The Controllable Preparation Of Carbon Fiber Supported Graphite Carbon Nitride Based Nanocomposite Catalytic Materials

Graphite carbon nitride（g-C₃N₄）is a metal free material,which comprises two dimensional layered structure,stable physical and chemical properties,low prices and easy preparation,so g-C₃N₄shows a good application prospect in catalysis,sensing,energy storage and other fields.In particular,g-C₃N₄,as a typical n-type semiconductor,has advantages in suitable band gap and visible-light absorption and intrinsic defects of uncondensated amino groups at the edge which can be used as a solid base to absorb and activate CO₂,and hence,the g-C₃N₄ has been widely used in the field of photocatalysis（photocatalytic hydrogen evolution,ect）and organic catalysis（CO₂cyclioaddition,ect）.However,the bulk g-C₃N₄prepared by traditional technology has some drawbacks,such as easy agglomeration,low specific surface area,high recombination rate of photogenerated charges,weak basicity,easy loss and difficult recovery.Based on the above problems,it is necessary to improve the catalytic activity of g-C₃N₄by introducing cocatalysts whose energy band and functional groups match that of carbon nitride.In this study,based on the traditional thermal polycondensation method to prepare g-C₃N₄,carbon nanofibers were applied as a carrier to synthesize the material that g-C₃N₄supported carbon fibers,and then Co,Bi metal cocatalysts were loaded to form a series of heterogeneous photocatalysts and thermal catalysts,which were used in the photocatalytic hydrogen evolution from water and CO₂cycloaddition reaction,showing good activity.The main contents of the paper are as follows:（1）One-dimensional carbon fibers（CNFs）obtained by electrospinning and high temperature calcination were used as the support carrier,and then Co₃O₄@g-C₃N₄/CNFs composite photocatalyst were prepared by vapor deposition,hydrothermal and roasting technology.The catalysts were analyzed by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and so on,and the results showed that g-C₃N₄and Co₃O₄were wrapped on the surface of CNFs,and CNFs acted as a support to disperse the active components.Meanwhile,the energy bands of g-C₃N₄and Co₃O₄had the potential difference,and the p-n structure formed at the interface between g-C₃N₄and Co₃O₄improved the separation ability of photoelectrons and holes.In the experiment of photocatalytic hydrogen evolution from water,the H₂production rate of Co₃O₄modified g-C₃N₄catalyst with the best performance was 67.17μmol g^-1h^-1under a UV-visible light,which was higher than that of single g-C₃N₄/CNFs(49.67μmol g^-1h^-1).In addition,the H₂evolution performance of the catalyst remained stable after five cycles.（2）A acid-base bifunctional heterogeneous catalyst with novel the morphology and structure was constructed by a simple one-pot composite method.One-dimensional multi-channel carbon fibers（CNFs）obtained by electrospinning and high temperature calcination technology were used as the support carrier,and then through the vapor deposition method,the heterogeneous catalyst BiCl₃@Bi@g-C₃N₄/CNFs that is rich in acid base sites were synthesized by taking advantage of the similar sublimation temperature of melamine and bismuth chloride.The results showed that g-C₃N₄can be successfully wrapped on the surface of CNFs,and Bi,BiCl₃have a dot linear structure.Furthermore,CNFs could contribute to the dispersion of the active components,and the channels of CNFs restricted the growth direction of Bi and BiCl₃and make them distribute linearly along the channels direction.The composite had high conversion and selectivity for CO₂cycloaddition reaction,and the conversion was 98.3%after five cycles.In conclusion,one-dimensional carbon nanofibers were introduced to stabilize and disperse the active materials,and to solve the problem that the powder catalytic materials were easy to be lost during use,in which the cost and time of recovery was saved,and the construction of these composite catalysts provided a new way for the design of active species fixation and multi-functional heterogeneous catalysts.