Preparation Of G-C₃N₄ Based Photocatalysts And Its Application On Photocatalytic Hydrogen Evolution

With the rapid consumption of global fossil energy and the deteriorating environment,exploiting environment-friendly,low-cost and resource-rich renewable energy has become an urgent issue for humanity.Hydrogen as a green clean new energy has received extensive attention from researchers.The use of photocatalytic technology to water splitting hydrogen evolution is one of the ideal methods for hydrogen production.Since 1972,Fujishima and Honda reported that H₂ and O₂production from water splitting on semiconductor TiO₂ single crystal electrode.Afterwards,researchers conducted extensive and in-depth studies on semiconductor photocatalytic materials.However,traditional photocatalytic materials represented by TiO₂ limit their applications due to wide bandgap and poor visible light response.Therefore,there are great theoretical and practical value to develop semiconductor materials with narrow bandgap and greater response in the visible light region.Graphite carbon nitride?g-C₃N₄?is a typical non-metal semiconductor photocatalyst with a 2D layered structure.It attracted the attention of researchers because of its high thermal and chemical stability,moderate bandgap and high activity in the visible region.However,its disadvantages such as high recombination rate of photoelectron-hole and low quantum efficiency limited its application.In this work,we used g-C₃N₄ as the research object,and improved the visible light utilization efficiency and photoelectron-hole separation efficiency of the photocatalyst by means of element doping and surface co-catalyst modification,and explored the best experimental conditions and methods to improve the performance of g-C₃N₄ materials.The main research content is as follows:The first part:We use urea and benzyl disulfide as raw materials,and use high-temperature polymerization to obtain sulfur-doped graphitic carbon nitride?g-S-C₃N₄ denoted by SCN?,and then SCN is composited with nickel by photodeposition.The Ni/gS-C₃N₄?denoted by NiSCN?photocatalyst with high-visible light photocatalytic activity was prepared.In this process,Ni elemental is formed by photo-electron reduction of divalent nickel ions,which can support Ni in the effective electron-accumulating sites of SCN.The ratio of Ni to SCN was adjusted by changing the concentration of nickel salt solution and obtained a series of NiSCN photocatalysts containing different amounts of nickel.The results show that,compared with pure g-C₃N₄ and SCN,Ni SCN exhibits excellent photocatalytic activity under visible light??>420nm?.On the one hand,compared with pure g-C₃N₄,after sulfur doping and nickel loading,the band gap of SCN and NiSCN is narrowed and its response range in the visible light region is extended.On the other hand,due to smaller nickel nanoparticles are uniformly deposited on the surface of the SCN,which is conducive to the effective separation of photogenerated electrons and holes,the photocatalytic activity is enhanced.The second part:Using melamine as carbon-nitrogen source and cobalt acetate as cobalt source.The mixture of cobalt hydroxide and melamine was firstly obtained by using sodium carbonate as precipitant in ethylene glycol solvent,then calcining the mixture by one-pot calcination method to obtain Co₃O₄@g-C₃N₄ core-shell structure.Finally,the core-shell photocatalyst of Co@g-C₃N₄ was obtained by in-situ reduction method.In this experiment,Co as a co-catalyst to promote effective charge separation and suppress the recombination of photoelectron-hole pairs.The construction of core-shell structure is beneficial to improve the photocatalytic activity of g-C₃N₄.