Synthesis, Modification And Photocatalytic Reduction Of Sn (VI) By SnS 2

Photocatalysis is a promising technology for Cr(VI)wastewater treatment.Using abundant solar energy to abate environmental pollution is a sustainable means.Development of efficient,economical and environmentally friendly semiconductor photocatalyst is the key to industrial application.SnS2 is a CdI2-type layered semiconductor with a medium bandgap of around 2.2 eV.It has recently attracted great research interest of many scholars as a promising visible light photocatalyst,due to its abundant source materials,easy synthesis,low cost,nontoxicity,and relatively high visible light-activated photocatalytic activity.Previous studies revealed that the photocatalytic performance of SnS2 strongly depends on its synthesis methods and synthesis conditions,as well as the application objects.However,most of the reported synthesis methods have difficulties in realizing the low cost large-scale production of SnS2 with high visible light-activated photocatalytic activity.Hence,it is still very meaningful to develop a scalable low cost,low temperature solid phase method for synthesizing SnS2 with high visible light-activated photocatalytic activity.Moreover,for sole SnS2,its photogenerated electrons and holes have a recombination rate,leadint to its limited photocatalytic efficiency.Based on our theoretical estimation,the formation of heterojunctions by coupling SnS2 with CeO2 and CeO2/polyaniline can enhance the separation of photogenerated electrons and holes,resulting in the improved photocatalytic activity.In view of the above issues,this thesis has completed the following studies:1.Flower-like SnS2 was synthesized via calcining the ground mixture of SnCl2·2H2O and CH4N2S powders at a certain temperature for 2 hours.The composition,structure and optical properties of the samples were characterized using X-ray diffractometer(XRD),Raman spectroscopy(Raman),X-ray photoelectron spectroscopy(XPS),field emission scanning electron microscopy(FESEM),N2 adsorption/desorption isotherms,Ultraviolet-visible diffuse reflectance spectroscopy(UV-vis DRS),Photoluminescence spectroscopy(PL)and electrochemical impedance spectroscopy(EIS).The Zeta potential of the samples were measured by Zeta potentiometers.The photocatalytic activities of SnS2-170 ?,SnS2-180 ?,and SnS2-1900C were evaluated in the reduction of Cr(VI)in 50 mg/L K2Cr2O7 under visible light(?>420 nm)irradiation.Besides,the effects of photocatalytic testing parameters(including dosage of photocatalyst,initial pH and concentration of K2Cr2O7 aqueous solution)on the Cr(VI)removal efficiency by SnS2-170 °C were also studied.The results showed that:(i)the lowest temperature to synthesize phase-pure SnS2 is 170?,and the resultant product had nanosheets-constructed porous flower-like hierarchical nanostructure;(?)SnS2-170 °C had the highest photocatalytic activity in the reduction of aqueous Cr(?);(?)with the increase of the dosage of SnS2-170 ?,photocatalytic reduction of Cr(?)proceeded more quickly;(?)the lower initial concentration and pH of Cr(?)aqueous solution,the higher efficiency in the adsorption and photocatalytic reduction of Cr(?)by SnS2-170 ?.2.CeO2 nanoparticles were synthesized via heating Ce(NO)3·6H2O in air at 450 ? for 3 h.Then CeO2/SnS2 nanocomposites with different compositions were synthesized via the hydrothermal reactions of 2 mmol SnCl4·5H2O and 5 mmol thioacetamide in the presence of different amounts of CeO2 nanoparticles at 170 ? for 12 h.The composition,structure and optical properties of the resultant CeO2/SnS2 nanocomposites were characterized by XRD,Raman,XPS,HRTEM,UV-vis DRS,PL and EIS.The flat band potentials of SnS2 and CeO2 were calculated using the Mott-Schottky curves.Zeta potentials of the samples were measured by Zeta potentiometers.The photocatalytic activities of the resultant CeO2/SnS2 nanocomposites were evaluated in the reduction of Cr(?)in 50 mg/L K2Cr2O7 under visible light(?>420 nm)irradiation,and compared with SnS2 and CeO2 nanoparticles.Besides,the effects of photocatalytic testing parameters(including dosage of photocatalyst,initial pH and concentration of K2Cr2O7 aqueous solution)on the Cr(?)removal efficiency by CeO2/SnS2-1.5/1 were also studied.The photocatalytic enhancement mechanism of CeO2/SnS2-1.5/1 was also discussed.The results showed that:(?)CeO2/SnS2-1.5/1 had heterojunction structure;(?)CeO2/SnS2-1.5/1 had the smallest fluorescence intensity and impedance value;(?)CeO2/SnS2-1.5/1 exhibited the highest photocatalytic activity;(?)with the increase of the dosage of CeO2/SnS2-1.5/1,photocatalytic reduction of Cr(?)proceeded more quickly;(?)the lower initial concentration and pH of Cr(?)aqueous solution,the higher efficiency in the adsorption and photocatalytic reduction of Cr(?)by CeO2/SnS2-1.5/1.3.CeO2 nanoparticles were synthesized via thermal decomposition of Ce(NO3)3·6H2O.Then Ce02/SnS2 nanocomposites were synthesized via the hydrothermal reactions of SnC14·5H2O and thioacetamide in the presence of CeO2 nanoparticles.Finally,the CeO2/SnS2/PANI nanocomposites were synthesized by mixing CeO2/SnS2 nanocomposites into PANI N,N-Dimethylformamide solution,then evaporation of N,N-Dimethylformamide.The composition,structure and optical properties of CeO2/SnS2/PANI composites were characterized by XRD,Raman,FT-IR,XPS,HRTEM,UV-vis DRS,PL and EIS.Zeta potentials of the samples were measured by Zeta potentiometers.The photocatalytic activities of the obtained products were evaluated in the reduction of Cr(VI)in 50 mg/L K2Cr2O7 under visible light(X>420 nm)irradiation.Besides,the effects of photocatalytic testing parameters(including dosage of photocatalyst,initial pH and concentration of K2Cr2O7 aqueous solution)on the Cr(VI)removal efficiency by CeO2/SnS2/PANI-3%were also studied.The results showed that:(i)CeO2/SnS2/PANI-3%had heterojunction structure;(ii)the visible light absorption capacity of CeO2/SnS2 was improved by coupling with PANI;(iii)the coupling with PANI enhanced the separation and transfer of photogenerated electrons and holes in CeO2/SnS2;(iv)CeO2/SnS2/PANI-3%exhibited the highest photocatalytic activity;(v)with the increase of the dosage of CeO2/SnS2/PANI-3%,photocatalytic reduction of Cr(VI)proceeded more quickly;(vi)the lower initial concentration and pH of Cr(VI)aqueous solution,the higher efficiency in the adsorption and photocatalytic reduction of Cr(VI)by CeO2/SnS2/PANI-3%.