Study On The Photocatalytic Performance Of Pt Modified Carbon Nitride With Low Polymeric Hierarchical Pores

Conversion of solar energy into high-efficiency and clean hydrogen fuel via semiconductor photocatalytic water splitting has always been considered as one of the effective ways to cope with the shortage of traditional energy.PCN（polymeric carbon nitride）is widely used in the field of photocatalytic hydrogen production due to its simple preparation process,suitable band structure and good stability.However,traditional PCN has disadvantages,such as poor light absorption and high recombination rate of photo-generated carrier.These factors cause the overall photocatalytic reaction efficiency to be generally low,so enhance light absorption and accelerate the separation efficiency of photogenerated carriers are very important.In a photocatalytic reaction system,the co-catalyst is also significant,and maximize the utilization rate of the co-catalyst is also an urgent issue.In order to solve the above problems,in this thesis U-PCN with low polymeric hierarchical pore structure was synthesized by a template-free pyrolysis method of needle-shaped urea,which enhances light absorption and accelerates the diffusion rate of formic acid into its interior.As a result,the in-situ removal of the holes in the U-PCN allows the electrons to easily diffuse to the surface of the photocatalyst to react with other reactants,thereby greatly improving the separation efficiency of photogenerated carriers.In order to improve the performance of hydrogen evolution,Pt nanoparticles and Pt atoms were loaded on PCN by different methods.The main research content of this thesis includes the following three parts:（I）U-PCN-T（T is 450℃,480℃,550℃,600℃）is prepared by a simple one-step pyrolysis method using needle-like urea,then volume insertion behavior and light absorption performance of these materials were investigated.The hierarchical pore structure（U-PCN-480）can not only enhance absorption intensity,also greatly improves the degree of volume insertion and diffusion rate of formic acid.（Ⅱ）Pt/U-PCN-480 shows the best photocatalytic hydrogen evolution activity in formic acid system(379μmol h^-1),the AQE（apparent quantum efficiency）of Pt/U-PCN-480 can reach 70.4%when the incident light wavelength is 380 nm and the light intensity is 30 m W cm^-2.The higher reaction efficiency of Pt/U-PCN-480 in the formic acid system is due to the cooperation of volume photocatalysis and enhanced light absorption.However,volume photocatalysis is even more significant.（Ⅲ）In order to improve the utilization rate of Pt and maintain high-efficiency photocatalytic performance,the single-atom catalyst Pt _SA/U-PCN-480 was prepared by rapid photoreduction（in seconds）.The Pt loading on U-PCN-480 is only 0.16 wt%,which is 6.25 times lower than the Pt loading（1.0 wt%）on U-PCN-480 prepared by chemical reduction.However,the activity of Pt _SA/U-PCN-480(369μmol h^-1)is close to Pt/U-PCN-480(379μmol h^-1).