Preparation And Photocatalytic Properties Of Carbon Nitride And Cobalt,Phosphorus Modified Carbon Nitride Composites

With the development of current industry,global environmental pollution and energy demand have become the focus of attention.Researchers have provided a sustainable alternative by converting biomass derivatives into high value-added chemicals and photocatalytic hydrogen production（H₂）.Graphitic carbon nitride（g-C₃N₄）was a layered semiconductor material with a unique tri-s-triazine unit structure.It had good physical and chemical stability,making it widely used in biomass conversion and photocatalytic hydrogen evolution.In this thesis,two ultra-thin carbon nitride nanosheets and a carbon nitride nanotube material were prepared by a simple thermal polycondensation method.In addition,phosphorus（P）doped Co₃O₄/CoO/g-C₃N₄/P composites were synthesized by a simple calcination method.Their structures were determined by corresponding characterization methods,and their catalytic properties in photocatalytic oxidation of5-hydroxymethylfurfural（HMF）and photocatalytic hydrogen production were investigated.1.Preparation of three carbon nitride catalysts.Preparation of g-C₃N₄:g-C₃N₄was obtained by high temperature thermal polymerization of urea and ultrasonication.Preparation of ultrathin carbon nitride nanosheets（UC₃N₄）:UC₃N₄was obtained by high temperature thermal polymerization of urea and ultrasonication under acidic conditions.Preparation of carbon nitride nanotubes（C₃N₄NTs）:C₃N₄NTs were obtained by simple solvent reaction and annealing treatment of melamine.The structure was determined by corresponding characterization methods,and the catalytic performance of these three carbon nitride materials for photocatalytic oxidation of HMF was investigated.The results showed that g-C₃N₄nanosheets exhibited the best HMF conversion performance under the conditions of acetonitrile,Xe lamp（λ>300nm）and oxygen.The yield of 2,5-diformylfuran（DFF）was up to50.41%and the selectivity was 89.72%.2.Preparation of Co₃O₄/CoO/g-C₃N₄/P composite materials.The first step:g-C₃N₄nanosheets were obtained by high temperature thermal polymerization of urea and ultrasonication.The second step:commercial red phosphorus（RP）was hydrothermally treated and ultrasonically activated to obtain activated RP;the third step:g-C₃N₄nanosheets,treated RP and purchased Co₃O₄nanoparticles were mixed and ground,and then annealed in.an Ar atmosphere at 350°C for 3 h to obtain Co₃O₄/CoO/g-C₃N₄/P composites.The structure was determined by corresponding characterization methods,and the catalytic performance of this multi-composite material for photocatalytic hydrogen production was explored.The results show that the average hydrogen evolution rate of Co₃O₄/CoO/g-C₃N₄/P composite was up to4233.69μmolg^-1·h^-1,when using LED white light（λ>420 nm）as the light source and triethanolamine（TEOA）as the electron donor,which was about 70 times that of pure g-C₃N₄.And speculate on the possible reaction mechanism.