The Application Of MOFs-based Composites In Photocatalytic Oxidation Reaction

In recent decades,with the increasingly prominent problems of energy crisis and environmental pollution,it is particularly urgent to find new clean energy or energy conversion technology.As a green and efficient energy conversion technology,photocatalytic reaction has become a research hotspot due to its green,mild and sustainable advantages.At present,the research on photocatalysis is mainly focused on the development of photocatalysts to broaden the spectral response range and reduce the photogenerated electron hole recombination.The commonly used photocatalysts are traditional semiconductor materials（i.e.Ti O₂ and Cd S）and new photocatalysts represented by metal organic frameworks（MOFs）and g-C₃N₄.Single semiconductor materials have the advantages of high stability and low price,but also have the disadvantages of narrow light absorption range,low effective utilization of solar energy,certain toxicity and light corrosion.Although single MOFs have high specific surface area and high porosity,they also have the problems of the limited types of MOFs and photogenerated carrier recombination.Therefore,combining the advantages of traditional semiconductor materials and new photocatalysts,heterojunction can effectively adjust the absorption range of visible light and enhance the photocatalytic efficiency.The specific research contents are as follows:（1）In this work,we construct MOFs as the main framework,melamine and urea as the mixed precursors a series of ZnO@g CN-UA/MA composites by designing a series of UA@ZIF-8@MA sandwich templates and then calcining these sandwich templates at high temperature.During the pyrolysis process,ZIF-8 and melamine precursors would convert into ZnO and g CN structure so as to form the ZnO@g CN composite at high temperature,while urea molecular would decompose to release ammonia molecules under high temperature condition which rush out from the interior of ZIF-8 to make the ZnO@g CN-UA/MA composites become fluffy and porous.UV-vis and PL characterization results reveal that the ZnO（0.1）@g CN-UA/MA composites exhibit enhanced spectral response range and the lower charge-carrier recombination rates.When being used in photocatalytic oxidative coupling of amines at low temperature under air condition,the optimal ZnO（0.1）@g CN-UA/MA catalyst exhibits excellent activity,affording the imine product with 96%yield.Moreover,the catalysts also exhibit a wide substrate compatibility and recyclability.（2）5-hydroxymethylfurfural（HMF）has been recognized as one of the top 10important biomass chemicals,the conversion of HMF to corresponding high value-added product product 5-diformylfuran（DFF）has attracted great attention.In the second experimental system,we constructed an efficient photocatalyst（Ti O₂@UIO-67-Zr/Ti）with microwave-assisted post synthesis metal exchange method to selective oxidative HMF to DFF with air as oxidant under low temperature.The Ti O₂@UIO-67-Zr/Ti catalyst is synthesized by first compositing the UIO-67-Zr assembled with mixed organic ligands in the hole of porous Ti O₂,and then treating the composite with microwave-assisted Ti-PSE（post-synthetic exchange）method.XRD,SEM,TEM and XPS characterization results confirm the formation of Ti O₂@UIO-67-Zr/Ti structure,UV-vis,FT-IR and Raman spectra show the existence of strong interaction between porous Ti O₂ and UIO-67-Zr/Ti.When being used as photocatalyst for oxidation HMF to DFF under air condition,Ti O₂@UIO-67-Zr/Ti exhibits tremendous enhanced photocatalytic performance to achieve 94%conversion with 66%yield.Moreover,this photocatalytic system also displays a wide range of compatibility.