Preparation Of Carbon/carbon Nitride Based Composite Photocatalysts By Molten Salt Method And Their Photocatalytic Properties

Graphitic carbon nitride（g-C₃N₄）has become a research hotspot in the field of photocatalysis.However,it usually shows moderate activity due to the rich defect in the structure.The defects often act as electron trap sites during the photocatalytic reac tions,thus constructing crystalline carbon nitrides with reduced defect density is considered to be a reasonable way to enhance the photocatalytic activity.Here the molten salt method was developed for the synthesis of carbon nitrides.Previous researches indicate that the use of salt melts results in the change of the carbon nitride building block from tri-s-triazine to s-triazine.And the as-prepared carbon nitride is often called polytriazine imide（PTI）.To achieve higher photocatalytic activities,we combined carbon self-doping with the molten salt method to prepare carbon/carbon nitride based photocatalysts.The main work is as follows:（1）C-PTI binary composite prepared by molten salt method for enhanced photocatalytic performances:The C-PTI binary composite was prepared via a facile and green method by using glucose as the carbon source.In the condensation,glucose could promote nanotube formation,affording the product larger surface areas.Moreover,the carbon self-doping induces an intrinsic change in the electronic structure thus optimizing the band structure and the electronic transport property.Therefore,the as-synthesized C-PTI exhibits remarkably enhanced photocatalytic activities for both hydrogen evolution and tetracycline degradation reactions.（2）C-PTI/ZnO temary composite prepared by molten salt method for enhanced visible-light-driven H₂ evolution:a ternary C-PTI/ZnO（CPZ）photocatalyst was developed via a simple one-step molten salt method.In the obtained CPZ sample,the carbon ring in-plane connects to the triazine ring,leading to the formation of C-PTI nanosheets.The carbon ring incorporation not only efficiently narrows the band gap of PTI,but also shifts its conduction band potential negatively and accelerates the photogenerated electron transport.In addition,ZnO nanoparticles are well dispersed on the C-PTI nanosheets,further promoting the charge carriers transfer and separation.As a result,the CPZ sample presents a photocatalytic H ₂evolution rate up to 52μmol·h^-1 under visible light,which is 60 and 179 times higher than that of C-PTI and PTI,respectively.（3）C/g-C₃N₄ binary composite prepared by post-calcination in molten salts:The C/g-C₃N₄（CNC）binary composites were obtained by the post-calcination of graphene oxide and g-C₃N₄in Li Cl/KCl molten salts.In the as-prepared CNC sample,the graphene is well dispersed on the surface of g-C₃N₄.The incorporation of graphene not only increases the specific surface area,but also improves the absorption of visible light.Moreover,the electron migration in g-C₃N₄is accelerated,and thus the separation efficiency of photogenerated electrons and holes is improved.The photocatalytic hydrogen production rate of the optimal product CNC20 reaches 286μmol·h^-1,which is 1.4 times that of the g-C₃N₄ prepared by post-calcination in molten salt and 44 times that of bulk g-C₃N₄.