Preparation,Modification And Photocatalytic Activities Of G-C₃N₄ Photocatalytic Materials

Since the beginning of 21st century,the majortwo problemsof energy shortage and environment pollution havebecome more and more seriousall around the world.Solar energy asaresource-rich andclean energy hasattracted tremendousattention.Semiconductor photocatalysis using solar energy to drive the photocatalytic reaction,such as photocatalytic pollutantdecomposition,photocatalytic water splitting and photocatalytic CO₂ reduction,is regarded as a long-term solution to address the globalenergy shortage and environmental problems.As a newly developedorganic semiconductor,g-C₃N₄has been applied in a variety of photocatalytic reactionsowing to its abundant raw materials,high physicochemical stability and nontoxic properties.However,pure g-C₃N₄hasshortcomings oflow surface area,low crystallinity and high electron-hole recombination efficiency,which greatly limitedit's applications in photocatalysis.In this thesis,surface modification and doping treatmentare employed topromote the photocatalytic performance of g-C₃N₄.The main contents are as follows:Firstly,in order to promote the CO₂ adsorption of g-C₃N₄ to improve its CO₂conversion efficiencyin CO₂ photoreduction reaction,amine-functionalizedg-C₃N₄was prepared through a facile oil-bath treatment.First,g-C₃N₄was prepared via simply polymerizing theinexpensiveurea at 500?C for 2 h.Then the synthesized g-C₃N₄ was modified with monoethanolamine?MEA?solution in an oil bath to obtain the amine-functionalizedg-C₃N₄.X-ray diffraction analysis?XRD?,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?,UV-vis diffuse reflectance spectroscopy?DRS?,N₂ adsorption-desorption,CO₂ adsorption test and Zeta-potential measurementwere usedto characterize a series of properties of the samples.It was found that after aminefunctionalization of g-C₃N₄,the surface charges of the samples changed which further resulted in enhanced CO₂ adsorption.Cosequently,the amine-functionalized g-C₃N₄ has shown improved photocatalytic CO₂ reduction efficiency as compared to the pure g-C₃N₄.This work demonstrates that the amine-functionalization of g-C₃N₄ is aneffective way to enhance the photocatalytic CO₂ reduction efficiency of g-C₃N₄.Secondly,ion doping was applied to suppress the recombination of photoinduced electrons andholes of g-C₃N₄in photocatalytic reactions.In this work,a series of phosphorus-doped g-C₃N₄ samples were prepared via a combined impregnation andcalcinationmethodusingmelamine and sodium tripolyphosphate as the precursors.The characterizations and tests such as XRD,TEM,UV-visDRS,XPS,BET,FTIR,photoluminescence spectra?PL?,photoelectrochemical measurements and simulated solar photocatalytic hydrogen production analysiswere carried out.It was found that a trace amount of phosphorus-doping can dramatically improve the photocatalytic activity.The optimal phosphorus-doped g-C₃N₄sample showed a photocatalytic activity about 2.18 times of pure g-C₃N₄.The doping of phosphorus introduced defects in the inner structure of g-C₃N₄ which can capture the photoinduced electron and promote the separation of photoinduced charge carriers.