Photocatalytic Hydrogen Production Perforamance Of Carbon Nitride With High Specific Surface And Low Polymerization

With the development of economy and society,human demand for energy has been increasing.As a result,the energy shortage and environmental pollution problems have become more and more serious.Therefore,the development of clean,efficient and renewable energy sources has become a popular research topic.Solar energy is abundant and inexhaustible.Semiconductor photocatalytic hydrogen production can convert low energy density solar energy into high energy density hydrogen for energy storage,which is the most promising approach to solve energy shortage.In recent years,the research of graphitic carbon nitride(g-C3N4)has been a hot field,which has many advantages:such as cheap raw materials,simple synthesis methods,non-toxic,good stability,and suitable band structure and so on.However,carbon nitride synthesized by conventional methods also has the disadvantages of low specific surface area,low response to light,high recombination probability of photo-generated electrons and photo-generated holes,and thus low photocatalytic activity.In this thesis,starting from the principle that small molecules of formic acid can diffuse into the oligomeric carbonitride phase prepared from melamine to efficiently remove holes and enhance the photocatalytic hydrogen production activity,by preparing carbonitride with high specific surface area and low degree of polymerization,to further improve the diffusion of formic acid in the bulk,and thus to enhance the photocatalytic efficiency.The main research contents of this thesis are:(Ⅰ)Melamine was mixed with the template agent urea and then calcinated at 520℃ to prepare PCN.The structure and optical properties of PCN was characterized by XRD,UV-vis DRS,BET and other means.By the aid of a large amount of gas which generates in the calcination process of urea,the carbon nitride with high specific surface area and rich pore structure has been obtained,which shows enhanced hydrogen production activity.It is found that carbon nitride prepared using urea as single precursor exhibits the higher activity than those prepared using mixed precursors.(Ⅱ)Urea was used as a precursor,and carbon nitrides with different polymerization degrees were synthesized by calcining at different temperatures(450℃,480℃,550℃,600℃).Via XRD,FT-IR,PL,UV-Vis DRS and TG Characterization methods,it is found that that samples synthesized at low temperature(450℃,480℃)possesses a lower polymerization degree,while samples synthesized at high temperature(550℃,600℃)a high polymerization degree.(Ⅲ)The intercalation effect of formic acid molecules in the carbon nitride bulk phase was verified by adsorption experiments and photocatalytic hydrogen production experiments.Via TG,FT-IR,XRD,and EIS,it is found that formic acid has a high degree of diffusion in low polymeric carbon nitride,and large spacing between layers,which is beneficial to the formic acid intercalation in cross-plane to consume photogenerated holes;meanwhile,the formic acid intercalation can reduce the distance between the layers,enhance the electrical conductivity,and thus enhance the photocatalytic hydrogen production capacity.The oligomer carbon nitride U-PCN-480 has better photocatalytic hydrogen production performance in formic acid system,reaching 421 μmol/h,and the apparent quantum efficiency of 74.1%at 385 nm;high polymeric carbon nitride,the degree of diffusion is low.By comparing with the experiment of triethanolamine intercalation and photocatalytic hydrogen production,the intercalation effect of the molecular volume of reactants and the polymerization degree of carbon nitride is explored.