Preparation And Properties Of Iron Metal-organic Framework-based Composite Photocatalysts

Nowadays,the treatment of refractory pollutants has become an urgent global environmental problem.Chlorophenols are toxic and harmful to the aquatic life,and these have been identified as potential carcinogens to humans.As an emerging treatment of environmental pollution,photocatalysis has aroused enormous interests from researchers with the exclusive utilization of optical energy and no secondary pollution.Developing the effective and eco-friendly photocatalysts has become even more necessary,which not only can degrade organics but also split water into H₂ and O₂ driven by visible-light.The composite photocatalysts of the iron-based metal organic frame are studied in this thesis.Fe-MOF has the hexagonal octahedron structure,suitable specific surface area,tunable pore channels and good optical properties.By loading ultrathin mesoporous g-C₃N₄ onto the Fe-MOF,electrons can be excited more easily under light irradiation.The optical response ability and the efficiency for solar energy utilization of the composites are improved.It can also be further applied to the degradation of highly toxic chlorophenols in water and to generate the clean energy.In this paper,the structure and composition of Fe-MOF composite photocatalysts are characterized in detail,and its ability to degrade pollutants,oxygen generating performance,photothermal effect and photocatalytic mechanism is studied in depth.The results are as follows:(1)The g-C₃N₄ photocatalyst with ultrathin mesoporous is synthesized by means of molecular self-assembly,ethanol intercalation,thermal dissociation and polymerization.Ultrathin mesoporous g-C₃N₄/NH₂-MIL-101(Fe)octahedron heterojunctions photocatalysts are successfully constructed through the solvothermal method of loading the ultrathin mesoporous g-C₃N₄(U-g-C₃N₄)onto NH₂-Iron metal-organic framework(Fe-MOF).Meanwhile,the loading quantity of U-g-C₃N₄ is regulated,which are 1,2,4,6 and 8%,respectively.The ultrathin mesoporous g-C₃N₄,NH₂-MIL-101(Fe)and their composite photocatalysts are characterized by SEM,TEM,AFM,BET,EDX,XPS,XRD and FT-IR.The homogeneous growth of U-g-C₃N₄ on NH₂-MIL-101(Fe)is not only distinctly conducive to the illumination to MOF substrate but also the diffusion of reactants and products.(2)The optimum heterojunction photocatalyst,M101-U₆(6%mass ratio of ultrathin g-C₃N₄),reveals a highest photocatalytic efficiency to degrade2,6-dichlorophen and 2,4,5-trichlorophenol,up to 98.7 and 97.3%respectively within3 h.The efficiency of photodegradation in aquatic oxygen reaches 402.5?mol h^-1 g^-1,which is 2.4 times and 1.6 times higher than the pure samples of U-g-C₃N₄ and NH₂-MIL-101(Fe).Under the light excitation,hydrogen peroxide can be generated spontaneously in U-g-C₃N₄/NH₂-MIL-101(Fe)system.The yield of hydrogen peroxide for M101-U₆ is raised to 69?M within 3 h.Due to the presence of iron trivalent in Fe-MOF,the Fenton-like system is formed,which can further promote the photocatalytic efficiency.In addition,the photo-thermal effect of M101-U₆ is enhanced for this heterojunction photocatalyst and Fenton-like coupling system.This two-in-one strategy of combining photocatalysis with Fenton-like has broad prospects on establishing novel photocatalysts for eliminating high-toxic organic pollutants and generating O₂ concurrently in aquatic environment.