Study On Photocatalytic Carbon Dioxide Reduction System With Cobalt-based Catalysts

Over the years,the consumption of fossil resources has been increasing,which has greatly accelerated the rate of resource depletion and the pollution of the earth.The massive production of carbon dioxide causes global warming and other environmental problems.An effective solution is to use solar energy to catalyze the conversion of carbon dioxide into fuel.Therefore,efforts have been made to find and develop stable,highly active and inexpensive catalysts and photosensitizers.MOFs can capture carbon dioxide molecules and their organic ligands are easy to modify,so they are ideal materials for the construction of photocatalytic carbon dioxide reduction system.Similarly,perovskite CoSn（OH）₆ is a promising raw material for carbon dioxide return which has been developed and applied in recent years.Using ZIF-67 as the catalyst,Proflavin was used as a photosensitizer to build three groups of catalytic carbon dioxide reduction systems.The system showed good stability and photocatalytic activity.The system worked well for more than 48 hours under visible light and displayed high photocatalytic efficiency of 25.6μmol for CO evolution.A significantly high turnover number（TON）of 13.5 was calculated based on the PS.The durability and efficiency of the PS are much better than those relatively reported works.The carbon source was confirmed by the ¹³C-labelled isotropic experiment.The carbon source was identified by ¹³C labeled isotropic experiments,and the fluorescence spectra showed that the excited state[PF*]was quenched by the oxidation of ZIF-67 catalyst,and the mechanism of photocatalytic reduction of carbon dioxide in this system was speculated.More importantly,the system uses protoflavin without precious metals as photosensitizer,which is cheap and easy to obtain.CoSn（OH）₆ nanocrystalline cubes were prepared by a simple co-precipitation method.The adsorption of nitrogen showed that CoSn（OH）₆ had a large specific surface area and regular pore structure,which promoted the adsorption of carbon dioxide.CoSn（OH）₆ as catalyst and proflavin as photosensitizer were used to build three groups of photocatalytic carbon dioxide reduction systems,which also showed good stability and photocatalytic activity.The reaction can last for 24 hours under light,and the final product is 22.3μmol carbon monoxide with a selectivity of 90.5%,which is better than most of the reported photocatalytic systems.The mechanism of photocatalytic reduction of carbon dioxide by this system was characterized by potential analysis and fluorescence spectrum analysis.CdS/Bi₂S₃/ZIF-67 hybrid photocatalyst was prepared,which can effectively reduce carbon dioxide to carbon monoxide and hydrogen under visible light irradiation.In this photocatalytic system,the semiconductor acts as the light collector,and the ZIF-67 catalyst acts as the catalytic center of carbon dioxide reduction.The formation of CdS/Bi₂S₃ heterojunction can improve the charge separation and utilization rate.Therefore,the CdS/Bi₂S₃-0.5h/ZIF-67hybrid photocatalyst yields 0.33 mmol/g carbon monoxide and 0.12 mmol/g hydrogen after 4h visible light irradiation.This work can provide a feasible method for exploring the efficient photocatalyst of photocatalysis CO₂.