Preparation And Properties Of Carbon Nitride Composite Photocatalyst

The environmental pollution and energy crisis have become the two major problems that human beings need to solve at present with the progress and development of society.The development of new energy sources and the research of new catalyst materials have become new goals for researchers.Graphitic carbon nitride（g-C₃N₄）,a metal-free organic polymer semiconductor material,with appealing electronic band structure,excellent thermal stability,physicochemical stability and resistance to acid and alkali corrosion.The preparation methods are simple and diverse.The characteristics have attracted the attention of many researchers and shined in the field of photocatalysis.However,the application of g-C₃N₄ is limited because of its low specific surface area and high recombination efficiency of photo-generated electron-hole pairs.Therefore,the research on the modification of g-C₃N₄ is imminent:regulating the morphology of g-C₃N₄,increasing its specific surface area,and the number of active sites for photocatalytic reactions;doping metal and non-metal elements,forming heterojunctions with other new materials to increase the electron transfer rate and inhibit the recombination of photogenerated electron-hole pairs.These are the means to improve the photocatalytic ability of g-C₃N₄ effectively.This dissertation focuses on the preparation and photocatalytic performance of carbon nitride-based composite photocatalysts.The specific contents are as follows:1.In-situ P-doped g-C₃N₄（P-CN）is prepared by one-step method using diammonium hydrogen phosphate（（NH₄）₂HPO₄）and urea（CO（NH₂）₂）.Then the CdS/P-CN composite photocatalyst shows high photocatalytic activity under visible light,which is prepared by hydrothermal method with P-CN,acetamide（TAA）and cadmium acetate（Cd（CH₃COO）₂）as raw materials.When the doping amount of phosphorus is 3%and the loading amount of CdS is 45%,the degradation rate of rhodamine B（Rh B）reaches 90%in 20 minutes.The CdS/P-CN composite photocatalyst exhibits excellent cycle stability by the result of cycle test.The enhancement of photocatalytic properties was attribute to the doping of P and forming heterojunction which improve the position of valence band and restrain the recombination rate of photogenerated electron-hole pairs.In order to explore the role of different reactive groups in the photocatalytic reaction,the corresponding free radical scavengers are added into the catalytic system.The results prove that·O₂-free radicals play the most important role in the photocatalytic degradation process.2.g-C₃N₄ is prepared by thermal polymerization method using urea as a precursor.Ni₅P₄/g-C₃N₄ composite photocatalyst is synthesized by simple calcination method using g-C₃N₄,red phosphorus（P）,and nickel chloride（NiCl₂）as raw materials.Ni₅P₄/g-C₃N₄ shows high photocatalytic degradation activity,hydrogen production ability and excellent cycle stability.The 3%wt Ni₅P₄/g-C₃N₄ demonstrates the highest photocatalytic activity.The degradation rate of Rh B reaches 95%in 25 minutes,and the hydrogen production efficiency is 1013.88μmol g^-1 h^-1.The EIS test is performed by an electrochemical workstation.The results indicate that the surface resistance of the nanocomposites is low,and a fast channel for electrons transport is formed at the hetero interface,which proves that the charge separation efficiency is effectively improved.In the reaction process of this photocatalytic system,·O₂-free radicals play the most important role.