Preparation And Properties Of NH₂-MIL-53(Al) Composite Visible Light Photocatalysts

The growth of the global population makes the environment more polluted and the demand for energy increases.In particular,the presence of pollutants in the aquatic environment has caused negative effects on terrestrial organisms and aquatic organisms,which has become a serious problem on a global scale.At present,there are many technologies used for environmental remediation and treatment of pollutants in water,such as adsorption,flocculation,electrocatalysis,photocatalysis,biochemical treatment and so on.Photocatalysis,as a technology that can only use sunlight as energy,has been studied vigorously in the treatment of water pollution for organic macromolecular pollutants that are resistant to degradation.Metal-organic frameworks(MOFs)are a unique class of periodic porous crystalline materials containing metal ions/clusters and organic linkers.In the past few decades,these materials have attracted more and more attention due to their outstanding characteristics such as good crystallinity,structural diversity,permanent porosity and adjustable functionality.In this paper,NH₂-MIL-53(Al)and its composite photocatalyst are prepared and their photocatalytic properties are studied.NH₂-MIL-53(Al)has the advantages of simple preparation process,large specific surface area,high water and thermal stability,easy recovery,and good optical properties.By loading Cd S nanoparticles on the gear-like surface of NH₂-MIL-53(Al),the separation efficiency of photogenerated electrons and solar energy utilization rate are further improved,and the photocatalytic efficiency is improved.A series of characterization analyses of NH₂-MIL-53(Al)and its composite materials are carried out,and the photocatalytic degradation of pollutants and hydrogen production of NH₂-MIL-53(Al)are studied.Finally,the photocatalytic mechanism is investigated.The specific research contents are as follows:Firstly,the gear NH₂-MIL-53(Al)is successfully prepared by hydrothermal method using aluminum nitrate as aluminum source and diaminoterephthalic acid as organic ligand.NH₂-MIL-53(Al)with different morphology and size is prepared by adjusting the hydrothermal time.By XRD,SEM,UV-Vis,FT-IR,BET and a series of analysis and the performance test of photocatalytic reduction of Cr(?)and dichlorophenol,the optimum hydrothermal synthesis time of NH₂-MIL-53(Al)is 4 h.This is because the morphology of NH₂-MIL-53(Al)synthesized at this time is regular and complete,and the specific surface area is the largest,which is more conducive to the separation of photogenic carriers and the inhibition of charge recombination.Secondly,in order to further improve the performance of NH₂-MIL-53(Al)based photocatalyst,p-n type heteronode NH₂-MIL-53(Al)/Cd S composite is prepared by hydrothermal synthesis of cadmium acetate and sodium sulfide on the basis of gear-shaped NH₂-MIL-53(Al).In order to obtain the best performance of NH₂-MIL-53(Al)/Cd S composite,the Cd S loading is adjusted to 3%,5%,7%and 9%(compared to the mass fraction of NH₂-MIL-53(Al)),respectively.The results of characterization and performance analysis show that the composite photocatalyst has the best performance when the Cd S loading is 7%.The photocatalytic degradation efficiency of Cr(?)and dichlorophenol reaches 99.23%and 98.25%within 150 min,respectively,and the photocatalytic hydrogen production capacity reaches 623.6?mol g^-1 h^-1,which is 6.8 times that of NH₂-MIL-53(Al).This can be attributed to the synergy between NH₂-MIL-53(Al)and Cd S by forming a tight heterojunction.NH₂-MIL-53(Al)and Cd S contact to form p-n heterojunction,the formation of p-n heterojunction can form a built-in electric field,which is conducive to space charge separation.According to the corresponding built electric field in the system,the negative movement of NH₂-MIL-53(Al)electrode potential and the positive movement of Cd S electrode potential,the Fermi level drive reaches equilibrium.The p-n type heterojunction composite photocatalyst is established to remove refractory pollutants from water,and a new idea is proposed for energy development.