The Design And Synthesis Of MOFs/Semiconductor Nanocomposites With Enhanced Performance For Photocatalytic CO₂ Reduction

The utilization of solar energy for the transformation of C02 into fuels and valuable chemical is one of the most attractive approaches to alleviate the energy crisis and global warming.However,the poor adsorption capability toward CO₂ obstructs the photocatalytic CO₂ reduction performance of the conventional semiconductors.Metal-organic frameworks?MOFs?are a class of crystalline porous materials with remarkable specific surface areas,well-defined nanometer-scale cavities,highly flexible stucture,as well as relatively high thermal/chemical stability.The incorporation of semiconductors with MOFs with remarkable CO₂ adsorption capacity will be a promising strategy to enhance the performance for photocatalytic CO₂ reduction.We performed our research as two parts:One is the design and synthesis of CPO-27-Mg/TiO₂ and Cu₂O/M/ZIF-8?M=Pt,Au?nanocomposites,the performance for photocatalytic CO₂ reduction is also studied to explore the role of the alkaline coordinatively unsaturated metal center and the imidazole-based organic ligand,respectively,in the adsorption and activation toward CO₂.The other part is about the constrction of Cu₂O/Cu/ZIF-8 and the role of CuO is also studied in the influence of the products distribution about the photocatalytic CO₂ reduction.The main conclusions obtained from our research are follows:?1?Artificial photosynthesis is achieved with CPO-27-Mg/TiO₂ nanocomposites under near ultraviolet,and enhanced photocatalytic performance is showed due to its high adsorption capacity toward CO₂ and the open alkaline metal sites existed in CPO-27-Mg.?2?The Cu₂O/M/ZIF-8?M=Pt,Au?nanocomposites showed enhanced performance for photocatalytic CO₂ reduction,and the product yield of HCOOH is almost 9 times over that of the pure Cu₂O.The enhanced of CO₂ reduction performance over the nanocomposites,on one hand,are benefited from the enhancement in separation of photo-generated electron-hole by Pt and Au,on the other hand,which should be attributed to the adsorpotion and activation toward CO₂ on the imidazole ligand in ZIF-8.?3?By futher introducing Cu₂O/M/ZIF-8 with CuO,we find that,the transformation from CO₂ to multi-carbon organic product is achived with high yield by means of photocatalytic over Cu₂O/Cu/ZIF-8.After the study about the reaction mechanism,the results shows that,the formation of benzyl acetate is closely related to the adsorption,splitting,as well as the further reduction and hydrogenation on the surface of copper.In this thesis we construct a series of MOFs/semiconductor nanocomposites for photocatalytic CO₂ reduction.For the first time,targeted research have been done on clarify the role of unsaturated alkali metal center and imidazole ligands on the adsorption and activation toward CO₂ in the process of CO₂ reduction,respectively.And this work highlights the promising prospect in constructing efficent MOF-based photocatalyst for CO₂ reduction.Moreover,by introducing CuO,the transformation from CO₂ to multi-carbon organic product is achived under visble light,and the possible mechanism is also proposed in this thesis.