Chemical Engineering Journal 231 (2013) 182–189

Contents lists available at SciVerse ScienceDirect

Chemical Engineering Journal

journal homepage: www.elsevier .com/locate /ce j

Catalytic degradation of a plasticizer, di-ethylhexyl phthalate, usingNx–TiO2�x nanoparticles synthesized via co-precipitation

1385-8947/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.cej.2013.07.020

⇑ Corresponding authors. Address: Nanomaterials and Solar Energy ConversionLab, Department of Chemistry, National Institute of Technology, Trichy 620 015,India. Tel.: +91 431 2303639; fax: +91 431 2300133 (S. Anandan). Tel./fax: +886 424517686 (J.J. Wu).

E-mail addresses: sanand@nitt.edu (S. Anandan), jjwu@fcu.edu.tw (J.J. Wu).

Sambandam Anandan b,a,⇑, Nalenthiran Pugazhenthiran b, Teresa Lana-Villarreal c, Gang-Juan Lee a,Jerry J. Wu a,⇑a Department of Environmental Engineering and Science, Feng Chia University, Taichung 407, Taiwanb Nanomaterials and Solar Energy Conversion Lab, Department of Chemistry, National Institute of Technology, Trichy 620 015, Indiac Institut Universitarid’Electroquímica, Departament de Química Física,Universitatd’Alacant, Apartat 99, E-03080 Alacant, Spain

h i g h l i g h t s

� Nx–TiO2�x nanoparticles weresuccessfully synthesized via co-precipitation procedure.� Nx–TiO2�x nanoparticles were used to

remove wastewater pollutantcontaining plasticizer.� The catalytic activity was tested by

coupling with ozone and visible light.

g r a p h i c a l a b s t r a c t

0 1 2 3 4 5 6 7 8 9 10

15 min

45 min60 min

30 min

0 min

Retention time (min)

Inte

nsity

(m

V)

a r t i c l e i n f o

Article history:Received 15 February 2013Received in revised form 6 July 2013Accepted 8 July 2013Available online 17 July 2013

Keywords:Nx–TiO2�x

NanoparticlesCo-precipitation synthesisXPSCatalytic ozonationDEHP

a b s t r a c t

There is an increasing concern in the decontamination of wastewater. Most of the advanced oxidationprocedures described so far are based on the use of different oxidation reactions including photocatalysisand ozonation. Doped titanium dioxide nanoparticles are photoactive under visible light illumination,being therefore possible to harvest solar energy for water decontamination. In this study, anataseNx–TiO2�x nanoparticles were successfully synthesized by a simple co-precipitation procedure basedon the oxidation of titanous (III) chloride in the presence of ammonia. The transmission electron micro-scope images of Nx–TiO2�x show nanoparticles with an average diameter size of �13 nm. The presence ofnitrogen (N1s) was verified using XPS analysis. The characteristic peak at 400 eV indicates the formationof O–Ti–N bonds. The Nx–TiO2�x nanoparticles were found to be useful for the removal of a wastewaterpollutant use as plasticizer (di-ethylhexyl phthalate) by a combined process of heterogeneous photoca-talysis under visible illumination coupled with ozonation. The photoactivity of the Nx–TiO2�x nanopow-der is enhanced compared to commercial TiO2 P25 nanoparticles due to the generation of electron/holepairs under visible irradiation together with a larger electrocatalytic activity towards oxygen reduction.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

Among the several advanced oxidation technology (AOTs)developed so far, the ozonation is the utmost technique for thelarge scale waste water remediation because ozone molecules rap-idly and selectively oxidize the contaminants in aqueous medium[1]. However, the ability of ozonation process suffers to oxidizethe ozonized by-products formed from the oxidation of organic

S. Anandan et al. / Chemical Engineering Journal 231 (2013) 182–189 183

pollutants and moreover, the practical use of ozonation for watertreatment is limited by its high-energy demand. In order to over-come the limitation of ozonation alone process is being modifiedto increase their oxidizing capability. Consequently, catalytic tech-nologies based on homogeneous or heterogeneous catalytic mate-rials in combination with ozone, a well-known advanced oxidationprocess (AOP), has become an attractive and increasingly impor-tant research field in the use of ozone [2]. The oxidation of organiccontaminants by homogeneous catalysis is not recommended as itsfetch notorious impact to the aquatic environment [3]. Howeverheterogeneous catalytic ozonation has received increasing atten-tion in recent years due to its potentially higher effectiveness inthe degradation and the mineralization of the harmful organic pol-lutants with less negative effects [4–6]. The foremost advantage ofheterogeneous catalytic ozonation system is facilitating to recoverthe catalysts and it can be reused. Additionally, the nanostructuredheterogeneous materials can generate higher number of �OH dur-ing the treatment of ozonation and also upon light irradiation[7]. This is because the nanostructured heterogeneous materialsas catalysts leads to exciting improvement in the catalytic activi-ties due to the enhanced surface to volume ratio and quantum-sizeeffect which make the properties and structural ability very differ-ent from their bulk counterparts [8].

Among all nanostructured heterogeneous materials, titaniumdioxide (TiO2) has been revealed as a prospective material inmany practical applications because it is chemically stable, inex-pensive, nontoxic and environmentally benign [9,10]. Synthesisof well-defined TiO2 nanostructures is indispensible to have anoptimized material for the photocatalytic application. In thissense, not only the size, but also the morphology, crystal faceand electronic structure will play a crucial role in the photocata-lytic degradation of organic pollutants. The band gap smaller than3.2 eV could be useful in those applications where the visible-lightabsorption induce generation of charge carriers. TiO2 nanostruc-tures can be sensitized to the visible light by different strategieslike coupling with a narrow band gap semiconductor, metal ionor non-metal ion doping, and noble metal deposition [11–13].Among the above strategies, non-metal ion doping is a promisingprocedure due to its simplicity. Many researchers have studiednitrogen-doped TiO2 from a fundamental point of view but alsofor applications where the narrowing of the band gap would bebeneficial [14–17].

Based on the mention above, our aim is to report a rapid andcontrollable synthesis of nitrogen-doped TiO2 nanoparticlesthrough a co-precipitation method based on the oxidation of tita-nium trichloride in the presence of ammonia acting as a nitrogensource. Photocatalytic activity of nitrogen-doped TiO2 nanoparti-cles has been investigated. The photocatalytic degradation of di-ethylhexyl phthalate (DEHP) has been studied paying attentionto the effect of combining it with other decontamination technol-ogies such as ozonation. DEHP has been selected as a model pollu-tant because DEHP is a refractory organic compound with lowwater solubility. However, it is widely used in a wide range of con-sumer goods, mostly as plasticizer [18–20]. Containers, wrappings,and food-processing equipment made of plastic or using plasticparts contain DEHP [18]. Finally, not only this material, but also,the stored food can get contaminated due to the reaction betweenDEHP and lipophilic material such as fats and oils present in food[18]. Many environmental protection agencies reported the riskassessment of DEHP and hence, a number of researchers have triedto remove the DEHP by hydrolysis, photodegradation, biodegrada-tion, etc. However up to now, the rate of degradation is very slow.Herein we developed a process that combines heterogeneous catal-ysis using nitrogen-doped TiO2 nanoparticles with ozonation andvisible light to remove effectively such environmental pollutantfrom aqueous solutions.

2. Experimental details

2.1. Preparation of Nx–TiO2�x nanoparticles

Unless otherwise specified, all the reagents used were of analyt-ical grade and the solutions were prepared using Millipore DDIwater (18.2 MX). The simple co-precipitation procedure wasfollowed for the preparation of Nx–TiO2�x, i.e., aqueous ammonia(Merck, 28%) was added drop by drop to 20 mL of Titanium (III)chloride (TiCl3, 20% in 3% HCl, Alfa Aesar) vigorously stirred atroom temperature (25 ± 2 �C) until the pH reached 4.7. Subse-quently, the resulting solution was diluted by adding 100 mL ofwater followed by bubbling Oxygen gas through it until the disap-pearance of the dark color ascribed to Ti3+ (i.e., until the completeoxidization of Ti3+ to Ti4+). The hydrous precipitate was then fil-tered, washed with distilled water several times until the filtratewas free of chloride ion (as confirmed by silver nitrate test) andthen dried in hot air-oven at 100 �C for 48 h to remove the watermolecules. The dried sample was calcinated at 400 �C for 6 h toyield yellow color compound.

2.2. Characterization technique

Structure, morphology and size of the prepared Nx–TiO2�x

nanoparticles were studied by XRD (measured using Rigaku dif-fractometer, Cu Ka radiation, Japan), and transmission electronmicroscopy (TEM; recorded using JEOL JEM 2100F model). X-rayphotoelectron spectroscopy (XPS) analysis of the Nx–TiO2�x wasperformed using a Physical Electronics PHI 5600 XPS spectropho-tometer with monochromatic Al Ka (1486.6 eV) excitation source.Raman spectra were recorded by a Bruker Raman spectrometerwith 1064 nm argon ion laser as excitation source. The surface areaof the prepared samples was measured with a SA3100 surface areaand pore size analyzer from Beckman Coulter using N2 as carriergas. Diffuse reflectance UV–vis spectra of the samples were re-corded using a Shimadzu UV–vis 2550 spectrophotometer. Forthe electrochemical measurements electrodes of Nx–TiO2�x andTiO2 were prepared on Fluorine doped Tin oxide (FTO) glass byspreading aqueous slurry and making a thermal treatment at450 �C. The cyclic voltammograms were measured in a nitrogen/oxygen saturated 0.1 M NaOH solution, using an Ag/AgCl and a Ptwire as reference and counter electrode, respectively. The mea-surements were performed using an Autolab PGSTAT30, with ascan rate of 20 mV s�1.

2.3. Evaluation of catalytic activity

The activity of the Nx–TiO2�x nanoparticles was tested for thedegradation of an organic pollutant concretely, di-ethylhexylphthalate, DEHP, by a process that combines visible light excitationwith ozonation. A 500 mL capacity borosilicate glass reactor wasused for these experiments. The degradation of DEHP was carriedout in atmospheric conditions (25 �C) at natural pH. The amountof catalyst and DEHP used for all the experiments were the same(200 mg per 200 mL of 5.0 � 10�4 M DEHP in aqueous solution).During the experiment, pH alters from 8.44 to 4.35. For theozone-assisted processes, ozone was introduced through a porousfrit that allows producing fine bubbles with diameter smaller than1 mm, as determined by a camera with a close-up lens and imageanalysis software Matrox Inspector 2.0. Ozone was produced frompure oxygen by a corona discharge using an ozone generator(Ozonia). The maximum ozone concentration was about 6% (byvolume) in the oxygen-enriched gas stream. The gas flow ratewas regulated at 200 mL min�1 by a gas flow controller (Brooks5850E) and the inflow ozone concentration was adjusted to

Fig. 1. High-resolution TEM images (a and b), SAED pattern (c) and EDX (d) of Nx–TiO2�x nanoparticles. TEM derived particle size distribution histogram is shown in the insetof (a).

184 S. Anandan et al. / Chemical Engineering Journal 231 (2013) 182–189

40 mg/L. The gaseous ozone concentration was determinedspectrophotometrically by the absorbance of ozone measured ina 2 mm flow-through quartz cuvette at the wavelength of258 nm. An extinction coefficient of 3000 M�1 cm�1 was used toconvert absorbance into concentration units [21,22]. The HPLCanalysis before and after stirring for 20 min in the dark, and inthe absence of ozone, indicated that there was no change in theconcentration of DEHP, implying that DEHP was not adsorbed onNx–TiO2�x nanoparticles (at least in a measurable extent). For thephotocatalytic experiments, the aqueous solution was irradiatedwith a 55 W Xenon lamp with k P 440 nm (intensity of irradiationis 20,200 ± 10 Lux measured using INS DX-200 LUX meter, Nor-way) immersed in a quartz well placed at the middle of the reactor.The apparent kinetics of disappearance of the DEPH was deter-mined by the peak area calculated from the HPLC analysis. HPLCinstrument used for this determination was a Spectral SystemChromquest 1000 model equipped with UV detector (225 nm)using an Agilent C18 column (4.6 � 250 mm) with a mobile phaseof acetonitrile/water (90/10, v/v) at a flow rate of 0.2 mL/min. Priorto the analysis, the catalyst was removed by centrifugation fol-lowed by filtration using a 0.45 lm (micrometer) polyvinylidenefluoride (PVDF) filter. The eluate (by-products) was analyzed usinga Varian ESI Fourier Transform mass spectrometer.

3. Results and discussion

3.1. Characterization of the Nx–TiO2�x nanoparticles

In the present study, Nx–TiO2�x nanoparticles have beenprepared by simple co-precipitation procedure. Briefly, titaniumhydroxide was first precipitated from a titanium trichloride

solution with ammonia. After drying at 100 �C, it was calcinatedat 400 �C for 6 h in air yielding a yellow color solid. In the litera-ture, the preparation of Nx–TiO2�x has been described to occur byin situ generation of ammonia during the thermal decompositionof urea, which acts as a nitrogen source [14–16]. In contrast, inour preparation process pure ammonia is used directly acting asa nitrogen source.

3.1.1. TEM, XRD and XPS analysisAs prepared Nx–TiO2�x nanoparticles were characterized by

transmission electron microscopy (TEM), XRD, XPS and nitrogenadsorption/desorption isotherms. The TEM image of the Nx–TiO2�x

nanoparticles (Fig. 1a) shows hierarchical structures of large aggre-gates composed of small nanocrystals with an average diameter of�13 nm. In the HR-TEM image (Fig. 1b), microscopic voids areclearly seen. Additionally the crystal fringes corresponding to 101planes with an interplanar spacing of d = 0.35 nm can be also dis-tinguished. Selected Area Electron diffraction (SAED) shows a dif-fraction ring pattern (Fig. 1c) indicating that the product ispolycrystalline in nature and in addition, that it corresponds toanatase (the signal ascribed to the lattice planes (101), (004),and (200) can be identified). The XRD of the calcinated Nx–TiO2�x

nanoparticles is depicted in Fig. 2a. For comparison the XRD pat-tern of prepared TiO2 nanopowder is also included. The X-ray dif-fraction peaks confirm the crystalline nature of the as-prepared ofNx–TiO2�x nanoparticles. The 2h peak values at 25.6, 37.9, 48.0,54.7, 63.1, 70.0, and 75.5 are in good agreement with the standardpattern of anatase TiO2 (JCPDS No. 21-1272). The particle size cal-culated from the full width at half maxima (FWHM) of the diffrac-tion pattern using Scherer formula was 13 ± 2 nm. The Nx–TiO2�x

XPS spectrum (Fig. 2b) shows two main peaks at 458.9 and

10 20 30 40 50 60 70 80

0

300

600

900

1200

(204

)

(211

)

(215

)(200

)

(004

)

(105

)

(101

)

TiO2

Nx-TiO2

Inte

nsity

(a.u

.)

2θ (Degree)455.0 457.5 460.0 462.5 465.0 467.5

0

2000

4000

6000

8000

10000

Ti 2p1/2

Cou

nts/

sec

Binding Energy (eV)

Ti 2p 3/2

395.0 397.5 400.0 402.5 405.0300

350

400

450

500

550

600

650

Cou

nts/

sec

Binding Energy (eV)

N1s

400 600

0

100

200

300

400 Eg

A1g 1gB1g

0

50

100

150

200

0 0.2 0.4 0.6 0.8 1

Relative Pressure (P/P0)

Que

ntity

Ads

orbe

d (c

m3 /g

STP

)

AdsorptionDesorption

200 300 400 500 600 700 800

0.0

0.2

0.4

0.6

0.8

1.0

2Nx-TiO2

2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.00.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Eg

Eg

(αhυ

)1/2

hυ (ev)

2x-TiO2

Rel

ativ

e In

tens

ity (a

.u.)

Raman Shift (cm-1)

Wavelength (nm)

Abso

rban

ce (a

.u.)

(a) (b)

(c) (d)

(e) (f )

Fig. 2. XRD (a), XPS (b and c), Raman spectroscopic analysis (d), BET (e) and diffused reflectance absorption spectra (e) of Nx–TiO2�x nanoparticles. Inset shows pore volume(2e) and Tauc plot (2f) of Nx–TiO2�x nanoparticles.

S. Anandan et al. / Chemical Engineering Journal 231 (2013) 182–189 185

464.5 eV, which are characteristic for the formation of Ti4+ (2p3/2)and Ti4+ (2p1/2) of TiO2. The presence of nitrogen was confirmedby the characteristic peak at 400 eV (Fig. 2c), which can be relatedto the formation of O–Ti–N bond. Furthermore, it can be assignedto N 1s [23]. The Raman spectra (Fig. 2d) show three clear Ramanfinger print peaks with index modes (398 (B1g), 516 (A1g + B1g) and640 (Eg) cm�1) that confirm that the as-prepared product is mainlyanatase Nx–TiO2�x nanoparticles, and no other crystalline phasesare present.

3.1.2. BET isotherm and DRS analysisRepresentative nitrogen adsorption/desorption isotherms of

Nx–TiO2�x nanoparticles obtained from the analysis of the

adsorption branch using the BJH (Barett–Joyner–Halenda) methodare shown in Fig. 2e. The Brunauer–Emmett–Teller (BET) surfacearea for Nx–TiO2�x nanoparticles is found to be as large as132 m2/g, which doubles the one for the commercial anatase De-gussa P25 (50 m2/g). Such a large surface area agrees well withthe small nanoparticle size. Accordingly, prepared Nx–TiO2�x nano-particles shows a pore size distribution with a maximum centeredat �6 nm (see inset of Fig. 2e). Diffused reflectance spectra ofNx–TiO2�x nanoparticles show a broad absorbance band in the vis-ible region which is absent for pure TiO2 (Fig. 2f). The Tauc plot re-veals a band gap of about 2.63 eV (see inset of Fig. 2f), which issignificantly smaller than the classical 3.2 eV of anatase TiO2. Ithas been evidenced that the absorption in the visible region is

0 1 2 3 4 5 6 7 8 9 10

15 min

45 min60 min

30 min

0 min

Retention time (min)

Inte

nsity

(mV)

0

1

2

Ligh

t + N

x-TiO

2-x

Ligh

t +

TiO

2

O3 +

ligh

t + N

x-Ti

O2-

x

O3 +

ligh

t + T

iO2

O3 +

Nx-

TiO

2-x

O 3 + T

iO2

O 3 + li

ght

O3

k x

103 s

-1

Catalyst

(b)

(c)

(a)

Fig. 3. (a) 3-D plot showing the evolution of the HPLC chromatogram as a functionof Nx–TiO2�x nanoparticles combined with ozonation and visible light (a) of DEHP(5 � 10�4 M). Mobile phase: acetonitrile/water (90/10, v/v) and detection wave-length = 225 nm. (b) Ct/Co vs time plot for various catalysts, and (c) comparison ofdegradation rate (60 min) for various catalysts. Concentrations are maintained asfollows: DEHP (5 � 10�4 M) and catalyst (1 g/L).

Fig. 4. Cyclic voltammograms of TiO2 and Nx–TiO2�x deposited on FTO in 0.1 MNaOH at scan rate of 20 mV s�1.

186 S. Anandan et al. / Chemical Engineering Journal 231 (2013) 182–189

due to the formation of an N-induced (occupied) midgap level,energetically located slightly above the valence band edge [24].

3.2. Catalytic degradation of plasticizer

Nx–TiO2�x nanoparticles were used for the photocatalytic deg-radation of di-ethylhexyl phthalate under visible irradiation inthe absence and in the presence of ozone. HPLC was employed torecord the degradation of di-ethylhexyl phthalate under differentreaction conditions in the dark and under visible light illuminationand in the presence and in the absence of ozone (For referenceprovided 3-D plot (Fig. 3a) showing the evolution of the HPLC chro-matogram as a function of Nx–TiO2�x nanoparticles combined withozonation and visible light). The diminution of the concentration(Ct/C0) (Fig. 3b) indicates the disappearance of DEPH in all cases.

However, the degradation rate is dependent on the particularexperiment. The change in the concentration as a function of reac-tion time was calculated by integrating the peak area of DEHP at�3.5 min. First order rate constants were calculated from theslopes of ln(Ct/C0) vs time plot (figure not shown).

As shown in Fig. 3c, the photocatalytic degradation undervisible light irradiation (k > 400 nm) is faster for Nx–TiO2�x thanfor TiO2 nanoparticles. There are several reasons that can beresponsible for this superior photoactivity. Among them, weshould underline that Nx–TiO2�x absorbs visible light, being possi-ble to photoexcite electrons from the nitrogen occupied midbandgap to the conduction band. The situation is rather different forthe undoped nanopowder (Degussa P25 nanopowder). In such acase, the light energy limits the generation of charge carriers. How-ever, some activity is observed as the light energy is less than3.1 eV and this energy is enough to photoexcite rutile nanoparti-cles present in the Degusssa P25 TiO2. Additionally, it is possibleto promote electrons from some occupied states near the valenceband to the conduction band or from the valence band to someunoccupied surface states. In this sense, it is well known that thepresence of an exponential trap distribution is just below the con-duction band [25]. Additionally, since photocatalytic reaction ratesare determined by the balance between hole and electron transfer,the larger photoactivity could be also ascribed to a more efficientelectron transfer. For this purpose, the oxygen reduction rate wasstudied using electrochemical measurements. Electrodes of Degus-sa P25 and of Nx–TiO2�x nanoparticles were prepared on FTO. Toeasily rationalize the results, the electrodes had the same surfacearea as it is evidenced by the charge accumulation region as shownin Fig. 4. In the presence of oxygen, a clear reduction wave is ob-served in the cyclic voltammogram, being the current larger forthe Nx–TiO2�x nanoparticles. A larger current indicates a fasterelectron transfer towards oxygen. This result also points to a largerphotocatalytic activity for the nitrogen-doped nanoparticles in anycase, whereas the degradation rate is considerable low undervisible light.

Molecular ozone is characterized by its oxidant power thatmakes it to instantaneously react with a variety of compounds.The action is not only due to the direct reaction but also due tothe generation of hydroxyl radicals during its decomposition. How-ever, as in the photocatalytic reactions the degradation rate byozonation alone is considerable slow, whereas, an enhancementis noticed in the presence of Nx–TiO2�x nanoparticles. Probablythe decomposition of ozone into hydroxyl radicals can be facili-tated at the interface, and these hydroxyl radicals can efficientlyphotooxidize DEPH. Similarly, the addition of suitable catalyst suchas activated carbon, perovskites, has been reported to increase thereaction yield [26].

Fig. 5. Mass spectra of DEHP (a) before ozonation, (b) after 30 min ozonation, (c) after 30 min ozonation combined with TiO2 nanoparticles, (d) 30 min ozonation combinedwith Nx–TiO2�xnanoparticles, (e) 30 min ozonation combined with TiO2 nanoparticles and visible light, and (f) 30 min ozonation combined with Nx–TiO2�x nanoparticles andvisible light.

S. Anandan et al. / Chemical Engineering Journal 231 (2013) 182–189 187

The degradation is highly enhanced if ozonation is combinedwith the photocatalytic reaction, particularly for Nx–TiO2�x nano-powder. In this system, ozone may act as a trapping agent ofphotogenerated electrons, generating hydroxyl radicals, whilephotogenerated holes can oxidize DEHP or they could be transfertowards to the water molecules, generating a new OH� radical.These radicals can initiate chain reaction both at the catalyst sur-face and in the bulk of the aqueous phase. The beneficial or evensynergic effect of combining photocatalysis and ozonation has alsobeen reported by other authors [27–30].

In this work an attempt has also been made to study the photo-oxidation mechanism. Mass spectra of samples (Fig. 5) collectedafter 30 min show a mass ionization peak corresponding tomono(2-ethylhexyl)phthalate (m/z 308) and phthalic acid (m/z179) in addition to low molecular weight compounds. One couldexpect that DEHP is attacked by OH� radicals to follow the degra-dation path mentioned in Fig. 6. First mono(2-ethylhexyl)phthalateand 2-ethylhexanol is formed as intermediate which is transforminto phthalic acid and identified through mass spectrometricanalysis.

Fig. 6. Degradation pathway of DEHP in the presence of Nx–TiO2�x under combination with ozonation and visible light.

188 S. Anandan et al. / Chemical Engineering Journal 231 (2013) 182–189

4. Conclusions

The synthesis of Nx–TiO2�x nanoparticles is described. The nano-powder is purely anatase as confirmed by X-ray diffraction and Ra-man spectrum. The characterization study revealed that thenanoparticles are relatively uniform in size (�13 nm) with a highsurface area (132 m2/g) and apparent band gap smaller than theone of pure anatase was also measured (2.63 eV). The catalytic activ-ity was tested using the degradation of DEHP by coupling with ozoneand visible light. HPLC and mass spectrophotometric analysis alsoconfirmed that this compound is more efficiently decomposed onthe nitrogen doped nanopowder compared with TiO2 Degussa P25.

Acknowledgements

The research described herein was Financially Supported by theNational Science Council (NSC) in Taiwan under the Contract No. of101-2221-E-035-031-MY3. S.A. also thanks the Feng Chia Univer-sity, Taiwan, for the Visiting Professor appointment. The authors,SA and TV thank Ministry of India and Spain for the sanction of In-dia–Spain collaborative Research Grant (DST/INT/Spain/P-37/11 dt.16th Dec 2011).

References

[1] L. Sanchez, X. Domenech, J. Casado, J. Peral, Solar activated ozonation of phenoland malic acid, Chemosphere 50 (2003) 1085–1093.

[2] F.J. Rivas, M. Carbajo, F.J. Beltran, B. Acedo, O. Gimeno, Perovskite catalyticozonation of pyruvic acid in water operating conditions influence and kinetics,Appl. Catal. B 62 (2006) 93–103.

[3] F.J. Beltran, F.J. Rivas, R. Montero-de-Espinosa, Ozone-enhanced oxidation ofoxalic acid in water with cobalt catalysts. 2. Heterogeneous catalyticozonation, Ind. Eng. Chem. Res. 42 (2003) 3218–3224.

[4] L. Yang, C. Hu, Y. Nie, J. Qu, Catalytic ozonation of selected pharmaceuticalsover mesoporous alumina-supported manganese oxide, Environ. Sci. Technol.43 (2009) 2525–2529.

[5] L. Zhao, Z. Sun, J. Ma, H. Liu, Enhancement mechanism of heterogeneouscatalytic ozonation by cordierite-supported copper for the degradation ofnitrobenzene in aqueous solution, Environ. Sci. Technol. 43 (2009) 2047–2053.

[6] Z.Z. Sun, J. Ma, L.B. Wang, L. Zhao, Degradation of nitrobenzene in aqueoussolution by ozone-ceramic honey-comb, J. Environ. Sci. 17 (2005) 716–721.

[7] L. Zhao, Z. Sun, J. Ma, Novel Relationship between hydroxyl radical initiationand surface group of ceramic honeycomb supported metals for the catalyticozonation of nitrobenzene in aqueous solution, Environ. Sci. Technol. 43 (2009)4157–4163.

[8] Y.X. Yang, J. Ma, Q.D. Qin, X.D. Zhai, Degradation of nitrobenzene by nano-TiO2

catalyzed ozonation, J. Mol. Catal. A 267 (2007) 41–48.[9] A. Weir, P. Westerhoff, L. Fabricius, K. Hristovski, N. Goetz, Titanium dioxide

nanoparticles in food and personal care products, Environ. Sci. Technol. 46(2012) 2242–2250.

[10] K. Maeda, K. Domen, Photocatalytic water splitting: recent progress and futurechallenges, J. Phys. Chem. Lett. 1 (2010) 2655–2661.

[11] R. Tayade, R. Kulkarni, R. Jasra, Transition metal ion impregnated mesoporoustio2 for photocatalytic degradation of organic contaminants in water, Ind. Eng.Chem. Res. 45 (2006) 5231–5238.

[12] J. Zhu, J. Ren, Y. Huo, Z. Bian, H. Li, Nanocrystalline Fe/TiO2 visiblephotocatalyst with a mesoporous structure prepared via a nonhydrolyticsol�gel route, J. Phys. Chem. C 111 (2007) 18965–18969.

[13] D. Dvoranova, V. Brezova, M. Mazur, M.A. Malati, Investigations of metal-doped titanium dioxide photocatalysts, Appl. Catal.: B Environ. 37 (2002) 91–105.

[14] R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, Y. Taga, Visible-light photocatalysisin nitrogen-doped titanium oxides, Science 293 (2001) 269–271.

[15] C. Burda, Y. Lou, X. Chen, A.C.S. Samia, J. Stout, J.L. Gole, Enhanced nitrogendoping in TiO2 nanoparticles, Nano Lett. 3 (2003) 1049–1051.

[16] T. Lindgren, J.M. Mwabora, E. Avendano, J. Jonsson, A. Hoel, C.G. Granqvist, S.E.Lindquist, Photoelectrochemical and optical properties of nitrogen dopedtitanium dioxide films prepared by reactive DC magnetron sputtering, J. Phys.Chem. B 107 (2003) 5709–5716.

[17] M. Pelaez, N.T. Nolan, S.C. Pillai, M.K. Seery, P. Falaras, A.G. Kontos, P.S.M.Dunlop, J.W.J. Hamilton, J.A. Byrne, K. O’Shea, M.H. Entezari, D.D. Dionysiou, Areview on the visible light active titanium dioxide photocatalysts forenvironmental application, Appl. Catal.: B Environ. 125 (2012) 331–349.

[18] E. Nielsen, X. Larsen, Toxicological Evaluation and Limit Values for DEHPand Phthalates over than DEHP, Danish Environmental Protection Agency,1996.

[19] B.C. Blont, K. Eric Milgram, M.J. Silva, N.A. Malek, J.A. Reidy, L.L. Needham, J.W.Brock, Quantitative detection of eight phthalate metabolites in human urineusing HPLC–APCI–MS/MS, Anal. Chem. 72 (2000) 4127–4134.

[20] N. Scholz, Ecotoxicity and biodegradation of phthalate monoester,Chemosphere 53 (2003) 921–926.

[21] S. Anandan, G.J. Lee, P.K. Chen, C. Fan, J.J. Wu, Removal of orange II dye in waterby visible light assisted photocatalytic ozonation using Bi2O3 and Au/Bi2O3

nanorods, Ind. Eng. Chem. Res. 49 (2010) 9729–9737.[22] S. Anandan, G.J. Lee, S.H. Hsieh, M. Ashokkumar, J.J. Wu, Amorphous titania-

coated magnetite spherical nanoparticles: sonochemical synthesis andcatalytic degradation of nonylphenol ethoxylate, Ind. Eng. Chem. Res. 50(2011) 7874–7881.

[23] H. Kominami, T. Matsuura, K. Iwai, B. Ohtani, S. Nishimoto, Y. Kera, Ultra-highly active titanium (IV) oxide photocatalyst prepared by hydrothermalcrystallization from titanium (IV) alkoxide in organic solvents, Chem. Lett. 24(1995) 693–694.

[24] R. Nakamura, T. Tanaka, Y. Nakato, Mechanism for visible light responses inanodic photocurrents at N-doped TiO2 film electrodes, J. Phys. Chem. B 108(2004) 10617–10620.

[25] T. Berger, D. Monllor-Satoca, M. Jankulovska, T. Lana-Villarreal, R. Gómez, TheElectrochemistry of nanostructured titanium dioxide electrodes, Chem. Phys.Phys. Chem. 13 (2012) 2824–2875.

S. Anandan et al. / Chemical Engineering Journal 231 (2013) 182–189 189

[26] M. Carbajo, F.J. Rivas, F. Beltrán, P. Alvarez, F. Medina, Effects of differentcatalysts on the ozonation of pyruvic acid in water, Ozone-Sci. Eng. 28 (2006)229–235.

[27] F. Javier Rivas, F.J. Beltrán, A. Encinas, Removal of emergent contaminants:integration of ozone and photocatalysis, J. Environ. Manage. 100 (2012) 10–15.

[28] J. Yuan, X. Huang, M. Chen, J. Shi, W. Shangguan, Ozone-assisted photocatalyticdegradation of gaseous acetaldehyde on TiO2/M-ZSM-5 (M = Zn, Cu, Mn),Catal. Today 201 (2012) 182–188.

[29] S. Lu, A. Wang, A.G. Buekens, J. Yan, X. Li, K. Cen, Photocatalytic decompositionof gaseous 1,2-dichlorobenzene on TiO2 films: effect of ozone addition, Chem.Eng. J. 195–196 (2012) 233–240.

[30] R.R. Giri, H. Ozaki, T. Ishida, R. Takanami, S. Taniguchi, Synergy of ozonationand photocatalysis to mineralize low concentration 2,4-dichlorophenoxyaceticacid in aqueous solution, Chemosphere 66 (2007) 1610–1617.