Several Preparations Of Graphitic Carbon Nitride-based Photocatalytic And Reserch For Photocatalytic Hydrogen Production

Hydrogen energy with the advantage of high calorific value,no pollution from combustion products,and various utilization forms produced by photocatalytic technology can not only greatly reduce the dependence on fossil fuels but also effectively deal with the predicament of energy shortage.Photocatalyst plays an important role in the process of photocatalytic hydrogen production.It was found out that non-metallic semiconductor graphitic carbon nitride（g-C₃N₄）has become a promising material due to the advantages of the suitable band gap,visible light response,excellent stability,and non-toxicity.However,the poor separation of photo-generated carriers and hardly response of near-infrared light hinder its further application.In this research,three kinds of g-C₃N₄-based composites were prepared for photocatalytic hydrogen production through the strategies of element doping and heterostructure construction of bulk g-C₃N₄.The specific research contents can be summarized as follows:1.Firstly,the specific surface area of bulk g-C₃N₄ was increased owning to the formation of nanosheet by high-temperature thermal polymerization.Subsequently,0D/2D Co₉S₈/g-C₃N₄ composite photocatalysts were prepared by loading Co₉S₈nanoparticles on g-C₃N₄ nanosheets through self-assembly method,which is verified by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,and high resolution transmission electron microscope（HRTEM）tests.Underλ>420 nm visible light irradiation,the photocatalyst shows enduring stability and 11.5 times higher hydrogen production activity than the bulk g-C₃N₄.The results of photoluminescence（PL）,time-resolved photoluminescence spectra（TRPL）,and electrochemical characterization show that the composite photocatalyst has a fast rate of migration.This work provides a new choice for the preparation of g-C₃N₄-based composite photocatalyst with excellent hydrogen production performance.2.To improve the conductivity of g-C₃N₄,we synthesized carbon self-doped g-C₃N₄（CCN）with highπdelocalization ability.In addition,the carbon self-doping method not only broadens the optical response of g-C₃N₄ but also avoids the formation of a new recombination center caused by the introduction of foreign heteroatoms into the g-C₃N₄ skeleton.Subsequently,Co₉S₈ nanoparticles with high conduction band were introduced into CCN to formation the composite photocatalyst Co₉S₈/CCN（CSCCN）with an excellent hydrogen production performance.Finally,we propose the possible mechanism of photocatalytic hydrogen production based on a series of test results.3.Considering that bulk g-C₃N₄ is difficult to utilize near-infrared light in the solar spectrum,we introduced Cu_7.2S₄ nanoparticles which are easily excited by near-infrared light into the surface of g-C₃N₄ nanosheet through in situ grown technology to construct the composite photocatalyst Cu_7.2S₄/g-C₃N₄ with the response of near-infrared light.Underλ>800 nm near-infrared light irradiation,it exhibits a remarkable hydrogen production rate of 82μmol g^-1 h^-1 which is better than most of the reported g-C₃N₄-based near-infrared composite photocatalysts.The excellent photocatalytic performance is linked to the extended optical absorption as well as the efficient separation efficiency of photoinduced carriers,which are evidenced by the UV-visible absorption spectroscopy and photoelectrochemical test.The electron transfer path was verified by in-situ photo-deposition experiments and the corresponding mechanism of near-infrared photocatalysis was proposed.The successful construction of this system provides a new approach for constructing a g-C₃N₄-based photocatalytic system for the transformation of near-infrared solar energy into hydrogen.