Controllable Doping Of Non-metallic Elements And Morphologic Regulation In Graphite Phase Carbon Nitride ?g-C₃N₄ ?

Recently,energy crises and environmental pollution have received increasing attention.Semiconductor photocatalysis technology has become one of the most attractive research fields for removing organic pollutants and converting solar energy.Metal-free photocatalyst,graphitic carbon nitride?g-C₃N₄?has attracted wide interest in the production of hydrogen by photolysis of water,photodegradation of organic pollutants,organic synthesis under visible light and photocatalytic reduction of CO₂.G-C₃N₄ has unique electronic structure,good physicochemical stability and suitable band gap?².7 eV?.However,g-C₃N₄ also has some disadvantages such as low visible light utilization efficiency,small specific surface area,and rapid recombination of photogenerated electron-hole pairs.To promote this photocatalyst,many researchers have begun to adopt many strategies,such as heteroatom doping,introduction of porosities,fabrication of nano-structuresand construction of heterojunctions with other semiconductors,etc.This dissertation optimizes the electronic structure and properties of g-C₃N₄ by doping with multi-component non-metallic elements in g-C₃N₄ and controlling its morphology.In addition,we use SEM,TEM,EDS,XRD,FTIR,UV-vis,PL,XPS to determine the morphology,structure and properties of the material,and by degrading Rhodamine B?RhB?and other organic dyes and antibiotics.The catalytic activity as well as its stability and general applicability were tested.Related work is as follows:1.S and B atoms were successfully introduced into the g-C₃N₄ framework by co-thermal polymerization of melamine with the S and B precursors.The prepared S,B co-doped carbon nitride?SBCN?material has an ultra-thin sheet-like morphology and these doped heteroatoms are evenly distributed in the sample.Compared to the original g-C₃N₄,SBCN reduces the band gap,enhances conductivity and promotes the separation of photogenerated electron-hole pairs.SBCN materials have excellent photocatalytic properties and good stability and reusability in photocatalytic degradation of organic dyes.In addition,we propose a possible photocatalytic mechanism for SBCN based on the energy band structure characteristics of the material and the experimental result of trapping active species.2.We prepared P,S co-doped g-C₃N₄ nanosheets?PSCNNS?by thermal polymerization of meilamine,and the P and S precursors with the assistance of NH₄Cl chemical blowing.Ammonium chloride is used as a blowing preparation to decompose at high temperature to form hydrogen chloride and ammonia,which would limit the polymerization of precursors and the ordered stacking of layers to obtain ultra-thin PSCNNS nanosheets.The obtained PSCNNS material enhances absorption in the visible region and the separation and transportation efficiency of photogenerated charges.Compared with the original,P or S doped and P,S co-doped g-C₃N₄ materials,the synergistic effect of element co-doping and nanosheet morphology makes PSCNNS have significant photocatalytic degradation performance of organic pollutants.In addition,the PSCNNS material has excellent photocatalytic stability and reusability.A possible photocatalytic mechanism was proposed based on the band structure and capture experiments of active species.3.Boron-phosphorus co-doped graphite carbon nitride?BPCN?was prepared by thermal polymerization of a precursor of a boron source and a phosphorus source.It was further transformed to BPCN nanosheets?BPCNNS?by thermal oxidation method.The introduction of B and P atoms can significantly change the electronic structure of g-C₃N₄ and enlarge its absorption spectrum in visible region.The nanosheet morphology provides ultrathin thickness,large surface area and short diffusion distance of charges.The synergistic effect of these two factors promotes the separation of photogenerated charges,therefore resulting in its much better photocatalytic performance for removing RhB and terramycin than g-C₃N₄,single-element doped g-C₃N₄ and co-doped g-C₃N₄.Meanwhile,BPCNNS showed good stability in photocatalytic degradation of RhB and terramycin.