Preparation Of Porous Carbon Nitride With Tunable Band Structure Structure And Study On Its Photocatalytic Performance

Photocatalyst technology can convert low-density solar energy into high-density chemical energy,which is an effective way to use solar energy to alleviate the energy crisis and solve environmental problems.Graphitic carbon nitride（g-C₃N₄）is a non-metallic semiconductor photocatalyst,which has the advantages of narrow band gap,high chemical and thermal stability,cheap and easy availability of raw materials,non-toxicity and simple preparation.However,the bulk g-C₃N₄ has the defects of small specific surface area,high photogenerated carrier recombination rate and low solar energy utilization rate,resulting in poor photocatalytic activity.The purpose of this paper is to prepare high-efficiency,stable and tunable energy band of modified g-C₃N₄ photocatalyst through a series of modification methods,and apply it to the fields of photocatalytic degradation of organic pollutants and photocatalytic organic synthesis.The main research contents of the paper are as follows:（1）In this work,a melamine derivative（2,4-diamino-6-phenoxy-[1,3,5]-triazine,MA-phO）was synthesized and used as a new doping molecule to prepare the modified carbon nitride materials by a facile supramolecular self-assembly method with melamine and cyanuric acid.The addition of the doping molecule MA-phO made the modified carbon nitride materials more favorable for forming nanostructure and increasing the specific surface areas.In addition,it also could promote the separation of photogenerated electron-hole pairs,and regulate the energy band structure of the modified carbon nitride materials.When the doping amount reached 0.5%,the prepared sample had the best photocatalytic activity for the organic pollutants.Finally,the mechanism of photocatalytic degradation of rhodamine B was analyzed.（2）Based on the previous work,a small amount of iron oxide was introduced to construct a carbon nitride/iron oxide heterojunction photocatalyst to further regulate the energy band structure.The chemical structure,morphology,and optoelectronic properties of the heterojunction photocatalyst were analyzed by various characterization methods.The carbon nitride/iron oxide Z-Scheme photocatalytic system was applied to the selective oxidation of amine to imine for the first time.The enhanced photocatalytic activity of the modified carbon nitride materials can be attributed to the enhancement of visible light absorption and the photo-generated carrier separation rate,and the Z-Scheme charge transfer mechanism also retains the strong redox ability of the composites.Finally,the mechanism of photocatalytic oxidation coupling reaction of benzylamine was analyzed.（3）The enhancement of g-C₃N₄ photocatalytic degradation of methyl orange（MO）via ethylenediaminetetraacetic acid（EDTA）addition was investigated.The effects of H⁺and carboxylate anions on the MO degradation were investigated in this reaction.An investigation by UV–vis diffuse reflectance spectroscopy（UV-vis DRS）reveals that the addition of EDTA has not changed the electronic structure and photoelectric property of g-C₃N₄.It was considered that the addition of EDTA trapped the holes and promoted the separation rate of the electron-hole pairs,resulting in an increase in photodegradation activity.It was verified that superoxide radical is the major oxide species during photocatalytic degradation process.Therefore,a plausible mechanism that EDTA promotes photodegradation of MO by g-C₃N₄ is proposed.