Research On The Reaction Mechanism Of Photothermal Catalytic Reduction Of CO₂ Using The Novel Photocatalyst SnTa₂O₆

This study aims to address the shortcomings of current photocatalytic reduction of CO₂ by developing a new type of SnTa₂O₆ photocatalyst and modifying it,exploring the reaction mechanisms of photocatalytic and photothermal catalytic reduction of CO₂.The main research contents are as follows:（1）SnTa₂O₆ nanosheets were prepared using a molten salt heating method,and the effects of heating time on their physicochemical properties and photocatalytic performance for CO₂ reduction were investigated.As the heating time increased,the synthesized SnII ternary oxide changed from octahedral Sn₂Ta₂O₇ to nanosheet-shaped SnTa₂O₆.The ultrathin nanosheet structure of SnTa₂O₆ not only exposed abundant active sites but also facilitated the separation of photogenerated charges.Under full-spectrum irradiation,the CO production rate of SnTa₂O₆ was 16.5 μmol h^-1 g^-1,which was 16.8 times and 2 times that of Sn₂Ta₂O₇ and TiO₂,respectively,and showed good stability.The high CO selectivity（about 100%）of SnTa₂O₆ can be attributed to the lower CO*Gibbs free energy and timely desorption of the products.（2）To further enhance the activity of SnTa₂O₆,an improved flame reduction method was used to quickly construct bridging oxygen vacancies in SnTa₂O₆ nanosheets,and the relationship between the molecular configuration of CO₂^-SnTa₂O_6-x and the reaction activity and oxygen vacancy stability was explored.The flame reduction time simultaneously affected the oxygen vacancy concentration and microstructure of SnTa₂O_6-x.Under visible light irradiation,the CO production rate of 40-SnTa₂O_6-x was 21.1 μmol h^-1 g^-1,which was about 7.5 times that of SnTa₂O₆ and remained active after five cycles.CO₂ is adsorbed onto the bridging oxygen vacancy sites of SnTa₂O_6-x through a more stable bidentate coordination.The enhanced adsorption is mainly attributed to the locally enhanced charge density and the positive shift of d-band center caused by the oxygen vacancy.The bidentate coordination configuration of CO₂ on SnTa₂O_6-x not only facilitates CO₂ activation but also avoids filling the oxygen vacancies,thereby ensuring stability.（3）SnTa₂O_6-x nanosheets containing stable oxygen vacancies were applied in the photocatalytic reduction of CO₂ through a photothermal process,revealing the mechanism of the photothermal synergistic catalytic reduction of CO₂ by SnTa₂O_6-x.SnTa₂O_6-x nanosheets with low/high oxygen vacancy concentration(L/H-SnTa₂O_6-x)were prepared by regulating the flame reduction time.The reaction activity of SnTa₂O₆ and L/H-SnTa₂O_6-x increased with increasing temperature.At a reaction temperature of 150℃,the CO production rate of the H-SnTa₂O_6-x photothermal catalytic reduction of CO₂ was as high as 210 μmol h^-1 g^-1,which was 13.6 and 26 times higher than that of H-SnTa₂O_6-x and SnTa₂O₆ at room temperature,respectively,and had good stability.Experimental results showed that the photothermal reaction was mainly dominated by photocatalysis,and the introduction of thermal energy enhanced the activation of CO₂ by H-SnTa₂O_6-x,producing highly active CO₂^-and b-CO₃^2-species.Increasing the temperature under light irradiation facilitated the capture of more photo-generated electrons by oxygen vacancies,promoting the formation of COOH*by CO₂^-and b-CO₃^2-with H*,thus improving the reaction performance.（4）A concentrator-integrated photothermal reactor was developed and effectively applied for the photothermal catalytic reduction of CO₂.Ti-Cr-Al photothermal sheets prepared by magnetron sputtering exhibited good photothermal conversion ability.The photothermal sheets were wrapped around a quartz inner tube,providing heat energy outwardly by absorbing light and preheating the reaction gas inwardly.The reactor effectively coupled the light-collecting ability of the trough concentrator,the heating ability of the photothermal sheet,and the heat preservation and mass transfer ability of the quartz reaction tube.Under illumination,the temperature of the reactor reached 113℃ within 200 seconds and remained stable.The reduction performance of SnTa₂O₆ and H-SnTa₂O₆ in the photothermal reactor was tested.The CO and CH4 yields of H-SnTa₂O₆ were 7.3 mmol h^-1 m^-2 and 0.65 mmol h^-1 m^-2,respectively,and the reaction performance of the photothermal reactor was about 7.1 times that of the plate-type photoreactor.