Fabrication And Modification Of Graphitic Carbon Nitride Film For Photoelectrochemical Performance

Graphitic carbon nitride, a metal-free polymeric photocatalyst has been widely used in photocatalytic water splitting and organic pollution degradation,due to its high chemical stability and visible light response. However, only small part of solar energy can be utilized by the carbon nitride via traditional thermal polymerization method, due to the narrow range of visible light absorption and high recombination of photo-induced carriers; On the other hand, the film preparation process is extremely complex and the film has poor stability, limiting the load and device of carbon nitride. To address these problems, in this paper three strategies were put forward through solvothermal film growth, fabricating TiO₂/g-CN double layer heterojunction structure and surface modification with layered double hydroxides. The obtained carbon nitride film resulted in better photoelectric performance because these strategies broadened the visible light absorption range and reduced recombination. The main achievements are listed as below:After heat treatment, the continuous and complete carbon nitride film was successfully grown on the conductive substrate via the copolymerization reaction between cyanuric chloride and melamine in acetonitrile solvent. The results show that, compared to carbon nitride obtained from solid thermal polymerization, carbon nitride via solvothermal owned high polymerization and low terminal defect,broadening light absorption to 600 nm. The film combined robustly with substrate, reducing the interfacial impedance. Thus, the photocurrent density of solvothermal film reached 3.7 ?A cm-2, 18 times to the solid thermal polymerization one under 0.6 V vs SCE.TiO₂-A/g-CN or TiO₂-A/g-CN double layer structure film was fabricated using TiO₂ as electron transfer layer and g-CN as visible light absorption layer. Here, anatase phase TiO₂-A thin film was prepared by spinning and sintering, while rutile phase TiO₂-R nanorod arrays was obtained by hydrothermal growth and g-CN was obtained by solvothermal growth. It turned out that,heterostructure was constructed between g-CN and TiO₂ with matching band potential, thus, reducing the recombination and improving the photoelectric conversion ability. TiO₂-R/g-CN nanorod core-shell arrays owned more outstanding photoelectrochemical performance, because the bulk effect was suppressed efficiently due to high orientation and the space between nanorods and light illumination direction separated from carriers transport pathway. Thus, the photocurrent density of TiO₂-R/g-CN reached 81 ?A cm-2, 16 times to g-CN under 0.6 V vs SCE.g-CN was modified with Ni-Co LDH through cathodic deposition. The results show that, LDHchanged the surface condition of g-CN. LDH layers with high specific surface area, rich in alcohol and water, are convenient for mass transfer through fast absorption and desorption of reactants and products, thus reducing the O-O band formation energy barrier and facilitating water oxidation. On the other hand, shunting was avoided by repairing the pores with LDH, which expose the conductive substrate to the electrolyte. Thus, As the deposited quantity of electric charge was 30 mC, the photocurrent density of g-CN/LDH reached 11 ?A cm-2, 2.5 times to g-CN under 0.6 V vs SCE.