Preparation Of G-C₃N₄-based And TiO₂-based Photo/thermal Catalytic Materials And Research On Degradation Of Indoor Pollutants

With the rapid development of social economy in our country,people’s substance level is greatly improved,and the demand for a green and healthy environment for living and production is also increasing.In modern society,people spend about 80%of their lives indoors,and indoor pollutants are more harmful to people’s health,production and life.Especially indoor organic pollutants（mainly divided into liquid-phase organic pollutants and gas-phase organic pollutants）,a small amount of exposure can cause headaches,nausea and other symptoms,and long-term exposure may cause serious consequences such as cancer.According to the different molecular structures of liquid and gas phase organic pollutants,the composites based on g-C₃N₄ and TiO₂ were prepared,and methylene blue and toluene were selected as liquid and gas phase target pollutants.The degradation activity of the supported structure Zn O@g-C₃N₄ composite catalytic material for methylene blue under visible light was explored;on this basis,the photothermal synergy system was constructed——C@MnO_x@TiO₂（ternary composite catalytic material）,the photothermal degradation activity of toluene under full spectrum was investigated.It provides a feasible solution to solve the problem of indoor organic pollution.The main research work is divided into the following parts:（1）In order to optimize the electronic energy level structure of g-C₃N₄,reduce the electron hole recombination rate and enhance its photocatalytic activity,taking advantage of the matching band structure of semiconductor g-C₃N₄ and Zn O,Zn O was loaded on g-C₃N₄ nanosheets by solution polarity self-assembly strategy to obtain the composite catalytic materials Zn O@g-C₃N₄（ZCN）.Theπ-πstacking thickness of the g-C₃N₄ nanosheets in the ZCN composite material is controlled by adjusting the reaction time.The degradation efficiency of the composite catalytic material ZCN for methylene blue is significantly better than that of g-C₃N₄ and Zn O.The composite catalytic material ZCN-12 obtained with a reflux time of 12 h has the highest degradation rate of methylene blue under visible light irradiation,and the degradation rate of 3 h is 88.3%,the apparent kinetic constant is 0.704 h^-1,which is 4 times that of g-C₃N₄ nanosheets(k=0.174 h^-1),and it has good stability.Because the composite catalytic material ZCN constructs a hybrid structure between g-C₃N₄ and Zn O,which reduces g-C₃N₄ structural defects.ZCN-12 further optimizes theπ-πstacking thickness of g-C₃N₄ nanosheets in ZCN and improved the transmission efficiency of photo-generated electrons,thereby enhancing its photocatalytic activity.（2）To improve photocatalytic degradation efficiency,the strategy of photothermal cohesive degradation of indoor gas phase organic pollutants is proposed:the carbon nanospheres of uniform size were prepared by hydrolysis of glucose;then the manganese titanium oxide is assembled on the surface of the carbon ball in an orderly manner;finally,a high-temperature solid-phase reaction is carried out in a helium atmosphere.Prepare the nano-core-shell structured catalytic material C@MnO_x@TiO₂（CMT）.The TiO₂ in the outermost layer of CMT can undergo photocatalytic reaction;the middle layer of CMT is MnO_x,and the active free radicals generated in the photocatalytic process drive the oxidation of MnO_x into MnO₂ with high-efficiency photothermal catalytic activity;the C core in the innermost layer of the CMT broadens the photoresponse range of the catalyst and improves the heat utilization rate,and its chemical inertness maintains the stability of the CMT three-layer structure.CMT conducted an experiment to degrade toluene under full light irradiation conditions.The degradation rate of toluene in 90 min was 99.1%,and the degradation rate of toluene was maintained above 95%in the 20-cycle degradation experiment.The degradation effect of CMT on toluene in different environments shows that it can achieve the purpose of photothermal synergistic catalysis and high efficiency degradation of toluene.Under full light irradiation,the composite catalytic material CMT has high-efficiency photothermal catalytic activity,which is attributed to the synergistic effect between the photocatalysis of TiO₂ and the photothermal catalysis of MnO_x.This synergistic effect is further promoted by the electrical conductivity of the C core,so it shows higher degradation efficiency for toluene.