Desalination 252 (2010) 46–52

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Photocatalytic degradation of amoxicillin, ampicillin and cloxacillin antibiotics inaqueous solution using UV/TiO2 and UV/H2O2/TiO2 photocatalysis

Emad S. Elmolla ⁎, Malay ChaudhuriDepartment of Civil Engineering, Universiti Teknologi PETRONAS, 31750 Tronoh, Perak, Malaysia

⁎ Corresponding author. Tel.: +60 14 9047313.E-mail address: em_civil@yahoo.com (E.S. Elmolla).

0011-9164/$ – see front matter © 2009 Elsevier B.V. Adoi:10.1016/j.desal.2009.11.003

a b s t r a c t

a r t i c l e i n f o

Article history:Received 10 September 2009Received in revised form 4 November 2009Accepted 4 November 2009Available online 27 November 2009

Keywords:AmoxicillinAmpicillinCloxacillinAntibioticsUV/H2O2/TiO2 photocatalysis

Degradation of amoxicillin, ampicillin and cloxacillin antibiotics in aqueous solution by TiO2 photocatalysisunder UVA (365 nm) irradiation was studied. Enhancement of photocatalysis by addition of H2O2 was alsoevaluated. The results showed that no significant degradation occurred by 300-min UVA irradiation per seand pH had a great effect on antibiotic degradation. Photocatalytic reactions approximately followed apseudo-first order kinetics and the rate constants (k) were 0.007, 0.003 and 0.029 min−1 for amoxicillin,ampicillin and cloxacillin, respectively. Addition of H2O2 at ambient pH∼5 and TiO2 1.0 g/L resulted incomplete degradation of amoxicillin, ampicillin and cloxacillin in 30 min. Dissolved organic carbon (DOC)removal, and nitrate (NO3

−), ammonia (NH3) and sulphate (SO42−) formation during degradation indicated

mineralization of organic carbon, nitrogen and sulphur. UV/H2O2/TiO2 photocatalysis is effective fordegradation of amoxicillin, ampicillin and cloxacillin in aqueous solution.

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© 2009 Elsevier B.V. All rights reserved.

1. Introduction

Pharmaceutical compounds including antibiotics have beenobserved in the aqueous environment. These compounds have beenobserved in surface water [1–3], ground water [3], sewage effluent[4,5] and even in drinking water [6]. Pharmaceutical compounds canreach the aquatic environment through various sources such aspharmaceutical industry, hospital effluent and excretion fromhumans and livestock [5,7,8]. Among all the pharmaceutical com-pounds that cause contamination of the environment, antibioticsoccupy an important place due to their high consumption rate in bothveterinary and human medicine. A problem that may be created bythe presence of antibiotics in low concentration in the environment isthe development of antibiotic resistant bacteria [9]. In recent years,the incidence of antibiotic resistant bacteria has increased and manypeople believe that the increase is due to the use of antibiotics [10].Furthermore, the presence of antibiotics in wastewaters has alsoincreased and their abatement will be a challenge in the near future.

It is useful to apply various treatment technologies to purifyeffluents containing pharmaceutical compounds. The advancedoxidation processes (AOPs) appear as interesting tools in comparisonwith other techniques such as activated carbon adsorption, airstripping and reverse osmosis. Indeed, many of these techniquesonly transfer the pollutants from one phase to another withoutdestroying them. Biological treatment is limited to wastewaters

which contain biodegradable substances and which are not toxic tothe biological culture. Among the different advanced oxidationprocesses, TiO2 photocatalysis has emerged as a promising wastewa-ter treatment technology. Themain advantages of the process are lackof mass transfer limitations and operation at ambient conditions, andthe catalyst is inexpensive, commercially available, non-toxic andphotochemically stable [11].

Reaction mechanisms of photocatalytic processes have beendiscussed in the literature [12–17]. Illumination of a semiconductorsuch as titanium dioxide (TiO2) by photons having an energy levelthat exceeds its band gap energy (hvNEbg=3.2 eV in the case ofanatase TiO2) excites electrons (e−) from the valence band to theconduction band and holes (h+) are produced in the valence band(Reaction (1)). The photogenerated valence band holes react witheither water (H2O) or hydroxyl ions (OH−) adsorbed on the catalystsurface to generate hydroxyl radicals (UOH)which are strong oxidants(Reactions (2) and (3)). The hydroxyl radical reacts readily withsurface adsorbed organic molecules, either by electron or hydrogenatom abstraction, forming organic radical cations, or by additionreactions to unsaturated bonds [17] (Reaction (4)). Since the reactionof the holes on the particle interface is faster than electrons, theparticles under illumination contain an excess of electrons. Removalof these excess electrons is necessary to complete the oxidationreaction by preventing the recombination of electrons with holes. Themost easily available electron acceptor is molecular oxygen and in thepresence of oxygen the predominant reaction of electrons is that withO2 to form radicalic superoxide ions (UO2

−) as in Reaction (5). In acidiccondition, superoxide ion combines with proton to form a hydroper-oxide radical and it reacts with conduction band electron to form

Fig. 1. Chemical structure and HPLC chromatograph of (A) amoxicillin, (B) ampicillinsodium and (C) cloxacillin sodium.

47E.S. Elmolla, M. Chaudhuri / Desalination 252 (2010) 46–52

hydroperoxide ion. The hydroperoxide ion reacts with proton to formhydrogen peroxide. Cleavage of hydrogen peroxide by the conductionband electrons yields further hydroxyl radicals and hydroxyl ions(Reaction (6)). The hydroxyl ions can then react with the valenceband holes to form additional hydroxyl radicals. Recombination of thephotogenerated electrons and holes may occur and indeed it has beensuggested that preadsorption of substrate (organic substance) ontothe photocatalyst is a prerequisite for highly efficient degradation.

TiO2 þ hv→ TiO2ðe− þ hþÞ ð1Þ

hþ þ H2O→H

þ þUOH ð2Þ

hþ þ OH

− → UOH ð3Þ

OrganicsþUOH→ Degradation Products ð4Þ

e− þ O2→

UO

−2 ð5Þ

H2O2 þ e−→U

OH þ OH− ð6Þ

The photocatalytic processes have been reported to be effective fordegradation of many organic pollutants such as carboxylic acids[18,19], chloroanilines [20], mono-chlorocarboxylic acids [21], chlor-ophenols [22–24], dyes [25–28], fungicides [29], herbicides [30],ketones [31], phenolics [32] and pharmaceuticals [8,33]. Degradationof lincomycin and sulfamethoxazole antibiotics by TiO2 photocatalysishave been reported [33,34].

Amoxicillin, ampicillin and cloxacillin are semi-synthetic penicillinobtaining their antimicrobial properties from the presence of aβ-lactamring. They are widely used in human and veterinary medicine. Someauthors have found amoxicillin and cloxacillin in wastewater [35,36].There are some reported studies on degradation of amoxicillin bydifferent AOPs. Zhang et al. [37] studied the treatment of amoxicillinwastewater by combination of extraction, Fenton oxidation andreverse osmosis. Also, different AOPs (O3/OH−, H2O2/UV, Fe2+/H2O2,Fe3+/H2O2, Fe2+/H2O2/UV and Fe3+/H2O2/UV) were evaluated as apretreatment process for real penicillin formulationwastewater [38].The degradation of amoxicillin by ozonation [39] and photo-Fenton[40] has been reported. In our previous work, we studied the deg-radation of amoxicillin, ampicillin and cloxacillin antibiotics usingFenton [41], photo-Fenton [42] and ZnO photocatalysis [43].However, no study on degradation of amoxicillin, ampicillin andcloxacillin antibiotics in aqueous solution by TiO2 photocatalysis hasbeen reported.

The present study was undertaken to examine the degradation ofamoxicillin, ampicillin and cloxacillin antibiotics in aqueous solutionby UV/TiO2 photocatalysis and the enhancement of photocatalysis byhydrogen peroxide addition.

2. Materials and methods

2.1. Chemicals

Analytical grades of amoxicillin (AMX) and ampicillin (AMP) werepurchased from Sigma and cloxacillin (CLX) from Fluka and they wereused to construct HPLC analytical curves for determination ofantibiotic concentration. AMX, AMP and CLX used to prepareantibiotic aqueous solution were obtained from a commercial source(Farmaniage Company). The commercial products were used asreceived without any further purification. Sodium hydroxide andsulphuric acid were purchased from HACH Company USA. Potassiumdihydrogen phosphate (KH2PO4) was purchased from Fluka and

acentonitrile HPLC grade from Sigma. TiO2 powder (anatase, purityN99%) was purchased from Fluka. Hydrogen peroxide (30% w/w) waspurchased from R & M Marketing, Essex, U.K. Fig. 1 shows thechemical structure and HPLC chromatograph of amoxicillin, ampicillinsodium and cloxacillin sodium.

2.2. Antibiotic aqueous solution

Antibiotic aqueous solution was prepared by dissolving specificamounts of AMX, AMP and CLX in distilled water (dissolved oxygen8.4 mg/L at 22 °C). The aqueous solution characteristics were AMX,AMP and CLX concentrations 104, 105 and 103 mg/L, respectively,pH∼5, COD 520 mg/L, BOD5/COD ratio∼0 and DOC 145 mg/L. Theantibiotic aqueous solution was prepared weekly and stored at 4 °C.

2.3. Analytical methods

Antibiotic concentration was determined by a High PerformanceLiquid Chromatograph (HPLC) (Agilent 1100 Series) equipped with amicro-vacuum degasser (Agilent 1100 Series), quaternary pump,diode array and multiple wavelength detector (DAD) (Agilent 1100Series) at wavelength 204 nm. The data was recorded by a chemista-tion software. The column was ZORBAX SB-C18 (4.6 mm×150 mm,5 µm) and its temperature was 60 °C. The mobile phase was 60%0.025 M KH2PO4 buffer solution in ultra pure water and 40%acentonitrile at a flow rate of 0.50 mL/min. Chemical oxygen demand(COD) was measured according to the Standard Methods [44]. Whenhydrogen peroxide was present in the sample, pH was increased toabove 10 to decompose hydrogen peroxide andminimize interferencein COD measurement [45]. A pH meter (HACH Sension 4) and a pHelectrode (HACH platinum series pH electrode model 51910, HACHCompany, USA) was used for pH measurement. Biodegradability wasmeasured by 5-day biochemical oxygen demand (BOD5) test accord-ing to the Standard Methods [44]. Dissolved oxygen (DO) wasmeasured by a YSI 5000 dissolved oxygen meter. Bacterial seed wasobtained from a municipal wastewater treatment plant. TOC analyzer

Fig. 3. Effect of TiO2 concentration on (A) AMX, (B) AMP and (C) CLX degradation.

48 E.S. Elmolla, M. Chaudhuri / Desalination 252 (2010) 46–52

(Model 1010, O & I analytical) was used for determining dissolvedorganic carbon (DOC). Ammonia (NH3) concentration was measuredby Nessler Method (Method 8038) [46], and nitrate (NO3

−) andsulphate (SO4

2−) by Hach Powder Pillow [46].

2.4. Experimental procedure

A 500 mL aliquot of the antibiotic aqueous solution was placed in a600 mL reactor with the required amount of TiO2 and was stirredmagnetically at room temperature (22±2 °C). pH of the mixture wasadjusted to the required value by 1 N H2SO4 or 1 N NaOH and themixture was kept in the dark for 30 min for dark adsorption beforesubjecting to UV irradiation. The source of UV irradiation was a UVlamp (Spectroline Model EA-160/FE; 230V, 0.17A, SpectronicsCorporation, New York, USA) with a nominal power of 6 W, emittingradiation at 365 nm and it was placed above the reactor. Samplesweretaken at pre-selected time intervals using a syringe and filteredthrough a 0.45 µm PTFE syringe filter for COD, BOD5 and DOCmeasurement, and through a 0.20 µm PTFE syringe filter for determi-nation of antibiotic concentration by HPLC.

3. Results and discussion

3.1. Effect of UV irradiation

To observe the effect of photolysis of antibiotics due to UVAirradiation, experiment was conducted at initial AMX, AMP and CLXconcentrations 104, 105, 103 mg/L, respectively and pH 5. By 300-minUV irradiation, degradationwas2.9, 3.8 and 4.9% forAMX,AMP andCLX,respectively (data not shown). Amoxicillin and cloxacillin showmaximum absorbance at 245 and 250 nm, respectively and they canabsorb light below300 nm(Fig. 2). Therefore, nosignificantdegradationwas expected due to UV 365 nm irradiation per se and presumably thedegradation was due to antibiotic hydrolysis. The hydrolysis reactionwould proceed through the attack of the nucleofile H2O to the β-lactamring followed by ring opening [39]. Consequently, degradation of thestudied antibioticswhen subjected to TiO2 photocatalysiswill bemainlydue to the active species produced during the photocatalytic process(e.g., hydroxyl radical, hole and superoxide ion).

3.2. Effect of TiO2 concentration

To observe the effect of TiO2 concentration, initial TiO2 concen-tration was varied in the range 0.5–2.0 g/L. The experimentalconditions were: AMX, AMP and CLX concentrations 104, 105 and103 mg/L, respectively and pH 5. Fig. 3 shows the degradation of AMX,AMP and CLX. Degradation percent after 300 min irradiation were42.3, 54.8, 55.8 and 58.7 for AMX (Fig. 3(A)), 33.3, 52.4, 54.3 and 52.4for AMP (Fig. 3(B)) and 46.6, 58.3, 59.2 and 60.2 for CLX (Fig. 3(C)) atTiO2 concentrations 0.5, 1.0, 1.5 and 2.0 g/L, respectively. Degradation

Fig. 2. Absorption spectra of AMX and CLX.

of antibiotics increased with increasing TiO2 concentration in therange 0.5–1.0 g/L. Further increase of TiO2 concentration above 1 g/Ldid not produce significant improvement in antibiotic degradation.This may be due to the decreasing light penetration, increasing lightscattering [47], agglomeration, and sedimentation of TiO2 under highcatalyst concentration [48,49]. The degradation of the antibiotics maydecrease in case of real wastewater due to the presence of interferinganions (e.g., chloride, bromide, sulphate, phosphate) and/or due todecrease of light density in turbid wastewater. These results agreewell with previous studies on degradation of bisphenol [50],chloramphenicol [51], hymatoxylin [33] and paracetamol [8]. Basedon the results, the optimum titanium dioxide concentration fordegradation of amoxicillin, ampicillin and cloxacillin antibiotics inaqueous solution is 1.0 g/L and it will be used to study the effect ofother parameters. It is worth noting that dissolved oxygen decreasedunder the experimental condition from initial value 8.4 to 6.8 mg/L in300 min. This may be due to the reaction of oxygen with conductionband electrons to form superoxide ions (UO2

−) as in Reaction (5). Therole of dissolved oxygen in photocatalytic degradation is dual. Itaccepts a photogenerated electron from the conduction band andthus promotes the charge separation (minimizing the electron-holepair recombination) and it also forms UOH radical via superoxideion (Reactions (5) and (6)). COD removal percent after 300 min

49E.S. Elmolla, M. Chaudhuri / Desalination 252 (2010) 46–52

irradiation were 6.2, 9.2, 10.0 and 9.6, respectively. No significantimprovement in biodegradability (BOD5/COD ratio) occurred and themaximum DOC removal was 2%.

3.3. Effect of pH

To study the effect of initial pH on degradation of AMX, AMPand CLX, experiments were conducted by varying the pH in the range3–11. The experimental conditions were AMX, AMP and CLX con-centrations 104, 105 and 103 mg/L, respectively, TiO2 1.0 g/L andinitial COD 520 mg/L. Fig. 4 shows the effect of pH on degradation ofAMX, AMP and CLX. Degradation percent after 300 min irradiationwere 61.2, 54.8, 59.2 and 70.9 for AMX (Fig. 4(A)), 78.1, 52.4, 74.3 and91.4 for AMP (Fig. 4(B)) and 95.2, 58.3, 81.7 and 100 for CLX (Fig. 4(C))at pH 3, 5, 8 and 11, respectively.

The effect of pH on antibiotic degradation in terms of COD removalwas also studied. COD removal after 300 min irradiation was 11.7, 9.2,10.2 and 11.2%, respectively. No significant improvement in BOD5/COD ratio occurred and the maximum DOC removal was 3%.

The effect of pH on antibiotic degradation can be explained bytaking into consideration the properties of both catalyst and antibiotics

Fig. 4. Effect of pH on (A) AMX, (B) AMP and (C) CLX degradation.

at different pH. For TiO2, as pH increases overall surface charge of TiO2

changes from positive (pKa1=2.6) to negative (pKa2=9.0)with pointof zero charge being pH 6.4 [52]. Chemie [53] reported that ionicamoxicillin species change from positive charge at acidic pH tonegative charge at alkaline pH as shown in Schematic 1. At acidic pH,both TiO2 and amoxicillin are positively charged and hence, theadsorption on the surface of TiO2 is limited. The high degradation ofantibiotics at acidic pH compared to that at neutral pH may be due tothe hydrolysis of antibiotics as reported by Hou and Poole [54]. Atalkaline pH, both amoxicillin and the TiO2 are negatively charged andso repulsive forces between the catalyst and the antibiotics aredeveloped. High degradation of antibiotics in alkaline condition maybe due to two facts. First is the enhancement of hydroxyl radicalformation at high pH due to the availability of hydroxyl ions on TiO2

surface that can easily be oxidized to form hydroxyl radical as inReaction (3) [8,55,56]. Second is the hydrolysis of the antibiotics due toinstability of the β-lactam ring at high pH [57].

3.4. Kinetics of photocatalytic degradation of amoxicillin, ampicillin andcloxacillin

To study the kinetics of photocatalytic degradation of amoxicillin,ampicillin and cloxacillin, experiments were conducted at TiO2

concentration 1.0 g/L, irradiation time 300 min and pH 11. The con-centration of AMX, AMP and CLX after 30 min dark adsorption wastaken as the initial AMX, AMP and CLX concentration for kineticanalysis. Fig. 5 shows the plots of ln ([Antibiotic] / [Antibiotic]0) versusirradiation time for amoxicillin, ampicillin and cloxacillin. Thelinearity of the plots as shown in Fig. 5 suggests that the photo-catalytic degradation approximately followed the pseudo-first orderkinetics. Degradation of cloxacillin exhibited the highest rate constant

Schematic 1. Anionic species of amoxicillin at different pH (Chemie [53]).

Fig. 5. Kinetic analysis of AMX, AMP and CLX degradation.

Fig. 6. Effect of H2O2 addition on (A) COD removal, (B) BOD5/COD ratio and (C) DOCremoval, (a) H2O2 concentrations 50, (b) 100, (c) 150, (d) 200 and (e) 300 mg/L.

50 E.S. Elmolla, M. Chaudhuri / Desalination 252 (2010) 46–52

(0.029 min−1) followed by amoxicillin (0.007 min−1) and ampicillin(0.004 min−1).

3.5. Effect of H2O2 addition

Addition of H2O2 to TiO2 suspensions is a well-known procedureand in many cases leads to an increase in the rate of photocatalyticoxidation [58,59]. In order to keep the efficiency of the added H2O2, itis necessary to choose the optimum concentration of H2O2 accordingto the type and concentration of the pollutants. H2O2 is considered tohave two functions in the photocatalytic oxidation. It accepts aphotogenerated electron from the conduction band of the semicon-ductor to form UOH radical (Reaction (6)). In addition, it forms UOHradicals according to Reaction (7) [60].

H2O2 þUOP

2 →UOH þ OH

P þ O2 ð7Þ

In order to investigate the effect of H2O2 addition, experimentswere conducted by varying the initial H2O2 concentration in the range50–300 mg/L. The experimental conditions were AMX, AMP and CLXconcentrations 104, 105 and 103 mg/L respectively, TiO2 1.0 g/L,ambient pH∼5 and initial COD 520 mg/L. Ambient pH∼5 was chosenbecause H2O2 decomposes at alkaline pH [45]. Fig. 6 shows the effectof H2O2 addition on antibiotic degradation in terms of COD removal,BOD5/COD ratio and DOC removal, respectively. COD removal percentafter 300 min illumination was 14.8, 26.3, 23.1, 16.3 and 12.3 at H2O2

concentrations 50, 100, 150, 200 and 300 mg/L, respectively (Fig. 6(A)).BOD5/COD ratio after 300 min illumination was 0.05, 0.10, 0.09, 0.07and 0.06 at H2O2 concentrations 50, 100, 150, 200 and 300 mg/L,respectively (Fig. 6(B)). DOC removal percent after 300 min illumina-tion was 6.4, 13.9, 9.6, 6.9 and 5.3 at H2O2 concentrations 50, 100, 150,200 and 300 mg/L, respectively (Fig. 6(C)). Maximum COD and DOCremoval percent were achieved at H2O2 concentration 100 mg/L.Degradation increased as the concentration of H2O2 increased and itreached the highest value at H2O2 concentration 100 mg/L. Furtherincrease in H2O2 concentration caused a decrease in COD and DOCremoval and BOD5/COD ratio. This may be due to the fact that excessH2O2 reactswith UOHand contributes to the UOHand hole scavenging toformHO2

U as in Reactions (8) and (9) [61,62]. This agreeswell with otherreported studies such as degradation of chloramphenicol [51]. Based onthese results, the optimum H2O2 concentration for antibiotic degrada-tion is 100 mg/L.

UOH þ H2O2→H2O þ HO

U2 ð8Þ

H2O2 þ hþ→H

þ þ HOU2 ð9Þ

3.6. Degradation of antibiotics and mineralization

To study the effect of H2O2 addition on the degradation of AMX,AMP and CLX, an experiment was conducted under the followingexperimental conditions: TiO2 1.0 g/L, H2O2 100 mg/L and pH 5. InitialAMX, AMP and CLX concentrations were 104, 105 and 103 mg/L,respectively and initial COD was 520 mg/L. Fig. 7 shows the effect ofH2O2 addition on AMX, AMP and CLX degradation. Completedegradation of amoxicillin and cloxacillin were achieved in 20 min,whereas complete degradation of ampicillin was achieved in 30 min.

TiO2 photocatalysis would result in the mineralization of organiccarbon, and release of nitrogen and sulphur from the antibioticmolecule. To assess the degree of mineralization, dissolved organiccarbon (DOC), nitrate (NO3

−), ammonia (NH3) and sulphate (SO42−) in

the solution were measured. The final degradation products weremeasured as NO3

−, NH3 and SO42− concentrations, whereas the small

organic molecules were measured as COD, BOD5 and DOC. Theexperimental conditions were TiO2 concentration 1.0 g/L, H2O2 concen-tration 100 mg/L, pH 5, initial AMX, AMP and CLX concentrations 104,105 and 103 mg/L, respectively and initial COD 520 mg/L. Mineraliza-tionof organic carbon, andnitrogenand sulphur compoundsare verified

Fig. 7. Effect of H2O2 addition on AMX, AMP and CLX degradation.

Fig. 9. Effect of irradiation time on NH3, NO3− and SO4

2− formation.

51E.S. Elmolla, M. Chaudhuri / Desalination 252 (2010) 46–52

by the results presented in Figs. 8 and 9. Fig. 8 shows the increaseof organic carbon release with irradiation time (DOC removal percent24.3 and 41.0 at 10 and 24 h, respectively). Fig. 9 shows the evolutionof the ionic species (NO3

−, NH3 and SO42−) formed during the

degradation of AMX, AMP and AMP. According to the structure of theantibiotics, each antibiotic has three nitrogen atoms and one sulphuratom. Photocatalytic transformation of the nitrogen moieties to N2,NH4

+,NO2−, orNO3

−depends on the initial oxidation state of nitrogenandon the structure of the organic molecules [63]. Low et al. [64] reportedthat ammonium to nitrate concentration ratio in aliphatic amminesis higher than that in compounds containing ring nitrogen. Foramoxicillin and ampicillin, each molecule contains three nitrogenatoms, two of them in aliphatic bond and the other in aromatic bond,and for cloxacillin, only one atom in aliphatic bond. This indicates thatmineralization of organic nitrogen in case of cloxacillin ismore complexthan that of amoxicillin and ampicillin. The results show that the initialNH3 concentration was 6.1 mg/L and slightly increased to 7.6 mg/L.TheNO3

− ions gradually increased fromzero (initial value) to1.2 mg/L in24 h. Sulphate ions were not detected in the first 6 h, but were detectedin small amount in the time between 6–10 h and in high concentrationof 39 mg/L after 24 h. This indicates that the release of sulphur atomsneeds long irradiation time. The results indicate that degradationof AMX, AMP and CLX antibiotics presumably involves cleavage ofβ-lactam ring followed by subsequent reactions to formcarbondioxide,water, nitrate, ammonia and sulphate.

4. Conclusions

Degradation of amoxicillin, ampicillin and cloxacillin antibiotics inaqueous solution by TiO2 photocatalysis under UVA (365 nm)irradiation was studied. No significant degradation occurred by 300-min UVA irradiation per se. pH had a great effect on antibiotic

Fig. 8. Effect of irradiation time on DOC concentration and removal.

degradation and the highest degradation was achieved at pH 11.Photocatalytic reactions approximately followed a pseudo-first orderkinetics and the rate constants (k) were 0.007, 0.003 and 0.029 min−1

for amoxicillin, ampicillin and cloxacillin, respectively.Addition of H2O2 at ambient pH∼5 and TiO2 1.0 g/L resulted in

complete degradation of amoxicillin, ampicillin and cloxacillin in30 min. Dissolved organic carbon (DOC) removal, and nitrate (NO3

−),ammonia (NH3) and sulphate (SO4

2−) formation during degradationindicated mineralization of organic carbon, nitrogen and sulphur. UV/H2O2/TiO2 photocatalysis is effective for degradation of amoxicillin,ampicillin and cloxacillin in aqueous solution.

Acknowledgement

The authors are thankful to the management and authorities of theUniversiti Teknologi PETRONAS for providing facilities for thisresearch.

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