Materials Research Bulletin 74 (2016) 387–396

Microwave-assisted polyol synthesis and characterization ofpvp-capped cds nanoparticles for the photocatalytic degradation oftartrazine

Maher Darwisha, Ali Mohammadia,b,*, Navid Assia

aDepartment of Drug and Food Control, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, IranbNanotechnology Research Centre, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran

A R T I C L E I N F O

Article history:Received 16 June 2015Received in revised form 1 November 2015Accepted 3 November 2015Available online 10 November 2015

Keywords:A. ChalcogenidesA. NanostructuresB. Chemical synthesisC. X-ray diffractionD. Catalytic properties

A B S T R A C T

Polyvinylpyrrolidone capped cadmium sulfide nanoparticles have been successfully synthesized by afacile polyol method with ethylene glycol. Microwave irradiation and calcination were used to control thesize and shape of nanoparticles. Characterization with scanning electron microscopy revealed a restrictednanoparticles growth comparing with the uncapped product, hexagonal phase and 48 nm averageparticle size were confirmed by X-ray diffraction, and finally mechanism of passivation was suggesteddepending on Fourier transform infrared spectra.The efficiency of nanoparticles was evaluated by the photocatalytic degradation of tartrazine in

aqueous solution under UVC and visible light irradiation. Complete degradation of the dye was observedafter 90 min of UVC irradiation under optimized conditions. Kinetic of reaction fitted well to the pseudo-first-order kinetic and Langmuir–Hinshelwood models. Furthermore, 85% degradation of the dye in 9 hunder visible light suggests that cadmium sulfide is a promising tool to work under visible light forenvironmental remediation.

ã 2015 Published by Elsevier Ltd.

Contents lists available at ScienceDirect

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1. Introduction

During the last two decades, photocatalytic materials received alarge quantity of research interest as they have a great potential tobe applied in detoxification of environmental organic pollutantsand as a clean energy source [1]. Semiconductor heterogeneousphotocatalysts such as TiO2, ZnO, SnO2, WO3, Fe2O3, and CdS havebeen intensively investigated in the area of water and airpurification and in remediation reactions [2].

Like other advanced oxidation procedures (AOPs), the commoncharacteristic of photocatalytic materials is the generation of veryreactive species such as, principally but not exclusively, hydroxylradicals (HO�), which initiate a series of reactions leadingeventually to the destruction of the target pollutant [3]. Recently,nanostructures of these photocatalysts have attracted moreconsideration as they are expected to have higher photocatalyticactivity than their bulk counterparts due to their smaller size,

* Corresponding author art: Department of Drug & Food Control andNanotechnology Research Centre, Faculty of Pharmacy, Tehran University ofMedical Sciences, P.O. Box 14155-6451, Tehran, Iran. Fax: +98 21 88358801.

E-mail addresses: m-darwish@razi.tums.ac.ir (M. Darwish),alimohammadi@tums.ac.ir (A. Mohammadi), navid_a30@yahoo.com (N. Assi).

http://dx.doi.org/10.1016/j.materresbull.2015.11.0020025-5408/ã 2015 Published by Elsevier Ltd.

higher surface area-to-volume ratio, and increased band-gabenergy which in turn lead to higher redox potentials [4].

Cadmium sulfide (CdS), a typical metal chalcogenide semicon-ductor with a direct band gap Eg� 2.43 eV at room temperature [5],has become one of the most considerable materials in researchcommunities due to its diverse promising applications in the fieldof solar cells, photoelectronic devices and photocatalysis [6]. Thismaterial has shown better catalytic functions compared to those ofTiO2 due to the rapid generation of electron–hole pairs byphotoexcitation [7]. Nevertheless, CdS has the fatal photocorrosionproblem due to the self-oxidation by the generated hole [8]. Toovercome such a problem, an effective approach is to cover thenanoparticle core surface with a polymeric capping agent whichmight also help to stabilize the surface, control the growth, andprevent agglomeration of the nanoparticles [9–11].

Many methods have been utilized for the synthesis of CdSnanostructures such as co-precipitation [7,12], polyol [13],solvothermal [14,15], hydrothermal [16], non-aqueous chemicalmethod [17], and chemical bath deposition [18]. Among thesedifferent processes, the polyol method appears as an easy to carryout with many other advantages: a uniform shape, a narrow sizedistribution, and a low degree of agglomeration [19]. This methodgenerally uses poly-alcohol like ethylene glycol (EG), diethylene

388 M. Darwish et al. / Materials Research Bulletin 74 (2016) 387–396

glycol (DEG) or 1,2-propanediol as both solvent and reducing agent[20]. Furthermore, due to the relatively high dipole moment andloss factor of polyol solvents, they are also suitable for microwaveassisted route. In this regard, using microwave in the synthesis ofnanoparticles is considered a modern and rapidly developingmethod. It has been evidenced that microwave irradiation gives anarrow particle size distribution of nanocrystals with a high purityin a short reaction time in addition of being cheap andenvironmentally friendly [21–23].

Tartrazine (Acid Yellow 23; FD&C Yellow No. 5), as an azo dye,has been chosen for this study due to its extensively use as acolorant in food, cosmetics, pharmaceuticals and textile industry[24], as well as its high stability against biodegradation andconventional wastewater treatment procedures after disposalfrom industrial effluent [25]. The toxic concentration of tartrazineon human has been reported to be 7.5 mg k�1 [26]. This compoundis known to cause allergic reactions such as asthma and urticariaand appears to cause more allergic and intolerance reactions thanother azo dyes [27].

Previously reported works on the removal of tartrazine fromaqueous solutions include mainly conventional methods likeadsorption [28,29], ecocoagulation [30], and filtration [31] whichare known not to effectively degrade pollutant but merely transferit to another phase where it is more concentrated [32]. Whereasother reports have shown that tartrazine could be degradedemploying AOPs like: ozonation [33], electrochemical oxidation[34], photo Fenton oxidation [35], UV/H2O2 [36,37], photolytic[38], and photocatalytic oxidation [27,39–46].

Most of photocatalytic methods have utilized TiO2, which wasextensively studied and known to have some drawbacks such asexpensive precursors and inability to absorb visible light [47,48].Hence, the aim of the present work was first, to fabricate CdSnanoparticles by a chemical synthesis utilizing the polyol methodwith ethylene glycol as a solvent and polyvinylpyrrolidone (PVP) asa capping agent. Microwave irradiation followed by calcinationwas used for size and shape controlling. Further, to investigate thestructure, size, and morphology of the synthesized products usingvarious characterization techniques. In second, the work aimed to

Fig. 1. A schematic of the preparat

study the catalytic properties of these nanoparticles for oxidationof tartrazine, as an organic pollutant, in aqueous solution underUVC and visible light irradiations, taking in consider the effect ofdifferent parameters such as initial pH of solution, amount ofnanoparticles, and concentration of pollutant in the degradationprocess.

2. Expermental

2.1. Materials and reagents

All reagents used in our experiments were of analytical gradeand used as received without any further purification. Tartrazinepowder (� 85%) was obtained from Sigma–Aldrich (Germany).Cadmium chloride 2.5-hydrate (CdCl2 2.5H2O) and thiourea (SC(NH2) 2) were obtained from Scharlau (Spain). Polyvinylpyrroli-done (MW � 25,000 g mol�1), ethylene glycol, glacial acetic acid,and ammonia solution (25%) were obtained from Merck(Germany). Double distilled water was used for the preparationof all samples.

2.2. Synthesis of nanoparticles

In a typical process, 9 g of cadmium chloride 2.5-hydrate and 3 gof PVP were separately dissolved in 30 mL and 20 mL of EG,respectively, and then heated with stirring for 60 min at 75 �C. Thetwo solutions were then mixed slowly and heated with stirring for40 min at 100 �C. Concurrently, 3 g of thiourea was dissolved in20 mL of EG and heated with stirring for 100 min at 75 �C and thenadded slowly to the hot solution of (PVP-Cd2+). The temperature ofthe new mixture was gradually raised to 170–180 �C within 45 minand kept at this temperature until most of the solvent wasevaporated. In this stage, the color of the solution changed fromlight yellow into a dark orange suspension indicating the formationof CdS. Next, the suspension was microwaved (LG MC-2820Smicrowave) for 5 min with a power of 720 W and 50% duty cycle(30 s of irradiation and 30 s stop). The obtained powder was thencalcined in a furnace (Sybron Thermolyne Type 1500) for 120 min

ion of PVP-CdS nanoparticles.

M. Darwish et al. / Materials Research Bulletin 74 (2016) 387–396 389

at 450 �C and finally, black crystallites of PVP-capped CdSnanoparticles were obtained. The scheme of preparation isillustrated in Fig. 1. A control synthesis in the absence of PVPand the exact other steps was carried out to evaluate the impact ofPVP on the yielded product.

2.3. Characterization of the CdS nanoparticles

The synthesized CdS nanoparticles were characterized usingvarious analytical techniques. Scanning electron microscopy(KYKY-EM3200 SEM) was used to investigate the morphologiesof nanoparticles. X-ray diffraction patterns of the nanoparticleswere recorded by a Bruker AXS D8-ADVANCE diffractometer fittedwith a (Cu Ka l = 1.5418 Å) radiation tube. The average crystallitesize of the synthesized CdS was calculated with well-knownScherrer’s equation (Eq. (1)) with full width at half maxima(FWHM) of X-ray diffraction pattern:

D ¼ 0:89lbcosu

ð1Þ

where l is the wavelength of X-ray radiation source, b is FWHM ofthe peak and u is Bragg’s diffraction angle.

Furthermore, in order to determine the chemical compositionof nanoparticles and study the behavior of PVP, Fourier transforminfrared spectra in the range of 400–4000 cm�1 of many samplesduring the synthesis process was recorded in transmission mode(Thermo Nicolet 8700 FTIR), the powder samples were groundedwith KBr and compressed into a pellet for analysis.

2.4. Photocatalytic activity under UVC light

Photocatalytic activity of the nanoparticles was evaluated bymeasuring the degradation of tartrazine which was used as a testpollutant. An amount of (5–50) mg of the catalyst was dispersed in200 mL of tartrazine aqueous solution (10–100) mg L�1. The pH ofthe suspension was adjusted to the desired value by ammonia orglacial acetic acid solutions and determined by a digital pH meter(Metrohm pH lab 827). The suspension in the photoreactioncontainer was exposed to UV light source (CH Lighting T8 30 WUVC) positioned 10 cm above for 90–180 min. At given intervals ofillumination, 5 mL samples were taken out and centrifuged(Hettich EPA 12) at 2500 rpm for 10 min in order to completelyremove all nanoparticles. The degradation ratio was monitoredusing UV–vis spectrophotometer (T80 + UV–vis Spectrometer PGInstruments Ltd.). According to the Beer–Lambert law, theconcentration of tartrazine is proportional to its absorbance.Hence, the degradation efficiency was calculated by the followingformula:

D% ¼ ðC0 � CÞC0

� �� 100 ¼ ðA0 � AÞ

A0

� �� 100 ð2Þ

C0 and A0 are the initial concentration and absorbance, respective-ly, while C and A are the concentration and absorbance afterintervals of illumination (t). The reaction rate constant (k) wascalculated using plots of ln (C/C0) versus illumination timeaccording to the following formula:

lnCC0

� �¼ �kt ð3Þ

2.5. Photocatalytic degradation and mineralization under visible light

After obtaining the optimal conditions for tartrazine degrada-tion with the synthesized nanoparticles under UVC, an assessmentof the activity of these nanoparticles under visible light was carried

out using (OSRAM HWL 160 W) lamp in the same experimentalsetup used under UVC irradiation. In addition, a light protectedexperiment under the same conditions of visible light experimentwas carried out and considered as a blank to assess themineralization of tartrazine after same time of irradiation. Sampleswere analyzed by a total organic carbon analyzer type (TOC-V,Shimadzu).

3. Results and discussion

3.1. Morphology and structure

The SEM images presented in Fig. 2 show that PVP-capped CdS(PVP-CdS) particles are in the range of nanometer with narrowerparticle size distribution (40–59 nm) and less agglomerationcomparing to those of the uncapped CdS which has an averageparticle size of 115 nm (75–180) indicating clearly the advantages ofPVP in restricting the growth and preventing agglomeration. This issimply due to the stereo-hindrance effect resulted from repulsiveforce among the polyvinyl groups of PVP and due to the restrainedOstwald ripening kinetics in such a way that the growth rate wasdecreased with the size of CdS nanoparticles. Consequently, smallerparticles with enhanced monodispersity were obtained.

X-ray powder diffraction patterns of the capped nanoparticlespresented in Fig. 3 show a perfect match with the hexagonal phaseof CdS (JCPDS No. 01-089-2944). Diffraction peaks of monoclinicsulfur are also found (JCPDS No. 01-074-2108). The average

Fig. 2. SEM images of (a) uncapped and (b) PVP-capped CdS nanoparticles.

Fig. 3. XRD patterns of the PVP-CdS nanoparticles.

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crystallite size of the capped nanoparticles calculated from XRDpatterns using the Scherrer’s equation was about 48 nm which is inagreement with the result obtained from SEM image.

FTIR spectra of pure PVP and PVP-CdS prior to and aftercalcination are shown in Fig. 4. In pure PVP spectrum, the O��Hstretching vibration observed as a broad and strong peak at3517 cm�1 is due to H2O absorption on the surface of the sample.The two bands at 2952 and 1423 cm�1 correspond to C��Hasymmetric stretching vibration and bending vibration, respec-tively. The broad peak with high intensity at 1665 cm�1 is ascribedto the C¼O bond stretching and the band at 1286 cm�1 correspondsto C��N bond stretching of the pyrrolidone structure.

Two observations can be found when comparing pure PVPspectrum with the other two spectra. First, a decrease in all peaksintensities after exposing the sample to microwave irradiation andmore decrease after calcination. This can be explained in the lightof thermal degradation of PVP. Loría-Bastarrachea et al. [49], inagreement with earlier reports, stated that at 450 �C the mainproduct obtained from thermal degradation of PVP is itscorresponding monomer, i.e., vinyl pyrrolidone or less unsaturatedcompounds such as PVP oligomers. The second observation is theshift to lower wavenumber of some peaks, specifically C¼O andC��N stretching vibrations. These shifting indicate the interactionbetween PVP and Cd2+. The mechanism of this interaction assuggested by Abdelghany et al. [50] implies the formation ofcoordinate bonds between nitrogen and/or oxygen atoms of thePVP with cadmium ions in four different probabilities as shown inFig. 5. Hence, the preceding findings indicate the formation of shortpolymeric chain-capped CdS nanoparticles.

3.2. Effect of tartrazine solution initial pH

The pH of the reaction medium is one of the most crucialparameters in photocatalytic degradation of organic pollutants. Itaffects the surface charges of both the catalyst and pollutant andconsequently the adsorption of the pollutant on catalyst surface[51].

In order to study the role of pH on the adsorption of tartrazineon the catalyst surface, 20 mg L�1 solutions of the dye and a fixed

amount of PVP-CdS (25 mg) were set at pH 3.5, 5.5, 7 or 11 and keptin dark place with constant stirring for 90 min in order to reach theequilibrium adsorption. In addition, photolysis experiments, in theabsence of catalyst and presence of UVC light with the same otherexperimental setup used in the adsorption study, were carried outalso over 90 min. The role of pH on photocatalytic degradation oftartrazine was investigated in the same conditions of photolysis inthe presence of 25 mg of PVP-CdS or uncapped CdS over 90 min.The results are shown in Fig. 6.

As can be seen, a decrease in the dye concentration between 3and 8% was obtained among the different pH values in the presenceof PVP-CdS only without UVC irradiation. Whereas about 4.5–12%of the initial tartrazine concentration was removed at different pHvalues in the presence of UVC irradiation alone without nano-particles. On the other hand, maximum photocatalytic degradationpercentage of PVP-CdS was observed in alkaline region. Thedegradation increased with increasing pH and reached itsmaximum value at pH 11. For uncapped CdS, neutral mediumwas favorable.

Our suggested interpretation is the following: tartrazine has apKa = 9.4 and so is negatively charged in alkaline medium due to itsionization to the related phenyl salt. Likewise, CdS has a zero pointcharge at about pH 7 and is also negatively charged in pH (8–12). Asa result, the adsorption of tartrazine on CdS surface is minimum atpH 11. Here, the enhancement of capped catalyst activity inalkaline medium could be imputed to the attachment of CdS withpyrrolidone ring that might have acted as a mediator to trap thecarriers generated in the catalyst and adsorb the water or dyemolecules or even the abundant hydroxyl ions, which wouldsubsequently facilitate the generation of hydroxyl radicals thatinitiate the oxidization of the pollutant.

Unsurprisingly, PVP-CdS has shown a superior activity overuncapped CdS in extreme acidic and basic conditions whereas inneutral conditions, the activities were nearly equivalent. This isascribed to two factors: first, the smaller particles size that offeredmore surface area for photocatalytic reaction in the case of PVP-CdS and second, the photocorrosin or dissolution that uncappedCdS might underwent in extreme conditions which has reduceddrastically its activity. Meanwhile, PVP-CdS maintained an

Fig. 4. FTIR spectra of (A) pure PVP, (B) PVP-CdS after microwave irradiation and, (C) PVP-CdS after calcination.

M. Darwish et al. / Materials Research Bulletin 74 (2016) 387–396 391

approximate percentages of degradation in acidic and neutralconditions as a consequence of PVP passivation.

3.3. Effect of the catalyst loading

Catalyst loading is a critical parameter in photodegradation oforganic pollutants. It affects the reaction rate and consequently thecost of treatment [52].

The effect of PVP-CdS dosage on the degradation of tartrazinewas investigated in the presence of different amount of catalyst (5–

50 mg) with 50 mg L�1 initial concentration of tartrazine at pH 11for 90 min of irradiation. The results are shown in Fig. 7.

As is noted, the photodegradation of the tartrazine was found toincrease with the increased catalyst loading within the range ofstudy. Increasing the catalyst loading gave a rise to a highernumber and density of nanoparticles, which in turn caused morephotons to be absorbed and dye molecules to be adsorbed leadingto better degradation [53]. The opacity of the suspension was notgreatly affected by the increased amount of PVP-CdS and nohindering to light penetration was observed. On the other hand,after 25 mg of catalyst amount there was no considerable

Fig. 4. (Continued)

Fig. 5. Suggested mechanism of interaction between PVP and Cd2+.Ref. [50].

392 M. Darwish et al. / Materials Research Bulletin 74 (2016) 387–396

enhancement in the degradation profile. Hence, 25 mg of PVP-CdSnanoparticles was chosen to be the optimal amount for furtherstudies.

Fig. 6. Effect of different pH values (3.5–11) on adsorption, photolysis and,photocatalytic degradation of tartrazine over 90 min.

3.4. Effect of the initial concentration of tartrazine

The influence of pollutant concentration on photocatalyticdegradation has also been studied. Experiments have been carriedout at different initial concentrations in the range (10–100) mg L�1

with constant amount of nanoparticles (25 mg) and initialsolution’s pH 11. The results shown in Fig. 8 indicate thatincreasing the concentration of tartrazine had decreased thedegradation from 100% (10 mg L�1) to 92.9% (50 mg L�1) and 36.2%(100 mg L�1) in 60 min.

This can be explained in the light of photocatalytic degradationmechanism; a single layer of adsorbed water molecules exists onthe surface of PVP-CdS. After photon is adsorbed, the holesgenerated in valence band transfer to the surface and oxidize watermolecules and hydroxyl ions to produce HO� radicals. Theseradicals rapidly attack tartrazine molecules and oxidize them tointermediates which in turn would be mineralized with subse-quent attacks of HO� radicals.

PVP � CdS þ hn ! eCB� þ hVBþ ð4Þ

Fig. 7. Photocatalytic degradation of tartrazine by varying the amount of PVP-CdSnanoparticles (5–50 mg) with Tartrazine concentration (50 mg L�1) and pH 11. Fig. 9. Plots of �ln (C/C0) versus illumination time for different concentrations of

tartrazine.

M. Darwish et al. / Materials Research Bulletin 74 (2016) 387–396 393

hþ þ H2O ! HO� þ Hþ ð5Þ

HO� þ TA ! Intermediates ð6Þ

HO� þ Intermediates ! CO2 þ H2O ð7ÞIncreasing the initial dye concentration means more tartrazine

molecules to surround the nanoparticles and decrease the pathlength of the photons entering the solution resulting in lowerphoton absorption by the catalyst and reaction sequence is sloweddown. Consequently, rate of degradation is decreased. At thisjuncture, we believe that PVP passivation has an important role inthe separation of the photogenerated carriers. This is attributed tothe prohibition of nonradiative decay of carriers by coveringdangling bonds that may work as exciton traps. Also, thecoordination of nanoparticles surface atoms which minimizesthe trap states lie within the band gap and increases quantum yieldby providing alternative pathways of electron–hole separation.More importantly, complexation between Cd and the lone pair ofnitrogen/oxygen makes pyrrolidone moiety of PVP act as a holeacceptor that traps the photogenerated holes and transfers them tothe target objects. It is worth mentioning here that partialdecomposition of PVP, during the synthesis process, was beneficialfor exposing trapping sites of pyrrolidone to those targeted objectsto promote the catalytic reaction sequence.

Fig. 8. Photocatalytic degradation of varying initial concentrations of tartrazine(10–100 mg L�1) with pH 11 and 25 mg amount of PVP-CdS nanoparticles.

3.5. Kinetic study

In order to study the pattern of the photodegradation reactionof tartrazine, Langmuir–Hinshelwood (L–H) model was used. Thismodel has been successfully used for heterogeneous photo-catalysis to describe the exact relationship between the rate ofdegradation and the concentration of pollutant in photocatalyticreaction [31]. The rate constant (k) of degradation reaction wascalculated according to the Formula (3). As shown in Fig. 9, a linearrelation between tartrazine concentrations and illumination timehas been observed implying a pseudo-first order kinetics of thephotodegradation reaction. The pseudo-first order rate constantdecreased dramatically with increased initial concentration oftartrazine. This is because, as aforementioned, with high concen-trations of the pollutant, less hydroxyl radicals in active sites of thecatalyst are generated and the majority of photons are absorbed bypollutant molecules rather than catalyst [54].

In order to cover the adsorption properties of the substrate onthe catalyst surface, the experimental data have been rationalizedin terms of the modified form of L–H kinetic model. The modifiedLangmuir–Hinshelwood expression that explains the kinetics ofheterogeneous catalytic systems is given by:

r ¼ �dcdt

¼ krKCð1 þ KCÞ ð8Þ

where r represents the rate of reaction that changes with time(mg L�1min�1), kr is the reaction rate constant (mg L�1min�1), andK is the adsorption coefficient of the reactant onto the catalystparticles (L mg �1).

Fig. 10. Plot of 1/r0 versus 1/C0 of the photocatalytic degradation of tartrazine.

Fig. 11. Reusability of PVP-CdS nanoparticles.

394 M. Darwish et al. / Materials Research Bulletin 74 (2016) 387–396

The applicability of L–H equation for the degradation has beenconfirmed by the linear plot obtained by plotting the reciprocal ofinitial rates (1/r0) against reciprocal of initial concentrations oftartrazine (1/C0) as shown in Fig. 10.

1r0

¼ 1kr

� �þ 1

krKC0

� �ð9Þ

In this study, a reasonable agreement (R2 = 0.969) was obtainedbetween the experimental results and the linear form of the L–Hexpression.

The values of kr and K have been determined from the slope andintercept of this plot and found to be 1.908 and 0.036, respectively,indicating that photocatalytic degradation is a dominant factor

Fig. 12. Photocatalytic degradation and mineralization of 50 mg L�1 tartrazine wi

when compared with pollutant adsorption onto the surface of thecatalyst.

3.6. Reusability

Reusability of capped catalyst was investigated in order toverify its stability and the protective role of PVP in preventingcatalyst degradation. After a first round of catalytic reaction, themixture (catalyst+slurry) was filtered and washed with a mixtureof water and ethanol (1:1) then dried in an oven at 65 �C for 6 h. Therecovered catalyst was used again to degrade tartrazine undersame conditions used before. A third round was carried out in thesame procedure. Results depicted in Fig. 11 show a very slightdeference in catalytic activity among the first used and reusedcatalysts. A small change in the kinetic could be seen but, theoverall degradation in 90 min of study was not importantlyaffected. It is our believe that photocorrosion suppression is due toprolonged life time of electron–hole pairs as a consequence of holetrapping and transferring mediated by PVP.

3.7. Photodegradation and mineralization under visible lightirradiation

A 50 mg L�1 solution of tartrazine with pH 11 was mixed with25 mg of PVP-CdS nanoparticles and exposed to visible lightirradiation in the same experimental setup used under UVCirradiation. As can be seen in Fig. 12, approximately 85% of the dyewas degraded and about 69% of the total organic content comparedwith the blank solution was removed after 9 h.

th pH 11 and 25 mg of PVP-CdS nanoparticles under visible light irradiation.

M. Darwish et al. / Materials Research Bulletin 74 (2016) 387–396 395

4. Conclusion

Polyol synthesis with microwave irradiation and calcinationhave been used as an efficient method to fabricate cadmium sulfidenanoparticles in an average crystallite size of about 48 nm whenPVP was used as a capping agent and about 115 nm withoutcapping. The prepared nanoparticles have been effectively used asa photocatalyst for the degradation of tartrazine in aqueoussolution. Total degradation of tartrazine was obtained after 90 minusing 25 mg of the PVP-CdS with initial dye concentration of50 mg L�1 and pH 11 under UVC irradiation. The role of PVP incontrolling the growth and stabilizing the nanoparticles wasdemonstrated by the compassion with the uncapped productwhich has shown more growing and less catalytic activity.

The Langmuir–Hinshelwood models indicated that tartrazineunderwent a pseudo first order kinetics of the reaction and thatphotocatalytic degradation was prevailing compared with pollut-ant adsorption on PVP-CdS surface. In addition, results has shownthat our nanoparticles can work sufficiently under visible lightwith about 85% abatement of initial tartrazine concentration and69% mineralization after 9 h of irradiation.

In conclusion, PVP-CdS nanoparticles synthesized in this workmight be used effectively in environmental treatment processes toremove organic pollutants from water. These nanoparticles arepromising to work under visible light sources to reduce greatly theexpense of treatment.

Acknowledgment

The authors wish to thank Tehran University of MedicalSciences for the financial and instrumental support of thisresearch.

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