Photocatalysts Based On Vacancy Engineering For CO₂ Reduction

Photocatalytic CO₂ reduction reaction is a process that utilizes sunlight to produce highly reductive electrons and convert CO₂ into valuable C-containing products.This offers an attractive opportunity to solve greenhouse gas emission and energy crisis.Introduction of vacancies into the lattice of semiconductor photocatalysts will change their electronic structure,create more active sites and extend the optical response range.Deep insights into the formation and effects of vacancies worth extensive efforts.This work focuses on constructing different vacancies in semiconductor photocatalysts and their improvement on photocatalytic performance.（1）Oxygen vacancy plays an important role in promoting CO₂ adsorption and reduction on photocatalysts.Bi was heavily doped into ceria,forming a solid solution catalyst meanwhile maintaining the fluorite structure,to increase the oxygen vacancy concentration.The sample Ce_0.6Bi_0.4O_2-δshowed the highest photocatalytic activity with a CO yield of～4.6 times that of the pristine ceria nanorods.Bi was homogeneously dispersed into the fluorite ceria as was confirmed by X-Ray Diffraction（XRD）and Energy Dispersive X-Ray Spectroscopy（EDX）elemental mapping images.It has been evidenced by the results of Raman and X-ray photoelectron spectroscopy（XPS）that Bi introduction boosts the concentration of oxygen vacancy in the solid solution that can facilitate the adsorption/activation of carbonate and bicarbonate intermediates on its surface according to in-situ FT-IR.（2）Indium oxide based materials are promising candidates for photothermal CO₂ reduction.However,stoichiometric indium oxide looks pale yellow with a wide bandgap（2.8 e V）.To overcome its disadvantages of low light absorption and lack of active sites,indium based MOFs are subject to calcination under reductive atmosphere and convert to black In₂O_3-xnanorods.The photothermal synergistic effect facilitates CO₂ reduction reaction.（3）Graphitic carbon nitride（C₃N₄）is a kind of low-cost and effective CO₂reduction catalyst.It is also used as support for single atoms or metal nanoclusters.Here we introduced carbon vacancies and nitrogen vacancies into this C₃N₄ support before Co was loaded onto it by oil bath.Among the samples,CN_vCo with abundant nitrogen vacancies showed the best CO₂ reduction performance,reaching 156μmol g^-1h^-1 of CO yield,with nearly 100%selectively.