Study On The Preparation Of In₂O₃-based Composite Semiconductors And Its Photocatalytic Performance For CO₂ Reduction

Photocatalytic CO₂ reduction coupled with the splitting of H₂O to produce fuel such as CH₄,CO and H₂,etc.using solar energy has been widely accepted as one of the most attractive strategies to address environmental concerns and energy shortages.In this paper,indium oxide was modified by semiconductor composite and transition metal doping to enhance its light response ability,photo-generated carriers separation efficiency,chemisorption of CO₂ and photocatalytic reduction of CO₂.By calcining the MOF precursor（MIL-68-In）,nano-indium oxide stacked in a hollow hexagonal prism shape was prepared,and then a series of In₂S₃/In₂O₃ composite catalysts with different ratios were synthesized via using in-situ sulfidation of indium oxide by hydrothermal method.The results showed that the accumulation mode of the obtained composite catalyst sample was gradually changed from a regular hollow hexagonal prism to an ellipsoid.The heterojunction formed between In₂S₃/In₂O₃ can effectively suppress the recombination of photo-generated electron-hole pairs,improve carrier separation efficiency and the visible light absorption capacity.With the increase in the amount of In₂S₃,the catalytic activity of In₂S₃/In₂O₃ increased first and then decreased.40%In₂S₃/In₂O₃ sample exhibited the highest photocatalytic activity,and the production rates of the main products CO and CH₄ were 2.6 and 14.3μmol·g^-1_cat·h^-1,respectively,the production rates of H₂ was 8.1μmol·g^-1_cat·h^-1.Porous In₂O₃ sheets and C₃N₄ thin films were obtained by ammonia precipitation and calcination,respectively,and the effects of C₃N₄ addition amount on the activity of photocatalytic CO₂reduction was investigated.The results showed that the overall morphology of cubic In₂O₃ gradually transformed into smaller particles,and stacked on the C₃N₄ thin film layer as the compound ratio increases.Moreover,the composites of In₂O₃ and carbon nitride can effectively reduce the forbidden band width,extend the visible light utilization range,and improve the photo-response ability of the catalyst sample.C₃N₄/In₂O₃ loaded with 0.4g carbon nitride showed the highest photocatalytic reduction rate of CO₂.The production rates of H₂,CO and CH₄ were 58.8,26.6 and67.4μmol·g^-1_cat·h^-1,respectively.Ni,Co and Cu-doped In₂O₃ samples were obtained by the ammonia precipitation method,and the influence of Ni,Co and Cu doping on the morphology and structure of In₂O₃,the photoelectric performance and the ability of CO₂ chemisorption were studied.It was found that after transition metal doping,In₂O₃ still maintains its porous plate-like structure,but particle size was decreased and the specific surface area was increased.On the other hand,defects caused by lattice distortion can be used as electron traps in photocatalytic reactions,effectually avoiding reorganization of photogenerated electron-hole pairs.In addition,the incorporation of transition metal elements also narrows the band gap of In₂O₃,widens the visible light response range,and enhances light absorption.Moreover,the incorporation of Ni,Co,and Cu also increased the alkalinity of the catalyst sample and enhanced the chemical adsorption capacity of CO₂.Therefore,Ni,Co,and Cu-doped In₂O₃ all exhibit higher photocatalytic reduction of CO₂ than pure In₂O₃.When the doping amounts of Co was 0.5%,the highest catalytic activity was obtained,and the production rates of H₂,CO and CH₄ were 26.6,20.9 and66.2μmol·g^-1_cat·h^-1,respectively.