Colloids and Surfaces A: Physicochem. Eng. Aspects 364 (2010) 67–71
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Colloids and Surfaces A: Physicochemical andEngineering Aspects
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Synthesis and characterization of lead(II) selective sodium dodecyl benzenesulphonate–cerium(IV) phosphate ion exchanger
Nazia Iqbal, M.Z.A. Rafiquee ∗
Department of Applied Chemistry, Z.H. College of Engineering and Technology, Aligarh Muslim University, Aligarh 202002, UP, India
a r t i c l e i n f o
Article history:Received 17 February 2010Received in revised form 24 April 2010Accepted 27 April 2010Available online 4 May 2010
Keywords:Fibrous ion exchangerCerium(IV) phosphateSodium dodecyl benzene sulphonateAdsorption studiesEnvironmental studies
a b s t r a c t
The surfactant based sodium dodecyl benzene sulphonate–cerium(IV) phosphate (SDBS–CeP) fibrousion exchanger has been synthesized and was characterized by using various physico-chemical methods.The X-ray, TGA/DTA, SEM and elemental analysis were used to characterize the ion exchanger. The ionexchange property was studied by carrying out the ion exchange capacity, elution, concentration andthermal behavior. Adsorption studies on the synthesized material have also been performed for heavymetal ions in alkalis and acidic media. The material has been found to be selective for Pb2+and therefore,the binary separations of Pb2+ from other metal ions have been performed on its column and observedto be quite effective in the presence of alkali, alkaline earth and transition metals.
Hybrid fibrous ion exchange materials [1] have shown to exhibitoutstanding chemical, mechanical and thermal stability and alsopossess the properties of selective metal ion adsorption. The intro-duction of organic species into an inorganic ion exchanger resulted[2–8] into enhanced reproducibility in ion exchange behavior andchemical stability to some extent. Surfactants or surface-activeagents is capable of reducing the interfacial tensions [9,10] betweensolid and liquid phases by adsorbing themselves on the solid sur-faces. The presence of surfactant helps and enhances the selectiveadsorption of some of the heavy metals onto the porous surface ofexchangers. In the present study, attempt has been made to synthe-size clean, durable and non-toxic ion exchanger by incorporatingsodium dodecyl benzene sulphonate in the matrix of Ce(IV) phos-phate. The reported ion exchanger has high ion exchange capacityand is observed to be mechanically stable as well as highly selec-tive towards Pb2+ ion in the presence of acid, alkali metals, alkalineearth metals and other transition metals. The higher moieties forPb2+ may be due to higher binding constant for Pb2+ on SDBS [11]molecules in the matrix of cerium(IV) phosphate.
Ceric sulphate [Ce(SO4)2·4H2O], cadmium nitrate was obtainedfrom CDH (India) while sodium dodecyl benzene sulphonate, sul-phuric acid(H2SO4), calcium nitrate, sodium nitrate were obtainedfrom Merck-Schuchardt (Germany) and phosphoric acid (H3PO4),cupper nitrate Cu(NO3), lead nitrate (Pb(NO3)) were obtained fromQualigens (India), respectively.
2.2. Instruments used
X-ray diffraction studies were performed on a Philips Analyt-ical X-ray B.V. diffractometer type PW 170 B.V. and IR studieswere carried out on Shimadzu 8201 PC spectrophotometer. ForTGA/DTA/DTG, PerkinElmer Pyris Diamond model was used. Ele-mental analysis was performed to check the presence of SDBSmolecule in the matrix of cerium(IV) phosphate by Heraeus CarloErba-1108 analyzer. Differential Pulse polarogrms were recordedby using an Elico CL-362 Pulse Polarograph and SEM studies wereperformed on SEM Hitachi-S520, Japan.
2.3. Preparation of the reagent solutions
Solution of 0.05 M ceric sulphate was prepared in 0.5 M H2SO4.The stock solutions of 0.01 M sodium dodecyl benzene sulphonate,6.0 M solution of phosphoric acid, 0.1 M sodium hydroxide, 1.0 Msodium nitrate, 0.01 M cadmium nitrate, 0.01 lead nitrate, 0.01 M
Table 2Variation of ion exchange capacity of SDBS–CeP with eluant concentrations.
Concentration of NaNO3 (M) Ion exchange capacity (meq/g)
0.2 1.350.4 1.680.6 1.700.8 1.801.0 2.171.2 2.17
zinc nitrate, 0.01 M copper nitrate, 0.1 M sodium nitrate, 0.1 M mag-nesium nitrate, 0.1 M potassium nitrate, 0.1 M calcium nitrate wereprepared in the demineralized water.
2.4. Synthesis of the ion exchange material
Samples of SDBS–CeP (sodium dodecyl benzene sulphoate basedcerium(IV) phosphate) were prepared by adding one volume of0.05 M ceric sulphate solution to two volumes of a (1:1) mixture of6.0 M H3PO4 and SDBS solutions drop-wise with constant stirringwith a magnetic stirrer at a temperature of 60 ± 5 ◦C. The resultingslurry, was stirred for 3½ h at this temperature, filtered and thenwashed with demineralized water till pH ∼ 4. The samples werethen left to dry at room temperature. Material in the form of sheetwas obtained. It was crushed into small pieces and then was kept in1.0 M HNO3 for 24 h to convert it into H+-form. It was then washedwith demineralized water, dried at 45 ◦C and sieved to obtain par-ticles of size 50–70 mesh. Table 1 provides details of the synthesisand ion exchange capacity of the samples. Sample-3 was selectedfor further studies because it possessed the highest ion exchangecapacity.
2.5. Ion exchange capacity (i.e.c)
The ion exchange capacity of the sample was determined by thecolumn method in which 1 g of the material (H+-form) was takenin a glass burette of internal diameter ∼1 cm, fitted with glass woolat its bottom. 250 ml of 1 M NaNO3 solution was used as eluant,maintaining a very slow flow rate (∼0.5 ml min−1). The effluent wastitrated against a 0.1 NaOH solution to determine the total H+-ionsliberated during ion exchange process (Table 1).
2.6. Concentration behavior
The extent of elution was dependent upon the concentration ofthe eluant. Hence, a fixed volume (250 ml) of the NaNO3 solution ofvarying concentrations was passed through the column containing1 g exchanger. The effluent was titrated against a standard alkalisolution for the H+-ions eluted out. Table 2 shows the variation ofion exchange capacity of the material with varying concentrationsof the eluant.
2.7. Elution behavior
A similar column (as above) containing 1 g exchanger was elutedwith 1.0 M NaNO3 solution in different 10 ml fractions with a min-
Fig. 1. Histograms showing the elution behavior of SDBS–CeP.
imum flow rate as described above. The histogram (Fig. 1) showsthe elution behavior of the exchanger.
2.8. Thermal stability
Several 1 g samples of the material were heated to 100 ◦C, 150 ◦Cand 300 ◦C in a muffle furnace for 1 h each and thereafter their ionexchange capacity was determined by the column process aftercooling them to room temperature. The results are reported inTable 3.
2.9. Adsorption studies
200 mg of the exchanger in H+-form was added to a mixture con-taining 18 ml of the acid solution and 2 ml of the metal ion solution.The mixture was kept for 24 h, shaking intermittently to achieveequilibrium. The amount of metal ions (Cu2+, Cd2+, Pb2+, Zn2+) inthe solution before and after equilibrium was determined by dif-ferential pulse polarographic method. The distribution coefficients(Kd) values were calculated by using the following formula and theresults are presented in Table 4
Kd = I − F
F
V
M
(ml g−1
)
where Kd is the distribution coefficient (ml g−1), I is the initialamount of metal ions in the solution, F is the final amount of metalions in the solution, V is the volume of the solution (ml), and M isthe amount of the exchanger taken (g).
The adsorption studies for Pb2+ were also carried out in the pres-ence of nitric acid, alkali and alkaline earth metal. The initial andfinal concentrations of Pb2+ were determined by differential pulsepolarographic method. The results are reported in Table 5. It wasobserved that Pb2+ is completely removed when passed through
Table 3Thermal stability of SDBS–CeP after heating to various temperatures for 1 h.
N. Iqbal, M.Z.A. Rafiquee / Colloids and Surfaces A: Physicochem. Eng. Aspects 364 (2010) 67–71 69
Table 5Kd values of Pb(II) on SDBS–CeP in the presence of0.1 M alkali and 0.1 alkali earth metals.
Metal ions Kd values
Na 153.72K 141.15Mg 123.04Ca 3675.58
the column containing 2 g of the synthesized material in the pres-ence of 0.01 M nitric acid, alkali, alkaline earth metal and transitionmetals The column with internal diameter ∼0.6 cm was washedthoroughly with the demineralized water and the mixture wasthen loaded onto it, maintaining a flow rate of ∼2–3 drops min−1
(0.15 ml min−1). The removal of Pb2+ in the presence of Cu2+,Cd2+, Zn2 is indicated by the differential pulse polarogram (Fig. 2)recorded before and after passing the mixture of these ions throughthe column.
3. Results and discussion
The most salient feature of SDBS–CeP has been its exceedinglyhigh selectivity towards Pb2+ ion in the presence of nitric acid (0.1 Mand 0.01 M), alkali metals (0.1 Na+ and 0.1 K+), alkaline earth metals(0.1 Mg2+ and 0.1 Ca2+) and other transition metal ions (e.g. 0.01 MCu2+, 0.01 M Cd2+, 0.01 M Zn2+ etc.). Tagasgira et al. [11] has demon-strated that pure and dry surfactants can be crystallized easily andhave lamellar structure. They determined the value of stability con-stant (−log Ks = 11.3) for the binding of Pb2+ with SDBS [11]. Duringthe extraction, all the Na+ ions in SDBS were completely replacedby the Pb2+-thiourea complex as evident from the increased inter-layer distances for SDBS and Pb2+-SDBS phases. In SDBS–CeP ionexchanger, the SDBS molecules are intercalated in the matrix ofcerium(IV) phosphate and due to higher affinity for Pb2+, the Pb2+
Fig. 2. Differential pulse polarogram of metal ions; before passing through the col-umn (upper curve) and after passing through the column (lower curve, marked asA–D) containing the SDBS–CeP ion exchanger.
Fig. 3. SEM photograph of SDBS–CeP.
ions are completely removed from the mixture of other metal ions.Na+ from SDBS is replaced by Pb2+ as counter ion during the ionexchange process and as a result Pb2+-DBS ion-pair is formed due tostrong electrostatic attractive force between the oppositely chargedbivalent Pb2+ and dodecyl benzene sulphonate ions. Additionally,the synthesized material possessed high ion exchange capacity forthe Na+ ions (2.17 meq/dry g) which is higher than the ion exchangecapacity of Ce(IV) phosphate alone, i.e., 1.3 meq/dry g [12]. Thismay be due to the incorporation of SDBS molecules in Ce(IV) phos-phate matrix to form an intercalated inorganic–organic fibrous ionexchanger as shown by SEM photograph in Fig. 3. Furthermore, thematerial can be obtained in the form of fibrous sheet.
The elution behavior reveals that the exchange is quite fast andalmost all the H+ ions are eluted out in the first 180 ml of the effluentfrom a column of 1 g exchanger (Fig. 1). Similarly, the optimumconcentration of the eluant was found to be 1.0 M NaNO3 (Table 2)for a complete removal of H+ ions from the above column.
The study on thermal stability reveals that SDBS–CeP is ther-mally more stable than cerium(IV) phosphate (CeP). The SDBS–CePion exchange capacity, of about 96.77% is retained on heatingup to 100 ◦C. On heating the material in the temperature range150–300 ◦C, it retains the ion exchange capacity of about 74.65% and71.88%, respectively, of its initial value (i.e. before heating) whileCeP retains 61.8% and 13.1% of its ion exchange capacity on heat-ing in the same temperature range. The results are summarized inTable 3.
The thermograms (Fig. 4) of the material show mass losses of16.92% up to 249 ◦C with the removal of external water moleculesas well as partial removal of SDBS. The further weight loss of 4.98%occurs on heating upto 499 ◦C due to the removal of the remainingpart of SDBS. Beyond 499 ◦C, weight becomes almost constant bycontinuing heating up to 800 ◦C with the formation of CeO2 [13].The data of thermal analysis (Table 3) reveals that the removal ofexternal water molecules has a little effect on ion exchange capacityof the material. A change in ion exchange capacity between 200 ◦Cand 300 ◦C may be associated with the partial removal of SDBS andalso due to removal of strongly co-ordinated water molecules. Astemperature is increased beyond 300 ◦C, a sharp decrease in ionexchange capacity is observed which may be due to the removalof SDBS followed by CeO2 formation and also due to disruption ofintercalated fibrous structure of the prepared material.
The IR spectrum of the material (Fig. 5) indicates the pres-ence of phosphate groups [14] by the peaks at 508.44 cm−1 and10731.9 cm−1, and metal-oxygen and metal-hydroxide bondingby the peak at 621.35 cm−1. The peak at 1637.56 cm−1 repre-sents the external water molecules in addition to its usual range
70 N. Iqbal, M.Z.A. Rafiquee / Colloids and Surfaces A: Physicochem. Eng. Aspects 364 (2010) 67–71
Fig. 4. TGA/DTA curves of SDBS–CeP.
at 3426.1 cm−1. The bands beyond at 3413.35 cm−1 correspondto –OH groups. The XRD study of the material shows that it issemi-crystalline in nature having tetragonal structure and latticetype P with space group P421C. The found cell parameters area = b = 6.9062, c = 5.4092, ˛ = ˇ = � = 90◦ with error 0.02. The indexedpeak confirms the semi-crystalline nature of the synthesized mate-rial (JCPDF file No. 811472) (Fig. 6).
The adsorption studies of the synthesized material for heavymetal ions have been performed in acidic media (Table 4). Theadsorption of Pb2+ ions has also been performed in alkali andalkaline earth media (Table 5). The presence of sodium dodecylbenzene sulphonate in the matrix of Ce(IV) phosphate not onlyenhances the ion exchange capacity of the material but also helpsPb2+ ions to adsorb preferentially. The adsorption studies revealedthat the adsorption of metal ions is higher on SDBS–CeP thanthat on CeP [9]. The Pb2+ ion has been effectively removed whenits mixture (containing 10−3 M Pb2+) with 10−1 M HNO3, Na+, K+,Ca2+, Mg2+ when passed through the thoroughly washed column.The enhanced adsorption and removal of Pb2+ by SDBS may be
Fig. 6. X-ray diffraction patterns of SDBS–CeP.
attributed to the formation of ion-pair complexes of surfactant withthe metal ions and also due to the reduction in interfacial tensionsbetween the solid and liquid phases due to amphiphilic nature ofsurfactant. These adsorption studies demonstrate that the mate-
Fig. 5. IR spectrum of SDBS–CeP.
N. Iqbal, M.Z.A. Rafiquee / Colloids and Surfaces A: Physicochem. Eng. Aspects 364 (2010) 67–71 71
rial is highly selective for Pb2+, one of the polluting ionic species.Its high selectivity towards Pb2+ reveals its importance in analyticaland environmental chemistry where the separation and removal ofPb2+ is required. Therefore, the potential role of SDBS–CeP in envi-ronmental studies has been demonstrated by achieving separationsof Pb2+ on the columns of SDBS–CeP.
4. Conclusions
A new surfactant based ion exchanger, SDBS–Ce(IV) phosphatewas synthesized in the laboratories and found to possess highion exchange capacity (2.17 meq/g). The elution of H+ from thematerial is quite fast and almost all the H+ ions are eluted out inthe first 180 ml of the effluent having optimum concentration of1.0 M. SDBS–CeP is thermally stable and retains the ion exchangecapacity∼74.65% and 71.88% at 150 ◦C and 300 ◦C, respectively, ofits initial value. The fibrous nature of SDBS–Ce(IV) phosphate is evi-dent from the SEM studies. The ion exchanger possesses very highselectivity towards Pb2+ ion making it potential candidate for Pb2+
separation and can be used in environmental pollution control.
Acknowledgement
The authors thank the Chairman, Department of AppliedChemistry, Aligarh Muslim University, Aligarh-202002, India forproviding research facilities.
References
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1953.[14] C.N.R. Rao, Chemical Applications of Infrared Spectroscopy, Academic Press,
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Chemical Engineering Journal 169 (2011) 43–49
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Chemical Engineering Journal
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Synthesis and characterization of sodium bis(2-ethylhexyl) sulfosuccinate basedtin(IV) phosphate cation exchanger: Selective for Cd2+, Zn2+ and Hg2+ ions
Nazia Iqbal, Mohammad Mobin, M.Z.A. Rafiquee ∗
Department of Applied Chemistry, Z.H. College of Engineering and Technology, Aligarh Muslim University, Aligarh 202002, India
a r t i c l e i n f o
Article history:Received 4 November 2010Received in revised form 16 February 2011Accepted 18 February 2011
Keywords:Fibrous ion exchangerTin(IV) chlorideSodium bis(2-ethylhexyl) sulfosuccinatetin(IV) phosphateAdsorption studiesEnvironmental studies
a b s t r a c t
The surfactant sodium bis(2-ethylhexyl) sulfosuccinate based tin(IV) phosphate (AOT-SnP) fibrous ionexchanger has been synthesized and characterized by using different physico-chemical methods. Thecharacterization of the exchanger was performed by using infrared (IR), X-ray diffraction (XRD), scan-ning electron microscopy (SEM) and elemental analysis. The ion exchange property was studied bydetermining the ion exchange capacity, elution and concentration behavior of the cation exchanger.The thermal behavior of exchanger was studied by performing ion exchange capacity at different tem-peratures. Adsorption studies on the synthesized material showed that it is highly selective for Cd2+,Zn2+and Hg2+ ions. Therefore, the separation of Cd2+, Zn2+and Hg2+ ions from the synthetic waste waterhas been performed on its column and observed to be quite effective in presence of acid, alkali, alkalineearth and other transition metals.
Toxic heavy metals such as cadmium, lead, chromium, etc. areconstantly released into the environment. Toxic metals are dan-gerous environmental pollutants and scientists are constantly insearch of the efficient, cost effective and easy techniques for theirremoval. Adsorption is the one of the important procedure for theremoval of the traces heavy metals from the environment [1–3].The main properties of the adsorbents for heavy metal removalare strong affinity and high loading capacity. Various substances,such as activated carbon, ion exchange resins, natural and syn-thetic zeolites and clay minerals have been used as adsorbentsfor the removal of heavy metals from water and wastewater.Among these techniques, ion exchange became one of the most fre-quently used chromatographic techniques for the removal of heavymetal pollutants from the waste water. It possesses high resolvingpower and high capacity. Hybrid fibrous ion exchange materials[4] have shown to exhibit outstanding chemical, mechanical andthermal stability and also have the properties of selective metalion adsorption. The introduction of organic moieties into inorganicion exchangers result [5–9] enhanced reproducibility. Surfactantsor surface-active agents are capable of reducing the interfacialtensions [10,11] between solid and liquid phases by adsorbingthemselves onto the solid surfaces. The surfactants [12–16] have
∗ Corresponding author. Present address: College of Engineering & Technology,Hoon, Libya. Mobile: +218 914862788.
been found to be quite selective for adsorption of some of the heavymetals onto the porous surface of exchangers owing to its ionic orpolar nature. In the present study, attempts have been made to syn-thesize clean, durable and non-toxic ion exchanger selective for theremoval of Cd2+, Zn2+ and Hg2+ ions by incorporating sodium bis(2-ethylhexyl) sulfosuccinate in the matrix of tin(IV) phosphate. Thision exchanger is found to possess high ion exchange capacity and isobserved to be thermally stable. This cationic exchanger was capa-ble of removing the ions of Cd2+, Zn2+and Hg2+ from the solutionscontaining acid, alkalis, alkaline earth metals and other transitionmetals. The removal of Cd2+, Zn2+and Hg2+ ions may be attributedto higher binding constant for these metal ions on AOT moleculesincorporated in the matrix of tin(IV) phosphate.
2. Experimental
2.1. Reagents and chemicals
Tin(IV) chloride (CDH, India), cadmium nitrate (CDH, India),magnesium nitrate (CDH, India), strontium nitrate (CDH, India),sodium bis(2-ethylhexyl) sulfosuccinate (Merck-Schuchardt,Germany), calcium nitrate (Merck-Schuchardt, Germany), bariumnitrate (Merck-Schuchardt, Germany), nickel(II) nitrate (Merck-Schuchardt, Germany), ferrous(II) nitrate (Merck-Schuchardt,Germany), sodium nitrate (Merck-Schuchardt, Germany) wereused during the studies. Phosphoric acid (Qualigens, India), cop-per(II) nitrate and lead(II) nitrate were obtained from Qualigens,India. Mercuric nitrate, zinc nitrate were obtained from ThomasBaker, UK.
44 N. Iqbal et al. / Chemical Engineering Journal 169 (2011) 43–49
2.2. Instruments used
X-ray diffraction studies were performed on a Philips Ana-lytical X-ray B. V. diffractometer type PW 170 B.V. and IRstudies were carried out on Shimadzu 8201 PC spectropho-tometer. The presence of AOT molecule in the matrix oftin(IV) phosphate was checked using elemental analysis by Her-aeus Carlo Erba-1108 analyzer. Differential Pulse polarogramswere recorded by using an Elico CL-362 Pulse Polarographand SEM studies were performed on SEM Hitachi-S520, Japan.For TGA/DTA/DTG Perkin Elmer Pyris Diamond model wasused.
2.3. Preparation of the reagent solutions
Solution of tin(IV) phosphate was prepared by adding tin(IV)chloride to 0.6 M H3PO4. The stock solutions of 0.01 M sodium bis(2-ethylhexyl) sulfosuccinate, 0.6 M solution of phosphoric acid, 0.1 Msodium hydroxide, 1.0 M sodium nitrate, 0.01 M cadmium nitrate,0.01 M lead nitrate, 0.01 M zinc nitrate, 0.01 M copper nitrate, 0.1 Msodium nitrate, 0.1 M magnesium nitrate, 0.1 M potassium nitrate,0.1 M calcium nitrate and nitric acid (0.1 M and 0.01 M) were pre-pared in the doubly distilled demineralized water.
2.4. Synthesis of the ion exchange material
The samples of AOT-SnP (bis(2-ethylhexyl) sulfosuccinate-tin(IV) phosphate) were prepared by adding one volume of 0.3 Mtin(IV) chloride solution to two volumes of a (1:1) mixture of 0.6 MH3PO4 and three different concentrations (namely, 0.01 M, 0.001 Mand 0.0001 M) of sodium bis(2-ethylhexyl) sulfosuccinate solutionsdrop-wise with constant stirring with a magnetic stirrer at tem-perature 60 ± 5 ◦C. The resulting slurry was stirred for 3.5 h at thistemperature. Then it was filtered and washed with demineral-ized water till pH∼4 was achieved. The samples were then left todry at room temperature. Sheet-like material was obtained. It wascrushed into small pieces and then was kept in 1.0 M HNO3 for 24 hto charge it into H+ form. The exchanger was washed with deminer-alized water, left to dry at 45 ◦C and then sieved to obtain particlesof size 50–70 mesh. The sample synthesized using 0.0001 M sodiumbis(2-ethylhexyl) sulfosuccinate solutions was selected for furtherstudies as it possessed the highest ion exchange capacity.
2.5. Ion exchange capacity (i.e.c)
The ion exchange capacity of the sample was determined by thecolumn method. 1.0 g of the material (in H+ form) was taken in aglass burette of internal diameter ∼1 cm, fitted with glass wool atthe bottom. 1.0 M NaNO3 solution was used as eluant. 250 mL ofthe solution was passed through the column with a very slow flowrate (∼0.5 mL min−1). The effluent was titrated against a standard-ized 0.10 M NaOH solution to determine the total H+ ions liberatedduring ion exchange process.
2.6. Concentration behavior
The extent of elution was dependent upon the concentrationof the eluant used. To obtain an optimum elution, a fixed vol-ume (250 mL) of the NaNO3 solution of varying concentrationswas passed through the column containing 1.0 g exchanger. The H+
ions eluted out was titrated against standardized sodium hydrox-ide solution. Table 1 shows the dependence of variation of ionexchange capacity of the material on the concentration of the elu-ant.
Table 1Dependence of variation in ion exchange capacity of AOT-SnP at different eluantconcentrations.
Concentration of NaNO3 (M) Ion exchange capacity (meq/g)
0.2 1.100.4 1.250.6 1.680.8 1.801.0 2.401.2 2.40
Table 2Thermal stability of AOT-SnP after heating to various temperatures for 1 h.
Dryingtemperature(◦C)
Na+-ion exchangecapacity (meq/g)
Change in colour % Retention ofion exchangecapacity
A similar column (as above) containing 1.0 g exchanger waseluted with 1.0 M NaNO3 solution in different 10 mL fractions witha minimum flow rate as described above. The histogram (Fig. 1)shows the elution behavior of the exchanger.
2.8. Thermal stability
Several 1 g samples of the material were heated at temperatures100 ◦C, 150 ◦C and 300 ◦C in a muffle furnace for 1 h. After cooling toroom temperature, their ion exchange capacity was determined bythe column process. The physical appearance and observed resultsare given in Table 2.
2.9. Adsorption studies
The study on the adsorption behavior of ion exchanger was car-ried out by taking 200 mg of the synthesized material in H+ formin a conical flask. To this exchanger, metal ion solution was addedin the presence of varying strength of acid to study the influenceof acid on the adsorption of metal ions by the exchanger. Similarly,the effect of strength of alkali metals on the adsorption of metalions was also studied. The mixture (containing the metal ion andacid/alkali) was thermostated at room temperature (25 ◦C) for 24 h,shaking intermittently to achieve equilibrium. The concentration of
Ca2+, Mg2+, Ba2+, Sr2+, Ni2+ and Hg2+ ions in the solution before andafter equilibrium was determined by titration with standardizeddisodium salt of EDTA solution. The concentration of Cu2+, Cd2+,Pb2+ and Zn2+ ions before and after adsorption was determined byusing differential pulse polarographic method. Spectrophotomet-ric method was used to determine the concentration of Fe2+. Thedistribution coefficient (Kd) for these metal ions was calculated byusing the following formula. Kd values of these metal ions are givenin Table 3.
Kd = I − F
F
V
M(mL g−1)
where, Kd is the distribution coefficient (mL g−1); I is the initialamount of metal ions in the solution; F is the final amount of metalions in the solution; V is the volume of the solution (mL); M is theamount of the exchanger taken (g).
To study the separation of metal ions, 2.0 g of the synthesizedmaterial was taken into a column with internal diameter ∼0.6 cm.The column was washed thoroughly with the demineralized waterand the mixture containing Ca2+, Mg2+, Ba2+, Sr2+, Cu2+, Cd2+, Pb2+
and Zn2+ ions was then loaded onto it, maintaining a flow rateof ∼2 to 3 drops min−1 (approx. 0.15 mL min−1). It was observedthat Cd2+ and Zn2+ were completely removed from the mixturewhen passed through the column. The study of separation wasrepeated by taking a mixture of Cu2+, Cd2+, Pb2+ and Zn2+ solu-tions in the presence of 0.01 M nitric acid as well as in the presenceof 0.01 M sodium hydroxide solution. It was observed that thesemetal ions were completely removed in the presence of nitric acidand also in presence of sodium hydroxide. The removal of Cd2+ andZn2+ in the presence of Cu2+and Pb2+ is evident from the differ-ential pulse polarogram (Fig. 2) recorded before and after passingthe mixture of these ions through the column. The Kd values ofmetal ions under the varying experimental conditions are given inTables 3 and 4.
Table 4Kd values of Cd2+ and Zn2+ on AOT-SnP exchanger in presence of 0.1 M alkali andalkali earth metals.
Fig. 2. Differential pulse polarogram of metal ions; before passing through the col-umn (upper curve) and after passing through the column (lower curve) containingthe AOT-SnP ion exchanger.
3. Results and discussion
The newly synthesized AOT-SnP ion exchanger has beenobserved to possess high selectivity towards Cd2+, Zn2+ and Hg2+
ions. The selectivity of these ions is retained in the presenceof 0.01 M nitric acid, 0.01 M alkali metal ions (Na+ and K+) and0.01 M alkaline earth metal ions (Mg2+ and Ca2+). The presenceof other transition metal ions (e.g. 0.01 M Cu2+, 0.01 M Pb2+, etc.)also did not influence the adsorption behavior of AOT-SnP forCd2+, Zn2+ and Hg2+ ions. Ionic surfactants bind the metal ionsreversibly as counter ions and have higher values of stability con-stants [17]. Studies by Sigimura et al. [18] show that the metalions are bonded to AOT molecule through SO group and is ionic innature. They have also demonstrated by the infrared spectral stud-ies that there was little coordination interaction of carbonyl groupswith metal ions. In AOT-SnP ion exchanger, the AOT molecules areintercalated in the matrix of tin(IV) phosphate and have higheraffinity for Cd2+, Zn2+ and Hg2+ ions. Therefore, Cd2+, Zn2+ andHg2+ ions are bonded to SO group of AOT during the exchangeprocess. Thus, due to strong adsorption of Cd2+, Zn2+ and Hg2+
ions to the SO group of AOT, these ions are completely removed
Fig. 3. SEM photograph of AOT-SnP.
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46 N. Iqbal et al. / Chemical Engineering Journal 169 (2011) 43–49
Fig. 4. IR spectrum of AOT-SnP.
Position [°2Theta] (Copper (Cu))
10 20 30 40 50 60 70
Counts
0
200
400
600
800
AOT+CCP
Fig. 5. X-ray diffraction patterns of AOT-SnP.
Table 5Binary separations of metal ions achieved on AOT-SnP column.
S. No Separation achieved Eluant used Volume of eluant (ml) Amount loaded (�g) Amount found (�g) Error (%)
1 Hg2+ 1 M HNO3 60 6852.4 6681.09 +2.50Mg2+ 1 M HNO3 70 5128.2 4999.90 −2.25
2 Hg2+ 1 M HNO3 70 6852.4 6852.40 0Ba2+ 1 M HNO3 70 5226.8 5357.47 −2.50
3 Hg2+ 1 M HNO3 70 6852.4 7195.02 +5.00Sr2+ 1 M HNO3 80 4232.2 4232.2 0
4 Hg2+ 1 M HNO3 70 6852.4 7023.71 +2.50Ni2+ 1 M HNO3 70 5816.2 5961.60 +2.49
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N. Iqbal et al. / Chemical Engineering Journal 169 (2011) 43–49 47
Fig. 6. TGA/DTA curve of AOT-SnP.
from the mixture. Therefore, during the ion exchange process,Na+ from AOT is replaced by Cd2+, Zn2+ and Hg2+ ions as counterion and as a result Cd2+-AOT, Zn2+-AOT and Hg2+-AOT ion-pairsare formed. The strong electrostatic attractive force is respon-sible for the binding between the oppositely charged bivalentCd2+, Zn2+ and Hg2+ ions and dioctyl sulfosuccinate ions. Theincorporation of dioctyl sulfosuccinate increased the ion exchangecapacity for the synthesized exchanger. Therefore, the ion exchangecapacity is higher (2.40 meq/g for Na+ ion) than that of tin(IV)phosphate (1.50 meq/g). The AOT molecule in tin(IV) phosphatematrix forms an intercalated inorganic–organic fibrous structureas shown by SEM photograph in Fig. 3. Being fibrous in nature,this material has an added advantage to obtain it in the form ofsheet.
The elution behavior reveals that the process of exchange isquite fast and almost all the H+ ions are eluted out in the first170 mL of the effluent from a column of 1.0 g exchanger (Fig. 1).Similarly, the optimum concentration of the eluant was found tobe 1.0 M NaNO3 (Table 1) for complete removal of H+ ions from theexchanger.
The IR spectrum of the material (Fig. 4) indicates the pres-ence of phosphate groups [19] by the appearance of peaksat 1164.28 cm−1; the overlapping between S O and; CH2, CH3deformation and CH2 wagging is represented by the band appear-ing in the range 1397.95–1520.73 cm−1 [20,21] and the peakat 1631.62 cm−1 represents the carbonyl group [22]. The bandsappearing at 3100.97 cm−1 for CH stretching [23], 3203.94 cm−1
and 3341.57 cm−1 for intermolecular hydrogen bonded OH stretch-ing [13]. The bands appearing at 3441.57 cm−1 correspond to –OHgroups [24], 3572.27 cm−1 for free OH stretching, 3754.45 cm−1forasymmetrical stretching of OH [25]. The XRD study of the mate-rial has been carried out by using Rigaku Cu K� radiation with thewavelength 1.54 A. It shows that the material is semi-crystalline innature having tetragonal structure with cell parameter a = b = 8.9 Aand c = 5.40 A. The h k l values at 2� = 29◦, 33◦, 47◦ are (0 0 2), (1 1 0)
and (2 0 0), respectively, and lattice is of type P with space groupP421C. The indexed peak confirms the semi-crystalline nature ofthe synthesized material (Fig. 5).
The study on thermal stability reveals that AOT-SnP is thermallystable up to 150 ◦C where the exchange capacity of 83.3% is retainedby the exchanger. On heating the material in the temperature range150–200 ◦C, the ion exchange capacity is reduced to about 43.3%.On further heating to 300 ◦C, the material possesses only 29.2% ofion exchange capacity of its initial value (i.e. before heating). Theresults are summarized in Table 2. The thermogravimetric analy-sis (TGA) curve in Fig. 6 shows ∼19% mass loss in the temperaturerange 100–150 ◦C, may be associated with the removal of exter-nal and interstitial water molecules. The weight loss of ∼6% onheating at temperature above 150 ◦C is attributed to the decom-position of bis-2-ethylhexyl sulfosuccinate molecules slowly andcompletely at 640 ◦C. The removal of organic part causes in lower-ing in the ion exchange capacity of the synthesized material. Theresidual mass (30%) at temperature above 650 ◦C may be due to thecomplete formation of oxides of metal after the removal of oxygenand phosphorus.
The adsorption studies on the synthesized material for heavymetal, alkali metal and alkaline earth metal ions in acidic media aregiven in Table 3. The adsorption of Cd2+ and Zn2+ ions on the AOT-SnP exchanger has also been performed in the presence of alkaliand alkaline earth metal ions and the results are given in Table 4.
The separation capability of the material has been demonstratedby achieving some binary separations involving viz. Hg2+–Mg2+,Hg2+–Ba2+, Hg2+–Sr2+ and Hg2+–Ni2+ of metal ions on the columnof the material. The sequential elution of the ions from the col-umn depends upon the metal ligand stability. The elution profiles ofmetal ion separated are shown in Fig. 7. The weakly retained metalions are eluted first and strongly retained metal ions are eluted inthe last. The separations are quite sharp and recovery of the metalions was found to be quantitative and reproducible. The results aresummarized in Table 5.
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48 N. Iqbal et al. / Chemical Engineering Journal 169 (2011) 43–49
0 20 40 60 80 100 120 140 1600.0
0.5
1.0
1.5
2.0Hg(II)
Mg(II)V
olu
me
of
ED
TA
(m
l)
Volume of effluent(ml)
B
0 20 40 60 80 100 120 140 160 1800.0
0.5
1.0
1.5
2.0
Vo
lum
e o
f E
DTA
(m
l)
Volume of effluent(ml)
Hg(II)
Ni(II)
B
0 20 40 60 80 100 120 140 160 1800.0
0.5
1.0
1.5
2.0 Hg(II)
Ba(II)
Volume of effluent(ml)
Vo
lum
e o
f E
DTA
(m
l)
B
0 20 40 60 80 100 120 140 160 1800.0
0.5
1.0
1.5
2.0
Vo
lum
e o
f E
DTA
(m
l)
Volume of effluent(ml)
Hg(II)
Ni(II)
B
Fig. 7. Chromatograms of binary separations of metal ions on AOT-SnP cation exchanger columns.
4. Conclusion
The presence of dioctyl sulfosuccinate ions in the matrix ofSn(IV) phosphate enhanced the ion exchange capacity of the mate-rial and also helped to remove Cd2+, Zn2+ and Hg2+ ions completelyin the presence of other metal ions from the synthetic wastewater. These Cd2+, Zn2+ and Hg2+ ions were removed from themixture containing Cd2+, Zn2+ and Hg2+, Na+, K+, Ca2+, Mg2+ ionswhen passed through the column containing the exchanger. Theenhanced adsorption and removal of Cd2+, Zn2+ and Hg2+ by AOT-SnP demonstrate that the material is highly selective for Cd2+, Zn2+
and Hg2+ ions. These metal ions are among the heavy metal pol-lutants of water. The high selectivity of exchanger towards Cd2+,Zn2+ and Hg2+ will be much helpful in analytical and environmen-tal chemistry for the separation and removal of these ions duringthe treatment of waste water. Thus, AOT-SnP may become potentialcandidate for the separations and removal of Cd2+, Zn2+ and Hg2+
ions in environmental studies.
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1
ABSTRACT
The ion exchange process has been in practice with the start of civilization for
obtaining soft water. But the modern study in this field started with the discovery of
the process by Thomson [1] and Way [2]. Ion exchange is probably the most
frequently used chromatographic technique for the separation and purification of
charged species. The technique of ion exchange chromatography is based on
interaction between solute molecules and ligands immobilized on a chromatography
matrix. Depending upon the charge on matrix and the ions taking part in ion exchange
process, exchanger may be anion exchanger or cation exchanger. If both types of
charged ions are taking part in an ion exchange process then this type of exchanger is
known as amphoteric exchanger. The matrix may be composed of materials such as
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