Synthesis Of Graphitic Carbon Nitride And Hierarchical Porous N-Doped Carbon Submicrospheres By Molten Salt Synthesis

Nitrogen-rich carbon materials have attracted considerable attention in the scientific community owing to its tunable structure and excellent properties.They possess great application prospects in many fields,such as electronics,optics,biomedicine,sensor,catalysis and energy storage.Controlling the microstructure of nitrogen-rich carbon materials is one of the common methods to optimize their properties.Molten salt synthesis method is a green and efficient preparation technique of inorganic material powders.Molten salt can provide a liquid reaction medium and be acted as a template,which is beneficial to the diffusion of reactants and acceleration of reactions.Moreover,the addition of salt powders can lower the reaction temperature,decrease the reaction time,and facilitate the formation of final product with special nanostructures.In this thesis,carbon nitride,sulfur-doped carbon,and hierarchical porous nitrogen-doped carbon microsphere were prepared via molten salt method respectively using dicyandiamide,melamine or diaminomalonitrile as nitrogen and carbon sources.The procedure parameters and the properties of the products were studied.The results showed that:?1?Irregular rod and granular carbon nitride powders were prepared at 500°C for3 h via the molten salt method using melamine as raw material and LiBr-KCl as molten salt medium.The photocatalytic degradation rate for methylene blue of as-prepared carbon nitride was more than twice as high as that of bulk carbon nitride.Carbon nitride nanosheets were prepared by a molten salt method using dicyandiamide as raw material and LiBr-KCl as molten salt medium with 3 h firing at 500°C.The photocatalytic degradation rate of as-prepared carbon nitride nanosheets was about four times higher than that of bulk carbon nitride.In addition,as-prepared carbon nitride nanosheets also had an excellent activity of visible-light photocatalytic reduction of CO₂ to CH₄.?2?Sulfur doped carbon nitride were prepared by a molten salt method respectively using dicyandiamide as raw material,thiocyanuric acid as a sulfur source?the mass ratio of thiocyanic acid to dicyandiamide was 5 wt%?,and LiBr-KCl as molten salt medium with 3 h firing at 500°C.The photocatalytic degradation rate for methylene blue of as-prepared sulfur doped carbon nitride was about 10 times as high as that of bulk carbon nitride.?3?The hierarchical porous nitrogen-doped carbon submicrosphere?HPNC?was synthesized by using the diamino-malayonitrile as the precursor and ZnCl₂-KCl as the molten salt medium.The specific surface area of the HPNC7 sample prepared with 7.1wt%FeCl₃·6H₂O as a catalyst was the highest?3155 m²/g?,wherein the micropore surface area was 808 m²/g,and the pore specific surface area was 2347 m²/g.As-prepared HPNC7 samples had excellent super capacitor performance,which showed outstanding specific capacitance up to 455 F/g in 6 M KOH electrolyte solution at a current density of 0.5 A/g,and a considerably high energy density of 93.6Wh/kg and high capacitance retention of 95%after 5000 cycles were obtained for the sample.Moreover,they exhibited high adsorption preformances for dyes?methylene blue and methyl orange?and CO₂.