Preparation And Organic Pollutants Degradation Activities Of MOFs-based Composite Photocatalysts

As a functional porous nanostructure material,metal-organic framework（MOFs）has been widely used in photocatalysis.There are many factors to limit the application of MOFs photocatalysis,which mainly include low conductivity,poor water stability and high photogenerated charges recombination rate.In order to improve the low photogenerated charge separation efficiency and poor water stability of MOFs materials,this thesis was based on a typical Fe based MOFs material MIL-88B（Fe）,combined it with a hot semiconductor material Bi₂Mo O₆ and a two-dimensional carbon material graphene oxide（GO）,and constructed Bi₂Mo O₆/MIL-88B（Fe）heterojunction and GO/MIL-88B（Fe）composite,respectively.Combing of various analysis and characterization techniques,this thesis studied structure composition,optical properties and photocatalysis performance of composite photocatalysis systemically.The effects of spatial charge separation on the photocatalysis efficiency were investigated,and the mechanism of photocatalysis process was speculated.In the respect of improving the spatial charge separation efficiency of MIL-88B（Fe）,a facile two steps solvothermal method was used to load the surface oxygen vacancy modified two-dimensional Bi₂Mo O₆nanosheet on the surface of the three-dimensional MIL-88B（Fe）hexagonal microrods,and synthesis the surface oxygen vacancy modified Bi₂Mo O₆/MIL-88B（Fe）heterojunction.Due to the existence of OVs and the construction of heterojunction,the Bi₂Mo O₆/MIL-88B（Fe）heterojunction exhibited significant enhancement of visible-light responsive range and possessed more efficient photocatalyst bulk and heterojunction interface charge separation.The optimal Bi₂Mo O₆/MIL-88B（Fe）heterojunction（3-BMO/M88）exhibited 99.5%removal efficiency of Rh B within 120 min and 100.0%removal efficiency of BPA within 60min in the presence of H₂O₂.In this study,we focused on improvement of photogenerated charge separation efficiency of MOFs,and proposed a new method of constructing surface oxygen vacancy modified heterojunction structure,which could promote the spatial photogenerated charge transfer at photocatalyst bulk and heterojunction interface charge separation simultaneously.And this provided a new idea for developing a new and efficient MOFs based photocatalyst.In the respect of improving the stability of MIL-88B（Fe）,ultrasonic method was used to disperse GO into the precursor solution of MIL-88B（Fe）.And then MIL-88B（Fe）was uniformly grown surface of GO by solvothermal method.Finally,GO was coated around MIL-88B（Fe）to form GO/MIL-88B（Fe）composite photocatalyst.After the introduction of GO,GO/MIL-88B（Fe）composite photocatalyst showed stronger light absorption ability and faster charge separation rate under visible light illumination.The MB solution degradation efficiency of GO/MIL-88B（Fe）composite photocatalyst is related to the content of GO,the concentration of catalyst and the initial solution p H.When p H=13 and catalyst concentration is 0.6 g·L^-1,the optimal sample 25-GO/MIL-88B（Fe）has the highest MB degradation efficiency,which can reach 98.0%in 120 min.Under alkaline condition,it is better to promote the photocatalytic degradation of MB solution by GO/MIL-88B（Fe）composite.In addition,the GO/MIL-88B（Fe）composite photocatalyst has a good circulation stability in the water phase because GO could protect the three-dimensional framework of MIL-88B（Fe）.After 5 cycles of experiments,25-GO/MIL-88B（Fe）sample still has high photocatalytic activity.In this study,we focused on improving the photocatalytic efficiency of MOFs and its stability in the water phase simultaneously,and used the combination of MOFs and two-dimensional functional materials to build the coating structure heterojunction,which provided a strategy for improving the photocatalytic activity and stability of MOFs.