Study On The Modification Of SnS₂ And Its Performance In Photocatalytic Reduction Of Cr???

In recent years,semiconductor photocatalysis technology,as an economical and environmentally friendly wastewater treatment technology,has broad application prospects in the reduction of Cr(VI).The development of low-cost,high-efficiency visible light catalysts is the key to industrialization.SnS2 is a layered visible light responsive catalyst with CdI2 type structure.However,due to the rapid recombination of its photogenerated electrons and holes,the photocatalytic performance of SnS2 is not satisfactory,which limits its development.Studies have shown that combination of SnS2 with semiconductors,conjugated polymers or graphene and its derivatives can significantly enhance its photocatalytic performance.This is because heterojunctions can be formed between them,which facilitates the separation efficiency of photogenerated electrons and holes.Therefore,cyclized polyacrylonitrile(CPAN),SnO2 and conjugated polyvinyl chloride derivative(CPVC),SnO2 and nitrogen-doped graphene(NG)were chosen to modify SnS2 to form SnS2/CPAN,SnO2/SnS2/CPVC and SnO2/SnS2/NG nanocomposites.The synthesized composites were evaluated for photocatalytic application in the reduction of Cr(VI)under visible light irradiation.The main contents that have been completed in this thesis are as follows:1.The synthesis of SnS2/CPAN nanocomposites was achieved by a three-step method.The composition,structure,optical and electrical properties of the samples were characterized by means of X-ray powder diffractometer(XRD),Fourier transform infrared spectroscopy(FTIR),Raman spectroscopy(Raman),X-ray photoelectron spectroscopy(XPS),field emission transmission electron microscopy(HRTEM),UV-visible diffuse reflectance spectroscopy(UV-vis DRS),fluorescence spectroscopy(PL)and electrochemical impedance(EIS).The specific surface areas of the samples were tested by nitrogen adsorption desorption curves.Adopting 50 mg/L K2Cr2O7 aqueous solution as the model pollutant,the photocatalytic properties of the products were evaluated under visible light irradiation.The effects of the initial dosage ratio of PAN to SnS2,and the pyrolysis temperature and time of SnS2/PAN on the photocatalytic activities of the products were investigated.In addition,the mechanism of photocatalytic reduction of Cr(VI)by SnS2/CPAN-2 was discussed.The results show that:(1)compared with SnS2,SnS2/CPAN-2 binary composite has higher photogenerated electron-hole separation efficiency and faster charge transfer rate;(2)as the mass ratio of PAN to SnS2 is 1%,the pyrolysis temperature and time of SnS2/PAN are 200 0C and 2 h,respectively,the synthesized SnS2/CPAN-2 nanocomposite has the highest photocatalytic activity;(3)The mechansism of photocatalytic reduction of Cr(VI)by SnS2/CPAN-2 is dominated by e-reduction.2.The synthesis of SnO2/SnS2/CPVC ternary composites was achieved by a four-step method.The composition,structure,optical and electrical properties of the samples were characterized by many testing methods.The photocatalytic activities of SnS2,SnO2,CPVC,SnO2/SnS2,SnS2/CPVC,SnO2/CPVC and SnO2/SnS2/CPVC products were compared.Moreover,the mechanism of photocatalytic reduction of Cr(VI)by SnO2/SnS2/CPVC-2 was studied.The results show that:(1)SnO2/SnS2/CPVC-2 composite has lower electron-hole pairs recombination rate and faster charge transfer rate than SnS2?SnO2/SnS2-1.0 h,SnS2/CPVC and SnO2/CPVC;(2)as the hydrothermal reaction between SnO2 and CH3CSNH2 proceed for 1.0 h,and the synthesized SnO2/SnS2-1.0 h has the highest photocatalytic activity;(3)as the mass ratio of PVC to SnO2/SnS2-1.1 h is 1%,the synthesized SnO2/SnS2/CPVC-2 has the highest visible light photocatalytic activity;(4)SnO2 and CP VC have synergistic effects in improving the photocatalytic activity of SnS2;(5)the mechanism of photocatalytic reduction of Cr(VI)by SnO2/SnS2/CPVC-2 is dominated by e-reduction.3.The synthesis of SnO2/SnS2/NG ternary nanocomposites was achieved by a two-step method.The composition,structure,optical and electrical properties of the samples were characterized by many testing techniques.The effect of the initial mass ratio of NG and SnO2/SnS2 on the photocatalytic activity of the products was investigated.Moreover,the mechanism of photocatalytic reduction of Cr(VI)by SnO2/SnS2/NG-2 was explored.The results show that:(1)compared with SnS2 and SnO2/SnS2,SnO2/SnS2/NG-2 ternary composite has lower photogenerated electron-hole pairs recombination rate and faster charge transfer rate;(2)as the mass ratio of NG to SnO2/SnS2 is 1%,the synthesized SnO2/SnS2/NG-2 nanocomposite has the highest photocatalytic activity;(3)SnO2 and NG have synergistic effects in improving the photocatalytic activity of SnS2;(4)The mechanism of photocatalytic reduction of Cr(VI)by SnO2/SnS2/NG-2 is dominated by e-reduction.