| China is rich in coal resources,it is a major issue that bears on China’s green sustainable development to deepen the development of new coal chemical industry,and accelerate the transformation and upgrading of the coal industry.Based on coal’s unique aromatic structure of organic macromolecules,the research and development of new coal-based carbon materials with high catalytic activity may bring a bright future to promote the utilization of high value-added of coal and CO2 resource conversion.In this dissertation,the functional coal-based graphene macroform series materials were prepared using coal as the raw material,and the fixed-bed photocatalytic reaction system were designed and constructed to evaluate the catalytic activity of the coal-based graphene macroform materials in the photocatalytic reduction of CO2 into chemicals.This article mainly did the following tasks:(1)Using TaiXi anthracite as raw material,high-temperature heat treatment,chemical oxidation,liquid self-assembly and thermal reduction techniques were integrated to prepare 3D-CG through structural assembly and surface chemical structure control.As a photocatalyst,the gas-liquid-solid three-phase fixed-bed photocatalytic reaction system was designed to investigate the photocatalytic reduction of CO2 into chemicals.The results showed that the surface chemical structure of 3D-CG has a great influence on their photocatalytic activity,the yield of methanol can reach up to 73.36 μmol/g cat under UV irradiation for 12 h,which is about 3.4 times in production activity in comparison with that of powder CGO in photocatalytic CO2 reduction,and it is ahout 3.0 times higher than that of pure TiO2.(2)Using 3D-CG as a carrier,hollow spherical ZnO/3D-CG composites were prepared by one-step hydrothermal method,and the properties of photocatalytic reduction of CO2 into chemicals were investigated.The results showed that the yield of methanol is up to 224.42μmol/g cat under UV irradiation for 12 h,which is about 3.1 times that of 3D-CG under the same conditions.Hollow spherical ZnO/3D-CG composite has stable photocatalytic activity.When used for 3 cycles,the methanol yield can still be maintained at 206.78 μmol/g cat,which is approximately 92.05%of the methanol production at the first use.(3)Nanosized C3N4/ZnO/3D-CG ternary composites were prepared by chemical bath deposition and calcination process using hollow spherical ZnO/3D-CG as a carrier to investigate the photocatalytic reduction of CO2 into chemicals.The results showed that the photocatalytic activity increases first and then decreases with the increase of the deposition times of g-C3N4 under UV irradiation.When the deposition times is three,the nanoflower-like C3N4/ZnO/3D-CG composite was obtained,and the yield of methanol was up to 420.14μmol/g·cat,which was about 1.9 times that of hollow spherical ZnO/3D-CG composite under the same conditions,and 5.7 times that of 3D-CG.In addition,hollow spherical nano-ZnO/3D-CG and nanoflower-like C3N4/ZnO/3D-CG composites can also maintain good photocatalytic activity under the visible light conditions.(4)The photocatalytic reaction mechanism of 3D-CG and their composites were investigated.The study indicates that the active group and surface structure of sp3 carbon atom on 3D-CG surface have the photocatalytic activity similar to that of semiconductor.The partially recovery of sp2 carbon conjugate structure on moderately reduced 3D-CG surface leads to the decreases of surface charge transfer resistance.It can rapidly capture the photoelectrons generated by ZnO and g-C3N4,promoting the efficient separation and transfer of photoelectron-holes pairs,and enriching the electrons on the surface of 3D-CG to increase the electron density significantly,which is beneficial to photocatalytic reduction of CO2 multi-electron reactions,thereby increasing the yield of methanol. |
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