Modified G-C₃N₄ And Its Photocatalytic Performance Towards H₂O₂ Production

As a mild,clean oxidant,Hydrogen peroxide（H₂O₂）is widely used in bleaching,wastewater purification,medical treatment,chemical synthesis.Photocatalytic production of H₂O₂is a green,sustainable and inexpensive process,using water and gaseous molecular oxygen as raw materials.Graphite-like carbon nitride（CN）,a typical polymer semiconductor photocatalyst possesses the advantages of suitable visible light absorption band gap,environmental friendliness,good thermochemical stability and easy preparation.However,the fact of high photocarrier recombination rate,weak visible light absorption ability and small specific surface area seriously limits CN application to hydrogen peroxide production.In this thesis,a series of modified CN photocatalysts are obtained through KCl etching,P doping and AQ loading,and the photocatalytic hydrogen peroxide production performance of the modified photocatalysts is evaluated under light.Combining with physical characterization,the main results obtained are summarized as follows:（1）A KCl etched CN（CN-K）photocatalyst is prepared by one-step thermal polymerization using Guanidine hydrochloride as the precursor of CN.The composition,morphology and structure of CN-K are characterized by X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,transmission electron microscopy（TEM）,scanning electron microscope（SEM）and specific surface area analyzer（BET）,and its photocatalytic performance of synthesis H₂O₂is investigated.The results display that the surface of CN-K shows obvious porous structure which causes the increasing specific surface area;the introduction of K⁺in the crystal lattice of CN enhances the charge conduction efficiency and inhibits the recombination of photogenerated carriers;the strong electron-absorbing cyano group is introduced on the triazine ring,which reduces the band gap of CN and increases the absorption capacity of visible light.CN-K exposured under light for 3 h,H₂O₂production rate is up to 1.27 mmol/g/h,which is 5.8 times as high as that of CN,meanwhile CN-K possesses good photocatalytic stability.（2）A KCl etched P-doped CN photocatalyst（PCN-K）is synthesized by synchronous thermal polymerization which Hexachlorotripolyphosphazene is used as phosphorus source and Guanidine hydrochloride as CN precursor,combining with KCl etching.The composition,structure and morphology of PCN-K are characterized by XRD,FT-IR,XPS,TEM,SEM and BET,and its photocatalytic performance of synthesis H₂O₂is studied.The results show that P atom replaces C atom in CN triazine ring,which further reduces the band gap and effectively enhances the visible light absorption capacity of PCN-K;Doping P element promotes the adsorption and activation of O₂on PCN-K surface and accelerates the reaction of O₂reduction to H₂O₂.PCN-K irradiated under light for 3 h,H₂O₂production rate reaches 2.25 mmol/g/h,which is 10.2 and 1.7 times as high as that of CN and CN-K15,respectively,and PCN-K maintains good photocatalytic stability.（3）An Anthraquinone（AQ）loaded CN photocatalyst composite（PCN-K/AQ）is prepared by adsorption method using PCN-K as carrier.The composition,structure and morphology of PCN-K/AQ are characterized by XRD,FT-IR,XPS,TEM,SEM and BET,and the effects of different AQ loading on the photocatalytic synthesis of H₂O₂are studied.The results show that AQ loading further reduces the recombination probability of PCN-K photogenerated carriers and improves the selectivity of O₂photocatalytic reduction.The rate of photocatalytic synthesis of H₂O₂by PCN-K/AQ is as high as 4.73 mmol/g/h,which is 21.5 times higher than that of the intrinsic CN.