Preparation Of G-C₃N₄-based Nanocomposites And Their Performance On Electrochemistry And Catalytic Reduction

Graphite phase carbon nitride（g-C₃N₄）,as a nitrogen-doped carbon material,has many advantages,such as its excellent chemical stability,rich resources,simple synthesis,environmentally friendly,so that we consider it as the multi-functional material to explore.In this thesis,in order to develop and improve the electrochemical and catalytic performance of the composites,g-C₃N₄-based nanocomposites were prepared by simple solid-state reaction.The phase,morphology and specific surface area of the nanocomposites were controlled through element doped,the reaction temperature and the ratio of precursor raw materials.The main content of this thesis was related to the characterization of the morphology and structure of the as-synthesized materials,and their performance,such as electrode materials（supercapacitors,electrocatalytic decomposition of water）and catalysts（catalytic reduction of organic and inorganic pollutants）.The main research contents and conclusions were as follows:（1）Study on the preparation and properties of g-C₃N₄@Ni nanocompositesThree kinds of g-C₃N₄@Ni＿t（t=700,800,and 900℃）core-shell nanocomposites were prepared by a simple solid-state method at different temperatures,and their properties as electrode materials and catalysts were also studied in details.Those results showed that the sample g-C₃N₄@Ni＿700 showed the best electrocatalytic and catalytic activity.The catalyst was used as the electrode material of supercapacitor,at the current density of 1 A/g its specific capacitance can reach 771 F/g.In the electrocatalytic hydrogen evolution reaction,its overpotential is 281 mV and the Tafel Slope is 113 mV/dec at 10 mA/cm² current density.In the process of catalytic reduction of nitrophenol（4-NP）,the discoloration rate of 4-NP is up to100%within 7 min,and the kinetic reaction rate constant(k_app)values is 0.43 min^-1.（2）Study on the preparation and properties of g-C₃N₄@Ni_xS_y nanocompositesFour kinds of g-C₃N₄@Ni_xS_y＿t（t=500,600,700,and 800℃;x and y represent the number of atoms）nanocomposites were prepared by a simple solid-state method at different temperature,and their properties as electrode materials and catalysts were studied in details.The results showed that the sample g-C₃N₄@Ni₃S₂＿700 showed good electrocatalytic activity in the electrocatalytic hydrogen evolution reaction.The overpotential is 275 mV,and the Tafel Slope is 140 mV/dec at 10 mA/cm² current density.In the process of catalytic reduction of4-NP,the fading rate of 4-NP is up to 100%within 3 min,and the k_app is as high as 1.17 min^-1.At the same time,it also showed good catalytic activity for the degradation of organic pollutants and Cr（VI）pollutants.（3）The preparation of g-C₃N₄@Ni S nanocomposite and their catalytic reduction of organic（inorganic）pollutantsFour kinds of g-C₃N₄＿x@Ni S（x represents the molar mass of melamine in the raw material）nanocomposites were prepared by a simple solid-state method at 600℃,and their properties as catalysts for the reduction of organic（inorganic）pollutants were studied in details.The results showed that the sample g-C₃N₄＿10@Ni S showed the best catalytic activity.In the process of catalytic reduction of 4-NP by the sample,the reduction rate of 4-NP is up to100%within 4 min,and the k_app is 0.85 min^-1.After six cycle stability tests,the k_appof the catalyst remained 96%in the sixth circle.In addition,it also presents high catalytic reduction activity for nitrophenols,azo dyes and Cr（VI）pollutants.