Preparation And Photocatalytic Activity Of Doped Graphitic Carbon Nitride

With the rapid development of industrial society,energy shortages and environmental pollution have become global problems that human beings urgently need to solve.Graphitic carbon nitride?g-C₃N₄?is a novel semiconductor photocatalyst that responds to visible light.It can effectively utilize solar energy photocatalytic degradation of organic pollutants in the environment,photocatalytic splitting water to prepare H₂,photocatalytic reduction CO₂ and photocatalytic sterilization.However,the inherent disadvantages of the original g-C₃N₄,such as low specific surface area,insufficient absorption of visible light,and high recombination rate of photogenerated electrons and holes,limit its practical application.In recent years,it has become a research hotspot to improve the photocatalytic activity of g-C₃N₄ by various strategies such as noble metal deposition,metal/nonmetal doping,and coupling heterojunction,etc.According to the above research background,this paper has studied in doped-g-C₃N₄.First,co-doping was research direction to prepare Na,Cl co-doped g-C₃N₄.Second,a small amount of Ag atoms were deposited on the basis of Na-doped g-C₃N₄with doping and noble metal modification as research direction.Third,the transition metal doping was used as research direction to prepare Mo doped g-C₃N₄.Fourth,cyano-modified g-C₃N₄ was prepared with non-metallic doping as research direction.The activity of the photocatalyst was evaluated by photocatalytic degradation experiment using dye rhodamine B?RhB?and antibiotic tetracycline hydrochloride?TC-HCl?as probe molecules.The specific content as follows:1.CN-NaCl-x was prepared by in-situ doping with dicyandiamide as precursor and sodium chloride as dopant.The crystal structure,surface chemical composition and morphology of the photocatalyst were characterized by X-ray diffraction?XRD?spectrum,X-ray photoelectron spectroscopy?XPS?,transmission electron microscopy?TEM?and high resolution transmission electron microscope?HRTEM?,respectively.The optical properties of the samples were characterized by UV-visible diffuse reflectance spectroscopy?UV-Vis DRS?and fluorescence spectroscopy?PL?.The photocurrent response,electrochemical impedance?EIS?and mott-schottky?MS?spectra were obtained by electrochemical experiments,further investigated the photocatalytic activity of g-C₃N₄ and obtained the band gap parameters of the photocatalyst.The results show that Na and Cl ions were successfully introduced into the g-C₃N₄ crystal.The photocatalytic activity of the prepared CN-NaCl-0.5photocatalyst was twice that of the g-C₃N₄.The RhB of 40 mL(the concentraion was 10mg L^-1)was degraded by 40 mg photocatalyst under visible light irradiation,and the degradation rate was 97.5%at 50 min.At the same ratio,the degradation rate of TC-HCl at a concentration of 10 mg L^-1 at 60 min was 70.0%.After 5 rounds of cycling experiments,the degradation rate of RhB was still 95%.On the basis of the above studies,active species capture experiments were carried out on CN-NaCl-0.5 to explore the photocatalytic mechanism.2.Melamine as the precursor,sodium sulfate as dopant,and trace of monoatomic Ag was deposited to prepare Agx-CN-Na₂SO₄.The RhB of 50 mL(the concentraion was 10 mg L^-1)was degraded by 25 mg photocatalyst under visible light irradiation,and the degradation rate was 96.5%at 50 min.At the same ratio,the degradation rate of TC-HCl(the concentraion was 10 mg L^-1)at 60 min was 70.0%.The morphology,crystal structure and surface chemical structure of the photocatalyst were characterized by HRTEM,XRD and XPS,respectively.The results show that Na⁺was successfully doped into the lattice of g-C₃N₄,and Ag atoms were successfully deposited on the surface of g-C₃N₄.The optical properties of the samples were characterized by UV-Vis DRS and PL spectroscopy.Photocurrent response,EIS and MS spectrum were obtained by electrochemical experiments to further investigat the photocatalytic activity of g-C₃N₄ and obtained the band gap parameters of the photocatalyst.The photocatalytic capture experiment of photocatalyst was also carried out,and the photocatalytic mechanism was explored.3.The Mo doped g-C₃N₄ was prepared by one-step thermal polycondensation method used dicyandiamide as the precursor and phosphomolybdic acid as the dopant.The RhB of 40 mL(the concentraion was 10 mg L^-1)was degraded by 20 mg optimum catalyst 0.25%Mo-CN under visible light irradiation,and the degradation rate was99.7%at 40 min.At the same ratio,the degradation rate of TC-HCl(20 mg L^-1)at 40min was 61.7%.After 5 cycles of cycling,the degradation rate of RhB still reached99.0%.Characterization by XPS confirmed that Mo⁶⁺was successfully incorporated into the bridged N atom of g-C₃N₄.Characterization by UV-Vis DRS and PL spectra confirmed that the optical absorption capacity of the sample was significantly enhanced,and the recombination rate of photogenerated electrons and holes was significantly reduced.The photoelectrochemical properties and band gap parameters were further investigated by electrochemical characterization?photocurrent response,EIS,MS?.Simultaneously,the active species capture experiment of optimum catalyst0.25%Mo-CN was carried out to explore the photocatalytic mechanism of photocatalyst.4.The preparation of CN-A-100 modified with cyano groups?-C?N?used thiourea as the precursor and aniline as the dopant.The RhB of 40 mL(the concentraion was 10 mg L^-1)was degraded by 40 mg optimum photocatalyst CN-A-100 under visible light irradiation,and the degradation rate was 99.0%at 40 min.At the same ratio,the degradation rate of TC-HCl(20 mg L^-1)at 60 min was 77.0%.After 5 cycles of cycling,the degradation rate of RhB still reached 98.3%.The characterization of the samples by XPS,FTIR show that cyano groups?-C?N?was successfully introduced into g-C₃N₄.The optical properties of the photocatalyst were characterized by UV-Vis DRS and PL spectroscopy.The results show that the absorption boundary of the samplse was red-shifted,and the recombination rate of photogenerated electrons and holes was significantly reduced.Electrochemical characterization?photocurrent response,EIS,MS?further investigated the photocatalytic activity and obtained the bandgap parameters.Simultaneously,the active species of the optimum photocatalyst CN-A-100 was captured to explore the photocatalytic mechanism of the photocatalyst.Through the research of the above four parts,the effect of doping strategy on the photocatalytic activity of g-C₃N₄ was explored from various angles.The results show that the doped g-C₃N₄ can be successfully prepared by using cheap and environment-friendly precursor materials and dopants,as well as a simple one-step thermal condensation preparation method,and the photocatalytic activity of g-C₃N₄ can be significantly enhanced,which lays a foundation for promoting the practical application of g-C₃N₄ in photocatalytic degradation of organic pollutants.