Studies On The Preparation Of Multi-defective In（OH）₃,doping Of Rare Earth Elements And Its Photocatalytic Performance For CO₂ Reduction

Photocatalytic reduction of CO₂ is one of the most promising green routes for carbon dioxide utilization.However,the catalytic conversion efficiency of CO₂ is relatively low by now.This paper aims to improve the efficiency of photocatalytic CO₂reduction of photocatalysts by introducing vacancies and rare earth doping.In this study,a series of In（OH）₃ with abundant indium vacancies were synthesized by hydrothermal method using mixed solvent of ethylenediamine（En）and water for photocatalytic reduction of CO₂with H₂O vapor.The morphology,particle size,crystallinity,pore structure,and vacancy concentration were successfully regulated by adjusting the ratio of En and water in mixed solvent,which were characterized by XRD,FT-IR,TG-DTA,SEM and HRTEM.Moreover,the effect of En/water ratio on the adsorption capacity of CO₂and photo-electrical properties of In（OH）₃ were further investigated by TPD,in-situ FTIR,PL spectra,UV-vis DRS,CV,and EIS.The experimental results show that In（OH）₃prepared in mixed solution exhibited much higher photocatalytic activity for CO₂ reduction with H₂O vapor compared to that prepared with water only solvent.When the ratio of ethylenediamine to water is 4:1,the prepared In（OH）₃ has the highest catalytic activity,and H₂,CO and CH₄ yields are15.3,10.2 and 28.2μmol/gcat/h,respectively.The enhanced photocatalytic performance can be attributed to the special morphology,smaller particle size,lager BET surface area and especially generated indium vacancies creating defect energy levels in the bandgap,which improved visible light absorption,carrier separation and CO₂ chemisorption.Secondly,a series of indium oxides were prepared by calcining the In（OH）₃precursors synthesized by hydrothermal method using the mixed solution of ethylenediamine and water as a solvent.The morphology,particle size,pore structure,crystallinity,CO₂ adsorption performance and photoelectric properties of the catalysts were analyzed by XRD,SEM,TEM,TPD,in situ FTIR,PL spectroscopy,UV-vis DRS,CV and EIS.The results revealed that In₂O₃ photocatalysts obtained from the precursor prepared in En containing solvent exhibited much higher photocatalytic activities for CO₂ reduction with H₂O when compared to that derived from the precursor prepared in pure water.This result can be ascribed to several reasons as following.Firstly,the En addition with a suitable amount can improve the crystallinity of In₂O₃ and decrease the surface defect concentration,which obviously depressed the recombination of photogenerated electrons and holes.Also,the addition of En during the preparation of precursor can decrease the particle size,increase specific surface area and pore structure,resulting into the increase of active sites.Finally,the band gap of In₂O₃ can be slightly narrowed after the addition of En,resulting in enhanced light absorption in the visible region.When the ratio of ethylenediamine to water is 1:1,the as-prepared In₂O₃exhibited the highest photocatalytic activity.Under visible light irradiation,the H₂,CO and CH₄ production rates of 5.3,8.3 and 27.2μmol/g_cat/h can be achieved,respectively.Finally,La,Ce and Pr doped In（OH）₃ was prepared by the same method using In（OH）₃ synthesized with the ratio of ethylenediamine to water of 4:1 as the based catalyst,characterized by XRD,SEM,TEM,PL,XPS,UV-vis DRS,CV and EIS and the photocatalytic reduction of CO₂ was evaluated.The results show that after La,Ce and Pr doped,In（OH）₃ catalysts still maintains the plate-like morphology,but the particle size is reduced because some rare earth ions are incorporated in In（OH）₃ lattice.The results show that after La,Ce and Pr doping,In（OH）₃ catalysts still maintain the plate-like morphologies,but the particle sizes are reduced because some rare earth ions were incorporated in the In（OH）₃ lattice,effectively suppressed the growth of In（OH）₃particle,thereby increasing the specific surface area.In addition,the introduction of rare earth elements reduces the forbidden band width of the catalysts and enhances its absorption in the visible region.Therefore,the photocatalytic reduction of CO₂ over rare earth elements doped In（OH）₃ is significantly improved.When the doping amount of La,Ce,and Pr is 1.5 wt%,0.5 wt%,and 0.5 wt%,respectively,the photocatalysts exhibited the best photocatalytic performance,and the production rate of H₂ is 54.3,42.4,49.2μmol/g_cat/h,respectively,the production rates of CO were 34.7,20.2,17.7μmol/g_cat/h,respectively,the production rates of CH₄ were 56.5,48.5,67.0μmol/g_cat/h,respectively.