Study On Controllable Preparation Of Graphite Phase Carbon Nitride And Photocatalytic Hydrogen Production

Semiconductor photocatalytic technology could convert solar energy to chemical energy under mild reaction condition, which is considered to be the idea pathway to solve the energy crisis and environmental pollution. Graphitic carbon nitride（g-C₃N₄） has good chemical inertness, thermal stability and bio-compatibility. Meanwhile, it exhibits a band gap of 2.7 eV, with appropriate conduction band and valence band position, it has great applied potential in photocatalytic field. However, the traditional g-C₃N₄ has many disadvantages, such as small specific surface area, fast recombination and low catalytic activity, many efforts has been made to enhance its photocatalytic performance without destroying the basic chemical structures. The main contents including:1. Melamine was selected as raw material, under phosphorous acid assisted hydrothermal conditions, then the regular and stable hexagonal cylinder precursors were finally prepared through the molecule self-assembly between melamine and cyanuric acid. After thermal polymerization the hexagonal cylinder precursors converted to hexagonal tube. The formation mechanism of hexagonal precursors was obtained by the control experiment of different reaction time. It exhibited enhanced visible-light photocatalytic properties owing to the hierarchical micro-nanostructure and the phosphorus doping.2. Different phosphate and melamine were reacted under hydrothermal conditions, due to the different ions’ size and pH values from different phosphate, a series of precursors with different morphology were obtained. After thermal polymerization, a set of corresponding phosphorus-doped carbon nitride were gained. The absorption edge of carbon nitride shift to visible light region was caused by the phosphorus doping. The recombination of photo generated electron-hole pairs was suppressed as well, result inthe improvement of hydrogen evolution rate under visible-light.3. Metal-free g-C₃N₄/rGO nanocomposites were synthesized by a facile one-pot impregnation–thermal reduction approach by direct polymerization of melamine in the presence of graphene oxide as a structure-directing agent. In the photocatalytic system, such a 2D architecture provides efficient light harvesting and a short diffusion distance for rapid interfacial charge separation. Compared with pure g-C₃N₄, the photocatalyst exhibits excellent hydrogen evolution performance and photocatalytic stability.