Micro/Nano Structure Regulation Of Photocatalysts Toward Photocatalyticreduction Of CO₂

Photocatalyticreduction of CO₂ into renewable hydrocarbons is one of the promising solutions to both global warming and energy shortage concerns.Photocatalytic CO₂ reduction performance of photocatalyst can be effectively enhanced through microstructure regulationand morphology regulation to generate hydrocarbons,such as methane,carbon monoxide,methanol,formic acid etc.In thisdissertation,three photocatalysts,GaN,ZnGa₂O₄,Bi₂MoO₆,were investigated through microstructure regulation and morphology regulation to effectively facilitate their photocatalytic efficiencies of generation of methane.The details are summarized as follows:?1?Double-shelled GaN hollow spheres are prepared for photocatalytic reductionof CO₂ through ammonia-gas nitridation of shape-analogous Ga₂O₃ hollowspheres.Small amount oxygen in situ doping narrows the bandgap of theGaN hollow sphere which significantly enhances the utilization of visiblelight.The large surface area of the hollow spheres provides more activity sitesfor the photoreduction reaction.The specific hollow structure also allows thetrapping of the incident light for a longer time during photocatalysis process,which provides more opportunities for light absorption.Loading of Pt andRuO2cocatalysts further enhances the separation of photogenerated electronsand holes to improve the CO₂ reduction activity.?2?Robust,double-shelled ZnGa₂O₄ hollow spheres were successfully fabricated by hydrothermal method followed by annealing at different temperature to enhance their crystallinity.The hollow structure is expected to trap incident photons toenhance the light absorbance.The sample annealed at 700 ? exhibited the optimized photocatalyticperformance in the reduction of CO₂ in the presence of water vapor to methane.This property is ascribedto the improved crystallinity of the sample,which has fewer defect centers for the recombination of electron-hole pairs compared with that annealed at 600 ?.The reduced performance of the sample done at 800 ?relative to the one annealed at 700 ? is attributed to the formation of additional impuritiesbesides ZnGa₂O₄,possibly due to partial Zn?II?evaporation at higher temperature leading to segregationof potential Ga-based oxides.RuO2 and Pt were loaded onto the sample surface to greatly enhance thephotocatalytic performance.The best photocatalytic performance was observed in the sample co-loadedwith Pt and RuO2.Its efficiency is more than 7 times as much as pristine sample.?3?A Bi₂MoO₆nanostrip-assembling network architecture was synthesized with a convenient route with sodium oleate as a surfactant.The generating Bi₂MoO₆ nanostrips intercross with each other to form this unique network structure.The time-evolution experiment was traced to reveal the formation mechanism of the Bi₂MoO₆ network.The photocatalytic reduction of CO₂ to CH4 of the Bi₂MoO₆ was evaluated,compared with the Bi₂MoO₆ nanoplate analogue synthesized in the absence of sodium oleate and that with solid state reaction.The Bi₂MoO₆nanostrips exhibit the best photocatalytic activity,which is assigned to high specific surface area,high light absorption intensity,thin thickness for fast carrier migration,and pores for reactant transport.