Structural Modification Of Graphitic Carbon Nitride And Study On The Photocatalytic H₂ Production Performance

After the industrial revolution,fossil fuel becomes the main energy source of people production and living.However,there are many problems for the Earth environment and human society in the course of fossil fuel mass use,such as climate extremes,energy wars between countries and so on.Hydrogen energy,as a kind of new energy with zero-carbon and wide application area,has been regarded as a promising candidate to replace the fossil energy.Among various hydrogen production technologies,photocatalytic hydrogen evolution technology gets more and more attention because it can transform the low energy density solar to hydrogen energy,which possesses the cheaper cost,non-pollution and so on merits.The key problem of photocatalytic hydrogen production technology is the preparation of high property photocatalyst.Recently,graphitic carbon nitride（g-C₃N₄）attracted more and more attention due to its easy preparation,superior photocatalytic activity and so on merits.However,the photocatalytic property of pristine g-C₃N₄ is still limited because of its narrowed light absorption range,small specific surface area and easily recombination of photoelectron-hole.Thus,the pristine g-C₃N₄ is far from to meet the requirements of practical application.In this paper,multiple methods are adopted to regulate g-C₃N₄ structure,including defects construction,heteroatom doping,heterocycle introduction and crystallinity regulation.Furthermore,the influence on photo response property,carrier separation ability and other properties of g-C₃N₄ are investigated when g-C₃N₄ structure changed.And the deep mechanism also is revealed for the enhanced photocatalytic hydrogen evolution activity of different g-C₃N₄structure.The specific research contents are as follow.1.A nitrogen and sulfur deficient sulfur doped g-C₃N₄ photocatalyst（SCND-x）is synthesized by a simple copolymerization approach.Double defects constructed and sulfur doped exhibit good synergy to enhance g-C₃N₄ photocatalytic hydrogen evolution activity.Construction nitrogen and sulfur defects further broad the light response range and promote the carrier separation of sulfur doped g-C₃N₄.This small molecule copolymerization approach makes SCND-3 form a thinner layered structure with 40.85 m² g^-1 specific surface area,which is 2.23 times greater than pristine g-C₃N₄.Therefore,SCND-3 shows a good photocatalytic hydrogen evolution activity with a test number up to 70.2μmol h^-1 under visible light irradiation.The apparent quantum efficiency（AQE）at 420 nm is reach to 3.3%.2.A facile template method is developed to obtain the O doped crystalline/amorphous homojunction g-C₃N₄ photocatalyst.There is an apparent temperature difference when different precursors form the highly crystalline g-C₃N₄photocatalyst.The temperature difference is used to accurately regulate the ratio of amorphous and crystalline g-C₃N₄.And this will make the most use of different crystallinity g-C₃N₄ merits.CMCCN-5 preserves the large amount of crystalline g-C₃N₄,which endows CMCCN-5 with highly efficient photocarrier separation ability.Furthermore,the introduction of amorphous g-C₃N₄ enriches the reaction activity sites of CMCCN-5 and promotes the photoinduced carriers to be efficiently used.Although the light absorption with limited broad（λ<460 nm）,the photocatalytic H₂ evolution activity of CMCCN-5 is up to 203.66μmol h^-1,about 86 times greater than pristine g-C₃N₄.The AQE number of CMCCN-5 is up to 26.9%at 420 nm.3.The pyridine ring doped g-C₃N₄ nanosheet with n-p transform photocatalysts（NCNS-x）are obtained crossing a simple co-calcined method.This method well preserves the initial nanosheet structure of g-C₃N₄ at the same time as introducing the pyridine ring.NCNS-7.5 exhibits a 3-4 nm thick nanosheet structure with 41.64 m² g^-1specific surface area,which is 2.36 times greater than pristine g-C₃N₄.The introduction of the pyridine ring also significantly expands the light absorption range and promotes the carrier efficient separation of g-C₃N₄.Furthermore,the g-C₃N₄ semiconductor transfer from n type to p type with the increasement amount of pyridine ring.And the experimental results show that n-type pyridine ring doped with electron as the dominant charge is more suitable for the photocatalytic hydrogen production reaction。...