Preparation Of LDHs Composite Photocatalyst And Its Photocatalytic Activity For CO₂ Reduction

With the rapid development of economy,the ecological environment problems and energy crisis are becoming more and more serious.Among them,the large amount of carbon dioxide（CO₂）emissions in the atmosphere caused by the global warming phenomenon is increasingly serious.The use of clean and abundant solar energy to simulate natural photosynthesis photocatalytic technology has attracted widespread attention.Currently,layered double hydroxides（LDHs）materials are low-cost,readily available clays that have shown a promising application prospect in the field of photocatalytic CO₂ reduction due to their layered structure,high porosity,and easy synthesis.However,the photocatalytic effect of conventional LDHs is generally poor due to the defects of easy agglomeration,slow electron mobility and poor recovery.Therefore,in order to overcome its shortcomings,the Fe₃O₄/Mg-AlLDH composite photocatalysts was prepared by introducing the magnetic materials into LDHs to improve separation efficiency and recovery;On the other hand,the Co-AlLDH photocatalyst modified by biomass carbon quantum dots（B-CQDs/Co-AlLDH）was constructed to solve the problems of poor dispersion and low stability.In addition,their reaction mechanism was investigated through a series of characterization methods.The research contents of this paper are as follows:（1）The two-dimensional（2D）ultrathin Mg-AlLDH modified by magnetic Fe₃O₄（Fe₃O₄/Mg-AlLDH）was successfully synthesized via the co-precipitation method.The results showed that the Fe₃O₄/Mg-AlLDH not only exhibits superior separation efficiency of charge carriers but also possesses signally enhanced photocatalytic activity for CO₂ reduction than Mg-AlLDH.The as-prepared Fe₃O₄/Mg-AlLDH affords the CO and CH₄ generation rate of 442.2 μmol g^-1 h^-1 and 223.9 μmol g^-1 h^-1.A series of experiments on photocatalytic performance showed that the enhanced reduction CO₂ activity mainly comes from synergetic effect of Fe₃O₄ and ultrathin Mg-AlLDH.And Fe₃O₄ can increase the separation efficiency of photogenerated electron-hole pairs,and ultrathin Mg-AlLDH can reduce the transmission resistance of charge carriers and enhance the photocatalytic reduction effect.（2）Biomass was prepared from renewable biomass sources widely distributed in nature,and the Co-AlLDH composite photocatalyst modified by the carbon quantum dots（B-CQDs）was further synthesized via hydrothermal method and the catalyst showed excellent photocatalytic reduction of CO₂.The SEM,EDS,TEM and other methods were used to analyze the structure,the results show that enhanced reduction CO₂ activity of B-CQDs/Co-AlLDH was mainly that the B-CQDs could be used as an attachment to increase the active site of Co-AlLDH,thus promoting the reaction between catalyst and CO₂.At the same time,the up-conversion PL property test of B-CQDs proves that the introduction of B-CQDs can effectively prevent the agglomeration and superposition between the layers of Co-AlLDH,thus facilitating electron hole pair transmission and enhancing the mobility.