Z-scheme Heterojunction Of Co₁-g-C₃N₄@α-Fe₂O₃ For Photocatalytic CO₂ Reduction

The rapid development of industrial society is leading to the growing consumption of fossil fuels,which is accompanied by excessive emission of CO₂ and severe climate issue.Therefore,developing high-efficiency photocatalysts to convert CO₂ into value-added chemicals has attracted worldwide interest.Driven by solar energy,the photocatalytic reduction of CO₂ can not only reduce the concentration of atmospheric CO₂ and remedy the global warming issue,but also contribute to an upgraded energy structure.A series of processes,such as the excitation and transportation of photo-induced charge carriers,the adsorption and desorption of molecules,and the formation of key intermediates,are involved in the elusive mechanism of photocatalytic CO₂reduction.Thus,it is important to understand the tailoring strategy for designing excellent catalysts.In this dissertation,a Z-scheme heterojunction featuring single-atomic site catalyst has been successfully constructed,and exhibits high efficiency in the visible-light-driven photocatalytic reduction of CO₂.With the help of various characterization techniques,we have investigated the mechanism for manipulating the charge carrier’s behavior by Z-scheme heterojunction,and unveiled the function of the single-atomic site in CO₂ adsorption.Furthermore,it has been found that the altered electronic structure of the active site triggered by the charge transfer inside the heterojunction plays a critical role in the adsorption and stabilization of key intermediate.The main results can be summarized as follows:1.Owing to the unique atomic structure,single-atomic site catalysts have exhibited remarkable performances in diverse reactions.Herein,single-atomic Co sites loaded on g-C₃N₄（denoted as Co₁-g-C₃N₄）has been synthesized for photocatalytic reduction of CO₂.The single-atomic Co sites can not only serve as efficient centers for the adsorption of CO₂,but also facilitate the separation and transportation of the photo-induced charge carriers,thereby enhancing the catalytic performance.2.The oriented migration of charge carriers can be realized by constructing Z-scheme heterojunction,thereby facilitating the separation of the photo-induced electrons and holes.Herein,we have constructed a direct Z-scheme heterojunction of Co₁-g-C₃N₄@α-Fe₂O₃,which composes by Co₁-g-C₃N₄ integrated withα-Fe₂O₃nanorod arrays,for efficient visible-light-driven CO₂ reduction coupled with water oxidation.A production rate as high as 14.9μmol g^-1h^-1 is achieved for CO with a selectivity approaching 100%;the value markedly increases to 25.2μmol g^-1h^-1 under full spectrum irradiation.Time-resolved photoluminescence（TRPL）analysis reveals that the Z-scheme mechanism and the single-atomic Co sites work synergistically to prolong the lifetime of photogenerated carriers.Moreover,the formation of Z-scheme heterojunction would lead to and altered charge density of the single-atomic Co sites.In situ diffuse reflectance infrared Fourier-transform spectroscopy and anion adsorption measurements reveal that the key intermediate CO₂^–can be efficiently stabilized by the positively charged Co sites in Co₁-g-C₃N₄@α-Fe₂O₃,thus enhancing the CO₂ reduction performance.