Modification And Photocatalytic Properties Of Graphite Phase Carbon Nitride（g-C₃N₄）

With the development and progress of the human society,the extensive use of fossil fuels and the abuse of antibiotics have made the greenhouse effect,energy crisis,and environmental pollution worse.In recent years,photocatalysis has become a research hotspot which is considered to solve or alleviate the above series of problems.Graphite phase carbon nitride（g-C₃N₄）has attracted wide attention due to its visible light response capability,environmental protection,non-toxicity,and low cost.However,g-C₃N₄ has low visible light utilization rate,only has a light response to blue-violet in visible light,and high recombination rate of photo-generated electrons and holes,resulting in poor photocatalytic ability.Increasing the photoresponse range of g-C₃N₄,accelerating the effective transfer and separation of photo-generated electrons are the main research strategies to improve the catalytic activity of g-C₃N₄.Currently,the photocatalytic activity of g-C₃N₄ can be improved by morphology control,element doping and compounding with semiconductors.Our research is focused on the morphology control and semiconductor recombination of g-C₃N₄,which is prepared by thermal polymerization,to promote the photoelectron separation and transfer capabilities and ultimately improve its photocatalytic activity.The main research contents are as follows:（1）The preparation of g-C₃N₄nanoscrolls and its performance in photocatalytic reduction of CO₂ to methyl formateFirst,g-C₃N₄ was prepared by a thermal polymerization method using melamine as a precursor.In accordance with that high temperature could cause the hydrogen bond of g-C₃N₄lamellar bond to break,further thermal peeling was performed by reheating After that,g-C₃N₄was ultrasonically peeled in an isopropanol solution to prepare g-C₃N₄ nanosheets.Freeze-dried,vacuum-dried,and sonicated were applied to induce g-C₃N₄ nanosheets curling into g-C₃N₄nanoscrolls.Photocatalyst morphology,structural characteristics,optical characteristics,photoelectron separation and transfer capabilities were analyzed by field emission scanning electron microscope（SEM）,X-ray diffraction spectrum（XRD）,Fourier infrared spectrum（FT-IR）,X-ray electron energy Spectral analysis（XPS）,specific surface and pore size analysis,UV-Vis DRS,fluorescence spectrometry（PL）,electrochemical impedance spectroscopy（EIS）and photocurrent transient response spectra.In the test for the preparation of methyl formate by photocatalytic reduction of CO₂,the g-C₃N₄ nanoscrolls showed the highest methyl formate conversion(737.3μmol·h^-1·g^-1),which was 1.88 times and 3.35 times that of g-C₃N₄ nanosheets and g-C₃N₄.The mechanism of photocatalytic conversion of CO₂ was analyzed based on characterization and test data.（2）Preparation of N and Ti³⁺doped TiO₂/g-C₃N₄ composite photocatalyst and its photocatalytic degradation of doxycycline hydrochlorideN-doped TiO₂ nanoparticles were prepared by solvothermal method,which used tetrabutyl titanate as the Ti source and urea as N source.After that,N-doped TiO₂ and the same amount of sodium borohydride were fully ground.And the,N and Ti³⁺doped TiO₂ nanoparticles(N-TiO_2-x)were prepared by calcination.The N-TiO_2-x/g-C₃N₄ composite photocatalyst was prepared by a hydrothermal method of N-TiO_2-x and g-C₃N₄.The structural composition,optical characteristics,and separation and transfer characteristics of photo-generated charges of as-prepared photocatalysts were been studied by SEM,energy dispersive X-ray spectroscopy（EDX）,XRD,FT-IR,XPS,Uv-Vis DRs,PL,EIS and photocurrent characterization analysis of transient response spectrum.In the photocatalytic degradation of doxycycline hydrochloride（DH）,the degradation rate constant of DH for N-TiO_2-x/g-C₃N₄ was 0.01977 min^-1,which was 2.06 and 1.47 times that of pure g-C₃N₄ and N-TiO_2-x.Finally,the mechanism of photodegradation of DH was proposed based on semiconductor band theory and valence band spectrum（VXPS）results.