Photocatalytic Carbon Dioxide Reduction Based On Accordion Structure Carbon Nitride

The conversion of CO₂into high value-added chemicals through artificial photosynthesis with the help of solar energy is an important way to achieve carbon peaking,carbon neutrality goals and to secure future energy supply.Catalysts are the technological core of the photocatalytic conversion process and determine the rate and efficiency of energy conversion.Graphitic carbon nitride（g-C₃N₄）is an efficient visible light responsive photocatalyst with the advantages of low cost,matched energy band structure,easy preparation,non-toxicity,and good stability.However,the limited light absorption efficiency,short carrier lifetime,and low active area in the bulk phase g-C₃N₄constrain its photocatalytic CO₂reduction performance.In this thesis,a series of accordion structured g-C₃N₄-based photocatalysts can be prepared and their surface interface structures can be rationally tuned to enhance the effective transfer of photogenerated carriers and the visible light absorption range of the catalyst to achieve efficient photocatalytic CO₂to CO conversion,the specific studies are as follows:1.We enhanced the photocatalytic CO₂reduction performance by doping boron atoms in the accordion structure g-C₃N₄to repair nitrogen vacancies,promote charge transfer and optimize intermediate adsorption.The accordion structure of g-C₃N₄not only enhances the specific surface area,but also changes the interlayer interactions to achieve the optimization of the energy band structure and the enhancement of visible light absorption.However,the large number of nitrogen defects as the center of the composite reduces the carrier migration efficiency.The small molecule modified oligomers were first synthesized,and the accordion structure g-C₃N₄with boron atoms embedded in the interlayer was synthesized by introducing boron atoms during high temperature thermal polymerization.Experimental results showed that the repair of nitrogen defects by boron atoms increased the crystallinity,improved the asymmetricπ-conjugation system of the heptazine ring,enhanced the electrical conductivity,and also enhanced the charge transfer efficiency,and compared with the pristine accordion g-C₃N₄,the photocatalytic carbon dioxide reduction rate was significantly enhanced.Theoretical calculations show that the doping of the embedded boron atoms can be used as active sites to optimize the free energy of CO*intermediate adsorption and accelerate the CO₂to CO reduction.This work proposes a new strategy to improve the photocatalytic efficiency of photocatalysts by tuning their defects.2.We achieved the enhancement of visible light absorption and photocatalytic CO₂reduction performance by loading Pd nanoparticles on accordion structured g-C₃N₄.Uniformly sized Pd nanoparticles were grown at the defects on the accordion g-C₃N₄surface by the solvothermal method,and the plasmonic effect of Pd nanoparticles broadened the spectral response range and effectively trapped photogenerated electrons,accelerated effective separation and transmission of photosynthetic electrons,and significantly enhanced the CO₂reduction performance with a yield of 2.65 times that of the pristine accordion structured g-C₃N₄.This strategy may provide an effective photocatalytic conversion method for the design and construction of graphitic carbon nitride based composites.