Study On The Synthesis And Performance Of Materials For CO₂ Photoreduction

With the increasing demand of energy resources for modern society,fossil fuels are depleting in a rising rate yearly.Meanwhile,the consumption of fossil fuels would accompany with the emission of massive carbon dioxide,resulting in serious global warming.Artificial photosynthesis——photoreduction of carbon dioxide to organics,could not only relieve the global warming but also resolve the problem of energy shortage,which is likely to kill two birds with one stone.Although great progress has been made in the research of artificial photosynthesis,the conversion efficiency of carbon dioxide is still pretty low.As a linear stable molecule,carbon dioxide is difficult to activate and transmute for the high dissociation energy of C=O.In addition,the process of water dissociation and oxidation is another significant factor that limits the efficiency of carbon dioxide photoreduction.In view of above problems,surface modification of basic OH groups is utilized to improve the adsorption of carbon dioxide.The ratio of surface acidic sites to basic sites is then adjusted to enhance the activation of carbon dioxide.Moreover,transition metal-doping in photocatalyst is conducted to adjust the electronic structure,so as to accelerate the processes of carbon dioxide activation and water oxidation.The specific research contents are as follows:?1?The impact of surface OH groups of CoAl-LDH on CO₂ adsorption and activation.CoAl-layered double hydroxide?CoAl-LDH?is synthesized to investigate the activity of CO₂ photoreduction.Coprecipitation method is adopted to synthesize CoAl-LDH nanosheets.In view of the good CO₂ adsorption ability of surface OH groups on LDH,constructing the hydroxide catalyst full of surface OH groups is conducive to CO₂ adsorption and electron transfer,accelerating CO₂ reduction and conversion.Meanwhile,Co ion may possess the property of water dissociation,which is in favor of proton generation and hydrogenating CO₂ when combined with electron.CoAl-layered double oxide?CoAl-LDO?with residual surface OH groups is synthesized to investigate the activity of CO₂ photoreduction.Generally,CO₂ activation is considered to be one of the main factors that limit the efficiency of artificial photosynthesis.Lewis acid-base pair,which is constructed by a Lewis acidic surface metal site situated proximal to an oxygen vacancy and a Lewis basic surface hydroxide site,is reported to possess the ability of activating small molecules?such as CO₂,H2?.Therefore,the surface OH groups of CoAl-LDH are adjusted by controlling heating temperature to form Lewis acid-base pairs,so as to enhance CO₂ activation and improve the efficiency of CO₂ photoreduction.?2?The impact of the electronic structure of BiVO₄ on CO₂ activation and water oxidation.Ultrathin Co-doped BiVO₄ nanosheets are synthesized to investigate the activity of CO₂ photoreduction.Two-dimensional nanosheets are often provided with the features of high specific area and affluent active sites.CTAB is utilized to construct the lamellar template for synthesizing ultrathin BiVO₄ nanosheets,and divalent Co ions are then doped in situ to synthesize Co-doped BiVO₄ nanosheets.CO₂ activation and the electrons number transferring to CO₂ molecules are greatly improved by adjusting the electronic structure of BiVO₄ via Co doping.Additionally,the top of valence band composed of Co 3d orbits could accelerate the process of water oxidation.