Controllable Preparation And Modification Of Inverse Opal Graphite Carbon Nitride Photocatalysts

With the continuous advancement of the global modern industrialization process and the needs of human production and life,various industries have been developed rapidly.While bringing people convenient living conditions,environmental pollution and energy shortages have become increasingly serious.In order to solve these problems,researchers have devoted lots of effort and made important progress,and photocatalysis technology is one of them.Photocatalytic technology can convert solar energy into clean energy-hydrogen,and degrade pollutants in the environment.In addition,photocatalytic technology is used in the reduction of carbon dioxide,disinfection and sterilization.Graphite carbon nitride（g-C₃N₄）is widly used in the field of photocatalysis due to its excellent performance.However,the photocatalytic activity of g-C₃N₄ is low because of the small specific surface area and the high recombination rate of photogenerated electron-hole pairs which limits its practical application.In this thesis,the photocatalytic performance of g-C₃N₄ was improved by morphology engineering,cocatalyst loading,and composite construction.The specific research contents are as follows:（1）Inverse opal（IO）structure g-C₃N₄ is prepared by using melamine as a precursor and densely packed silica microspheres as a hard template by vapor deposition.It is found that the hydrogen evolution rate of IO g-C₃N₄ photocatalyst is21.22μmol·h^-1,which is almost 6 times the hydrogen evolution rate of bulk g-C₃N₄(3.65μmol·h^-1).This is due to the follow facts:The specific surface area of IO g-C₃N₄is 450.2 m²?g^-1,which is about 33 times that of bulk g-C₃N₄(13.8 m²?g^-1),providing more catalytic reaction active sites.The interconnected ordered porous structure can better capture light and increase the mass transfer capacity.The order-disorder interface formed within IO g-C₃N₄ layer can promote the separation of charge carriers,and the existing N vacancies intensify local electron density,which helps increasing photoexcitons.This work provides an important contribution to the structural design and property modulation of photocatalysts.（2）The Step-scheme heterostructure Co₃O₄/g-C₃N₄（Co₃O₄/g-CN）composite photocatalyst material was prepared by a hydrothermal method.The research found that the Co₃O₄/g-CN composite photocatalyst exhibits the best photocatalytic hydrogen evolution activity(57.71μmol·h^-1)when the composite ratio of Co₃O₄ is 1 wt%.It is due to the fact:Co₃O₄/g-CN step-scheme heterajunction photocatalysts retain the strong oxidation reduction ability of the catalysts,while effectively separating their photogenerated carriers.The photogenerated electrons on the CB of Co₃O₄ recombine with the holes on the VB of g-C₃N₄,which inhibits the recombination of photogenerated electron-hole pairs of g-C₃N₄ and Co₃O₄.The photogenerated electrons on the CB of g-C₃N₄ and the holes on the VB of Co₃O₄ remain,maintaining their strong redox ability,thereby improving its photocatalytic water splitting activity.（3）The IO Pt-g-C₃N₄（Pt-g CN）composite photocatalyst with inverse opal structure was prepared by the hard template method,loaded Pt on the inner surface of porous g-C₃N₄.When the proportion of Pt particles reaches 1.2 wt%,the IO 1.2 wt%Pt-g CN composite photocatalyst shows the best photocatalytic hydrogen evolution activity(220.48μmol·h^-1),which is almost 60 times of the bulk hydrogen evolution rate of g-C₃N₄(3.65μmol·h^-1).In the case of the same Pt loading,the photocatalytic hydrogen activity of randomly loading Pt nanoparticles onto the surface of IO g-C₃N₄（recorded as IO 1.2 wt%Pt-g CN-R）by photoreduction method is only 150.2μmol·h^-1.It is due to:The inner surface of IO g-C₃N₄ has a greater electron density,which helps to enrich the photogenerated electrons to the Pt nanoparticles loaded on the inner surface.The multiple scattering and reflection of incident photons inside the porous structure will increase the photogenerated carriers on the inner wall of the hole,and loading Pt on the porous inner wall will promote the photogenerated carriers to participate in the reaction process of water reduction and hydrogen production.In addition,the pore structure helps the mass transfer process of the reactants.The synergistic effect of these factors gives Pt/IO g-C₃N₄ high photocatalytic performance.