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Visible-light-driven photocatalytic and chemical sensing properties

of SnS2nano?akes

Ahmad Umar a,b,n,M.S.Akhtar c,G.N.Dar b,e,M.Abaker b,e,A.Al-Hajry b,d,S.Baskoutas e

a Department of Chemistry,College of Science and Arts,Najran University,P.O.Box1988,Najran11001,Kingdom of Saudi Arabia

b Promising Centre for Sensors and Electroni

c Devices(PCSED),Najran University,P.O.Box1988,Najran11001,Kingdom of Saudi Arabia

c New an

d Renewabl

e Energy Materials Development Center(NewREC),Chonbuk National University,Jeonbuk,South Korea

d Department of Physics,Faculty of Sciences and Arts,Najran University,P.O.Box1988,Najran-11001,Kingdom of Saudi Arabia

e Department o

f Materials Science,University of Patras,Patras,Greece

a r t i c l e i n f o

Article history:

Received4February2013

Received in revised form

19March2013

Accepted20March2013

Available online28March2013

Keywords:

SnS2

Nano?akes

Photocatalytic degradation

Rhodamine B

Nitroaniline

Chemical sensors

a b s t r a c t

This work demonstrated the successful and facile large-scale synthesis and characterizations of SnS2

nano?akes.The detailed morphological studies revealed that the synthesized products were nano?akes

and were grown in large quantity.The XRD pattern and detailed compositional studies con?rmed that

the synthesized SnS2nano?akes were well-crystalline and possessing hexagonal SnS2phase.The

synthesized SnS2nano?akes were used as ef?cient photocatalysts for photocatalytic degradation and

effective electron mediators for the fabrication of chemical sensor.The photocatalytic properties of SnS2

nano?akes towards the photocatalytic degradation of Rhodamine B dye under visible light irradiation

showed reasonably good degradation of～61%.Moreover,the as-synthesized SnS2nano?akes were used

as ef?cient electron mediators for the fabrication of nitroaniline chemical sensor by simple I-V technique.

Very high-sensitivity of～505.8270.02mAcm?2.(mole/L)?1and experimental detection limit of

～15?10?6(mole/L)in a short response time of～10.0s with LDR in the range of15.6?10?6–

0.5?10?3mole L?1were observed for the fabricated nitroaniline chemical sensor.The observed results

indicated that the SnS2nano?akes can ef?ciently be used as visible-light-driven photocatalysts and the

fabrication of ultra-high sensitive chemical sensors.

1.Introduction

The aquatic environmental imbalance mainly occurs by the

contamination of water with the harmful non-biodegradable

materials[1–3].Various textile and chemical industries release

many harmful organic macromolecules and dyes[4,5].Particularly

the disposable of colored organic waste water from the textile

dyeing industries causes a serious problem to aquatic ecosystem

and hence contaminate the environment which cause a serious

threat to the living organisms[6].Among various water soluble

dyes,Rhodamine B(RhB)with non-volatile nature and bright

reddish violet in color are extensively used in various prospect

applications such as?uorescence microscopy,?ow cytometry,

?uorescence correlation spectroscopy and ELISA[7]and also

applied for dying cottons,bamboo,weed,stamp pad inks etc.

The waste of RhB dye hazardously affects natural environments

especially aquatic life and lead the mutagenic effects to humans

and other living organisms[8,9].Conventionally,a biological

treatment or degradation process utilizes to decolorize the dyes,

but it is ineffective for the complete removal and degradation of

https://www.wendangku.net/doc/2c12840245.html,st few years,the catalytic process derived by solar energy or

other radiation energy has been studied for the successful degra-

dation of harmful organic dyes into environmental friendly mate-

rials[10].In this regard,because of the unique band gap and

various other physical and chemical properties,the nanoscale

inorganic semiconductors such as metal oxides,metal sul?des

etc.were used as active catalysts for the degradation/oxidation of

organic dyes and reported in the literature[11].The photocatalytic

degradation occurs due to the effective separation of excited

electron in conduction band(CB)and hole in valance band(VB)

under the light illumination,which could capture by some surface

species in the surroundings such as hydroxyl or O2groups[12].

These catalysts are usually active under the UV-light.Among

various semiconducting materials,the metal sul?des have

received a great deal of interest as promising photocatalysts under

Contents lists available at ScienceDirect

journal homepage:https://www.wendangku.net/doc/2c12840245.html,/locate/talanta

Talanta

https://www.wendangku.net/doc/2c12840245.html,/10.1016/j.talanta.2013.03.050

n Corresponding author at:Najran University,Centre for Advanced Materials and

Nanoengineering(CAMNE),Centre for Advanced Materials and Najran11001,Saudi

Arabia.Tel.:+966534574597.

E-mail address:ahmadumar786@https://www.wendangku.net/doc/2c12840245.html,(A.Umar).

Talanta114(2013)183–190

the visible light illumination[13].Domen et al.demonstrated a high photo-activity for hydrogen evolution over the surface of synthesized nanostructured CdS under visible light[14].

Recently,the IV–VI group semiconductors such as tin sul?des (SnS,SnS2)have received much attention owing to their strong anisotropy of optical properties and potential applications in solar cells as well as electrical switchings[15–20].Among large number of binary tin sul?des(SnS,SnS2,Sn2S3,Sn3S4,Sn4S SnS and SnS2), the SnS2possesses special place due to its own properties and wide applications in solar cells,lithium-ion batteries,optoelec-tronics,photoluminescence and so on[21].The SnS2is an n-type semiconductor and is receiving much attention owing to its layered hexagonal CdI2-type crystal structure with two layers of close-packed sulfur anions and tin cations sandwiched between them in an octahedral coordination manner.Due to its absorption tunable band gap of 2.2eV,the crystalline SnS2could be a promising photocatalytic material for the photocatalytic degrada-tion of organic dyes in the presence of visible-light[22].Moreover, SnS2nanomaterials possess good oxidative and thermal stability in acid and neutral environment[23,24].

In this work,we demonstrate the facile and large-scale synth-esis of well-crystalline SnS2nano?akes by simple hydrothermal process.The synthesized nano?akes were characterized in detail in terms of their morphological,structural and compositional properties.The as-synthesized nano?akes were used as ef?cient photocatalysts for photocatalytic degradation of Rhodamine B dye under visible light.Moreover,the prepared nano?akes were used as ef?cient electron mediators for the fabrication of nitroaniline chemical sensor by simple I–V technique.

2.Experimental details

2.1.Synthesis of SnS2nano?akes

All the chemicals utilized for the synthesis of SnS2nano?akes were purchased from Sigma-Aldrich and used without further puri?cation.Distilled water(DW)was used for all the synthesis process.Well-crystalline SnS2nano?akes were synthesized by facile low-temperature hydrothermal process.In a typical reaction process,aqueous solutions of0.02M SnCl45H2O and0.05mol/L thiourea,both prepared in50mL DI water,were mixed well under constant stirring.After constant and vigerous stirring for30min, the resultant solution was transferred to te?on lined autoclave, sealed and heated upto1401C for3h.After desired reaction time, the autoclave was allowed to cool at room-temperature and?nally yellowish precipitate was obtained which was extensively washed several times with DW,ethanol and acetone,sequentially and dried at551C for3h.During the reaction,the thiourea reacts with water and produces H2S which is further reacted with Sn4+ions obtained from SnCl4.The chemical reactions involved in the synthesis process can be written as:

NH2CSNH2+2H2O-2NH3+H2S+CO2

Sn4++H2S-SnS2↓+4H+

The dried powder was then characterized in detail in terms of their morphological,structural and compositional properties and utilized as ef?cient photocatalyst for photocatalytic degradation of Rhodamine B and as an electron mediator for the fabrication of reproducible and highly sensitive nitro-aniline chemical sensor.

2.2.Characterizations of as-synthesized SnS2nano?akes

The as-synthesized SnS2nano?akes were characterized in detail by various analytical tools.The general and detailed morphologies of as-synthesized nano?akes were done by?eld emission scanning electron microscopy(FESEM;JEOL-JSM-7600F) and transmission electron microscopy(TEM)equipped with high-resolution TEM(HR-TEM).For HRTEM analysis,the synthesized products were ultrasonically dispersed in acetone and a drop of acetone solution,which contains the SnS2nanostructures,was placed on a copper grid and examined.The crystallinity and crystal phases were examined by the X-ray diffraction(XRD;PANanaly-tical Xpert Pro.)pattern measured with Cu-Kαradiation (λ?1.54178?)in the range of10–651.The chemical composition of the as-synthesized SnS2nano?akes was examined by Fourier transform infrared(FT-IR)spectroscopy,measured at room-tem-perature,in the range of400–4000cm?1.To prepare the sample for FTIR measurements,small amount of the as-synthesized SnS2 nano?akes was mixed well with the potassium bromide(KBr)and subsequently compressed under high-pressure(～4t)for pellet preparation.The obtained pellet,composed of SnS2nano?akes and KBr,was used for the FTIR measurements.

2.3.Photocatalytic decomposition of rhodamine B dye using

as-synthesized SnS2nano?akes

The photocatalytic performance of the synthesized SnS2nano-?akes was examined by studying the photocatalytic decomposi-tion of rhodamine B(RhB)dye.The photocatalytic degradation of RhB dye was performed under the illumination of Xenon arc lamp (300W,Hamamatus:L2479),attached with UV cut-off?lter of wavelength400nm(FSQGG-400)which limited the illumination in a range of400–800nm,i.e.visible light.The degradation of RhB dye was calculated by measuring the UV–vis absorbance at 552nm wavelength at certain time intervals.The photo-catalytic degradation was established in a250ml beaker using150ml of RhB dye solution(10ppm).Prior to the light illumination,the prepared RhB dye solution was bubbled with oxygen for30min to allow the equilibrium of the system.For the photocatalytic experiments,150mg of the as-synthesized SnS2nano?akes as photocatalyst were added to the RhB dye solution and stirred for 10min for the initial physical adsorption of dye over SnS2nano-?akes surfaces.The decomposed dye solution was measured by using(UV–vis spectrophotometer Perkin Elmer-UV/VIS-Lambda 950)after regular time intervals.

2.4.Fabrication and characterization of nitro-aniline chemical sensor by I–V technique

To modify the electrode surface,?rstly,the surface of glassy carbon electrode(GCE)was polished with commercially available alumina,followed by rinsing with DW thoroughly.For the GCE surface modi?cation for nitro-aniline chemical sensor,slurry of SnS2nano?akes were made by mixing an appropriate composition of SnS2nano?akes and conducting agent(butyl carbital acetate). Finally,a small amount of the slurry was casted on GCE(surface area0.0316cm2)surface,and then the modi?ed electrode was dried in electric oven at60751C for4h.The sensor analytical performance was investigated using I–V technique as discussed in our previous reports[25].For I–V measurements,an electrometer (Keithley,6517A,USA)was used as a voltage source and the SnS2 nano?akes/GCE was used as a working electrode while Pt wire was employed as a counter electrode.The current response was measured from0.0to2.0V while the time delaying and response time were1.0s and10.0s,respectively.The amount of10.0mL phosphate buffer solution was kept constant for all the measure-ments.For the concentration studies,a wide range of nitroaniline concentrations(15.6?10?6mol/L–1?10?3mol/L)was used.The sensitivity of the fabricated nitro-aniline chemical sensor was estimated from the slope of the current versus concentration from

A.Umar et al./Talanta114(2013)183–190 184

the calibration plot divided by the value of active surface area of sensor/electrode.All the sensing experiments were carried out at room-temperature.3.Results and discussion

3.1.Structural,morphological and compositional properties of SnS 2nano ?akes

Prior to any applications,the as-synthesized SnS 2nano ?akes were characterized in terms of their structural,morphological and com-positional properties.To examine the crystallinity and crystal phase,the as-synthesized SnS 2nano ?akes were examined by X-ray diffrac-tion (XRD).Fig.1exhibits the typical XRD pattern for as-synthesized nano ?akes.All the re ?ections in the diffraction pattern are well

matched with the typical SnS 2crystals and can be indexed to the hexagonal SnS 2phase with a lattice constant a ?3.649?and c ?5.899?.The observed XRD results are well matched with already reported literature (JCPDPS card no.22–0951).Moreover,no other re ?ection,except SnS 2re ?ections are seen in the pattern which con ?rms the formation of pure SnS 2nanomaterials.

The general morphologies of as-prepared SnS 2nanomaterials were examined by FESEM and shown in Fig.2(a)and (b).Fig.2(a)exhibits the typical low-magni ?cation image and revealed that the prepared SnS 2nanomaterials possess ?ake-shaped morphology and are synthesized in large quantity.It is clear from the high-resolution images that the ?akes are thin nanosheets which are curly in shape and randomly arranged (Fig.2(b)).Moreover,due to larger size,the nanosheets are interconnected with each other in such a manner that they made some porous architecture structures and hence possess larger surface area.Therefore,these materials are promising candidates for photocatalysts and sensors applications.The typical thicknesses of the nanosheets are in the range of 60720nm with several micrometers in width.The detailed mor-phological investigations of as-synthesized SnS 2nano ?akes were examined by TEM equipped with high-resolution TEM (HRTEM).For the TEM analysis,the prepared SnS 2nano ?akes were ultrasonically dispersed in acetone and a drop of acetone which contains the nano ?akes was placed on the TEM grid and examined.

Fig.2(c)exhibits the typical low-resolution TEM image of the as-synthesized SnS 2nano ?akes.It is clear from the TEM image that the nano ?akes were made by the thin SnS 2nanosheets.Moreover,due to large size,the nanosheets are interconnected with each other which leads to the formation of some porous architecture.The typical thicknesses of the nanosheets are in the range of 60720nm.It is also clear from the observed TEM image that the nano ?akes are synthesized in large quantity.All the TEM observations regarding shape,size and thickness are well matched with the obtained FESEM results.For further structural properties,the nano ?akes were investigated by HRTEM and results are shown in Fig.2(d).The observed HRTEM exhibits a very clear

and

Fig.1.XRD pattern of the as-synthesized SnS 2nano ?akes prepared by facile hydrothermal process at

low-temperature.

Fig.2.(a)Low and (b)high-magni ?cation FESEM,(c)low-and (d)high-resolution TEM images of the as-synthesized SnS 2nano ?akes prepared by facile hydrothermal process at low-temperature.

A.Umar et al./Talanta 114(2013)183–190185

well-de ?ned lattice fringes with the lattice spacing of ～0.32nm,which is fully consistent with the distance of (100)crystalline plane of the hexagonal SnS 2.The obtained HRTEM results are well matched with the XRD observations.

The chemical composition of as-synthesized SnS 2nano ?akes was examined by using FTIR spectroscopy,as shown in Fig.3.Several well-de ?ned absorption bands were observed in the spectrum at 631,1411and 1641cm ?1.The peak appeared at 631cm ?1in the spectrum is due to the formation of Sn –S bond [26].The origination of two very week peaks at 1411and 1641cm ?1are due to the formation of C –H and C –O bands,

respectively [26].Finally,due to the presence of Sn –S bond,it is con ?rmed that the synthesized nanomaterial is SnS 2.

3.2.Visible-light driven photocatalytic properties of SnS 2nano ?akes To de ?ne the photocatalytic activity of synthesized SnS 2nano-?akes,the degradation of RhB dye was performed under the visible light irradiation.The degradation rate of RhB dye was estimated by the following relation [27(a)];Degradation rate ?(A 0–A/A 0)?100?(C 0–C/C 0)100

where,C 0represents the initial concentration,C the variable concentration,A 0the initial absorbance,and A the variable absorbance.Fig.4depicts the UV –vis absorption spectra (a),(b)%degradation rate versus time;(c)a plot for A 0/A versus time and (d)pie degradation chart of decomposed RhB dye solution by synthesized SnS 2nano ?akes under the visible light irradiation.The photocatalytic degradation was monitored by measuring the maximum absorbance at the wavelength of 552nm in regular time intervals (10min)under visible light.Interestingly,it was observed that the relative absorption intensity continuously decreases as increasing the visible light exposure time which indicates that the RhB dye decomposes gradually over the surface of the photocatalyst,i.e.SnS 2nano ?akes (Fig.4(a)).Under visible light irradiation,the synthesized SnS 2nano ?akes signi ?cantly degraded the RhB dye by ～61%within 120min as shown in Fig.4(b).However,the degradation rate of RhB dye was almost negligible when photocatalytic reaction is performed under visible light irradiation without SnS 2nano ?akes which clearly suggested that the degradation rate increases in presence of the photocata-lyst,i.e.SnS 2nano ?akes.Fig.4(c)shows the plot of the variation in the relative concentration (A/A 0)versus time interval for the photo-degradation of RhB dye over the surface of SnS 2nano ?akes under visible light irradiation.Interestingly,the obtained

results

Fig.3.FTIR spectrum of the as-synthesized SnS 2nano ?akes prepared by facile hydrothermal process at

low-temperature.

Fig.4.(a)UV –Vis absorbance spectra of decomposed RhB dye solution over as-synthesized SnS 2nano ?akes under visible light irradiation,(b)degradation rate (%)and (c)extent of decomposition (A/Ao)of RhB dye with respect to time intervals,(d)pie degradation chart of degraded RhB dye.

A.Umar et al./Talanta 114(2013)183–190

186

clearly display the gradual degradation of RhB dye over the surface of synthesized catalyst.The relative concentration of RhB dye decreases with increasing the visible light irradiation exposure time while in the absence of synthesized SnS2nano?akes catalyst, negligible degradation is detected under visible light irradiation. The pie degradation chart of RhB dye(Fig.4(d))reveals that most of dye molecules are degraded in80min and afterward the degradation rate slows down.Conclusively,the synthesized SnS2 nano?akes as photocatalyst are able to degrade harmful RhB dye into the environment friendly residues under visible light irradia-tion.The mass spectroscopy of RhB dye before and after photo-catalytic reaction has been examined to investigate the possible degradation products/intermediates of photocatalytic degradation of RhB dye,as shown in Fig.5(a).At0min,RhB dye solution shows a strong mass signal at m/z?451.1,which is close to the mass of RhB dye.It is seen that a number of mass signals are detected in the RhB dye solution after120min,indicating the degradation of RhB dye over the surface of SnS2nano?akes under visible light. The main mass signal at m/z?451.1becomes weak after120min and splits into various mass signals.Fig.5(b)depicts the possible degradation intermediates during the photocatalytic reactions which are illustrated on the observed mass signals.These possible reaction intermediates from fragmentations of the RhB dye con-tain the oxy groups in their rings.Thus,the formations of these intermediates might be helpful for the complete mineralization of organic dye[27(b)].

The schematic illustration to understand the degradation mechanism of RhB dye over the surface of SnS2nano?akes was presented in Fig.6.In general,the generation of oxyraicals such as hydroxyl(OH )and superoxide(O2d,HO2d)are responsible for the degradation of organic dyes under light irradiation and these radicals are formed over the surface of semiconductors by the separation of electron–hole pairs[28].Importantly,the presence of carbon species on surface of SnS2catalyst is responsible for creating active sites which is helpful for the degradation of dye under light illumination[29].From the mechanism,upon light illumination SnS2nano?akes absorbs the visible light and the electron(ē)from VB excites to CB which effectively causes a separation between

Fig.5.(a)Mass spectra of RB dye solutions over as synthesized SnS2nano?akes after0min and120min with the scan100–500m/z and(b)the possible reaction intermediates after the photocatalytic reaction.

A.Umar et al./Talanta114(2013)183–190187

and hole (h +)pairs [30].The RhB dye molecules ?rstly adsorb on the surface of the SnS 2nano ?akes photocatalyst which reacts with water on the surface of SnS 2nano ?akes photocatalyst to generate RhB +d and OH d radicals.The ?akes morphology of synthesized SnS 2nanomaterial suf ?ciently produces the large number of RhB +d under visible light irradiation and credit to the easy transformation or oxidation of harmful organic dye into less harmful chemicals.Moreover,the unique band gap and large surface area (34.6m 2/g)of synthesized SnS 2nano ?akes photocatalyst could able to provide ef ?cient ēand h +separation,resulting in the formation of large number of RhB +d and OH d radicals [31].In this work,the high degradation of RhB dye is due to morphologies of nano ?akes and generation of RhB +d and OH d radicals on the surface of SnS 2nano ?akes.

3.3.Nitroaniline chemical sensor application of as-synthesized SnS 2nano ?akes

The detailed methodology to modify the GC electrode with SnS 2nano ?akes is described in experimental details section.Fig.7(a)exhibits the schematic representation of nitro-aniline chemical

sensor fabricated based on SnS 2nano ?akes coated GCE electrode and its sensing mechanism by I-V technique.Brie ?y,slurry of SnS 2nano ?akes was made by mixing it with appropriate amount of binder and casted on GC electrode.In two electrode system,the SnS 2modi ?ed electrode was used as working electrode while the Pt wire was employed as counter electrode.The current (I )–voltage (V )measurements have been carried out to evaluate the sensing proper-ties such as sensitivity,detection limit,correlation coef ?cient,etc of SnS 2nano ?akes electrode towards nitroaniline chemical.Fig.7(b)shows the proposed mechanism of nitroaniline sensing over the SnS 2nano ?akes electrode.The detection of nitroaniline chemical over the surface of SnS 2nano ?akes electrode might explain by the push-pull system which depends on the existing functional groups in conjugated π–πbackbone [32].In case of nitroaniline,the amino group acts as electron donor or pushing group and nitro group acts as electron acceptor or pulling group.In electrochemical system or sensor,the active sites on the surface of SnS 2nano ?akes electrode are easily attracted amino group [33].On the other hand,nitro group recombines with ēand simultaneously reacts with H 2O to form non harmful nitroso compound which responses in the I –V measure-ments in the form of increment of

current.

Fig.6.A schematic illustration of photocatalytic activity of SnS 2nano ?

akes.

Fig.7.(a)Schematic representation of nitroaniline chemical sensor fabricated based on I –V technique using SnS 2nano ?akes modi ?ed GC electrode as working electrode;(b)chemical reaction describing the sensing mechanism.

A.Umar et al./Talanta 114(2013)183–190

188

Fig.8(a)depicts the I –V measurements of the fabricated chemical sensor based on SnS 2nano ?akes modi ?ed GC electrode without and with nitro-aniline.A sharp increase in the current of ～20.3m A is observed after the addition of nitro-aniline (15.6?10?6mol/L)as compared to chemical sensor without nitro-aniline,suggesting the electrocatalytic activity of SnS 2electrode towards the nitro-aniline chemical.The sensing parameters of fabricated nitro aniline chemical sensor with SnS 2nano ?akes electrode are evaluated by performing a series of the I –V measurements with different concentration of nitro-aniline in PBS.To the best of our knowledge,it is the ?rst report on the sensing behavior of SnS 2nano ?akes electrode towards the detection of nitro-aniline.To investigate the detailed sensing performance of the SnS 2nano ?akes modi ?ed electrode,systematic I –V measurement experiments have been done by varying the concentration of nitro-aniline in 10ml of PBS (0.1M).Fig.8(b)exhibits the I –V responses of SnS 2nano ?akes modi ?ed GCE towards various concentrations of nitro-aniline (from 15.6?10?6mol/L to 1?10?3mol/L).It is clear from the observed graph that the current gradually increases as increasing the nitro-aniline concentrations ranging from ～15.6?10?6mol/L to 1?10?3mol/L which reveals that the modi ?ed SnS 2nano ?akes electrode based chemical sensor presents the good sensing response to the nitro-aniline.It is reported that incremental enhance-ment in current is related to the generation of ions and enlargement in ionic strength of PBS solution.In our case,the incremental addition of nitro-aniline might generate the large number of ions and hence increase the ionic strength of the solution.To evaluate the sensitivity of the fabricated sensor,a calibration curve of current versus nitro-aniline concentrations has been plotted and shown in Fig.8(c).Importantly,the calibrated current linearly increases up to the nitro-aniline concentrations of ～0.5?10?3mol/L.This phenomenon sug-gests the good linearity of fabricated chemical sensor based on SnS 2nano ?akes electrode in the range of 15.6?10?6mol/L –0.5?10?3mol/L.In other words,the unique nano ?akes morphology of SnS 2might provide the enough active sites over the surface of modi ?ed electrode,

which results the high adsorption of nitro-aniline through SnS 2nano ?akes electrode.The sensitivity of fabricated nitro-aniline sensor was estimated by the slope of the calibrated current curve.A high and a reproducible sensitivity of ～505.8270.02mA cm ?2.(mole/L)?1with the experimental detection limit of ～15?10?6mol/L in a short response time of ～10.0s is achieved by the fabricated nitro-aniline chemical sensor based on SnS 2nano ?akes electrode.

To examine the reproducibility and stability of the fabricated chemical sensor based on SnS 2nano ?akes electrode,the sensing responses of the fabricated sensor was measured for three con-secutive weeks.After each experiment,the fabricated sensor was stored in phosphate buffer solution (pH ?7.0).Interestingly,no signi ?cant decrease was observed in the sensing parameters for three weeks which conclude that the fabricated sensor possess good reproducibility and stability.Finally,due to very speci ?c morphology and various interesting physical and chemical proper-ties,it is proposed that of SnS 2nano ?akes is very potential,promising and effective electrocatalytic material for the detection of hazardous chemicals like nitro-aniline.

4.Conclusion

In summary,well-crystalline SnS 2nano ?akes have synthesized by facile hydrothermal process at low-temperature.The detailed studies reveal that the synthesized products are well-crystalline nano ?akes and are grown in large quantity.The synthesized SnS 2nano ?akes are used as ef ?cient photocatalyst for photocatalytic degradation of Rhodamine B dye and as an electron mediator for the fabrication of reproducible and highly sensitive nitro-aniline chemical sensor.The photocatalytic degradation based on SnS 2nano ?akes photocatalyst of Rhodamine B dye under visible light irradiation exhibit about 61%degradation.The fabricated chemical sensor exhibits a very high sensitivity of ～505.8270.02mA.cm ?2

Fig.8.(a)Typical I –V responses of SnS 2nano ?akes in (GCE)in 10ml,0.1mol/L PBS solution,(■)with nitro-aniline (15.6?10?6mol/L)and ( )without nitro-aniline;(b)I –V response for various concentrations of nitro-aniline (from 15.6?10?6mol/L to 1?10?3mol/L)and (c)calibration curve.

A.Umar et al./Talanta 114(2013)183–190189

(mole/L)?1and experimental detection limit of～15?10?6mole/L in a short response time of～10.0s.This research exhibits that the synthesized SnS2nano?akes can effectively be used as visible-light-driven photocatalysts and chemical sensors applications. Acknowledgements

Authors would like to acknowledge the support of the Ministry of Higher Education,Kingdom of Saudi Arabia for this research through a grant(PCSED-001–11)under the Promising Centre for Sensors and Electronic Devices(PCSED)at Najran University, Kingdom of Saudi Arabia.M.S.Akhtar acknowledge the Research Funds of Chonbuk National University in2011.

References

[1]H.S.Nalwa,Encyclopedia of Nanoscience and Nanotechnology,11–25ed.,

American Scienti?c Publishers,USA,2011.

[2]T.Y.Tseng,H.S.Nalwa,Handbook of Nanoceramics and Their Based Nanode-

vices,1–5,American Scienti?c Publishers,USA,2009.

[3]B.Jia,W.Jia,X.Wu,F.Qu,Sci.Adv.Mater.4(2012)1127–1133.

[4](a)Y.He,Chin.Particuol.2(2004)168;

(b)B.Jia,W.Jia,Y.Ma,X.Wu,F.Qu,Sci.Adv.Mater.4(2012)702–707.

[5](a)E.Hu,Y.Z.Wang,Chemosphere39(1999)2107;

(b)S.S.Arbuj,R.R.Hawaldar,S.Varma,S.B.Waghmode,B.N.Wani,Sci.Adv.

Mater.4(2012)568–572.

[6](a)G.M.Colonna,T.Caronna,B.Marcandalli,Dyes Pigm.41(1999)211–220;

(b)D.Tassalit,https://www.wendangku.net/doc/2c12840245.html,ou?,F.Bentahar,Sci.Adv.Mater.3(2011)944–948.

[7](a)K.P.Mishra,P.R.Gogate,J.Environ.Manage.92(2011)1972–1977;

(b)Q.Sun,Y.Lu,Y.Liu,J.Nanoeng.Nanomanuf.2(2012)46–48.

[8](a)O.J.Hao,H.Kim,P.C.Chiang,Environ.Sci.Technol.30(2000)449–505;

(b)L.S.Roselin,R.Selvin,Sci.Adv.Mater.3(2011)113–119;

(c)Z.Jin,G.T.Fei,X.Y.Hu,M.Wang,L.D.Zhang,J.Nanoeng.Nanomanuf.2

(2012)49–53.

[9](a)P.R.Gogate,A.B.Pandit,AIChE J.50(2004)1051–1079;

(b)H.G.Oliveira,B.C.Fitzmorris,C.Longo,J.Z.Zhang,Sci.Adv.Mater.4(2012)

673–680;

(c)S.Barreca,S.Orecchio,A.Pace,Talanta103(2013)349–354.

[10](a)H.X.Li,X.Y.Zhang,Y.N.Huo,J.Zhu,Environ.Sci.Technol.41(2007)4410;

(b)P.Tang,H.Chen,F.Cao,G.Pan,K.Wang,M.Xu,Y.Tong,Mater.Lett.65

(2011)450–452;

(c)Y.C.Zhang,Z.N.Du,K.W.Li,M.Zhang,Sep.Purif.Technol.81(2011)

101–107.

[11](a)J.C.Colmenares,M.A.Aramendia,A.Marinas,J.M.Marinas,F.J.Urbano,

Appl.Catal.A306(2006)120;

(b)Thaís https://www.wendangku.net/doc/2c12840245.html,ao,Vagner R.de Mendon?a,Vinícius D.Araújo,W.Avansi,

C.Ribeiro,E.Longo,M.I.Bernardi,Sci.Adv.Mater.4(2012)54–60.

[12]H.Zhang,R.L.Zong,J.A.Zhao,Y.F.Zhu,Environ.Sci.Technol.42(2008)3803.

[13]W.M.Du,J.Zhu,S.X.Li,X.F.Qian,Cryst.Growth Des.8(2008)2130.

[14]N.Z.Bao,L.M.Shen,T.Takata,K.Domen,Chem.Mater.20(2008)110.

[15]A.Agarwal,P.D.Patel,https://www.wendangku.net/doc/2c12840245.html,kshminarayana,J.Cryst.Growth142(1994)344.

[16]V.V.Ivanovskaya,A.N.Enyashin,A.L.Ivanovskii,J.Struct.Chem.45(2004)151.

[17]T.Brousse,S.M.Lee,L.Pasquereau,D.De?ves,D.M.Schleich,Solid State Ionics

151(1998)51.

[18]D.B.Mitzi,J.Mater.Chem.14(2004)2355.

[19]G.Domingo,R.S.Itoga,C.R.Kannewurf,Phys.Rev.143(1966)536.

[20]C.D.Lokhande,J.Phys.D23(1990)1703.

[21](a)T.Jiang,G.A.Ozin,J.Mater.Chem.8(1998)1099;

(b)J.Chao,Z.Xie,X.B.Duan,Y.Dong,Z.Wang,J.Xu,B.Liang,B.Shan,J.Ye,

D.Chen,G.Shen,https://www.wendangku.net/doc/2c12840245.html,mun.14(2012)3163–3168.

[22](a)X.L.Gou,J.Chen,P.W.Shen,Mater.Chem.Phys.93(2005)557;

(b)Xi Li,J.Zhu,H.Li,Appl.Catal.B Environ.123–124(2012)174–181.

[23](a)C.Yang,W.Wang,Z.Shan, F.Huang,J.Solid State Chem.182(2009)

807–812;

(b)Y.C.Zhang,Z.N.Du,K.W.Li,M.Zhang,Sep.Purif.Technol.81(2011)

101–107.

[24](a)D.Vollath,D.V.Szab?,Acta Mater.48(2000)953;

(b)Y.C.Zhang,J.Li,M.Zhang,D.D.Dionysiou,Environ.Sci.Technol.45(2011)

9324–9331.

[25]A.Umar,F.Al-Hazmi,G.N.Dar,S.A.Zaidi,R.M.Al-Tuwirqi,F.Alnowaiserb,A.

A.Al-Ghamdi,S.W.Hwang,Sens.Actuat.B Chem.166–167(2012)97–102.

[26](a)K.Nakamoto,IR Spectra of Inorganic and Coordination,Compounds-2nd

Ed.,Wiley Eastern NY,1970;

(b)R.A.Nyquist,R.O.Kagel,Infrared Spectra of Inorganic Compounds,Aca-

demic Press,Inc.,New York,London220.

[27](a)L.X.Zhang,P.Liu,Z.X.Su,Polym.Degrad.Stab.91(2006)2213;

(b)L.Xueyan,W.Desong,C.Guoxiang,L.Qingzhi,A.Jing,W.Yanhong,Appl.

Catal.B Environ.81(2008)267–273.

[28](a)S.Ameen,M.S.Akhtar,Y.S.Kim,H.S.Shin,Appl.Catal.B Envron.103(2011)

136–142;

(b)X.Y.Li,D.S.Wang,G.X.Cheng,Q.Z.Luo,J.An,Y.H.Wang,Appl.Catal.B81

(2008)267.

[29](a)T.A.Saleh,V.K.Gupta,J.Coll.Interf.Sci.371(2012)101–106;

(b)L.Fuks,D.Filipiuk,M.Majdan,J.Mol.Struct.792–793(2006)104–109.

[30]Y.Li,J.Hagen,D.Haarer,Synth.Mat.94(1998)273.

[31]S.A.Khayyat,M.S.Akhtar,A.Umar,Mater.Lett.81(2012)239–241.

[32]M.M.Miranda,https://www.wendangku.net/doc/2c12840245.html,o,Colloids Surf.A249(2004)79.

[33]B.C.Roy,M.D.Gupta,J.K.Ray,Macromolecules28(1995)1727.

A.Umar et al./Talanta114(2013)183–190 190

Journal of Mate-2014-Enhanced photocatalytic 1

Supplementary information Enhanced Photocatalytic Mechanism for the Hybrid g-C 3N 4/MoS 2 Nanocomposite Jiajun Wang,1 Zhaoyong Guan,1 Jing Huang,1, 2 Qunxiang Li,1, * and Jinlong Yang 1, 3 1Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China 2School of Materials and Chemical Engineering, Anhui Jianzhu University, Hefei, Anhui 230022, China 3Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China Email: liqun@https://www.wendangku.net/doc/2c12840245.html, When g-C 3N 4/MoS 2 nanocomposite is illuminated with light, the photogenerated electrons in g-C 3N 4 layer can easily move to the CB of MoS 2 sheet due to the observed CBO, as shown in Fig. 4. At the same time, the polarized field between C 3N 4 and MoS 2 sheets in the nanocomposite prevents the photogenerated electrons migrating from C 3N 4 to MoS 2 sheet. Clearly, there is a competitive role in electron-hole separation between the band alignment and electric polarized field. To evaluate which one gives the dominative role in migration of the photogenerated electrons, we estimate their electric field strengths. The field strength (E) coming from the band alignment is estimated to be about 2.8×109 V/m (E=U/d 0, U is the CBO, d 0 is the separation between g-C 3N 4 and MoS 2 sheets in the nanocomposite, U=0.83 V, d 0=2.97×10-10 m), which is about three times larger than the dipole-induced polarized field strength of 9.8×108 V/m (here, E=P/εr ε0Sd 0, P is the dipole and P=qd, εr is the relative dielectric constant, ε0 is the permittivity of free space, S is the surface area of the nanocomposite, q=0.06 e , d=2.0×10-10 m, εr =1.0, ε0=8.85×10-12 F/m, S=7.5×10-19 m 2, d 0=2.97×10-10 m). This result indicates that the migration of photogenerated electrons in g-C 3N 4/MoS 2 nanocomposite is dominated by the strong driving force provided by the type II band alignment. Electronic Supplementary Material (ESI)for Journal of Materials Chemistry A.This journal is ?The Royal Society of Chemistry 2014

Graphene-based photocatalytic composites

Graphene-based photocatalytic composites Xiaoqiang An and Jimmy C.Yu * Received 29th June 2011,Accepted 1st September 2011DOI:10.1039/c1ra00382h The use of graphene to enhance the efficiency of photocatalysts has attracted much attention.This is because of the unique optical and electrical properties of the two-dimensional (2-D)material.This review is focused on the recent significant advances in the fabrication and applications of graphene-based hybrid photocatalysts.The synthetic strategies for the composite semiconductor photocatalysts are described.The applications of the new materials in the degradation of pollutants,photocatalytic hydrogen evolution and antibacterial systems are presented.The challenges and opportunities for the future development of graphene-based photocatalysts are also discussed. 1.Introduction Photocatalytic nanomaterials are attracting more and more attention because of their potential for solving environmental and energy problems,which are the biggest challenges of the 21st century.1Many research papers and review articles are dedicated to this topic.2,3Recently,the design and potential applications of nanostructured semiconductor materials for environment,energy and water disinfection have been reviewed by our group.4,5However,several fundamental issues must be addressed before the photocatalysts are economically viable for large scale industrial applications.For example,the fast recombination of electron–hole pairs and the mismatch between the band gap energy and solar radiation spectrum limit the applicability of TiO 2,which is considered as one of the best photocatalysts.6As shown in Fig.1,upon absorption of photons with energy larger than the band gap of a photocatalyst,electrons are excited from the valence band to the conduction band,creating electron–hole pairs.These charge carriers either recombine or migrate to the surface to initiate a series of photocatalytic reactions.The photocatalysis process usually involves several highly reactive species,such as ?OH,?O 22,and H 2O 2. In order to improve the photocatalytic activities of photo-catalysts,three key points should be addressed.They are:(1)the extension of excitation wavelength,(2)a decrease of charge carrier recombination,and (3)the promotion of active sites around the surface.7,8Attempts have been made and several strategies have been developed including:(1)doping with either anions or cations,9,10(2)surface coupling with metals or semiconductors,11,12and (3)improving the structure of photo-catalysts in order to increase their surface area,porosity or reactive facets.13–15Fig.2shows the common types of 0-D,1-D,2-D and 3-D photocatalysts with enhanced photocatalytic performance.Despite these developments,the commercial installation of photocatalytic systems for water splitting and chemical waste treatment is yet to be realized.16 Carbonaceous nanomaterials have unique structures and properties that can add attractive features to photocatalysts.17,18The coupling of carbon nanotubes (CNTs)to titanium dioxide has been reviewed by Sigmund and co-workers.19Generally,the photocatalytic enhancement is ascribed to the suppressed recombination of photogenerated electron–hole pairs,extended excitation wavelength and increased surface-adsorbed reactant,although the underlying mechanisms are still unclear.The recent progress in the development of TiO 2/nanocarbon photocatalysts has been reported by Westwood et al.,covering activated carbon,[60]-fullerenes,carbon nanotubes,graphene and other novel carbonaceous nanomaterials.20 As the most recently discovered carbonaceous material,graphene has attracted immense attention.21,22With a unique sp 2hybrid carbon network,it shows great applications such as nanoelectronics,sensors,catalysts and energy conversion.23–28The application of graphene-based assemblies to boost the efficiency of solar energy conversion has been reviewed.29–32 Department of Chemistry and Institute of Environment,Energy and Sustainability,The Chinese University of Hong Kong,Shatin,New Territories,Hong Kong,China.E-mail:jimyu@https://www.wendangku.net/doc/2c12840245.html,.hk;Fax:(+852)2603-5057;Tel: (+852)3943-6268 Fig.1Photoexcitation of a semiconductor and the subsequent genera-tion of radicals or intermediate species,which are involved in the photocatalytic reaction. RSC Advances Dynamic Article Links Cite this:RSC Advances ,2011,1,1426–https://www.wendangku.net/doc/2c12840245.html,/advances REVIEW D o w n l o a d e d o n 04/04/2013 14:57:24. P u b l i s h e d o n 28 O c t o b e r 2011 o n h t t p ://p u b s .r s c .o r g | d o i :10.1039/C 1R A 00382H View Article Online / Journal Homepage / Table of Contents for this issue

Photocatalytic degradation of tetracycline in aqueous solution by nanosized TiO2

Photocatalytic degradation of tetracycline in aqueous solution by nanosized TiO 2 Xiang-Dong Zhu,Yu-Jun Wang,Rui-Juan Sun,Dong-Mei Zhou ? Key Laboratory of Soil Environment and Pollution Remediation,Institute of Soil Science,Chinese Academy of Sciences,Nanjing 210008,China h i g h l i g h t s NH t 4ions were the end-product of photocatalytic degradation of TC by TiO 2. The photocatalysis eliminated 95%of TC after 60min irradiation. Photocatalytic pathway of TC was proposed based on the identi?ed intermediates. The toxicities of reaction solution and free radical were discerned. a r t i c l e i n f o Article history: Received 30October 2012 Received in revised form 21February 2013Accepted 27February 2013 Available online 27March 2013Keywords:Tetracycline TiO 2 Photocatalysis Mechanism a b s t r a c t Tetracyclines are widely-used antibiotics in the world.Due to their poor absorption by human beings,or poultry and livestocks,most of them are excreted into the environment,causing growing concern about their potential impact,while photodegradation has been found to dominate their sequestration and bio-availability.Coupling with high-performance liquid chromatography–mass spectroscopy (HPLC–MS),gas chromatography–mass spectroscopy (GC–MS)and electron spin resonance (ESR),the mechanism of pho-tocatalytic degradation of TC in aqueous solution by nanosized TiO 2(P25)under UV irradiation was investigated.The photocatalysis eliminated 95%of TC and 60%of total organic carbon (TOC)after 60min irradiation,and NH t4ion was found to be one of the end-products.Bioluminescence assay showed that the toxicity of TC solution reached the maximum after 20min irradiation and then gradually decreased.The degradation of TC included electron transfer,hydroxylation,open-ring reactions and cleavage of the central carbon.A possible photocatalytic degradation pathway of TC was proposed on the basis of the identi?ed intermediates.Overall,the TiO 2photocatalysis was found to be a promising process for removing TC and its intermediates. ó2013Elsevier Ltd.All rights reserved. 1.Introduction Tetracyclines (TCs)are one of the most widely-used antibiotics in aquaculture and veterinary medicines (Palominos et al.,2009).Due to their poor absorption,most of them are excreted through feces and urine as un-metabolized parent compound.The most dangerous effect of antibiotics in the environment is the develop-ment of multi-resistant bacterial strains that can no longer be trea-ted with the presently known drugs (Addamo et al.,2005).Hence,the occurrence,fate and behavior of antibiotics in the environment have been the subject of growing concern and scienti?c interest (Verma et al.,2007;Gómez-Pacheco et al.,2011;Yuan et al.,2011).Signi?cant amount of TCs have been detected in super?cial,potable water and sludge due to their ineffective removal by the conventional water treatment methods.It seems that traditional biological methods could not effectively eliminate antibiotics (Bau-titz and Nogueira,2007;Palominos et al.,2009;Wang et al.,2011a ).Therefore,to develop effective techniques for rapid degra-dation of TCs is of environmental interest. TiO 2photocatalysis is a promising method in water treatment for removal and mineralization of organic pollutants (So et al.,2002;Zhang et al.,2005;Pelaez et al.,2011;Yahiat et al.,2011;Wang et al.,2011a ).Photocatalytic degradation of organic pollu-tants could lead to produce end-products,but they are usually un-clear.In addition to that,the intermediates possibly induce negative effects to the environmental ecosystem function (Jiao et al.,2008),which suggested that the variations of toxicity of the solution after photocatalytic reaction should be examined.The intermediates of TC photolysis and ozonation have been iden-ti?ed (Dalmázio et al.,2007;Jiao et al.,2008;Wang et al.,2011b ),however,to our best knowledge,intermediates and possible path-way of TC photocatalytic degradation were seldom addressed.In this study,the photocatalytic degradation of TC in aqueous solution was investigated using nanosized TiO 2(P25)as the photo-catalyst under UV irradiation,and the effects of solution pH and 0045-6535/$-see front matter ó2013Elsevier Ltd.All rights reserved.https://www.wendangku.net/doc/2c12840245.html,/10.1016/j.chemosphere.2013.02.066 Corresponding author.Tel.:+862586881180;fax:+862586881000. E-mail address:dmzhou@https://www.wendangku.net/doc/2c12840245.html, (D.-M.Zhou).