Preparation and Structure-Property Relationship of Carbon Nitride/Narrow Bandgap Semiconductor Nano Composite Photocatalvsts
Author:You Zeng Yu
Supervisor:yang hui shen qian hong
The increasing issues of energy shortage and environmental pollution have been posing potential risks to sustainable development of human society,which are also hot topics in science research.Recent decades,semiconductor photocatalysis has attracted a wide attention for its promising application in environmental purification and energy production.Many remarkable breakthroughs have been made in the field of new systems and new structures of materials.Since the year of 2009 when it has been firstly proposed to be a photocatalyst for hydrogen production from water,graphitic carbon nitride(g-C3N4)has drawn tremendous interest due to its 2D structure,tunable electronic structure,metal-free composition and easy preparation.However,the pure g-C3N4 still suffered from a few drawbacks such as insufficient visible-light absorption and rapid recombination of photo-generated charge carriers,therefore restricting its further utilization.Much work has been performed,such as constructing nano structure,element doping,noble metal deposition and constructing heterojunction between g-C3N4 and other semiconductors,to find high efficient g-C3N4-based photocatalyst.In this paper,we report the preparation of g-C3N4-based heterojunction and the investigation of its nanostructure.The g-C3N4 nanorod/InVO4 hollow sphere composite,core-shell g-C3N4/MCNTs/BiOI nanocomposite,surficial dispersive g-C3N4 nanoparticles/flower-like BiOI and g-C3N4 nanoparticles/porous g-C3N4 were prepared with enhanced separation ability of photo-generated charge carriers and photocatalytic activity.The main research contents and results are as follows:(1)Study on the preparation and performance of g-C3N4 nanorod/InVO4 hollow sphere composite.A novel g-C3N4 nanorod/InVO4 hollow sphere composite was fabricated through a facile template-free method.The structure-property relationship was analyzed,and the formation mechanism of such structure and morphology was also proposed based on the observation from time-dependent morphology evolvement.The results show that bulk g-C3N4 experiences a possible peeling process to form the rod-like structure,during which the mass ratio of InVO4 and ultraphonic process play a key role.Moreover,bubble-template is believed to determine the formation of InVO4 hollow spheres which uniformly load on the surface of g-C3N4 nanorod and thus forming the heterojunction.This unique nanorod/hollow sphere nanostructure can promote the absorption of visible-light and result in low recombination efficiency of photo-generated electron-hole pairs through Z-scheme transfer mechanism,thereby achieving enhanced photocatalytic activity.The composite shows the highest photocatalytic decomposition rate which is 25 and 16 times higher than that of g-C3N4 and InVO4,respectively.(2)Study on the preparation and performance of core-shell g-C3N4/MCNTs/BiOI nanocomposite.A novel core-shell g-C3N4/MCNTs/BiOI Z-scheme heterojunction was successfully designed and fabricated through filling multi-walled carbon nanotubes(MCNTs)with g-C3N4,followed by the loading of BiOI on the outer surface of the MCNTs.The structure-property relationship was analyzed in details.The results show that the BiOI nanoparticles are uniformly loaded on the surface of the MCNTs which are fully filled by g-C3N4.The MCNTs connect the two semiconductors of g-C3N4 and BiOI,and serve as electron mediating conductors to promote the transfer of the photo-generated electrons,thereby constructing a Z-scheme heterojunction between g-C3N4 and BiOI.This unique nanostructure result in low recombination efficiency and high redox ability of photogenerated electron-hole pairs through the S-C-S Z-scheme transfer mechanism,thereby achieving enhanced photocatalytic activity.The as-prepared samples exhibit enhanced photocatalytic degradation ability towards MB under visible-light irradiation,which is 1.4 and 1.3 times higher than that of BiOI and g-C3N4.(3)Study on the preparation and performance of g-C3N4 nanoparticles/flower-like BiOI composite.Firstly,flower-like BiOI and g-C3N4 nanoparticles were prepared by solvothermal method and acid etching reflux method,respectively.Then,g-C3N4 nanoparticles/flower-like BiOI composite was constructed by simply loading g-C3N4 nanoparticles on flower-like BiOI through electrostatic self-assembly process.The structure-property relationship was discussed.The results show that flower-like BiOI are composed of BiOI nanosheets that have a thickness ranging from 20 nm to 50 nm with smooth and large exposed surface.The g-C3N4 nanoparticles are uniformly loaded on the surface of BiOI nanosheets and thus forming an intimate interface.The promoted photocatalytic activities may originate from more effective separation and transfer of photo-generated carriers which was promoted by the well crystallization and surficial dispersive heterojunction structure.The as-prepared samples exhibit enhanced photocatalytic degradation ability towards MO under visible-light irradiation,which is 2.3 times higher than that of BiOI.(4)Study on the preparation and performance of g-C3N4 nanoparticles/porous g-C3N4 composite.Porous g-C3N4 was prepared by hydrothermal method with the aid of ammonium hydroxide.Then,g-C3N4 nanoparticles/porous g-C3N4 composite was constructed by simply loading g-C3N4 nanoparticles on porous g-C3N4 based on the electrostatic self-assembly of g-C3N4 nanoparticles.The structure-property relationship was discussed in detail.The results show that as,prepared porous g-C3N4 has a porous nanostructure composed of 2D nanosheets and interconnected pores.Compared with bulk g-C3N4,porous g-C3N4 exhibits higher photo-generated carriers transfer ability and lager exposed surface area which is able to provide sufficient anchor sites for g-C3N4 nanoparticles.The g-C3N4 nanoparticles are uniformly loaded on the surface of porous g-C3N4 via electrostatic self-assembly process and thus forming an intimate interface,which can further promote the separation efficiency of photo-generated carriers.The as-prepared sample exhibit enhanced photocatalytic activity in MB degradation under visible-light irradiation,which is 3.4 and 1.6 times higher than that of bulk g-C3N4 and porous g-C3N4,respectively.