantum-chemi-cal computational simulations of suitable models have madethis prevailing tool increasingly available to corrosion scien-tists for theoretical investigation of corrosion inhibition
2 ISRN Physical Chemistry
mechanism Such computations have been widely used toanalyze the molecular electronic structures of a wide rangeof adsorption-type inhibitors using a number of quantumchemical descriptors which has given important physi-cal insights on corrosion inhibition mechanisms [20ndash25]Accordingly inhibition efficiency is correlated to the molec-ular and structural parameters that can be obtained throughtheoretical calculations such as chemical selectivity reactiv-ity and charge distribution Other quantum chemical resultsare the frontier molecular orbital HOMO (higher occupiedmolecular orbital) energy the LUMO (lower unoccupiedmolecular orbital) energy chemical potential (120583) and hard-ness (120578) electronegativity (120594) and electron transfer number(Δ119873) among others
The main objective of corrosion inhibitor computationalresearch is to gain insight into the mechanisms by whichinhibitors added to a fluid aggressive environment retard themetal-corrodent interaction Indeed the effectiveness of theoverall process is a function of the metal surface corrosivemediamolecular and electronic structure and concentrationof the inhibitor as well as temperature and other environ-mental considerations [7ndash15 25] Several organic compoundshave been studied by computational simulations but theoret-ical reports on dyes are rather scarce In this present study weare reporting theoretical study on electronic and molecularstructures of 37-bis(Dimethylamino)-phenothiazin-5-iumchloride (Methylene Blue dye (MB)) Tris(4-(dimethylami-no)phenyl) methylium chloride (Crystal Violet dye (CV))and 221015840-Bis(23-dihydro-3-oxoindolyliden) (Indigo Bluedye (IB)) and to determine relationship between molecularstructure of the compounds and inhibition efficiency onmild steel from gas phase This was done by discussing thequantum chemical and structural parameters local reactivityindices such as the Fukui function and the adsorptioncharacteristics of the three dye molecules on the iron surfaceusing quench molecular dynamics simulations Figure 1shows the Lewis structures of the investigated dyes and theiroptimized structures
2 Computations
Quantum chemical methods and molecular modeling tech-niques enable the definition of a large number of molecularquantities characterizing the reactivity shape and bindingproperties of a complete molecule However molecularmechanics simulation is relatively coarser than quantumchemical calculation because the former only carries outtotal atom calculations while the latter executes total elec-tron calculations With molecular mechanics methods theadsorption state of inhibitor monolayer formed onmetal sur-face can be investigated via analysis of interfacial configura-tion interaction betweenmonolayer andmetal surface cohe-sive energy ofmonolayer and so forth [26ndash28]The geometryoptimization process was carried out for the studied dyesMB CV IB and the Fe surface using an iterative processin which the atomic coordinates are adjusted until the totalenergy of the structure corresponds to a local minimum inthe potential energy surface (without imaginary frequency)These were modeled by Materials Studio MS Modeling
version 40 [29] high-quality quantum mechanics computerprogram (available from Accelrys San Diego CA USA)Theelectronic structures of inhibitormolecules and the Fe surfacewere modeled by means of the DFT electronic structureprogram DMol3 using a Mulliken population analysis as wellas a Hirshfeld numerical integration procedure Electronicparameters for the simulation include restricted spin polar-ization using the DNP basis set and local potential Perdewand Wang (PWC) exchange-correlation potential functional[25] To clearly account for all electrons and introduce somerelativistic effects into the core we used all-electron relativis-tic (AER) as the core treatment 2times 2times 1mesh parameters wasset as 119896 point with custom grid for the metal surface and den-sity mixing charge was set to default using Direct Inversion inan Iterative Subspace (DIIS) with 014 eV thermal smearingapplied to the orbital occupation to speed up convergencealongside convergence tolerancemaximum force at 011 eVAMolecular dynamics (MD) simulation of the interactionbetween single inhibitor molecules and the Fe surface wasperformed using Forcite quench molecular dynamics [25] inthe MS Modeling 40 software to sample many different low-energy configurations and identify the low-energy minimaThe Fe crystal was relaxed via minimizing its energy bygeometry optimization and the surface cleaved along the(110) plane The symmetry was increased and its periodicitychanged by constructing a supercell 12 times 10 with a vacuumslab of 20 A height modeled as a representative part of theinterface devoid of arbitrary boundary effects Calculationswere carried out using the COMPASS (condensed-phaseoptimizedmolecular potentials for atomistic simulation stud-ies) force field and the Smart algorithm in a simulationbox 2979 A times 2479 A times 2405 A with periodic boundaryconditions temperaturewas fixed at 303KwithNVE (micro-canonical) ensemble with a time step of 01 fs and simulationtime of 05 psThe system was quenched every 250 steps withconvergence tolerance energy at 10minus3 kcalmol
The local reactivity of the molecules was analyzedthrough an evaluation of the Fukui function as a measure-ment of the chemical reactivity indicative of the reactiveregions that is the nucleophilic and electrophilic behaviourof the molecule Calculations are based on the finitedifference approximations and partitioning of the electrondensity 120588(119903) between atoms in a molecular system [30]
119891+= 119892119896(119873 + 1) minus 119892
119896(119873) (nucleophilic attack) (1)
119891minus= 119892119896(119873) minus 119892
119896(119873 minus 1) (electrophilic attack) (2)
Herein119892119896is the gross charge of atom 119896 in themolecule and119873
is the number of electrons The condensed Fukui function islocal reactivity descriptor and can be used only for comparingreactive atomic centres within the same molecule The bind-ing energy (119864Bind) of iron surface with inhibitor moleculeswas calculated according to the following equation [11]
119864Bind = 119864Fe-inhibitor minus (119864Fe + 119864Inh) (3)
Herein 119864Fe-inh is the total energy of the Fe crystal togetherwith the adsorbed inhibitor molecule (119864Fe and 119864Inh) is thetotal energy of the iron crystal and free inhibitor molecule
ISRN Physical Chemistry 3
Clminus
Clminus
H3C
H
H
O
O
N
N
N
N
N
NN
N+
CH3
CH3
CH3
S
Methylene blue dye
Crystal violet dye
Indigo blue dye
(a) (b) (c)
+
Figure 1 (a) Lewis structures of the investigated dyes (b) names (c) geometry-optimized structures [C gray H white N blue O red Clgreen]
respectively The number of electrons transferred (Δ119873)from the inhibitor molecule to the metallic atom was alsocalculated using the following equation [30]
Δ119873 =120594Fe minus 120594Inh
2 (120578Fe + 120578Inh) (4)
Herein 120594Fe and 120594Inh represent the absolute electronegativityof iron and the inhibitor molecule respectively 120578Fe and 120578Inhrepresent the absolute hardness of iron and the inhibitormolecule
3 Results and Discussion
31 Molecular Reactivity Themolecular reactivity was inves-tigated via analysis of the frontiermolecular orbital and Fukuifunctions The highest occupied molecular orbital (HOMO)and the lowest unoccupied molecular orbital (LUMO) of thedye molecules are showed in Figure 2 while the Fukui indicesand electron density are shown in Figure 6 It could be seenthat the HOMO orbitals of IB dye molecule are generallydelocalized around the double bond and heteroatoms Thiskind of orbital distribution could be ascribed to the highelectron density around the centre of the molecule due tothe p-120587 conjugation effect As a result the centre of themoleculewould be preferentially adsorbed ontometal surfaceas active sites During adsorption the inhibitor molecule
could donate electrons to form coordinate bond with unoc-cupied d-orbitals of metal accept electrons from d-orbitalof metal and form back-donating bonds as well High119864HOMO facilitates adsorption (inhibition) by influencing thetransport process through the adsorbed layer whereas low-lying LUMO induces a backdonation of charge from themetalto themolecule [31]We found that CV had its HOMOorbitalchiefly on the Cl29 and C9=C10 double bond had a littleeffect as also confirmed inMulliken atomic charges (Table 1)Analyzing the HOMO orbital of MB we observed it to bepredominant at Cl21 and S10ndashC11 had contributions to theelectron density These could possibly mean a coordinatebond during adsorption to protect anodic areas and reducethe inherent reactivity of the metal at the sites where theyare attached It is considered that MB and CV are preferablyadsorbed on the iron surface by electron acceptance that ischemisorptions by backdonation rather than by donation ofp-electrons to the metal We examined these HOMO orbitalsand found that susceptibility of the molecules towards attackby electrophiles and their tenacity to donate electrons arein the following order IB gt MB gt CV with 119864HOMO valuesminus4981 eV minus4518 eV and minus3872 eV respectively Figure 3shows a linear relationship between the HOMO energy levelsand the experimental corrosion inhibition efficiency of thedyes as iron corrosion inhibitor
Similarly the LUMO orbital of IB dye molecule was prin-cipally found around aldehyde function and the amines
4 ISRN Physical Chemistry
HOMO LUMO
(a) (b)
Methylene blue
Crystal violet
Indigo blue
Figure 2 The frontier molecular orbital density distributions of the three dyes HOMO (a) LUMO (b)
Table 1 Condensed Fukui indices (Mulliken analyses) of IB MBand CV in gas phase
consequently these are favorite sites for interaction with themetal It could also be seen in Figure 2 that LUMO orbitalof MB and CV is delocalized but comparing the net atomic
Figure 3 Correlation of HOMO energy with percent inhibitionefficiency of dye molecules
charges of their Cl atom (Table 1) it is found that MB hasa stronger interaction with iron and has a better corrosioninhibition effect on iron than CV According to the frontiermolecular orbital theory low values of 119864LUMO should alsoindicate a strong tendency of electron-accepting abilitiesof the molecule and as seen in Figure 3 in the order of
ISRN Physical Chemistry 5
Table 2 119864HOMO 119864LUMO chemical potential (120583) global chemicalhardness (120578) number of electrons transferred (Δ119873) and inhibitionefficiency (IE) for the three dyes molecules in gas phase
IB gtMB gt CV which is in good agreement with inhibitionefficiency (IE ) of the experimental results see [28 29 32]
In addition inhibition efficiency is closely related tothe reactivity of individual molecular orbital contributionsto the response of the whole molecular continuum Thefully optimized geometries obtained from the calculationsof condense Fukui functions are shown in Figure 6 theresults for Fukui function (Table 1) support the trend of thefrontier molecular orbital observed for the studied moleculesindicating the zones through which the molecule will beadsorbed onto the Fe(110) surfaceThe119891minusmeasures reactivitywith respect to electrophilic attack or the characteristic ofthemolecule to donate electrons while119891+measure reactivitywhich relates to nucleophilic attack or the propensity of themolecule to accept electrons [30] The highest 119891minus for IB isat O19 and O20 indicating the zone for transfer of electronas seen in the electron density cloud (Figure 6) while thehighest 119891+ is associated with the same O19 and O20 showingthe ability for a backdonation through the same zone whichmight result in chemisorption Moreover the highest 119891minus forMB and CV is related to the Cl atom but the value forMB is higher than CV and might readily form adsorption-active centers validating that MB has a higher iron corrosioninhibition efficiency than CV Calculated results in Table 1show that the highest 119891+ is also at the Cl atom for MB andCV confirming the favorite sites for adsorption
Furthermore the global parameters including chemicalpotential (120583) and hardness (120578) electronegativity (120594) and thenumber of electrons transferred during the adsorption (Δ119873)were also calculated and the results are shown in Table 2Since the capability of donating electron of a molecule canbe determined by the chemical potential and hardness theless negative these values are the higher is the capabilityof donating electrons [30] So from Table 2 it could beseen that the order of electron-donating capability of thedye molecules is IB gt MB gt CV On the other handas for the electronegativity which denotes the electron-accepting capability of a molecule it could also be deducedfrom Table 2 that the electron-accepting capability of thesemolecules follows the similar trendGenerally the same orderof donating capability and accepting electrons of the threeinhibitor molecules indicates that the inhibition efficiencywould follow the same order of IB gt MB gt CV which is inaccordance with the analysis of frontier molecular orbitalThe relationship between corrosion inhibition efficiency andthe number of electrons transferred for these three dyes isplotted in Figure 4 As clearly seen in the figure there is a lin-earity between inhibition efficiency and number of electrons
Table 3 Binding energy interaction energy and total energy (mini-mum) for the molecular dynamic simulations
119864Bind (eV) 119864Interaction (eV) Total energy (kcalmol)IB 12137 minus12137 minus4914MB 5962 minus5962 minus1683CV 3997 minus3997 minus8644
CV
MB
IB
505
58
655
73
IE (
)
205 255 305 355Δ119873 (e)
Figure 4 Correlation of number of electrons transferred withpercent inhibition efficiency of dye molecules
transferred In Figure 5 inhibition efficiency is plotted againstthe chemical potential showing the inhibition efficiencyincreased with decrease in the chemical potential energy
Table 2 provides calculated quantum chemical parame-ters using (4) number of electrons transferred (Δ119873) Valuesof 120594 and 120578 were calculated by using the values of 119868 (minus119864HOMO)and 119860 (minus119864
119871119880119872119874) obtained from quantum chemical calcula-
tions In order to calculate Δ119873 a theoretical value for theelectronegativity of bulk iron was used 120594Fe asymp 7 eV and aglobal hardness of 120578Fe asymp 0 by assuming that for a metallicbulk 119868 = 119860 because they are softer than the neutral metallicatoms [17] According to Lukovits ifΔ119873 lt 36 the inhibitionefficiency increased with increasing electron-donating abilityat the metal surface [6] It can be inferred from the calculatedresults that inhibitors investigated in this study were donorsof electrons and the iron surface was the acceptor
32 Molecular Dynamics To quantitatively evaluate themostsuitable adsorptionmodes between eachmolecule and the Fesurface the adsorption energy (119864Bind) was calculated usingthe relationship in (3) In each case the potential energieswerecalculated by averaging the energies of the five structuresof the lowest energy [25] The obtained values are shown inTable 3 we discovered that IB exhibited the highest bindingenergy during the simulation process and the order of 119864Bindis IB gtMB gt CV in accordance with experimental inhibitionefficiency (IE ) The high values of the binding energy forthe dye molecules could be as a result of dissociative adsorp-tion which is favourable to crack the intramolecular bond ofthe adsorbate molecule This is an indication of chemisorp-tion which contrasts the experimentally found physisorptionfor the dye molecules From the high values of 119864bind obtainedfor the three dye molecules only a probable chemisorptionis expected which affirms the observed electron acceptanceand backdonation of electrons at the same site The very highbinding energy of IB could be attributed to its O
Figure 5 Correlation of chemical potential with percent inhibition efficiency of dye molecules
Methylene blue
Crystal violet
Indigo blue
(a) (b)
Figure 6 The Fukui indices density distributions of the three dyes 119891minus (a) 119891+ (b)
which dissociate on adsorption It can also be seen fromFigure 7 that there is a linear correlation between the bindingenergy and inhibition efficiency indicating that the higher thebinding energy the higher the inhibition efficiency Table 3shows the values obtained for binding energy interactionenergy and total energy It can be seen that the trend of 119864Bindsupports experimental results for the three dye molecules
The high inhibition efficiency of IB could be attributedto a number of lone pair electrons on O atoms as well as
the N atoms providing electrons to the unfilled 3d orbitalsof iron surface thereby forming a protective layer Suchprotective film may act as a steric barrier that hinders thereactive ionsspecies from the aggressive environment fromcoming into contact with the metal surface thus slowingdown corrosion process To determine the global minimumvarious different low-energy minima were sampled Figures8(a)ndash8(c) show snapshots of the side view and top view(inset) of the lowest energy adsorption configurations for
ISRN Physical Chemistry 7
CVMB
IB
505
58
655
73
38 63 88 113IE
()
119864binding (eV)
Figure 7 Correlation of binding energy with percent inhibition efficiency of dye molecules
CV
(a)
MB
(b)
IB
(c)
Figure 8 Representative snapshots of (a) CV (b) MB and (c) IB adsorbed on Fe(110) Inset images show the on-top views emphasizing themolecular backbone aligning with vacant sites on the fcc lattice atop the metal surface
single inhibitor molecules studied on the Fe(110) surfacefrom our simulations respectively Close inspection of theon-top view of adsorbed single molecule on Fe(110) revealsa very clear fashion in the adsorption configuration of allthe molecules wherein polarizable atoms (N O S) in themolecular backbone align with vacant sites on the fcc latticeatop the metal surface and virtually avoid contact with the Featoms on the surface plane
4 Conclusion
In this study the three dye molecules were the donators ofelectrons and the iron surface was the acceptor The com-pounds were adsorbed to themetal surface and hence formedinhibitive adsorption layer against the corrosive media Theinhibition efficiency is in order of IB gtMB gt CV which sub-stantiates the experimental results The research by quantum
8 ISRN Physical Chemistry
chemistry revealed that the reactive sites of dye moleculesformed coordinate and back-donating bonds with atoms onmetal surface Further comparison revealed that the zones forelectron donation were the same as the zones for acceptingelectrons which could indicate a probable chemisorptionIB had the highest inhibition efficiency because it hadthe greatest ability of offering electrons and CV had thelowest inhibition efficiency A linear correlationwas observedbetween inhibition efficiencies and the inhibitor chemicalpotential as well as the extent of charge transfer to the metalsFurthermore the distribution of electronic density shows thatthe dyemolecules hadmany negatively charged active centerswith exception of IB The electron density was found to bepositively correlated with its linear structure which couldbe the effect for increase in inhibition efficiency The zonescontaining N O and S atoms are the most possible sites foradsorption of the metal iron surface This study suggests thattheoretical method might be an effective approach to assessthe inhibition performance of new inhibitors
References
[1] A D Becke ldquoDensity-functional exchange-energy approxima-tion with correct asymptotic behaviorrdquo Physical Review A vol38 pp 3098ndash3100 1988
[2] I B Obot and N O Obi-Egbedi ldquoTheoretical study of ben-zimidazole and its derivatives and their potential activity ascorrosion inhibitorsrdquo Corrosion Science vol 52 no 2 pp 657ndash660 2010
[3] M Sahin G Gece F Karcı and S Bilgic ldquoExperimental andtheoretical study of the effect of some heterocyclic compoundson the corrosion of low carbon steel in 35 NaCl mediumrdquoJournal of Applied Electrochemistry vol 38 no 6 pp 809ndash8152008
[4] D X Wang and H M Xiao ldquoQuantum chemical calculationon chemical adsorption energy of imidazolines and Fe atomrdquoJournal of Molecular Science vol 16 pp 102ndash105 2000
[5] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[6] E Jamalizadeh S M A Hosseini and A H Jafari ldquoQuantumchemical studies on corrosion inhibition of some lactones onmild steel in acid mediardquo Corrosion Science vol 51 no 6 pp1428ndash1435 2009
[7] M Karelson V S Lobanov and A R Katritzky ldquoQuantum-chemical descriptors in QSARQSPR studiesrdquo ChemicalReviews vol 96 no 3 pp 1027ndash1043 1996
[8] M A Amin K F Khaled QMohsen andH A Arida ldquoA studyof the inhibition of iron corrosion in HCl solutions by someamino acidsrdquo Corrosion Science vol 52 pp 1684ndash1695 2010
[9] G Gece S Bilgic and O Turksen ldquoQuantum chemical studiesof some amino acids on the corrosion of cobalt in sulfuric acidsolutionrdquo Materials and Corrosion vol 61 no 2 pp 141ndash1462010
[10] C Gruber and V Buss ldquoQuantum-mechanically calculatedproperties for the development of quantitative structure-activi-ty relationships (QSARrsquoS) pKA-values of phenols and aromaticand aliphatic carboxylic acidsrdquo Chemosphere vol 19 no 10-11pp 1595ndash1609 1989
[11] J Fu S Li Y Wang L Cao and L Lu ldquoComputational andelectrochemical studies of some amino acid compounds as cor-rosion inhibitors for mild steel in hydrochloric acid solutionrdquoJournal of Materials Science vol 45 pp 6255ndash6265 2010
[12] J Fang and J Li ldquoQuantum chemistry study on the relationshipbetween molecular structure and corrosion inhibition effi-ciency of amidesrdquo Journal ofMolecular Structure THEOCHEMvol 593 pp 179ndash185 2002
[13] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface by sub-stituted uracilsrdquo Applied Surface Science vol 255 no 5 part 1pp 2433ndash2441 2008
[14] A Yurt G Bereket and C Ogretir ldquoQuantum chemical studieson inhibition effect of amino acids and hydroxy carboxylic acidson pitting corrosion of aluminium alloy 7075 in NaCl solutionrdquoJournal of Molecular Structure THEOCHEM vol 725 no 1ndash3pp 215ndash221 2005
[15] G Gece ldquoThe use of quantum chemical methods in corrosioninhibitor studiesrdquo Corrosion Science vol 50 no 11 pp 2981ndash2992 2008
[16] G Zhang and C B Musgrave ldquoComparison of DFT methodsfor molecular orbital eigenvalue calculationsrdquo Journal of Physi-cal Chemistry A vol 111 no 8 pp 1554ndash1561 2007
[17] G Bereket E Hur and C Ogretir ldquoQuantum chemical studieson some imidazole derivatives as corrosion inhibitors for iron inacidic mediumrdquo Journal of Molecular Structure THEOCHEMvol 578 pp 79ndash88 2002
[18] J Vosta and J Eliasek ldquoStudy on corrosion inhibition fromaspect of quantum chemistryrdquo Corrosion Science vol 11 pp223ndash229 1971
[19] E E Oguzie Y Li S G Wang and F Wanga ldquoUnderstandingcorrosion inhibition mechanisms-experimental and theoreticalapproachrdquo RSC Advances vol 1 pp 866ndash873 2011
[20] S Xia M Qiu L Yu F Liu and H Zhao ldquoMolecular dynamicsand density functional theory study on relationship betweenstructure of imidazoline derivatives and inhibition perform-ancerdquo Corrosion Science vol 50 no 7 pp 2021ndash2029 2008
[21] F Kandemirli and S Sagdinc ldquoTheoretical study of corrosioninhibition of amides and thiosemicarbazonesrdquo Corrosion Sci-ence vol 49 no 5 pp 2118ndash2130 2007
[22] C D Taylor R G Kelly and M Neurock ldquoA first-principlesanalysis of the chemisorption of hydroxide on copper underelectrochemical conditions a probe of the electronic interac-tions that control chemisorption at the electrochemical inter-facerdquo Journal of Electroanalytical Chemistry vol 607 no 1-2 pp167ndash174 2007
[23] D Wanga S Lia Y Yinga M Wanga H Xiaob and Z CheldquoTheoretical and experimental studies of structure and inhi-bition efficiency of imidazoline derivativesrdquo Corrosion Sciencevol 41 no 10 pp 1911ndash1919 1999
[24] J Bartley N Huynh S E Bottle H Flitt T Notoya and D PSchweinsberg ldquoComputer simulation of the corrosion inhibi-tion of copper in acidic solution by alkyl esters of 5-carboxyben-zotriazolerdquo Corrosion Science vol 45 no 1 pp 81ndash96 2003
[25] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquo Journal of Physical Chemistry C vol 113 no 19pp 8420ndash8429 2009
[26] L M Rodrıguez-Valdez A Martınez-Villafane and D Gloss-man-Mitnik ldquoComputational simulation of the molecularstructure and properties of heterocyclic organic compounds
ISRN Physical Chemistry 9
with possible corrosion inhibition propertiesrdquo Journal of Molec-ular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash70 2005
[27] A Lesar and I Milosev ldquoDensity functional study of the corro-sion inhibition properties of 124-triazole and its amino deriva-tivesrdquo Chemical Physics Letters vol 483 no 4ndash6 pp 198ndash2032009
[28] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[29] E E Oguzie ldquoCorrosion inhibition ofmild steel in hydrochloricacid solution by methylene blue dyerdquo Materials Letters vol 59no 8-9 pp 1076ndash1079 2005
[30] W Yang andR Parr ldquoHardness softness and the fukui functionin the electronic theory of metals and catalysisrdquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 82 pp 6723ndash6726 1985
[31] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2 M sulphuric acid solu-tion by methylene blue dyerdquo Materials Chemistry and Physicsvol 89 no 2-3 pp 305ndash311 2005
[32] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
mechanism Such computations have been widely used toanalyze the molecular electronic structures of a wide rangeof adsorption-type inhibitors using a number of quantumchemical descriptors which has given important physi-cal insights on corrosion inhibition mechanisms [20ndash25]Accordingly inhibition efficiency is correlated to the molec-ular and structural parameters that can be obtained throughtheoretical calculations such as chemical selectivity reactiv-ity and charge distribution Other quantum chemical resultsare the frontier molecular orbital HOMO (higher occupiedmolecular orbital) energy the LUMO (lower unoccupiedmolecular orbital) energy chemical potential (120583) and hard-ness (120578) electronegativity (120594) and electron transfer number(Δ119873) among others
The main objective of corrosion inhibitor computationalresearch is to gain insight into the mechanisms by whichinhibitors added to a fluid aggressive environment retard themetal-corrodent interaction Indeed the effectiveness of theoverall process is a function of the metal surface corrosivemediamolecular and electronic structure and concentrationof the inhibitor as well as temperature and other environ-mental considerations [7ndash15 25] Several organic compoundshave been studied by computational simulations but theoret-ical reports on dyes are rather scarce In this present study weare reporting theoretical study on electronic and molecularstructures of 37-bis(Dimethylamino)-phenothiazin-5-iumchloride (Methylene Blue dye (MB)) Tris(4-(dimethylami-no)phenyl) methylium chloride (Crystal Violet dye (CV))and 221015840-Bis(23-dihydro-3-oxoindolyliden) (Indigo Bluedye (IB)) and to determine relationship between molecularstructure of the compounds and inhibition efficiency onmild steel from gas phase This was done by discussing thequantum chemical and structural parameters local reactivityindices such as the Fukui function and the adsorptioncharacteristics of the three dye molecules on the iron surfaceusing quench molecular dynamics simulations Figure 1shows the Lewis structures of the investigated dyes and theiroptimized structures
2 Computations
Quantum chemical methods and molecular modeling tech-niques enable the definition of a large number of molecularquantities characterizing the reactivity shape and bindingproperties of a complete molecule However molecularmechanics simulation is relatively coarser than quantumchemical calculation because the former only carries outtotal atom calculations while the latter executes total elec-tron calculations With molecular mechanics methods theadsorption state of inhibitor monolayer formed onmetal sur-face can be investigated via analysis of interfacial configura-tion interaction betweenmonolayer andmetal surface cohe-sive energy ofmonolayer and so forth [26ndash28]The geometryoptimization process was carried out for the studied dyesMB CV IB and the Fe surface using an iterative processin which the atomic coordinates are adjusted until the totalenergy of the structure corresponds to a local minimum inthe potential energy surface (without imaginary frequency)These were modeled by Materials Studio MS Modeling
version 40 [29] high-quality quantum mechanics computerprogram (available from Accelrys San Diego CA USA)Theelectronic structures of inhibitormolecules and the Fe surfacewere modeled by means of the DFT electronic structureprogram DMol3 using a Mulliken population analysis as wellas a Hirshfeld numerical integration procedure Electronicparameters for the simulation include restricted spin polar-ization using the DNP basis set and local potential Perdewand Wang (PWC) exchange-correlation potential functional[25] To clearly account for all electrons and introduce somerelativistic effects into the core we used all-electron relativis-tic (AER) as the core treatment 2times 2times 1mesh parameters wasset as 119896 point with custom grid for the metal surface and den-sity mixing charge was set to default using Direct Inversion inan Iterative Subspace (DIIS) with 014 eV thermal smearingapplied to the orbital occupation to speed up convergencealongside convergence tolerancemaximum force at 011 eVAMolecular dynamics (MD) simulation of the interactionbetween single inhibitor molecules and the Fe surface wasperformed using Forcite quench molecular dynamics [25] inthe MS Modeling 40 software to sample many different low-energy configurations and identify the low-energy minimaThe Fe crystal was relaxed via minimizing its energy bygeometry optimization and the surface cleaved along the(110) plane The symmetry was increased and its periodicitychanged by constructing a supercell 12 times 10 with a vacuumslab of 20 A height modeled as a representative part of theinterface devoid of arbitrary boundary effects Calculationswere carried out using the COMPASS (condensed-phaseoptimizedmolecular potentials for atomistic simulation stud-ies) force field and the Smart algorithm in a simulationbox 2979 A times 2479 A times 2405 A with periodic boundaryconditions temperaturewas fixed at 303KwithNVE (micro-canonical) ensemble with a time step of 01 fs and simulationtime of 05 psThe system was quenched every 250 steps withconvergence tolerance energy at 10minus3 kcalmol
The local reactivity of the molecules was analyzedthrough an evaluation of the Fukui function as a measure-ment of the chemical reactivity indicative of the reactiveregions that is the nucleophilic and electrophilic behaviourof the molecule Calculations are based on the finitedifference approximations and partitioning of the electrondensity 120588(119903) between atoms in a molecular system [30]
119891+= 119892119896(119873 + 1) minus 119892
119896(119873) (nucleophilic attack) (1)
119891minus= 119892119896(119873) minus 119892
119896(119873 minus 1) (electrophilic attack) (2)
Herein119892119896is the gross charge of atom 119896 in themolecule and119873
is the number of electrons The condensed Fukui function islocal reactivity descriptor and can be used only for comparingreactive atomic centres within the same molecule The bind-ing energy (119864Bind) of iron surface with inhibitor moleculeswas calculated according to the following equation [11]
119864Bind = 119864Fe-inhibitor minus (119864Fe + 119864Inh) (3)
Herein 119864Fe-inh is the total energy of the Fe crystal togetherwith the adsorbed inhibitor molecule (119864Fe and 119864Inh) is thetotal energy of the iron crystal and free inhibitor molecule
ISRN Physical Chemistry 3
Clminus
Clminus
H3C
H
H
O
O
N
N
N
N
N
NN
N+
CH3
CH3
CH3
S
Methylene blue dye
Crystal violet dye
Indigo blue dye
(a) (b) (c)
+
Figure 1 (a) Lewis structures of the investigated dyes (b) names (c) geometry-optimized structures [C gray H white N blue O red Clgreen]
respectively The number of electrons transferred (Δ119873)from the inhibitor molecule to the metallic atom was alsocalculated using the following equation [30]
Δ119873 =120594Fe minus 120594Inh
2 (120578Fe + 120578Inh) (4)
Herein 120594Fe and 120594Inh represent the absolute electronegativityof iron and the inhibitor molecule respectively 120578Fe and 120578Inhrepresent the absolute hardness of iron and the inhibitormolecule
3 Results and Discussion
31 Molecular Reactivity Themolecular reactivity was inves-tigated via analysis of the frontiermolecular orbital and Fukuifunctions The highest occupied molecular orbital (HOMO)and the lowest unoccupied molecular orbital (LUMO) of thedye molecules are showed in Figure 2 while the Fukui indicesand electron density are shown in Figure 6 It could be seenthat the HOMO orbitals of IB dye molecule are generallydelocalized around the double bond and heteroatoms Thiskind of orbital distribution could be ascribed to the highelectron density around the centre of the molecule due tothe p-120587 conjugation effect As a result the centre of themoleculewould be preferentially adsorbed ontometal surfaceas active sites During adsorption the inhibitor molecule
could donate electrons to form coordinate bond with unoc-cupied d-orbitals of metal accept electrons from d-orbitalof metal and form back-donating bonds as well High119864HOMO facilitates adsorption (inhibition) by influencing thetransport process through the adsorbed layer whereas low-lying LUMO induces a backdonation of charge from themetalto themolecule [31]We found that CV had its HOMOorbitalchiefly on the Cl29 and C9=C10 double bond had a littleeffect as also confirmed inMulliken atomic charges (Table 1)Analyzing the HOMO orbital of MB we observed it to bepredominant at Cl21 and S10ndashC11 had contributions to theelectron density These could possibly mean a coordinatebond during adsorption to protect anodic areas and reducethe inherent reactivity of the metal at the sites where theyare attached It is considered that MB and CV are preferablyadsorbed on the iron surface by electron acceptance that ischemisorptions by backdonation rather than by donation ofp-electrons to the metal We examined these HOMO orbitalsand found that susceptibility of the molecules towards attackby electrophiles and their tenacity to donate electrons arein the following order IB gt MB gt CV with 119864HOMO valuesminus4981 eV minus4518 eV and minus3872 eV respectively Figure 3shows a linear relationship between the HOMO energy levelsand the experimental corrosion inhibition efficiency of thedyes as iron corrosion inhibitor
Similarly the LUMO orbital of IB dye molecule was prin-cipally found around aldehyde function and the amines
4 ISRN Physical Chemistry
HOMO LUMO
(a) (b)
Methylene blue
Crystal violet
Indigo blue
Figure 2 The frontier molecular orbital density distributions of the three dyes HOMO (a) LUMO (b)
Table 1 Condensed Fukui indices (Mulliken analyses) of IB MBand CV in gas phase
consequently these are favorite sites for interaction with themetal It could also be seen in Figure 2 that LUMO orbitalof MB and CV is delocalized but comparing the net atomic
Figure 3 Correlation of HOMO energy with percent inhibitionefficiency of dye molecules
charges of their Cl atom (Table 1) it is found that MB hasa stronger interaction with iron and has a better corrosioninhibition effect on iron than CV According to the frontiermolecular orbital theory low values of 119864LUMO should alsoindicate a strong tendency of electron-accepting abilitiesof the molecule and as seen in Figure 3 in the order of
ISRN Physical Chemistry 5
Table 2 119864HOMO 119864LUMO chemical potential (120583) global chemicalhardness (120578) number of electrons transferred (Δ119873) and inhibitionefficiency (IE) for the three dyes molecules in gas phase
IB gtMB gt CV which is in good agreement with inhibitionefficiency (IE ) of the experimental results see [28 29 32]
In addition inhibition efficiency is closely related tothe reactivity of individual molecular orbital contributionsto the response of the whole molecular continuum Thefully optimized geometries obtained from the calculationsof condense Fukui functions are shown in Figure 6 theresults for Fukui function (Table 1) support the trend of thefrontier molecular orbital observed for the studied moleculesindicating the zones through which the molecule will beadsorbed onto the Fe(110) surfaceThe119891minusmeasures reactivitywith respect to electrophilic attack or the characteristic ofthemolecule to donate electrons while119891+measure reactivitywhich relates to nucleophilic attack or the propensity of themolecule to accept electrons [30] The highest 119891minus for IB isat O19 and O20 indicating the zone for transfer of electronas seen in the electron density cloud (Figure 6) while thehighest 119891+ is associated with the same O19 and O20 showingthe ability for a backdonation through the same zone whichmight result in chemisorption Moreover the highest 119891minus forMB and CV is related to the Cl atom but the value forMB is higher than CV and might readily form adsorption-active centers validating that MB has a higher iron corrosioninhibition efficiency than CV Calculated results in Table 1show that the highest 119891+ is also at the Cl atom for MB andCV confirming the favorite sites for adsorption
Furthermore the global parameters including chemicalpotential (120583) and hardness (120578) electronegativity (120594) and thenumber of electrons transferred during the adsorption (Δ119873)were also calculated and the results are shown in Table 2Since the capability of donating electron of a molecule canbe determined by the chemical potential and hardness theless negative these values are the higher is the capabilityof donating electrons [30] So from Table 2 it could beseen that the order of electron-donating capability of thedye molecules is IB gt MB gt CV On the other handas for the electronegativity which denotes the electron-accepting capability of a molecule it could also be deducedfrom Table 2 that the electron-accepting capability of thesemolecules follows the similar trendGenerally the same orderof donating capability and accepting electrons of the threeinhibitor molecules indicates that the inhibition efficiencywould follow the same order of IB gt MB gt CV which is inaccordance with the analysis of frontier molecular orbitalThe relationship between corrosion inhibition efficiency andthe number of electrons transferred for these three dyes isplotted in Figure 4 As clearly seen in the figure there is a lin-earity between inhibition efficiency and number of electrons
Table 3 Binding energy interaction energy and total energy (mini-mum) for the molecular dynamic simulations
119864Bind (eV) 119864Interaction (eV) Total energy (kcalmol)IB 12137 minus12137 minus4914MB 5962 minus5962 minus1683CV 3997 minus3997 minus8644
CV
MB
IB
505
58
655
73
IE (
)
205 255 305 355Δ119873 (e)
Figure 4 Correlation of number of electrons transferred withpercent inhibition efficiency of dye molecules
transferred In Figure 5 inhibition efficiency is plotted againstthe chemical potential showing the inhibition efficiencyincreased with decrease in the chemical potential energy
Table 2 provides calculated quantum chemical parame-ters using (4) number of electrons transferred (Δ119873) Valuesof 120594 and 120578 were calculated by using the values of 119868 (minus119864HOMO)and 119860 (minus119864
119871119880119872119874) obtained from quantum chemical calcula-
tions In order to calculate Δ119873 a theoretical value for theelectronegativity of bulk iron was used 120594Fe asymp 7 eV and aglobal hardness of 120578Fe asymp 0 by assuming that for a metallicbulk 119868 = 119860 because they are softer than the neutral metallicatoms [17] According to Lukovits ifΔ119873 lt 36 the inhibitionefficiency increased with increasing electron-donating abilityat the metal surface [6] It can be inferred from the calculatedresults that inhibitors investigated in this study were donorsof electrons and the iron surface was the acceptor
32 Molecular Dynamics To quantitatively evaluate themostsuitable adsorptionmodes between eachmolecule and the Fesurface the adsorption energy (119864Bind) was calculated usingthe relationship in (3) In each case the potential energieswerecalculated by averaging the energies of the five structuresof the lowest energy [25] The obtained values are shown inTable 3 we discovered that IB exhibited the highest bindingenergy during the simulation process and the order of 119864Bindis IB gtMB gt CV in accordance with experimental inhibitionefficiency (IE ) The high values of the binding energy forthe dye molecules could be as a result of dissociative adsorp-tion which is favourable to crack the intramolecular bond ofthe adsorbate molecule This is an indication of chemisorp-tion which contrasts the experimentally found physisorptionfor the dye molecules From the high values of 119864bind obtainedfor the three dye molecules only a probable chemisorptionis expected which affirms the observed electron acceptanceand backdonation of electrons at the same site The very highbinding energy of IB could be attributed to its O
Figure 5 Correlation of chemical potential with percent inhibition efficiency of dye molecules
Methylene blue
Crystal violet
Indigo blue
(a) (b)
Figure 6 The Fukui indices density distributions of the three dyes 119891minus (a) 119891+ (b)
which dissociate on adsorption It can also be seen fromFigure 7 that there is a linear correlation between the bindingenergy and inhibition efficiency indicating that the higher thebinding energy the higher the inhibition efficiency Table 3shows the values obtained for binding energy interactionenergy and total energy It can be seen that the trend of 119864Bindsupports experimental results for the three dye molecules
The high inhibition efficiency of IB could be attributedto a number of lone pair electrons on O atoms as well as
the N atoms providing electrons to the unfilled 3d orbitalsof iron surface thereby forming a protective layer Suchprotective film may act as a steric barrier that hinders thereactive ionsspecies from the aggressive environment fromcoming into contact with the metal surface thus slowingdown corrosion process To determine the global minimumvarious different low-energy minima were sampled Figures8(a)ndash8(c) show snapshots of the side view and top view(inset) of the lowest energy adsorption configurations for
ISRN Physical Chemistry 7
CVMB
IB
505
58
655
73
38 63 88 113IE
()
119864binding (eV)
Figure 7 Correlation of binding energy with percent inhibition efficiency of dye molecules
CV
(a)
MB
(b)
IB
(c)
Figure 8 Representative snapshots of (a) CV (b) MB and (c) IB adsorbed on Fe(110) Inset images show the on-top views emphasizing themolecular backbone aligning with vacant sites on the fcc lattice atop the metal surface
single inhibitor molecules studied on the Fe(110) surfacefrom our simulations respectively Close inspection of theon-top view of adsorbed single molecule on Fe(110) revealsa very clear fashion in the adsorption configuration of allthe molecules wherein polarizable atoms (N O S) in themolecular backbone align with vacant sites on the fcc latticeatop the metal surface and virtually avoid contact with the Featoms on the surface plane
4 Conclusion
In this study the three dye molecules were the donators ofelectrons and the iron surface was the acceptor The com-pounds were adsorbed to themetal surface and hence formedinhibitive adsorption layer against the corrosive media Theinhibition efficiency is in order of IB gtMB gt CV which sub-stantiates the experimental results The research by quantum
8 ISRN Physical Chemistry
chemistry revealed that the reactive sites of dye moleculesformed coordinate and back-donating bonds with atoms onmetal surface Further comparison revealed that the zones forelectron donation were the same as the zones for acceptingelectrons which could indicate a probable chemisorptionIB had the highest inhibition efficiency because it hadthe greatest ability of offering electrons and CV had thelowest inhibition efficiency A linear correlationwas observedbetween inhibition efficiencies and the inhibitor chemicalpotential as well as the extent of charge transfer to the metalsFurthermore the distribution of electronic density shows thatthe dyemolecules hadmany negatively charged active centerswith exception of IB The electron density was found to bepositively correlated with its linear structure which couldbe the effect for increase in inhibition efficiency The zonescontaining N O and S atoms are the most possible sites foradsorption of the metal iron surface This study suggests thattheoretical method might be an effective approach to assessthe inhibition performance of new inhibitors
References
[1] A D Becke ldquoDensity-functional exchange-energy approxima-tion with correct asymptotic behaviorrdquo Physical Review A vol38 pp 3098ndash3100 1988
[2] I B Obot and N O Obi-Egbedi ldquoTheoretical study of ben-zimidazole and its derivatives and their potential activity ascorrosion inhibitorsrdquo Corrosion Science vol 52 no 2 pp 657ndash660 2010
[3] M Sahin G Gece F Karcı and S Bilgic ldquoExperimental andtheoretical study of the effect of some heterocyclic compoundson the corrosion of low carbon steel in 35 NaCl mediumrdquoJournal of Applied Electrochemistry vol 38 no 6 pp 809ndash8152008
[4] D X Wang and H M Xiao ldquoQuantum chemical calculationon chemical adsorption energy of imidazolines and Fe atomrdquoJournal of Molecular Science vol 16 pp 102ndash105 2000
[5] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[6] E Jamalizadeh S M A Hosseini and A H Jafari ldquoQuantumchemical studies on corrosion inhibition of some lactones onmild steel in acid mediardquo Corrosion Science vol 51 no 6 pp1428ndash1435 2009
[7] M Karelson V S Lobanov and A R Katritzky ldquoQuantum-chemical descriptors in QSARQSPR studiesrdquo ChemicalReviews vol 96 no 3 pp 1027ndash1043 1996
[8] M A Amin K F Khaled QMohsen andH A Arida ldquoA studyof the inhibition of iron corrosion in HCl solutions by someamino acidsrdquo Corrosion Science vol 52 pp 1684ndash1695 2010
[9] G Gece S Bilgic and O Turksen ldquoQuantum chemical studiesof some amino acids on the corrosion of cobalt in sulfuric acidsolutionrdquo Materials and Corrosion vol 61 no 2 pp 141ndash1462010
[10] C Gruber and V Buss ldquoQuantum-mechanically calculatedproperties for the development of quantitative structure-activi-ty relationships (QSARrsquoS) pKA-values of phenols and aromaticand aliphatic carboxylic acidsrdquo Chemosphere vol 19 no 10-11pp 1595ndash1609 1989
[11] J Fu S Li Y Wang L Cao and L Lu ldquoComputational andelectrochemical studies of some amino acid compounds as cor-rosion inhibitors for mild steel in hydrochloric acid solutionrdquoJournal of Materials Science vol 45 pp 6255ndash6265 2010
[12] J Fang and J Li ldquoQuantum chemistry study on the relationshipbetween molecular structure and corrosion inhibition effi-ciency of amidesrdquo Journal ofMolecular Structure THEOCHEMvol 593 pp 179ndash185 2002
[13] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface by sub-stituted uracilsrdquo Applied Surface Science vol 255 no 5 part 1pp 2433ndash2441 2008
[14] A Yurt G Bereket and C Ogretir ldquoQuantum chemical studieson inhibition effect of amino acids and hydroxy carboxylic acidson pitting corrosion of aluminium alloy 7075 in NaCl solutionrdquoJournal of Molecular Structure THEOCHEM vol 725 no 1ndash3pp 215ndash221 2005
[15] G Gece ldquoThe use of quantum chemical methods in corrosioninhibitor studiesrdquo Corrosion Science vol 50 no 11 pp 2981ndash2992 2008
[16] G Zhang and C B Musgrave ldquoComparison of DFT methodsfor molecular orbital eigenvalue calculationsrdquo Journal of Physi-cal Chemistry A vol 111 no 8 pp 1554ndash1561 2007
[17] G Bereket E Hur and C Ogretir ldquoQuantum chemical studieson some imidazole derivatives as corrosion inhibitors for iron inacidic mediumrdquo Journal of Molecular Structure THEOCHEMvol 578 pp 79ndash88 2002
[18] J Vosta and J Eliasek ldquoStudy on corrosion inhibition fromaspect of quantum chemistryrdquo Corrosion Science vol 11 pp223ndash229 1971
[19] E E Oguzie Y Li S G Wang and F Wanga ldquoUnderstandingcorrosion inhibition mechanisms-experimental and theoreticalapproachrdquo RSC Advances vol 1 pp 866ndash873 2011
[20] S Xia M Qiu L Yu F Liu and H Zhao ldquoMolecular dynamicsand density functional theory study on relationship betweenstructure of imidazoline derivatives and inhibition perform-ancerdquo Corrosion Science vol 50 no 7 pp 2021ndash2029 2008
[21] F Kandemirli and S Sagdinc ldquoTheoretical study of corrosioninhibition of amides and thiosemicarbazonesrdquo Corrosion Sci-ence vol 49 no 5 pp 2118ndash2130 2007
[22] C D Taylor R G Kelly and M Neurock ldquoA first-principlesanalysis of the chemisorption of hydroxide on copper underelectrochemical conditions a probe of the electronic interac-tions that control chemisorption at the electrochemical inter-facerdquo Journal of Electroanalytical Chemistry vol 607 no 1-2 pp167ndash174 2007
[23] D Wanga S Lia Y Yinga M Wanga H Xiaob and Z CheldquoTheoretical and experimental studies of structure and inhi-bition efficiency of imidazoline derivativesrdquo Corrosion Sciencevol 41 no 10 pp 1911ndash1919 1999
[24] J Bartley N Huynh S E Bottle H Flitt T Notoya and D PSchweinsberg ldquoComputer simulation of the corrosion inhibi-tion of copper in acidic solution by alkyl esters of 5-carboxyben-zotriazolerdquo Corrosion Science vol 45 no 1 pp 81ndash96 2003
[25] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquo Journal of Physical Chemistry C vol 113 no 19pp 8420ndash8429 2009
[26] L M Rodrıguez-Valdez A Martınez-Villafane and D Gloss-man-Mitnik ldquoComputational simulation of the molecularstructure and properties of heterocyclic organic compounds
ISRN Physical Chemistry 9
with possible corrosion inhibition propertiesrdquo Journal of Molec-ular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash70 2005
[27] A Lesar and I Milosev ldquoDensity functional study of the corro-sion inhibition properties of 124-triazole and its amino deriva-tivesrdquo Chemical Physics Letters vol 483 no 4ndash6 pp 198ndash2032009
[28] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[29] E E Oguzie ldquoCorrosion inhibition ofmild steel in hydrochloricacid solution by methylene blue dyerdquo Materials Letters vol 59no 8-9 pp 1076ndash1079 2005
[30] W Yang andR Parr ldquoHardness softness and the fukui functionin the electronic theory of metals and catalysisrdquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 82 pp 6723ndash6726 1985
[31] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2 M sulphuric acid solu-tion by methylene blue dyerdquo Materials Chemistry and Physicsvol 89 no 2-3 pp 305ndash311 2005
[32] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
Figure 1 (a) Lewis structures of the investigated dyes (b) names (c) geometry-optimized structures [C gray H white N blue O red Clgreen]
respectively The number of electrons transferred (Δ119873)from the inhibitor molecule to the metallic atom was alsocalculated using the following equation [30]
Δ119873 =120594Fe minus 120594Inh
2 (120578Fe + 120578Inh) (4)
Herein 120594Fe and 120594Inh represent the absolute electronegativityof iron and the inhibitor molecule respectively 120578Fe and 120578Inhrepresent the absolute hardness of iron and the inhibitormolecule
3 Results and Discussion
31 Molecular Reactivity Themolecular reactivity was inves-tigated via analysis of the frontiermolecular orbital and Fukuifunctions The highest occupied molecular orbital (HOMO)and the lowest unoccupied molecular orbital (LUMO) of thedye molecules are showed in Figure 2 while the Fukui indicesand electron density are shown in Figure 6 It could be seenthat the HOMO orbitals of IB dye molecule are generallydelocalized around the double bond and heteroatoms Thiskind of orbital distribution could be ascribed to the highelectron density around the centre of the molecule due tothe p-120587 conjugation effect As a result the centre of themoleculewould be preferentially adsorbed ontometal surfaceas active sites During adsorption the inhibitor molecule
could donate electrons to form coordinate bond with unoc-cupied d-orbitals of metal accept electrons from d-orbitalof metal and form back-donating bonds as well High119864HOMO facilitates adsorption (inhibition) by influencing thetransport process through the adsorbed layer whereas low-lying LUMO induces a backdonation of charge from themetalto themolecule [31]We found that CV had its HOMOorbitalchiefly on the Cl29 and C9=C10 double bond had a littleeffect as also confirmed inMulliken atomic charges (Table 1)Analyzing the HOMO orbital of MB we observed it to bepredominant at Cl21 and S10ndashC11 had contributions to theelectron density These could possibly mean a coordinatebond during adsorption to protect anodic areas and reducethe inherent reactivity of the metal at the sites where theyare attached It is considered that MB and CV are preferablyadsorbed on the iron surface by electron acceptance that ischemisorptions by backdonation rather than by donation ofp-electrons to the metal We examined these HOMO orbitalsand found that susceptibility of the molecules towards attackby electrophiles and their tenacity to donate electrons arein the following order IB gt MB gt CV with 119864HOMO valuesminus4981 eV minus4518 eV and minus3872 eV respectively Figure 3shows a linear relationship between the HOMO energy levelsand the experimental corrosion inhibition efficiency of thedyes as iron corrosion inhibitor
Similarly the LUMO orbital of IB dye molecule was prin-cipally found around aldehyde function and the amines
4 ISRN Physical Chemistry
HOMO LUMO
(a) (b)
Methylene blue
Crystal violet
Indigo blue
Figure 2 The frontier molecular orbital density distributions of the three dyes HOMO (a) LUMO (b)
Table 1 Condensed Fukui indices (Mulliken analyses) of IB MBand CV in gas phase
consequently these are favorite sites for interaction with themetal It could also be seen in Figure 2 that LUMO orbitalof MB and CV is delocalized but comparing the net atomic
Figure 3 Correlation of HOMO energy with percent inhibitionefficiency of dye molecules
charges of their Cl atom (Table 1) it is found that MB hasa stronger interaction with iron and has a better corrosioninhibition effect on iron than CV According to the frontiermolecular orbital theory low values of 119864LUMO should alsoindicate a strong tendency of electron-accepting abilitiesof the molecule and as seen in Figure 3 in the order of
ISRN Physical Chemistry 5
Table 2 119864HOMO 119864LUMO chemical potential (120583) global chemicalhardness (120578) number of electrons transferred (Δ119873) and inhibitionefficiency (IE) for the three dyes molecules in gas phase
IB gtMB gt CV which is in good agreement with inhibitionefficiency (IE ) of the experimental results see [28 29 32]
In addition inhibition efficiency is closely related tothe reactivity of individual molecular orbital contributionsto the response of the whole molecular continuum Thefully optimized geometries obtained from the calculationsof condense Fukui functions are shown in Figure 6 theresults for Fukui function (Table 1) support the trend of thefrontier molecular orbital observed for the studied moleculesindicating the zones through which the molecule will beadsorbed onto the Fe(110) surfaceThe119891minusmeasures reactivitywith respect to electrophilic attack or the characteristic ofthemolecule to donate electrons while119891+measure reactivitywhich relates to nucleophilic attack or the propensity of themolecule to accept electrons [30] The highest 119891minus for IB isat O19 and O20 indicating the zone for transfer of electronas seen in the electron density cloud (Figure 6) while thehighest 119891+ is associated with the same O19 and O20 showingthe ability for a backdonation through the same zone whichmight result in chemisorption Moreover the highest 119891minus forMB and CV is related to the Cl atom but the value forMB is higher than CV and might readily form adsorption-active centers validating that MB has a higher iron corrosioninhibition efficiency than CV Calculated results in Table 1show that the highest 119891+ is also at the Cl atom for MB andCV confirming the favorite sites for adsorption
Furthermore the global parameters including chemicalpotential (120583) and hardness (120578) electronegativity (120594) and thenumber of electrons transferred during the adsorption (Δ119873)were also calculated and the results are shown in Table 2Since the capability of donating electron of a molecule canbe determined by the chemical potential and hardness theless negative these values are the higher is the capabilityof donating electrons [30] So from Table 2 it could beseen that the order of electron-donating capability of thedye molecules is IB gt MB gt CV On the other handas for the electronegativity which denotes the electron-accepting capability of a molecule it could also be deducedfrom Table 2 that the electron-accepting capability of thesemolecules follows the similar trendGenerally the same orderof donating capability and accepting electrons of the threeinhibitor molecules indicates that the inhibition efficiencywould follow the same order of IB gt MB gt CV which is inaccordance with the analysis of frontier molecular orbitalThe relationship between corrosion inhibition efficiency andthe number of electrons transferred for these three dyes isplotted in Figure 4 As clearly seen in the figure there is a lin-earity between inhibition efficiency and number of electrons
Table 3 Binding energy interaction energy and total energy (mini-mum) for the molecular dynamic simulations
119864Bind (eV) 119864Interaction (eV) Total energy (kcalmol)IB 12137 minus12137 minus4914MB 5962 minus5962 minus1683CV 3997 minus3997 minus8644
CV
MB
IB
505
58
655
73
IE (
)
205 255 305 355Δ119873 (e)
Figure 4 Correlation of number of electrons transferred withpercent inhibition efficiency of dye molecules
transferred In Figure 5 inhibition efficiency is plotted againstthe chemical potential showing the inhibition efficiencyincreased with decrease in the chemical potential energy
Table 2 provides calculated quantum chemical parame-ters using (4) number of electrons transferred (Δ119873) Valuesof 120594 and 120578 were calculated by using the values of 119868 (minus119864HOMO)and 119860 (minus119864
119871119880119872119874) obtained from quantum chemical calcula-
tions In order to calculate Δ119873 a theoretical value for theelectronegativity of bulk iron was used 120594Fe asymp 7 eV and aglobal hardness of 120578Fe asymp 0 by assuming that for a metallicbulk 119868 = 119860 because they are softer than the neutral metallicatoms [17] According to Lukovits ifΔ119873 lt 36 the inhibitionefficiency increased with increasing electron-donating abilityat the metal surface [6] It can be inferred from the calculatedresults that inhibitors investigated in this study were donorsof electrons and the iron surface was the acceptor
32 Molecular Dynamics To quantitatively evaluate themostsuitable adsorptionmodes between eachmolecule and the Fesurface the adsorption energy (119864Bind) was calculated usingthe relationship in (3) In each case the potential energieswerecalculated by averaging the energies of the five structuresof the lowest energy [25] The obtained values are shown inTable 3 we discovered that IB exhibited the highest bindingenergy during the simulation process and the order of 119864Bindis IB gtMB gt CV in accordance with experimental inhibitionefficiency (IE ) The high values of the binding energy forthe dye molecules could be as a result of dissociative adsorp-tion which is favourable to crack the intramolecular bond ofthe adsorbate molecule This is an indication of chemisorp-tion which contrasts the experimentally found physisorptionfor the dye molecules From the high values of 119864bind obtainedfor the three dye molecules only a probable chemisorptionis expected which affirms the observed electron acceptanceand backdonation of electrons at the same site The very highbinding energy of IB could be attributed to its O
Figure 5 Correlation of chemical potential with percent inhibition efficiency of dye molecules
Methylene blue
Crystal violet
Indigo blue
(a) (b)
Figure 6 The Fukui indices density distributions of the three dyes 119891minus (a) 119891+ (b)
which dissociate on adsorption It can also be seen fromFigure 7 that there is a linear correlation between the bindingenergy and inhibition efficiency indicating that the higher thebinding energy the higher the inhibition efficiency Table 3shows the values obtained for binding energy interactionenergy and total energy It can be seen that the trend of 119864Bindsupports experimental results for the three dye molecules
The high inhibition efficiency of IB could be attributedto a number of lone pair electrons on O atoms as well as
the N atoms providing electrons to the unfilled 3d orbitalsof iron surface thereby forming a protective layer Suchprotective film may act as a steric barrier that hinders thereactive ionsspecies from the aggressive environment fromcoming into contact with the metal surface thus slowingdown corrosion process To determine the global minimumvarious different low-energy minima were sampled Figures8(a)ndash8(c) show snapshots of the side view and top view(inset) of the lowest energy adsorption configurations for
ISRN Physical Chemistry 7
CVMB
IB
505
58
655
73
38 63 88 113IE
()
119864binding (eV)
Figure 7 Correlation of binding energy with percent inhibition efficiency of dye molecules
CV
(a)
MB
(b)
IB
(c)
Figure 8 Representative snapshots of (a) CV (b) MB and (c) IB adsorbed on Fe(110) Inset images show the on-top views emphasizing themolecular backbone aligning with vacant sites on the fcc lattice atop the metal surface
single inhibitor molecules studied on the Fe(110) surfacefrom our simulations respectively Close inspection of theon-top view of adsorbed single molecule on Fe(110) revealsa very clear fashion in the adsorption configuration of allthe molecules wherein polarizable atoms (N O S) in themolecular backbone align with vacant sites on the fcc latticeatop the metal surface and virtually avoid contact with the Featoms on the surface plane
4 Conclusion
In this study the three dye molecules were the donators ofelectrons and the iron surface was the acceptor The com-pounds were adsorbed to themetal surface and hence formedinhibitive adsorption layer against the corrosive media Theinhibition efficiency is in order of IB gtMB gt CV which sub-stantiates the experimental results The research by quantum
8 ISRN Physical Chemistry
chemistry revealed that the reactive sites of dye moleculesformed coordinate and back-donating bonds with atoms onmetal surface Further comparison revealed that the zones forelectron donation were the same as the zones for acceptingelectrons which could indicate a probable chemisorptionIB had the highest inhibition efficiency because it hadthe greatest ability of offering electrons and CV had thelowest inhibition efficiency A linear correlationwas observedbetween inhibition efficiencies and the inhibitor chemicalpotential as well as the extent of charge transfer to the metalsFurthermore the distribution of electronic density shows thatthe dyemolecules hadmany negatively charged active centerswith exception of IB The electron density was found to bepositively correlated with its linear structure which couldbe the effect for increase in inhibition efficiency The zonescontaining N O and S atoms are the most possible sites foradsorption of the metal iron surface This study suggests thattheoretical method might be an effective approach to assessthe inhibition performance of new inhibitors
References
[1] A D Becke ldquoDensity-functional exchange-energy approxima-tion with correct asymptotic behaviorrdquo Physical Review A vol38 pp 3098ndash3100 1988
[2] I B Obot and N O Obi-Egbedi ldquoTheoretical study of ben-zimidazole and its derivatives and their potential activity ascorrosion inhibitorsrdquo Corrosion Science vol 52 no 2 pp 657ndash660 2010
[3] M Sahin G Gece F Karcı and S Bilgic ldquoExperimental andtheoretical study of the effect of some heterocyclic compoundson the corrosion of low carbon steel in 35 NaCl mediumrdquoJournal of Applied Electrochemistry vol 38 no 6 pp 809ndash8152008
[4] D X Wang and H M Xiao ldquoQuantum chemical calculationon chemical adsorption energy of imidazolines and Fe atomrdquoJournal of Molecular Science vol 16 pp 102ndash105 2000
[5] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[6] E Jamalizadeh S M A Hosseini and A H Jafari ldquoQuantumchemical studies on corrosion inhibition of some lactones onmild steel in acid mediardquo Corrosion Science vol 51 no 6 pp1428ndash1435 2009
[7] M Karelson V S Lobanov and A R Katritzky ldquoQuantum-chemical descriptors in QSARQSPR studiesrdquo ChemicalReviews vol 96 no 3 pp 1027ndash1043 1996
[8] M A Amin K F Khaled QMohsen andH A Arida ldquoA studyof the inhibition of iron corrosion in HCl solutions by someamino acidsrdquo Corrosion Science vol 52 pp 1684ndash1695 2010
[9] G Gece S Bilgic and O Turksen ldquoQuantum chemical studiesof some amino acids on the corrosion of cobalt in sulfuric acidsolutionrdquo Materials and Corrosion vol 61 no 2 pp 141ndash1462010
[10] C Gruber and V Buss ldquoQuantum-mechanically calculatedproperties for the development of quantitative structure-activi-ty relationships (QSARrsquoS) pKA-values of phenols and aromaticand aliphatic carboxylic acidsrdquo Chemosphere vol 19 no 10-11pp 1595ndash1609 1989
[11] J Fu S Li Y Wang L Cao and L Lu ldquoComputational andelectrochemical studies of some amino acid compounds as cor-rosion inhibitors for mild steel in hydrochloric acid solutionrdquoJournal of Materials Science vol 45 pp 6255ndash6265 2010
[12] J Fang and J Li ldquoQuantum chemistry study on the relationshipbetween molecular structure and corrosion inhibition effi-ciency of amidesrdquo Journal ofMolecular Structure THEOCHEMvol 593 pp 179ndash185 2002
[13] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface by sub-stituted uracilsrdquo Applied Surface Science vol 255 no 5 part 1pp 2433ndash2441 2008
[14] A Yurt G Bereket and C Ogretir ldquoQuantum chemical studieson inhibition effect of amino acids and hydroxy carboxylic acidson pitting corrosion of aluminium alloy 7075 in NaCl solutionrdquoJournal of Molecular Structure THEOCHEM vol 725 no 1ndash3pp 215ndash221 2005
[15] G Gece ldquoThe use of quantum chemical methods in corrosioninhibitor studiesrdquo Corrosion Science vol 50 no 11 pp 2981ndash2992 2008
[16] G Zhang and C B Musgrave ldquoComparison of DFT methodsfor molecular orbital eigenvalue calculationsrdquo Journal of Physi-cal Chemistry A vol 111 no 8 pp 1554ndash1561 2007
[17] G Bereket E Hur and C Ogretir ldquoQuantum chemical studieson some imidazole derivatives as corrosion inhibitors for iron inacidic mediumrdquo Journal of Molecular Structure THEOCHEMvol 578 pp 79ndash88 2002
[18] J Vosta and J Eliasek ldquoStudy on corrosion inhibition fromaspect of quantum chemistryrdquo Corrosion Science vol 11 pp223ndash229 1971
[19] E E Oguzie Y Li S G Wang and F Wanga ldquoUnderstandingcorrosion inhibition mechanisms-experimental and theoreticalapproachrdquo RSC Advances vol 1 pp 866ndash873 2011
[20] S Xia M Qiu L Yu F Liu and H Zhao ldquoMolecular dynamicsand density functional theory study on relationship betweenstructure of imidazoline derivatives and inhibition perform-ancerdquo Corrosion Science vol 50 no 7 pp 2021ndash2029 2008
[21] F Kandemirli and S Sagdinc ldquoTheoretical study of corrosioninhibition of amides and thiosemicarbazonesrdquo Corrosion Sci-ence vol 49 no 5 pp 2118ndash2130 2007
[22] C D Taylor R G Kelly and M Neurock ldquoA first-principlesanalysis of the chemisorption of hydroxide on copper underelectrochemical conditions a probe of the electronic interac-tions that control chemisorption at the electrochemical inter-facerdquo Journal of Electroanalytical Chemistry vol 607 no 1-2 pp167ndash174 2007
[23] D Wanga S Lia Y Yinga M Wanga H Xiaob and Z CheldquoTheoretical and experimental studies of structure and inhi-bition efficiency of imidazoline derivativesrdquo Corrosion Sciencevol 41 no 10 pp 1911ndash1919 1999
[24] J Bartley N Huynh S E Bottle H Flitt T Notoya and D PSchweinsberg ldquoComputer simulation of the corrosion inhibi-tion of copper in acidic solution by alkyl esters of 5-carboxyben-zotriazolerdquo Corrosion Science vol 45 no 1 pp 81ndash96 2003
[25] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquo Journal of Physical Chemistry C vol 113 no 19pp 8420ndash8429 2009
[26] L M Rodrıguez-Valdez A Martınez-Villafane and D Gloss-man-Mitnik ldquoComputational simulation of the molecularstructure and properties of heterocyclic organic compounds
ISRN Physical Chemistry 9
with possible corrosion inhibition propertiesrdquo Journal of Molec-ular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash70 2005
[27] A Lesar and I Milosev ldquoDensity functional study of the corro-sion inhibition properties of 124-triazole and its amino deriva-tivesrdquo Chemical Physics Letters vol 483 no 4ndash6 pp 198ndash2032009
[28] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[29] E E Oguzie ldquoCorrosion inhibition ofmild steel in hydrochloricacid solution by methylene blue dyerdquo Materials Letters vol 59no 8-9 pp 1076ndash1079 2005
[30] W Yang andR Parr ldquoHardness softness and the fukui functionin the electronic theory of metals and catalysisrdquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 82 pp 6723ndash6726 1985
[31] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2 M sulphuric acid solu-tion by methylene blue dyerdquo Materials Chemistry and Physicsvol 89 no 2-3 pp 305ndash311 2005
[32] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
consequently these are favorite sites for interaction with themetal It could also be seen in Figure 2 that LUMO orbitalof MB and CV is delocalized but comparing the net atomic
Figure 3 Correlation of HOMO energy with percent inhibitionefficiency of dye molecules
charges of their Cl atom (Table 1) it is found that MB hasa stronger interaction with iron and has a better corrosioninhibition effect on iron than CV According to the frontiermolecular orbital theory low values of 119864LUMO should alsoindicate a strong tendency of electron-accepting abilitiesof the molecule and as seen in Figure 3 in the order of
ISRN Physical Chemistry 5
Table 2 119864HOMO 119864LUMO chemical potential (120583) global chemicalhardness (120578) number of electrons transferred (Δ119873) and inhibitionefficiency (IE) for the three dyes molecules in gas phase
IB gtMB gt CV which is in good agreement with inhibitionefficiency (IE ) of the experimental results see [28 29 32]
In addition inhibition efficiency is closely related tothe reactivity of individual molecular orbital contributionsto the response of the whole molecular continuum Thefully optimized geometries obtained from the calculationsof condense Fukui functions are shown in Figure 6 theresults for Fukui function (Table 1) support the trend of thefrontier molecular orbital observed for the studied moleculesindicating the zones through which the molecule will beadsorbed onto the Fe(110) surfaceThe119891minusmeasures reactivitywith respect to electrophilic attack or the characteristic ofthemolecule to donate electrons while119891+measure reactivitywhich relates to nucleophilic attack or the propensity of themolecule to accept electrons [30] The highest 119891minus for IB isat O19 and O20 indicating the zone for transfer of electronas seen in the electron density cloud (Figure 6) while thehighest 119891+ is associated with the same O19 and O20 showingthe ability for a backdonation through the same zone whichmight result in chemisorption Moreover the highest 119891minus forMB and CV is related to the Cl atom but the value forMB is higher than CV and might readily form adsorption-active centers validating that MB has a higher iron corrosioninhibition efficiency than CV Calculated results in Table 1show that the highest 119891+ is also at the Cl atom for MB andCV confirming the favorite sites for adsorption
Furthermore the global parameters including chemicalpotential (120583) and hardness (120578) electronegativity (120594) and thenumber of electrons transferred during the adsorption (Δ119873)were also calculated and the results are shown in Table 2Since the capability of donating electron of a molecule canbe determined by the chemical potential and hardness theless negative these values are the higher is the capabilityof donating electrons [30] So from Table 2 it could beseen that the order of electron-donating capability of thedye molecules is IB gt MB gt CV On the other handas for the electronegativity which denotes the electron-accepting capability of a molecule it could also be deducedfrom Table 2 that the electron-accepting capability of thesemolecules follows the similar trendGenerally the same orderof donating capability and accepting electrons of the threeinhibitor molecules indicates that the inhibition efficiencywould follow the same order of IB gt MB gt CV which is inaccordance with the analysis of frontier molecular orbitalThe relationship between corrosion inhibition efficiency andthe number of electrons transferred for these three dyes isplotted in Figure 4 As clearly seen in the figure there is a lin-earity between inhibition efficiency and number of electrons
Table 3 Binding energy interaction energy and total energy (mini-mum) for the molecular dynamic simulations
119864Bind (eV) 119864Interaction (eV) Total energy (kcalmol)IB 12137 minus12137 minus4914MB 5962 minus5962 minus1683CV 3997 minus3997 minus8644
CV
MB
IB
505
58
655
73
IE (
)
205 255 305 355Δ119873 (e)
Figure 4 Correlation of number of electrons transferred withpercent inhibition efficiency of dye molecules
transferred In Figure 5 inhibition efficiency is plotted againstthe chemical potential showing the inhibition efficiencyincreased with decrease in the chemical potential energy
Table 2 provides calculated quantum chemical parame-ters using (4) number of electrons transferred (Δ119873) Valuesof 120594 and 120578 were calculated by using the values of 119868 (minus119864HOMO)and 119860 (minus119864
119871119880119872119874) obtained from quantum chemical calcula-
tions In order to calculate Δ119873 a theoretical value for theelectronegativity of bulk iron was used 120594Fe asymp 7 eV and aglobal hardness of 120578Fe asymp 0 by assuming that for a metallicbulk 119868 = 119860 because they are softer than the neutral metallicatoms [17] According to Lukovits ifΔ119873 lt 36 the inhibitionefficiency increased with increasing electron-donating abilityat the metal surface [6] It can be inferred from the calculatedresults that inhibitors investigated in this study were donorsof electrons and the iron surface was the acceptor
32 Molecular Dynamics To quantitatively evaluate themostsuitable adsorptionmodes between eachmolecule and the Fesurface the adsorption energy (119864Bind) was calculated usingthe relationship in (3) In each case the potential energieswerecalculated by averaging the energies of the five structuresof the lowest energy [25] The obtained values are shown inTable 3 we discovered that IB exhibited the highest bindingenergy during the simulation process and the order of 119864Bindis IB gtMB gt CV in accordance with experimental inhibitionefficiency (IE ) The high values of the binding energy forthe dye molecules could be as a result of dissociative adsorp-tion which is favourable to crack the intramolecular bond ofthe adsorbate molecule This is an indication of chemisorp-tion which contrasts the experimentally found physisorptionfor the dye molecules From the high values of 119864bind obtainedfor the three dye molecules only a probable chemisorptionis expected which affirms the observed electron acceptanceand backdonation of electrons at the same site The very highbinding energy of IB could be attributed to its O
Figure 5 Correlation of chemical potential with percent inhibition efficiency of dye molecules
Methylene blue
Crystal violet
Indigo blue
(a) (b)
Figure 6 The Fukui indices density distributions of the three dyes 119891minus (a) 119891+ (b)
which dissociate on adsorption It can also be seen fromFigure 7 that there is a linear correlation between the bindingenergy and inhibition efficiency indicating that the higher thebinding energy the higher the inhibition efficiency Table 3shows the values obtained for binding energy interactionenergy and total energy It can be seen that the trend of 119864Bindsupports experimental results for the three dye molecules
The high inhibition efficiency of IB could be attributedto a number of lone pair electrons on O atoms as well as
the N atoms providing electrons to the unfilled 3d orbitalsof iron surface thereby forming a protective layer Suchprotective film may act as a steric barrier that hinders thereactive ionsspecies from the aggressive environment fromcoming into contact with the metal surface thus slowingdown corrosion process To determine the global minimumvarious different low-energy minima were sampled Figures8(a)ndash8(c) show snapshots of the side view and top view(inset) of the lowest energy adsorption configurations for
ISRN Physical Chemistry 7
CVMB
IB
505
58
655
73
38 63 88 113IE
()
119864binding (eV)
Figure 7 Correlation of binding energy with percent inhibition efficiency of dye molecules
CV
(a)
MB
(b)
IB
(c)
Figure 8 Representative snapshots of (a) CV (b) MB and (c) IB adsorbed on Fe(110) Inset images show the on-top views emphasizing themolecular backbone aligning with vacant sites on the fcc lattice atop the metal surface
single inhibitor molecules studied on the Fe(110) surfacefrom our simulations respectively Close inspection of theon-top view of adsorbed single molecule on Fe(110) revealsa very clear fashion in the adsorption configuration of allthe molecules wherein polarizable atoms (N O S) in themolecular backbone align with vacant sites on the fcc latticeatop the metal surface and virtually avoid contact with the Featoms on the surface plane
4 Conclusion
In this study the three dye molecules were the donators ofelectrons and the iron surface was the acceptor The com-pounds were adsorbed to themetal surface and hence formedinhibitive adsorption layer against the corrosive media Theinhibition efficiency is in order of IB gtMB gt CV which sub-stantiates the experimental results The research by quantum
8 ISRN Physical Chemistry
chemistry revealed that the reactive sites of dye moleculesformed coordinate and back-donating bonds with atoms onmetal surface Further comparison revealed that the zones forelectron donation were the same as the zones for acceptingelectrons which could indicate a probable chemisorptionIB had the highest inhibition efficiency because it hadthe greatest ability of offering electrons and CV had thelowest inhibition efficiency A linear correlationwas observedbetween inhibition efficiencies and the inhibitor chemicalpotential as well as the extent of charge transfer to the metalsFurthermore the distribution of electronic density shows thatthe dyemolecules hadmany negatively charged active centerswith exception of IB The electron density was found to bepositively correlated with its linear structure which couldbe the effect for increase in inhibition efficiency The zonescontaining N O and S atoms are the most possible sites foradsorption of the metal iron surface This study suggests thattheoretical method might be an effective approach to assessthe inhibition performance of new inhibitors
References
[1] A D Becke ldquoDensity-functional exchange-energy approxima-tion with correct asymptotic behaviorrdquo Physical Review A vol38 pp 3098ndash3100 1988
[2] I B Obot and N O Obi-Egbedi ldquoTheoretical study of ben-zimidazole and its derivatives and their potential activity ascorrosion inhibitorsrdquo Corrosion Science vol 52 no 2 pp 657ndash660 2010
[3] M Sahin G Gece F Karcı and S Bilgic ldquoExperimental andtheoretical study of the effect of some heterocyclic compoundson the corrosion of low carbon steel in 35 NaCl mediumrdquoJournal of Applied Electrochemistry vol 38 no 6 pp 809ndash8152008
[4] D X Wang and H M Xiao ldquoQuantum chemical calculationon chemical adsorption energy of imidazolines and Fe atomrdquoJournal of Molecular Science vol 16 pp 102ndash105 2000
[5] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[6] E Jamalizadeh S M A Hosseini and A H Jafari ldquoQuantumchemical studies on corrosion inhibition of some lactones onmild steel in acid mediardquo Corrosion Science vol 51 no 6 pp1428ndash1435 2009
[7] M Karelson V S Lobanov and A R Katritzky ldquoQuantum-chemical descriptors in QSARQSPR studiesrdquo ChemicalReviews vol 96 no 3 pp 1027ndash1043 1996
[8] M A Amin K F Khaled QMohsen andH A Arida ldquoA studyof the inhibition of iron corrosion in HCl solutions by someamino acidsrdquo Corrosion Science vol 52 pp 1684ndash1695 2010
[9] G Gece S Bilgic and O Turksen ldquoQuantum chemical studiesof some amino acids on the corrosion of cobalt in sulfuric acidsolutionrdquo Materials and Corrosion vol 61 no 2 pp 141ndash1462010
[10] C Gruber and V Buss ldquoQuantum-mechanically calculatedproperties for the development of quantitative structure-activi-ty relationships (QSARrsquoS) pKA-values of phenols and aromaticand aliphatic carboxylic acidsrdquo Chemosphere vol 19 no 10-11pp 1595ndash1609 1989
[11] J Fu S Li Y Wang L Cao and L Lu ldquoComputational andelectrochemical studies of some amino acid compounds as cor-rosion inhibitors for mild steel in hydrochloric acid solutionrdquoJournal of Materials Science vol 45 pp 6255ndash6265 2010
[12] J Fang and J Li ldquoQuantum chemistry study on the relationshipbetween molecular structure and corrosion inhibition effi-ciency of amidesrdquo Journal ofMolecular Structure THEOCHEMvol 593 pp 179ndash185 2002
[13] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface by sub-stituted uracilsrdquo Applied Surface Science vol 255 no 5 part 1pp 2433ndash2441 2008
[14] A Yurt G Bereket and C Ogretir ldquoQuantum chemical studieson inhibition effect of amino acids and hydroxy carboxylic acidson pitting corrosion of aluminium alloy 7075 in NaCl solutionrdquoJournal of Molecular Structure THEOCHEM vol 725 no 1ndash3pp 215ndash221 2005
[15] G Gece ldquoThe use of quantum chemical methods in corrosioninhibitor studiesrdquo Corrosion Science vol 50 no 11 pp 2981ndash2992 2008
[16] G Zhang and C B Musgrave ldquoComparison of DFT methodsfor molecular orbital eigenvalue calculationsrdquo Journal of Physi-cal Chemistry A vol 111 no 8 pp 1554ndash1561 2007
[17] G Bereket E Hur and C Ogretir ldquoQuantum chemical studieson some imidazole derivatives as corrosion inhibitors for iron inacidic mediumrdquo Journal of Molecular Structure THEOCHEMvol 578 pp 79ndash88 2002
[18] J Vosta and J Eliasek ldquoStudy on corrosion inhibition fromaspect of quantum chemistryrdquo Corrosion Science vol 11 pp223ndash229 1971
[19] E E Oguzie Y Li S G Wang and F Wanga ldquoUnderstandingcorrosion inhibition mechanisms-experimental and theoreticalapproachrdquo RSC Advances vol 1 pp 866ndash873 2011
[20] S Xia M Qiu L Yu F Liu and H Zhao ldquoMolecular dynamicsand density functional theory study on relationship betweenstructure of imidazoline derivatives and inhibition perform-ancerdquo Corrosion Science vol 50 no 7 pp 2021ndash2029 2008
[21] F Kandemirli and S Sagdinc ldquoTheoretical study of corrosioninhibition of amides and thiosemicarbazonesrdquo Corrosion Sci-ence vol 49 no 5 pp 2118ndash2130 2007
[22] C D Taylor R G Kelly and M Neurock ldquoA first-principlesanalysis of the chemisorption of hydroxide on copper underelectrochemical conditions a probe of the electronic interac-tions that control chemisorption at the electrochemical inter-facerdquo Journal of Electroanalytical Chemistry vol 607 no 1-2 pp167ndash174 2007
[23] D Wanga S Lia Y Yinga M Wanga H Xiaob and Z CheldquoTheoretical and experimental studies of structure and inhi-bition efficiency of imidazoline derivativesrdquo Corrosion Sciencevol 41 no 10 pp 1911ndash1919 1999
[24] J Bartley N Huynh S E Bottle H Flitt T Notoya and D PSchweinsberg ldquoComputer simulation of the corrosion inhibi-tion of copper in acidic solution by alkyl esters of 5-carboxyben-zotriazolerdquo Corrosion Science vol 45 no 1 pp 81ndash96 2003
[25] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquo Journal of Physical Chemistry C vol 113 no 19pp 8420ndash8429 2009
[26] L M Rodrıguez-Valdez A Martınez-Villafane and D Gloss-man-Mitnik ldquoComputational simulation of the molecularstructure and properties of heterocyclic organic compounds
ISRN Physical Chemistry 9
with possible corrosion inhibition propertiesrdquo Journal of Molec-ular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash70 2005
[27] A Lesar and I Milosev ldquoDensity functional study of the corro-sion inhibition properties of 124-triazole and its amino deriva-tivesrdquo Chemical Physics Letters vol 483 no 4ndash6 pp 198ndash2032009
[28] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[29] E E Oguzie ldquoCorrosion inhibition ofmild steel in hydrochloricacid solution by methylene blue dyerdquo Materials Letters vol 59no 8-9 pp 1076ndash1079 2005
[30] W Yang andR Parr ldquoHardness softness and the fukui functionin the electronic theory of metals and catalysisrdquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 82 pp 6723ndash6726 1985
[31] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2 M sulphuric acid solu-tion by methylene blue dyerdquo Materials Chemistry and Physicsvol 89 no 2-3 pp 305ndash311 2005
[32] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
Table 2 119864HOMO 119864LUMO chemical potential (120583) global chemicalhardness (120578) number of electrons transferred (Δ119873) and inhibitionefficiency (IE) for the three dyes molecules in gas phase
IB gtMB gt CV which is in good agreement with inhibitionefficiency (IE ) of the experimental results see [28 29 32]
In addition inhibition efficiency is closely related tothe reactivity of individual molecular orbital contributionsto the response of the whole molecular continuum Thefully optimized geometries obtained from the calculationsof condense Fukui functions are shown in Figure 6 theresults for Fukui function (Table 1) support the trend of thefrontier molecular orbital observed for the studied moleculesindicating the zones through which the molecule will beadsorbed onto the Fe(110) surfaceThe119891minusmeasures reactivitywith respect to electrophilic attack or the characteristic ofthemolecule to donate electrons while119891+measure reactivitywhich relates to nucleophilic attack or the propensity of themolecule to accept electrons [30] The highest 119891minus for IB isat O19 and O20 indicating the zone for transfer of electronas seen in the electron density cloud (Figure 6) while thehighest 119891+ is associated with the same O19 and O20 showingthe ability for a backdonation through the same zone whichmight result in chemisorption Moreover the highest 119891minus forMB and CV is related to the Cl atom but the value forMB is higher than CV and might readily form adsorption-active centers validating that MB has a higher iron corrosioninhibition efficiency than CV Calculated results in Table 1show that the highest 119891+ is also at the Cl atom for MB andCV confirming the favorite sites for adsorption
Furthermore the global parameters including chemicalpotential (120583) and hardness (120578) electronegativity (120594) and thenumber of electrons transferred during the adsorption (Δ119873)were also calculated and the results are shown in Table 2Since the capability of donating electron of a molecule canbe determined by the chemical potential and hardness theless negative these values are the higher is the capabilityof donating electrons [30] So from Table 2 it could beseen that the order of electron-donating capability of thedye molecules is IB gt MB gt CV On the other handas for the electronegativity which denotes the electron-accepting capability of a molecule it could also be deducedfrom Table 2 that the electron-accepting capability of thesemolecules follows the similar trendGenerally the same orderof donating capability and accepting electrons of the threeinhibitor molecules indicates that the inhibition efficiencywould follow the same order of IB gt MB gt CV which is inaccordance with the analysis of frontier molecular orbitalThe relationship between corrosion inhibition efficiency andthe number of electrons transferred for these three dyes isplotted in Figure 4 As clearly seen in the figure there is a lin-earity between inhibition efficiency and number of electrons
Table 3 Binding energy interaction energy and total energy (mini-mum) for the molecular dynamic simulations
119864Bind (eV) 119864Interaction (eV) Total energy (kcalmol)IB 12137 minus12137 minus4914MB 5962 minus5962 minus1683CV 3997 minus3997 minus8644
CV
MB
IB
505
58
655
73
IE (
)
205 255 305 355Δ119873 (e)
Figure 4 Correlation of number of electrons transferred withpercent inhibition efficiency of dye molecules
transferred In Figure 5 inhibition efficiency is plotted againstthe chemical potential showing the inhibition efficiencyincreased with decrease in the chemical potential energy
Table 2 provides calculated quantum chemical parame-ters using (4) number of electrons transferred (Δ119873) Valuesof 120594 and 120578 were calculated by using the values of 119868 (minus119864HOMO)and 119860 (minus119864
119871119880119872119874) obtained from quantum chemical calcula-
tions In order to calculate Δ119873 a theoretical value for theelectronegativity of bulk iron was used 120594Fe asymp 7 eV and aglobal hardness of 120578Fe asymp 0 by assuming that for a metallicbulk 119868 = 119860 because they are softer than the neutral metallicatoms [17] According to Lukovits ifΔ119873 lt 36 the inhibitionefficiency increased with increasing electron-donating abilityat the metal surface [6] It can be inferred from the calculatedresults that inhibitors investigated in this study were donorsof electrons and the iron surface was the acceptor
32 Molecular Dynamics To quantitatively evaluate themostsuitable adsorptionmodes between eachmolecule and the Fesurface the adsorption energy (119864Bind) was calculated usingthe relationship in (3) In each case the potential energieswerecalculated by averaging the energies of the five structuresof the lowest energy [25] The obtained values are shown inTable 3 we discovered that IB exhibited the highest bindingenergy during the simulation process and the order of 119864Bindis IB gtMB gt CV in accordance with experimental inhibitionefficiency (IE ) The high values of the binding energy forthe dye molecules could be as a result of dissociative adsorp-tion which is favourable to crack the intramolecular bond ofthe adsorbate molecule This is an indication of chemisorp-tion which contrasts the experimentally found physisorptionfor the dye molecules From the high values of 119864bind obtainedfor the three dye molecules only a probable chemisorptionis expected which affirms the observed electron acceptanceand backdonation of electrons at the same site The very highbinding energy of IB could be attributed to its O
Figure 5 Correlation of chemical potential with percent inhibition efficiency of dye molecules
Methylene blue
Crystal violet
Indigo blue
(a) (b)
Figure 6 The Fukui indices density distributions of the three dyes 119891minus (a) 119891+ (b)
which dissociate on adsorption It can also be seen fromFigure 7 that there is a linear correlation between the bindingenergy and inhibition efficiency indicating that the higher thebinding energy the higher the inhibition efficiency Table 3shows the values obtained for binding energy interactionenergy and total energy It can be seen that the trend of 119864Bindsupports experimental results for the three dye molecules
The high inhibition efficiency of IB could be attributedto a number of lone pair electrons on O atoms as well as
the N atoms providing electrons to the unfilled 3d orbitalsof iron surface thereby forming a protective layer Suchprotective film may act as a steric barrier that hinders thereactive ionsspecies from the aggressive environment fromcoming into contact with the metal surface thus slowingdown corrosion process To determine the global minimumvarious different low-energy minima were sampled Figures8(a)ndash8(c) show snapshots of the side view and top view(inset) of the lowest energy adsorption configurations for
ISRN Physical Chemistry 7
CVMB
IB
505
58
655
73
38 63 88 113IE
()
119864binding (eV)
Figure 7 Correlation of binding energy with percent inhibition efficiency of dye molecules
CV
(a)
MB
(b)
IB
(c)
Figure 8 Representative snapshots of (a) CV (b) MB and (c) IB adsorbed on Fe(110) Inset images show the on-top views emphasizing themolecular backbone aligning with vacant sites on the fcc lattice atop the metal surface
single inhibitor molecules studied on the Fe(110) surfacefrom our simulations respectively Close inspection of theon-top view of adsorbed single molecule on Fe(110) revealsa very clear fashion in the adsorption configuration of allthe molecules wherein polarizable atoms (N O S) in themolecular backbone align with vacant sites on the fcc latticeatop the metal surface and virtually avoid contact with the Featoms on the surface plane
4 Conclusion
In this study the three dye molecules were the donators ofelectrons and the iron surface was the acceptor The com-pounds were adsorbed to themetal surface and hence formedinhibitive adsorption layer against the corrosive media Theinhibition efficiency is in order of IB gtMB gt CV which sub-stantiates the experimental results The research by quantum
8 ISRN Physical Chemistry
chemistry revealed that the reactive sites of dye moleculesformed coordinate and back-donating bonds with atoms onmetal surface Further comparison revealed that the zones forelectron donation were the same as the zones for acceptingelectrons which could indicate a probable chemisorptionIB had the highest inhibition efficiency because it hadthe greatest ability of offering electrons and CV had thelowest inhibition efficiency A linear correlationwas observedbetween inhibition efficiencies and the inhibitor chemicalpotential as well as the extent of charge transfer to the metalsFurthermore the distribution of electronic density shows thatthe dyemolecules hadmany negatively charged active centerswith exception of IB The electron density was found to bepositively correlated with its linear structure which couldbe the effect for increase in inhibition efficiency The zonescontaining N O and S atoms are the most possible sites foradsorption of the metal iron surface This study suggests thattheoretical method might be an effective approach to assessthe inhibition performance of new inhibitors
References
[1] A D Becke ldquoDensity-functional exchange-energy approxima-tion with correct asymptotic behaviorrdquo Physical Review A vol38 pp 3098ndash3100 1988
[2] I B Obot and N O Obi-Egbedi ldquoTheoretical study of ben-zimidazole and its derivatives and their potential activity ascorrosion inhibitorsrdquo Corrosion Science vol 52 no 2 pp 657ndash660 2010
[3] M Sahin G Gece F Karcı and S Bilgic ldquoExperimental andtheoretical study of the effect of some heterocyclic compoundson the corrosion of low carbon steel in 35 NaCl mediumrdquoJournal of Applied Electrochemistry vol 38 no 6 pp 809ndash8152008
[4] D X Wang and H M Xiao ldquoQuantum chemical calculationon chemical adsorption energy of imidazolines and Fe atomrdquoJournal of Molecular Science vol 16 pp 102ndash105 2000
[5] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[6] E Jamalizadeh S M A Hosseini and A H Jafari ldquoQuantumchemical studies on corrosion inhibition of some lactones onmild steel in acid mediardquo Corrosion Science vol 51 no 6 pp1428ndash1435 2009
[7] M Karelson V S Lobanov and A R Katritzky ldquoQuantum-chemical descriptors in QSARQSPR studiesrdquo ChemicalReviews vol 96 no 3 pp 1027ndash1043 1996
[8] M A Amin K F Khaled QMohsen andH A Arida ldquoA studyof the inhibition of iron corrosion in HCl solutions by someamino acidsrdquo Corrosion Science vol 52 pp 1684ndash1695 2010
[9] G Gece S Bilgic and O Turksen ldquoQuantum chemical studiesof some amino acids on the corrosion of cobalt in sulfuric acidsolutionrdquo Materials and Corrosion vol 61 no 2 pp 141ndash1462010
[10] C Gruber and V Buss ldquoQuantum-mechanically calculatedproperties for the development of quantitative structure-activi-ty relationships (QSARrsquoS) pKA-values of phenols and aromaticand aliphatic carboxylic acidsrdquo Chemosphere vol 19 no 10-11pp 1595ndash1609 1989
[11] J Fu S Li Y Wang L Cao and L Lu ldquoComputational andelectrochemical studies of some amino acid compounds as cor-rosion inhibitors for mild steel in hydrochloric acid solutionrdquoJournal of Materials Science vol 45 pp 6255ndash6265 2010
[12] J Fang and J Li ldquoQuantum chemistry study on the relationshipbetween molecular structure and corrosion inhibition effi-ciency of amidesrdquo Journal ofMolecular Structure THEOCHEMvol 593 pp 179ndash185 2002
[13] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface by sub-stituted uracilsrdquo Applied Surface Science vol 255 no 5 part 1pp 2433ndash2441 2008
[14] A Yurt G Bereket and C Ogretir ldquoQuantum chemical studieson inhibition effect of amino acids and hydroxy carboxylic acidson pitting corrosion of aluminium alloy 7075 in NaCl solutionrdquoJournal of Molecular Structure THEOCHEM vol 725 no 1ndash3pp 215ndash221 2005
[15] G Gece ldquoThe use of quantum chemical methods in corrosioninhibitor studiesrdquo Corrosion Science vol 50 no 11 pp 2981ndash2992 2008
[16] G Zhang and C B Musgrave ldquoComparison of DFT methodsfor molecular orbital eigenvalue calculationsrdquo Journal of Physi-cal Chemistry A vol 111 no 8 pp 1554ndash1561 2007
[17] G Bereket E Hur and C Ogretir ldquoQuantum chemical studieson some imidazole derivatives as corrosion inhibitors for iron inacidic mediumrdquo Journal of Molecular Structure THEOCHEMvol 578 pp 79ndash88 2002
[18] J Vosta and J Eliasek ldquoStudy on corrosion inhibition fromaspect of quantum chemistryrdquo Corrosion Science vol 11 pp223ndash229 1971
[19] E E Oguzie Y Li S G Wang and F Wanga ldquoUnderstandingcorrosion inhibition mechanisms-experimental and theoreticalapproachrdquo RSC Advances vol 1 pp 866ndash873 2011
[20] S Xia M Qiu L Yu F Liu and H Zhao ldquoMolecular dynamicsand density functional theory study on relationship betweenstructure of imidazoline derivatives and inhibition perform-ancerdquo Corrosion Science vol 50 no 7 pp 2021ndash2029 2008
[21] F Kandemirli and S Sagdinc ldquoTheoretical study of corrosioninhibition of amides and thiosemicarbazonesrdquo Corrosion Sci-ence vol 49 no 5 pp 2118ndash2130 2007
[22] C D Taylor R G Kelly and M Neurock ldquoA first-principlesanalysis of the chemisorption of hydroxide on copper underelectrochemical conditions a probe of the electronic interac-tions that control chemisorption at the electrochemical inter-facerdquo Journal of Electroanalytical Chemistry vol 607 no 1-2 pp167ndash174 2007
[23] D Wanga S Lia Y Yinga M Wanga H Xiaob and Z CheldquoTheoretical and experimental studies of structure and inhi-bition efficiency of imidazoline derivativesrdquo Corrosion Sciencevol 41 no 10 pp 1911ndash1919 1999
[24] J Bartley N Huynh S E Bottle H Flitt T Notoya and D PSchweinsberg ldquoComputer simulation of the corrosion inhibi-tion of copper in acidic solution by alkyl esters of 5-carboxyben-zotriazolerdquo Corrosion Science vol 45 no 1 pp 81ndash96 2003
[25] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquo Journal of Physical Chemistry C vol 113 no 19pp 8420ndash8429 2009
[26] L M Rodrıguez-Valdez A Martınez-Villafane and D Gloss-man-Mitnik ldquoComputational simulation of the molecularstructure and properties of heterocyclic organic compounds
ISRN Physical Chemistry 9
with possible corrosion inhibition propertiesrdquo Journal of Molec-ular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash70 2005
[27] A Lesar and I Milosev ldquoDensity functional study of the corro-sion inhibition properties of 124-triazole and its amino deriva-tivesrdquo Chemical Physics Letters vol 483 no 4ndash6 pp 198ndash2032009
[28] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[29] E E Oguzie ldquoCorrosion inhibition ofmild steel in hydrochloricacid solution by methylene blue dyerdquo Materials Letters vol 59no 8-9 pp 1076ndash1079 2005
[30] W Yang andR Parr ldquoHardness softness and the fukui functionin the electronic theory of metals and catalysisrdquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 82 pp 6723ndash6726 1985
[31] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2 M sulphuric acid solu-tion by methylene blue dyerdquo Materials Chemistry and Physicsvol 89 no 2-3 pp 305ndash311 2005
[32] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
Figure 5 Correlation of chemical potential with percent inhibition efficiency of dye molecules
Methylene blue
Crystal violet
Indigo blue
(a) (b)
Figure 6 The Fukui indices density distributions of the three dyes 119891minus (a) 119891+ (b)
which dissociate on adsorption It can also be seen fromFigure 7 that there is a linear correlation between the bindingenergy and inhibition efficiency indicating that the higher thebinding energy the higher the inhibition efficiency Table 3shows the values obtained for binding energy interactionenergy and total energy It can be seen that the trend of 119864Bindsupports experimental results for the three dye molecules
The high inhibition efficiency of IB could be attributedto a number of lone pair electrons on O atoms as well as
the N atoms providing electrons to the unfilled 3d orbitalsof iron surface thereby forming a protective layer Suchprotective film may act as a steric barrier that hinders thereactive ionsspecies from the aggressive environment fromcoming into contact with the metal surface thus slowingdown corrosion process To determine the global minimumvarious different low-energy minima were sampled Figures8(a)ndash8(c) show snapshots of the side view and top view(inset) of the lowest energy adsorption configurations for
ISRN Physical Chemistry 7
CVMB
IB
505
58
655
73
38 63 88 113IE
()
119864binding (eV)
Figure 7 Correlation of binding energy with percent inhibition efficiency of dye molecules
CV
(a)
MB
(b)
IB
(c)
Figure 8 Representative snapshots of (a) CV (b) MB and (c) IB adsorbed on Fe(110) Inset images show the on-top views emphasizing themolecular backbone aligning with vacant sites on the fcc lattice atop the metal surface
single inhibitor molecules studied on the Fe(110) surfacefrom our simulations respectively Close inspection of theon-top view of adsorbed single molecule on Fe(110) revealsa very clear fashion in the adsorption configuration of allthe molecules wherein polarizable atoms (N O S) in themolecular backbone align with vacant sites on the fcc latticeatop the metal surface and virtually avoid contact with the Featoms on the surface plane
4 Conclusion
In this study the three dye molecules were the donators ofelectrons and the iron surface was the acceptor The com-pounds were adsorbed to themetal surface and hence formedinhibitive adsorption layer against the corrosive media Theinhibition efficiency is in order of IB gtMB gt CV which sub-stantiates the experimental results The research by quantum
8 ISRN Physical Chemistry
chemistry revealed that the reactive sites of dye moleculesformed coordinate and back-donating bonds with atoms onmetal surface Further comparison revealed that the zones forelectron donation were the same as the zones for acceptingelectrons which could indicate a probable chemisorptionIB had the highest inhibition efficiency because it hadthe greatest ability of offering electrons and CV had thelowest inhibition efficiency A linear correlationwas observedbetween inhibition efficiencies and the inhibitor chemicalpotential as well as the extent of charge transfer to the metalsFurthermore the distribution of electronic density shows thatthe dyemolecules hadmany negatively charged active centerswith exception of IB The electron density was found to bepositively correlated with its linear structure which couldbe the effect for increase in inhibition efficiency The zonescontaining N O and S atoms are the most possible sites foradsorption of the metal iron surface This study suggests thattheoretical method might be an effective approach to assessthe inhibition performance of new inhibitors
References
[1] A D Becke ldquoDensity-functional exchange-energy approxima-tion with correct asymptotic behaviorrdquo Physical Review A vol38 pp 3098ndash3100 1988
[2] I B Obot and N O Obi-Egbedi ldquoTheoretical study of ben-zimidazole and its derivatives and their potential activity ascorrosion inhibitorsrdquo Corrosion Science vol 52 no 2 pp 657ndash660 2010
[3] M Sahin G Gece F Karcı and S Bilgic ldquoExperimental andtheoretical study of the effect of some heterocyclic compoundson the corrosion of low carbon steel in 35 NaCl mediumrdquoJournal of Applied Electrochemistry vol 38 no 6 pp 809ndash8152008
[4] D X Wang and H M Xiao ldquoQuantum chemical calculationon chemical adsorption energy of imidazolines and Fe atomrdquoJournal of Molecular Science vol 16 pp 102ndash105 2000
[5] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[6] E Jamalizadeh S M A Hosseini and A H Jafari ldquoQuantumchemical studies on corrosion inhibition of some lactones onmild steel in acid mediardquo Corrosion Science vol 51 no 6 pp1428ndash1435 2009
[7] M Karelson V S Lobanov and A R Katritzky ldquoQuantum-chemical descriptors in QSARQSPR studiesrdquo ChemicalReviews vol 96 no 3 pp 1027ndash1043 1996
[8] M A Amin K F Khaled QMohsen andH A Arida ldquoA studyof the inhibition of iron corrosion in HCl solutions by someamino acidsrdquo Corrosion Science vol 52 pp 1684ndash1695 2010
[9] G Gece S Bilgic and O Turksen ldquoQuantum chemical studiesof some amino acids on the corrosion of cobalt in sulfuric acidsolutionrdquo Materials and Corrosion vol 61 no 2 pp 141ndash1462010
[10] C Gruber and V Buss ldquoQuantum-mechanically calculatedproperties for the development of quantitative structure-activi-ty relationships (QSARrsquoS) pKA-values of phenols and aromaticand aliphatic carboxylic acidsrdquo Chemosphere vol 19 no 10-11pp 1595ndash1609 1989
[11] J Fu S Li Y Wang L Cao and L Lu ldquoComputational andelectrochemical studies of some amino acid compounds as cor-rosion inhibitors for mild steel in hydrochloric acid solutionrdquoJournal of Materials Science vol 45 pp 6255ndash6265 2010
[12] J Fang and J Li ldquoQuantum chemistry study on the relationshipbetween molecular structure and corrosion inhibition effi-ciency of amidesrdquo Journal ofMolecular Structure THEOCHEMvol 593 pp 179ndash185 2002
[13] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface by sub-stituted uracilsrdquo Applied Surface Science vol 255 no 5 part 1pp 2433ndash2441 2008
[14] A Yurt G Bereket and C Ogretir ldquoQuantum chemical studieson inhibition effect of amino acids and hydroxy carboxylic acidson pitting corrosion of aluminium alloy 7075 in NaCl solutionrdquoJournal of Molecular Structure THEOCHEM vol 725 no 1ndash3pp 215ndash221 2005
[15] G Gece ldquoThe use of quantum chemical methods in corrosioninhibitor studiesrdquo Corrosion Science vol 50 no 11 pp 2981ndash2992 2008
[16] G Zhang and C B Musgrave ldquoComparison of DFT methodsfor molecular orbital eigenvalue calculationsrdquo Journal of Physi-cal Chemistry A vol 111 no 8 pp 1554ndash1561 2007
[17] G Bereket E Hur and C Ogretir ldquoQuantum chemical studieson some imidazole derivatives as corrosion inhibitors for iron inacidic mediumrdquo Journal of Molecular Structure THEOCHEMvol 578 pp 79ndash88 2002
[18] J Vosta and J Eliasek ldquoStudy on corrosion inhibition fromaspect of quantum chemistryrdquo Corrosion Science vol 11 pp223ndash229 1971
[19] E E Oguzie Y Li S G Wang and F Wanga ldquoUnderstandingcorrosion inhibition mechanisms-experimental and theoreticalapproachrdquo RSC Advances vol 1 pp 866ndash873 2011
[20] S Xia M Qiu L Yu F Liu and H Zhao ldquoMolecular dynamicsand density functional theory study on relationship betweenstructure of imidazoline derivatives and inhibition perform-ancerdquo Corrosion Science vol 50 no 7 pp 2021ndash2029 2008
[21] F Kandemirli and S Sagdinc ldquoTheoretical study of corrosioninhibition of amides and thiosemicarbazonesrdquo Corrosion Sci-ence vol 49 no 5 pp 2118ndash2130 2007
[22] C D Taylor R G Kelly and M Neurock ldquoA first-principlesanalysis of the chemisorption of hydroxide on copper underelectrochemical conditions a probe of the electronic interac-tions that control chemisorption at the electrochemical inter-facerdquo Journal of Electroanalytical Chemistry vol 607 no 1-2 pp167ndash174 2007
[23] D Wanga S Lia Y Yinga M Wanga H Xiaob and Z CheldquoTheoretical and experimental studies of structure and inhi-bition efficiency of imidazoline derivativesrdquo Corrosion Sciencevol 41 no 10 pp 1911ndash1919 1999
[24] J Bartley N Huynh S E Bottle H Flitt T Notoya and D PSchweinsberg ldquoComputer simulation of the corrosion inhibi-tion of copper in acidic solution by alkyl esters of 5-carboxyben-zotriazolerdquo Corrosion Science vol 45 no 1 pp 81ndash96 2003
[25] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquo Journal of Physical Chemistry C vol 113 no 19pp 8420ndash8429 2009
[26] L M Rodrıguez-Valdez A Martınez-Villafane and D Gloss-man-Mitnik ldquoComputational simulation of the molecularstructure and properties of heterocyclic organic compounds
ISRN Physical Chemistry 9
with possible corrosion inhibition propertiesrdquo Journal of Molec-ular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash70 2005
[27] A Lesar and I Milosev ldquoDensity functional study of the corro-sion inhibition properties of 124-triazole and its amino deriva-tivesrdquo Chemical Physics Letters vol 483 no 4ndash6 pp 198ndash2032009
[28] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[29] E E Oguzie ldquoCorrosion inhibition ofmild steel in hydrochloricacid solution by methylene blue dyerdquo Materials Letters vol 59no 8-9 pp 1076ndash1079 2005
[30] W Yang andR Parr ldquoHardness softness and the fukui functionin the electronic theory of metals and catalysisrdquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 82 pp 6723ndash6726 1985
[31] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2 M sulphuric acid solu-tion by methylene blue dyerdquo Materials Chemistry and Physicsvol 89 no 2-3 pp 305ndash311 2005
[32] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
Figure 7 Correlation of binding energy with percent inhibition efficiency of dye molecules
CV
(a)
MB
(b)
IB
(c)
Figure 8 Representative snapshots of (a) CV (b) MB and (c) IB adsorbed on Fe(110) Inset images show the on-top views emphasizing themolecular backbone aligning with vacant sites on the fcc lattice atop the metal surface
single inhibitor molecules studied on the Fe(110) surfacefrom our simulations respectively Close inspection of theon-top view of adsorbed single molecule on Fe(110) revealsa very clear fashion in the adsorption configuration of allthe molecules wherein polarizable atoms (N O S) in themolecular backbone align with vacant sites on the fcc latticeatop the metal surface and virtually avoid contact with the Featoms on the surface plane
4 Conclusion
In this study the three dye molecules were the donators ofelectrons and the iron surface was the acceptor The com-pounds were adsorbed to themetal surface and hence formedinhibitive adsorption layer against the corrosive media Theinhibition efficiency is in order of IB gtMB gt CV which sub-stantiates the experimental results The research by quantum
8 ISRN Physical Chemistry
chemistry revealed that the reactive sites of dye moleculesformed coordinate and back-donating bonds with atoms onmetal surface Further comparison revealed that the zones forelectron donation were the same as the zones for acceptingelectrons which could indicate a probable chemisorptionIB had the highest inhibition efficiency because it hadthe greatest ability of offering electrons and CV had thelowest inhibition efficiency A linear correlationwas observedbetween inhibition efficiencies and the inhibitor chemicalpotential as well as the extent of charge transfer to the metalsFurthermore the distribution of electronic density shows thatthe dyemolecules hadmany negatively charged active centerswith exception of IB The electron density was found to bepositively correlated with its linear structure which couldbe the effect for increase in inhibition efficiency The zonescontaining N O and S atoms are the most possible sites foradsorption of the metal iron surface This study suggests thattheoretical method might be an effective approach to assessthe inhibition performance of new inhibitors
References
[1] A D Becke ldquoDensity-functional exchange-energy approxima-tion with correct asymptotic behaviorrdquo Physical Review A vol38 pp 3098ndash3100 1988
[2] I B Obot and N O Obi-Egbedi ldquoTheoretical study of ben-zimidazole and its derivatives and their potential activity ascorrosion inhibitorsrdquo Corrosion Science vol 52 no 2 pp 657ndash660 2010
[3] M Sahin G Gece F Karcı and S Bilgic ldquoExperimental andtheoretical study of the effect of some heterocyclic compoundson the corrosion of low carbon steel in 35 NaCl mediumrdquoJournal of Applied Electrochemistry vol 38 no 6 pp 809ndash8152008
[4] D X Wang and H M Xiao ldquoQuantum chemical calculationon chemical adsorption energy of imidazolines and Fe atomrdquoJournal of Molecular Science vol 16 pp 102ndash105 2000
[5] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[6] E Jamalizadeh S M A Hosseini and A H Jafari ldquoQuantumchemical studies on corrosion inhibition of some lactones onmild steel in acid mediardquo Corrosion Science vol 51 no 6 pp1428ndash1435 2009
[7] M Karelson V S Lobanov and A R Katritzky ldquoQuantum-chemical descriptors in QSARQSPR studiesrdquo ChemicalReviews vol 96 no 3 pp 1027ndash1043 1996
[8] M A Amin K F Khaled QMohsen andH A Arida ldquoA studyof the inhibition of iron corrosion in HCl solutions by someamino acidsrdquo Corrosion Science vol 52 pp 1684ndash1695 2010
[9] G Gece S Bilgic and O Turksen ldquoQuantum chemical studiesof some amino acids on the corrosion of cobalt in sulfuric acidsolutionrdquo Materials and Corrosion vol 61 no 2 pp 141ndash1462010
[10] C Gruber and V Buss ldquoQuantum-mechanically calculatedproperties for the development of quantitative structure-activi-ty relationships (QSARrsquoS) pKA-values of phenols and aromaticand aliphatic carboxylic acidsrdquo Chemosphere vol 19 no 10-11pp 1595ndash1609 1989
[11] J Fu S Li Y Wang L Cao and L Lu ldquoComputational andelectrochemical studies of some amino acid compounds as cor-rosion inhibitors for mild steel in hydrochloric acid solutionrdquoJournal of Materials Science vol 45 pp 6255ndash6265 2010
[12] J Fang and J Li ldquoQuantum chemistry study on the relationshipbetween molecular structure and corrosion inhibition effi-ciency of amidesrdquo Journal ofMolecular Structure THEOCHEMvol 593 pp 179ndash185 2002
[13] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface by sub-stituted uracilsrdquo Applied Surface Science vol 255 no 5 part 1pp 2433ndash2441 2008
[14] A Yurt G Bereket and C Ogretir ldquoQuantum chemical studieson inhibition effect of amino acids and hydroxy carboxylic acidson pitting corrosion of aluminium alloy 7075 in NaCl solutionrdquoJournal of Molecular Structure THEOCHEM vol 725 no 1ndash3pp 215ndash221 2005
[15] G Gece ldquoThe use of quantum chemical methods in corrosioninhibitor studiesrdquo Corrosion Science vol 50 no 11 pp 2981ndash2992 2008
[16] G Zhang and C B Musgrave ldquoComparison of DFT methodsfor molecular orbital eigenvalue calculationsrdquo Journal of Physi-cal Chemistry A vol 111 no 8 pp 1554ndash1561 2007
[17] G Bereket E Hur and C Ogretir ldquoQuantum chemical studieson some imidazole derivatives as corrosion inhibitors for iron inacidic mediumrdquo Journal of Molecular Structure THEOCHEMvol 578 pp 79ndash88 2002
[18] J Vosta and J Eliasek ldquoStudy on corrosion inhibition fromaspect of quantum chemistryrdquo Corrosion Science vol 11 pp223ndash229 1971
[19] E E Oguzie Y Li S G Wang and F Wanga ldquoUnderstandingcorrosion inhibition mechanisms-experimental and theoreticalapproachrdquo RSC Advances vol 1 pp 866ndash873 2011
[20] S Xia M Qiu L Yu F Liu and H Zhao ldquoMolecular dynamicsand density functional theory study on relationship betweenstructure of imidazoline derivatives and inhibition perform-ancerdquo Corrosion Science vol 50 no 7 pp 2021ndash2029 2008
[21] F Kandemirli and S Sagdinc ldquoTheoretical study of corrosioninhibition of amides and thiosemicarbazonesrdquo Corrosion Sci-ence vol 49 no 5 pp 2118ndash2130 2007
[22] C D Taylor R G Kelly and M Neurock ldquoA first-principlesanalysis of the chemisorption of hydroxide on copper underelectrochemical conditions a probe of the electronic interac-tions that control chemisorption at the electrochemical inter-facerdquo Journal of Electroanalytical Chemistry vol 607 no 1-2 pp167ndash174 2007
[23] D Wanga S Lia Y Yinga M Wanga H Xiaob and Z CheldquoTheoretical and experimental studies of structure and inhi-bition efficiency of imidazoline derivativesrdquo Corrosion Sciencevol 41 no 10 pp 1911ndash1919 1999
[24] J Bartley N Huynh S E Bottle H Flitt T Notoya and D PSchweinsberg ldquoComputer simulation of the corrosion inhibi-tion of copper in acidic solution by alkyl esters of 5-carboxyben-zotriazolerdquo Corrosion Science vol 45 no 1 pp 81ndash96 2003
[25] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquo Journal of Physical Chemistry C vol 113 no 19pp 8420ndash8429 2009
[26] L M Rodrıguez-Valdez A Martınez-Villafane and D Gloss-man-Mitnik ldquoComputational simulation of the molecularstructure and properties of heterocyclic organic compounds
ISRN Physical Chemistry 9
with possible corrosion inhibition propertiesrdquo Journal of Molec-ular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash70 2005
[27] A Lesar and I Milosev ldquoDensity functional study of the corro-sion inhibition properties of 124-triazole and its amino deriva-tivesrdquo Chemical Physics Letters vol 483 no 4ndash6 pp 198ndash2032009
[28] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[29] E E Oguzie ldquoCorrosion inhibition ofmild steel in hydrochloricacid solution by methylene blue dyerdquo Materials Letters vol 59no 8-9 pp 1076ndash1079 2005
[30] W Yang andR Parr ldquoHardness softness and the fukui functionin the electronic theory of metals and catalysisrdquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 82 pp 6723ndash6726 1985
[31] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2 M sulphuric acid solu-tion by methylene blue dyerdquo Materials Chemistry and Physicsvol 89 no 2-3 pp 305ndash311 2005
[32] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
chemistry revealed that the reactive sites of dye moleculesformed coordinate and back-donating bonds with atoms onmetal surface Further comparison revealed that the zones forelectron donation were the same as the zones for acceptingelectrons which could indicate a probable chemisorptionIB had the highest inhibition efficiency because it hadthe greatest ability of offering electrons and CV had thelowest inhibition efficiency A linear correlationwas observedbetween inhibition efficiencies and the inhibitor chemicalpotential as well as the extent of charge transfer to the metalsFurthermore the distribution of electronic density shows thatthe dyemolecules hadmany negatively charged active centerswith exception of IB The electron density was found to bepositively correlated with its linear structure which couldbe the effect for increase in inhibition efficiency The zonescontaining N O and S atoms are the most possible sites foradsorption of the metal iron surface This study suggests thattheoretical method might be an effective approach to assessthe inhibition performance of new inhibitors
References
[1] A D Becke ldquoDensity-functional exchange-energy approxima-tion with correct asymptotic behaviorrdquo Physical Review A vol38 pp 3098ndash3100 1988
[2] I B Obot and N O Obi-Egbedi ldquoTheoretical study of ben-zimidazole and its derivatives and their potential activity ascorrosion inhibitorsrdquo Corrosion Science vol 52 no 2 pp 657ndash660 2010
[3] M Sahin G Gece F Karcı and S Bilgic ldquoExperimental andtheoretical study of the effect of some heterocyclic compoundson the corrosion of low carbon steel in 35 NaCl mediumrdquoJournal of Applied Electrochemistry vol 38 no 6 pp 809ndash8152008
[4] D X Wang and H M Xiao ldquoQuantum chemical calculationon chemical adsorption energy of imidazolines and Fe atomrdquoJournal of Molecular Science vol 16 pp 102ndash105 2000
[5] E E Oguzie C K Enenebeaku C O Akalezi S C Okoro AA Ayuk and E N Ejike ldquoAdsorption and corrosion-inhibitingeffect ofDacryodis edulis extract on low-carbon-steel corrosionin acidic mediardquo Journal of Colloid and Interface Science vol349 no 1 pp 283ndash292 2010
[6] E Jamalizadeh S M A Hosseini and A H Jafari ldquoQuantumchemical studies on corrosion inhibition of some lactones onmild steel in acid mediardquo Corrosion Science vol 51 no 6 pp1428ndash1435 2009
[7] M Karelson V S Lobanov and A R Katritzky ldquoQuantum-chemical descriptors in QSARQSPR studiesrdquo ChemicalReviews vol 96 no 3 pp 1027ndash1043 1996
[8] M A Amin K F Khaled QMohsen andH A Arida ldquoA studyof the inhibition of iron corrosion in HCl solutions by someamino acidsrdquo Corrosion Science vol 52 pp 1684ndash1695 2010
[9] G Gece S Bilgic and O Turksen ldquoQuantum chemical studiesof some amino acids on the corrosion of cobalt in sulfuric acidsolutionrdquo Materials and Corrosion vol 61 no 2 pp 141ndash1462010
[10] C Gruber and V Buss ldquoQuantum-mechanically calculatedproperties for the development of quantitative structure-activi-ty relationships (QSARrsquoS) pKA-values of phenols and aromaticand aliphatic carboxylic acidsrdquo Chemosphere vol 19 no 10-11pp 1595ndash1609 1989
[11] J Fu S Li Y Wang L Cao and L Lu ldquoComputational andelectrochemical studies of some amino acid compounds as cor-rosion inhibitors for mild steel in hydrochloric acid solutionrdquoJournal of Materials Science vol 45 pp 6255ndash6265 2010
[12] J Fang and J Li ldquoQuantum chemistry study on the relationshipbetween molecular structure and corrosion inhibition effi-ciency of amidesrdquo Journal ofMolecular Structure THEOCHEMvol 593 pp 179ndash185 2002
[13] R M Issa M K Awad and F M Atlam ldquoQuantum chemicalstudies on the inhibition of corrosion of copper surface by sub-stituted uracilsrdquo Applied Surface Science vol 255 no 5 part 1pp 2433ndash2441 2008
[14] A Yurt G Bereket and C Ogretir ldquoQuantum chemical studieson inhibition effect of amino acids and hydroxy carboxylic acidson pitting corrosion of aluminium alloy 7075 in NaCl solutionrdquoJournal of Molecular Structure THEOCHEM vol 725 no 1ndash3pp 215ndash221 2005
[15] G Gece ldquoThe use of quantum chemical methods in corrosioninhibitor studiesrdquo Corrosion Science vol 50 no 11 pp 2981ndash2992 2008
[16] G Zhang and C B Musgrave ldquoComparison of DFT methodsfor molecular orbital eigenvalue calculationsrdquo Journal of Physi-cal Chemistry A vol 111 no 8 pp 1554ndash1561 2007
[17] G Bereket E Hur and C Ogretir ldquoQuantum chemical studieson some imidazole derivatives as corrosion inhibitors for iron inacidic mediumrdquo Journal of Molecular Structure THEOCHEMvol 578 pp 79ndash88 2002
[18] J Vosta and J Eliasek ldquoStudy on corrosion inhibition fromaspect of quantum chemistryrdquo Corrosion Science vol 11 pp223ndash229 1971
[19] E E Oguzie Y Li S G Wang and F Wanga ldquoUnderstandingcorrosion inhibition mechanisms-experimental and theoreticalapproachrdquo RSC Advances vol 1 pp 866ndash873 2011
[20] S Xia M Qiu L Yu F Liu and H Zhao ldquoMolecular dynamicsand density functional theory study on relationship betweenstructure of imidazoline derivatives and inhibition perform-ancerdquo Corrosion Science vol 50 no 7 pp 2021ndash2029 2008
[21] F Kandemirli and S Sagdinc ldquoTheoretical study of corrosioninhibition of amides and thiosemicarbazonesrdquo Corrosion Sci-ence vol 49 no 5 pp 2118ndash2130 2007
[22] C D Taylor R G Kelly and M Neurock ldquoA first-principlesanalysis of the chemisorption of hydroxide on copper underelectrochemical conditions a probe of the electronic interac-tions that control chemisorption at the electrochemical inter-facerdquo Journal of Electroanalytical Chemistry vol 607 no 1-2 pp167ndash174 2007
[23] D Wanga S Lia Y Yinga M Wanga H Xiaob and Z CheldquoTheoretical and experimental studies of structure and inhi-bition efficiency of imidazoline derivativesrdquo Corrosion Sciencevol 41 no 10 pp 1911ndash1919 1999
[24] J Bartley N Huynh S E Bottle H Flitt T Notoya and D PSchweinsberg ldquoComputer simulation of the corrosion inhibi-tion of copper in acidic solution by alkyl esters of 5-carboxyben-zotriazolerdquo Corrosion Science vol 45 no 1 pp 81ndash96 2003
[25] E E Oguzie S G Wang Y Li and F H Wang ldquoInfluenceof iron microstructure on corrosion inhibitor performance inacidic mediardquo Journal of Physical Chemistry C vol 113 no 19pp 8420ndash8429 2009
[26] L M Rodrıguez-Valdez A Martınez-Villafane and D Gloss-man-Mitnik ldquoComputational simulation of the molecularstructure and properties of heterocyclic organic compounds
ISRN Physical Chemistry 9
with possible corrosion inhibition propertiesrdquo Journal of Molec-ular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash70 2005
[27] A Lesar and I Milosev ldquoDensity functional study of the corro-sion inhibition properties of 124-triazole and its amino deriva-tivesrdquo Chemical Physics Letters vol 483 no 4ndash6 pp 198ndash2032009
[28] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[29] E E Oguzie ldquoCorrosion inhibition ofmild steel in hydrochloricacid solution by methylene blue dyerdquo Materials Letters vol 59no 8-9 pp 1076ndash1079 2005
[30] W Yang andR Parr ldquoHardness softness and the fukui functionin the electronic theory of metals and catalysisrdquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 82 pp 6723ndash6726 1985
[31] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2 M sulphuric acid solu-tion by methylene blue dyerdquo Materials Chemistry and Physicsvol 89 no 2-3 pp 305ndash311 2005
[32] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
with possible corrosion inhibition propertiesrdquo Journal of Molec-ular Structure THEOCHEM vol 713 no 1ndash3 pp 65ndash70 2005
[27] A Lesar and I Milosev ldquoDensity functional study of the corro-sion inhibition properties of 124-triazole and its amino deriva-tivesrdquo Chemical Physics Letters vol 483 no 4ndash6 pp 198ndash2032009
[28] E E Oguzie C Unaegbu C N Ogukwe B N Okolue and AI Onuchukwu ldquoInhibition of mild steel corrosion in sulphuricacid using indigo dye and synergistic halide additivesrdquoMateri-als Chemistry and Physics vol 84 no 2-3 pp 363ndash368 2004
[29] E E Oguzie ldquoCorrosion inhibition ofmild steel in hydrochloricacid solution by methylene blue dyerdquo Materials Letters vol 59no 8-9 pp 1076ndash1079 2005
[30] W Yang andR Parr ldquoHardness softness and the fukui functionin the electronic theory of metals and catalysisrdquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 82 pp 6723ndash6726 1985
[31] E E Oguzie G N Onuoha and A I Onuchukwu ldquoInhibitorymechanism of mild steel corrosion in 2 M sulphuric acid solu-tion by methylene blue dyerdquo Materials Chemistry and Physicsvol 89 no 2-3 pp 305ndash311 2005
[32] E E Oguzie V O Njoku C K Enenebeaku C O Akalezi andC Obi ldquoEffect of hexamethylpararosaniline chloride (crystalviolet) on mild steel corrosion in acidic mediardquo CorrosionScience vol 50 no 12 pp 3480ndash3486 2008
