Study On The Design,synthesis And Photocatalysis Of G-C₃N₄ Composites Loaded With Metal Nanoparticles

Graphite phase carbonitride?g-C₃N₄?,with the advantages of suitable band structure,high stability and low price,has become one of the spot hots in the research of photocatalysis materials.The metal or alloy nanoparticles modified g-C₃N₄ can increase the catalytic activity of CO₂ conversion and regulate the product distribution.This thesis,through the controllable synthesis of g-C₃N₄ composites metal nanoparticles with different exposed crystal faces and sizes can be controlled and synthesized and the design synthesis of metal-co-catalyst modified g-C₃N₄ composites with different composite structures,endeavors to characterize and study its microscopic interface structure by experiments and theoretical calculations;By photocatalytic conversion of CO₂ to CH₄ as a probe reaction,the photocatalytic properties of composites with different structures were tested,the photocatalytic properties of composites with different structures and the microscopic catalysis of composites with g-C₃N₄ and metal nanoparticles were studied.The acquaintance of the relationship between the structure and the photocatalytic reaction mechanism that it produces provides an important technical and theoretical support for the design of high performance photocatalytic materials and the study of photocatalytic mechanism.For the measurement,transmission electron microscopy?TEM?,X-ray diffraction?XRD?,UV-visible diffuse reflectance spectroscopy?UV-Vis?,fluorescence spectroscopy?PL?,X-ray photoelectron spectroscopy?XPS?,infrared spectroscopy?FT-IR?,photocurrent?I-t?and other testing instruments were taken for performance characterization and further analysis of the sample.The research contents are mainly as follows:1.Research on improving photocatalyst activity of CO₂ reduction by the phase design of co-catalyst.In this work,the surface-centered cubic Ru metal?fcc Ru?and the hexagonal Ru metal?hcp Ru?were grown in situ on the C₃N₄ nanosheets to form different C₃N₄-Ru hybrid structures.It is found that the hexagonal phase of Ru metal?hcp Ru?has a higher ability to convert CO₂ to CO and CH₄ than the face-centered cubic phase of Ru metal?fcc Ru?,but the ability to produce hydrogen is lower than the face-centered cube Phase Ru metal?fcc Ru?.According to the experimental characteristics and theoretical calculations,the surface reaction of the surface-centered cubic phase of Ru metal?fcc Ru?and the hexagonal phase of the Ru metal?hcp Ru?promoter result in corresponding photocatalytic properties.The adsorptivity of the CO₂ molecule on the main crystal plane?10^—11?of the Ru metal?hcp Ru?of the hexagonal phase is higher than that of the Ru metal?fcc Ru?of the CO₂ molecule in the face centered cubic phase?111?.Therefore,the strong interaction between the CO₂ molecule and the hexagonal Ru metal?hcp Ru?can increase the photocatalytic activity and the selectivity of C₃N₄-hcp Ru in the CO₂ reduction reaction.This work emphasizes the importance of the crystal phase structure of the promoter in the photocatalytic reduction of CO₂.2.Research on the effect of alloying and hydrogenation of metal co-catalyst on the reduction of CO₂ to CH₄.In this work,it is first proposed that the alloying and hydrogenation of metal co-catalysts can significantly improve the efficiency of photocatalytic reduction of CO₂ to CH₄.The results show that the isolated Cu and H atoms in the Pd lattice gap play three roles in improving the catalytic conversion of CO₂ to CH₄:?1?Cu atoms provide a catalytically active site for the reduction of CO₂ to CO,and then continue to reduce to CH₄,while inhibiting the H₂ reaction;?2?The H atom increases the electron trapping ability of the promoter;?3?The H atom accelerates the rate of CO conversion to CH₄,which is also the rapid control step for the catalytic conversion of CO₂ to CH₄.Under the synergistic action of Pd-H and Cu-CO sites,15mg C₃N₄-Pd₉Cu₁H_x had 100%selectivity for the formation of CH₄ under visible light irradiation,with an average rate of 0.018?mol h^-1.This study provides insights into the design of synergistic catalysts for highly selective carbon dioxide conversion at atomic accuracy.