Design,Synthesis And Photocatalytic CO₂ Reduction Activity Of CdS/Bi_xO_yX_z Composite Photocatalyst

With the rapid development of society,the demand and consumption of fossil energy are growing with each passing day.However,the massive consumption of fossil fuels has led to a rapid increase of carbon dioxide?CO₂?in the atmosphere,and also caused a series of environmental problems.Converting CO₂ into valuable chemical fuels through semiconductor photocatalysis offers great potential that not only reduce the content of CO₂ in the atmosphere,but also solve environmental problems and energy crisis.Solar photocatalytic conversion of CO₂ into renewable fuels is considered to be a promising and eco-friendly way.Photocatalysts play a vital role in the field of photoreduction CO₂.Bismuth oxyhalides-based photocatalysts have received extensive attention for their controllable band structure and unique layered structure.However,their solar-to-fuel conversion efficiency is still restricted by the fast charge recombination,weak redox ability and limited light absorption.Given to the above-mentioned problems,we synthesized CdS/BiOCl,CdS/BiOI and CdS/Bi₁₂O₁₇Cl₂composite photocatalysts by means of crystal facets control,heterostructure construction,and band structure adjustment,so as to enhance the light absorption of photocatalysts,to promote the separation and migration of photogenerated carriers,and to improve the photocatalytic CO₂ reduction activity of the composites.By means of radical trapping test,EPR test,photoelectrochemical test and other characterizations,the factors that affect photocatalytic CO₂ reduction activity,the separation mechanism of photogenerated charges and the photocatalytic CO₂ reduction mechanism were systematically studied.The main research results are as follows:1.BiOCl exposed with?001?or?010?crystal facets were synthesized by controlling the pH of the precursor solution,then we loaded CdS on the surface of BiOCl to synthesize a series of CdS/BiOCl composites.The photocatalytic CO₂ reduction performance of the as-synthesized CdS/BiOCl composites was investigated under simulated solar light irradiation.The results demonstrated that the CO₂ reduction activity of the composites was significantly enhanced.After 4 h irradiation,the yields of CO and CH₄ for CdS/BiOCl-001 optimal composite are 2.0 and 6.85?mol·g^-1,respectively.Under the same conditions,the yields of CO and CH₄ for CdS/BiOCl-010optimal composite are 1.35 and 1.90?mol·g^-1,respectively.Pt deposition experiment and photoelectrochemical test results demonstrated that the Z-scheme charge transfer mode and effective separation of photogenerated carriers is beneficial to the improvement of photocatalytic activity.Moreover,the exposed facets of BiOCl have a significant effect on the interfacial charge separation efficiency.In this study,the effective separation and migration of photogenic carriers were realized by combining crystal facet engineering with heterojunction construction,and the photocatalytic CO₂reduction activity of composites was improved significantly.2.BiOI nanosheets were synthesized by hydrothermal method,then CdS was loaded on BiOI nanosheets by chemical deposition method,and a series of CdS/BiOI heterojunction photocatalysts were synthesized.The photocatalytic CO₂ reduction activity of the as-prepared samples was measured under visible light irradiation???400 nm?.The results showed that the composites exhibit higher photocatalytic activity than pure CdS and BiOI.After 3 h irradiation,the yields of CH₄ and CO for the optimal composite reached 0.54 and 3.32?mol·g^-1,respectively.According to UV-vis diffuse reflectance spectrum test,radical trapping experiment and electron paramagnetic resonance experiment,the photogenerated charges in the CdS/BiOI heterojunction follow Z-scheme transfer mode,which not only enhance the light absorption of composites,but also promote the photogenerated charge separation and migration.At the same time,the photostability of CdS/BiOI composites was greatly improved.According to the CO₂ absorption-desorption experiment and CO₂ temperature programmed desorption test,the composite BC-5 can absorb CO₂ more powerfully than pure BiOI and CdS,which is beneficial to improve the photocatalytic performance of the composite systems.3.Bi₁₂O₁₇Cl₂ nanobelts were synthesized by hydrothermal method,then CdS nanoparticles were loaded on the surface of Bi₁₂O₁₇Cl₂ to prepare a series of CdS/Bi₁₂O₁₇Cl₂ composite photocatalysts.The crystal phase,morphology,band structure and photoelectrochemical properties of the synthesized materials were characterized.The photocatalytic CO₂ reduction activity of the as-prepared samples was measured under visible light irradiation???400 nm?.The results demonstrated that the CO₂ conversion efficiency of Bi₁₂O₁₇Cl₂ was significantly improved by loading CdS nanoparticles.After 3 h irradiation,the yields of CO and CH₄ for the optimal composite C1 reached 6.78 and 0.81?mol·g^-1,respectively.The close contact between CdS and Bi₁₂O₁₇Cl₂ is beneficial to the formation of type-II heterojunction,moreover,it is conducive to the separation and migration of photogenerated carriers,thereby greatly improving the photocatalytic CO₂ reduction activity of composite systems.