Research On Structure Regulation And Photocatalytic Purification Of NO_x And Hydrogen Production Performance Of G-C₃N₄ Matrix Composites

Photocatalytic technology is a low-energy,high-efficiency new environmental protection technology developed in recent years.It uses active free radicals generated by photon excitation to degrade and mineralize macromolecular pollutants into carbon dioxide,water and other small molecular substances.Graphite phase carbon nitride（g-C₃N₄）has C and N atoms in its structure hybridized with sp2 to form a highly delocalizedπconjugated system with a triazine ring（C₃N₃）unit.It is a non-metallic semiconductor material.It was used in energy photocatalysis（photolysis of water to produce hydrogen）and environmental photocatalysis（degradation of pollutants）.However,carbon nitride has a high photogenerated electron-hole recombination rate and its own photocatalytic efficiency is not high.In order to enhance the photocatalytic properties of g-C₃N₄,carbon nitride was modified as follows:（1）preparation of BaWO₄/g-C₃N₄ composite material with excellent dual-function photocatalytic performance;（2）preparation of NaLa（WO₄）₂/g-C₃N₄ composite material to improve photocatalytic performance.XRD,XPS,SEM,TEM,BET,PL,UV-visDRS,FT-IR,In-situ DRIFTS and other characterization methods were used to analyze the microstructure,optical properties,conversion process of the prepared catalyst.The photocatalytic performances of these samples were evaluated by NO photocatalytic oxidation and photocatalytic hydrogen production.The following tasks are mainly carried out:（1）Preparation of BaWO₄/g-C₃N₄ composite materials with excellent dual-function photocatalytic performance:a novel bifunctional BaWO₄/g-C₃N₄photocatalyst with heterojunction was first synthesized by a hydrothermal-calcination method.The prepared catalyst was applied to the removal of low-concentration NOx and photocatalytic hydrogen production.The chemical composition of BaWO₄/g-C₃N₄ was optimized and composites with 7%BaWO₄（7%-Ba-CN）exhibited the best photocatalytic performance.In 30min,the NOx removal ratio of the composite photocatalyst increased by 14%compared with the pure g-C₃N₄.According to in situ DRIFTS spectra analysis,the transformation pathways of photocatalytic purification of NO on pure g-C₃N₄ and 7%-Ba-CN were elucidated and compared,and a new adsorption band at 2164 cm^-1 associated with NO⁺intermediate was discovered on 7%-Ba-CN.In addition,the photocatalytic hydrogen production rate of7%-Ba-CN was 2743.98μmol/g/h,which was 4 times higher than that of pure g-C₃N₄.This research highlights that charge transfer rates can be controlled by constructing heterojunctions.The promotion of the charge separation,transmission and conversion could simultaneously enhance the oxidation and reduction capacity of the composite photocatalyst.（2）Preparation of NaLa（WO₄）₂/g-C₃N₄ composite material to improve photocatalytic performance:a new type of heterostructured NaLa（WO₄）₂/g-C₃N₄composite material was prepared by one-step in-situ thermal polymerization.The prepared catalyst is used for purifying NOx in air pollution.By optimizing the chemical composition of NaLa（WO₄）₂/g-C₃N₄,1-NaLaW-CN exhibited the best photocatalytic performance.In 30min,the NOx removal ratio of the composite photocatalyst increased by 16%compared with the pure g-C₃N₄.In this study,based on the light absorption range of the luminescent material may be more extensive and the photocatalytic advantage of g-C₃N₄,a heterojunction was constructed using an alkali metal rare earth ditungstate luminescent material and g-C₃N₄.NaLa（WO₄）₂ and g-C₃N₄ build a heterojunction to control the charge transfer rate,achieve electron-directed transport,extend the fluorescence lifetime of carriers,promote charge separation,and reduce the electron-hole recombination efficiency to enhance the photocatalytic performance of the composite photocatalyst.