Study On The Synthesis Of Metal/Covalent Organic Frameworks Photocatalytic Materials And Their Selective Oxidation Performance

The rapid development of photocatalytic technology makes it possible for human beings to explore green and sustainable development.After decades of research,various types of photocatalytic materials have been developed.However,most photocatalytic materials still have some shortcomings,such as low catalytic activity,poor photocarrier migration ability and unsatisfactory cycle stability,which limit their wide application in industrial production.Therefore,the development of photocatalytic materials with high catalytic activity and high stability has become the hotspot in this field.It is found that MOF may have higher potential application value in photocatalytic reaction.Despite its response to visible light is still in a lower level,the photocatalytic efficiency of MOF can be improved by introducing organic functional groups into MOF or synthesizing MOF photocatalytic materials with other photocatalysts.In addition,as a class of special materials with long range ordered crystal structure,Covalent Organic Framework(COF)exhibits excellent photochemical and photophysical properties.However,due to the low valence band position of COF,there is still a lack of corresponding systematic studies in photocatalytic oxidation and other fields.The photocatalytic activity and corresponding oxidation mechanism of COF haven’t been effectively analyzed by finding suitable substrate for catalytic oxidation.Therefore,this paper attempts to prepare a variety of photocatalysts,to investigate the visible light catalytic performance of NH2-MIL-125(Ti),COF-TpPa and other materials,and establish an efficient visible light catalytic oxidation system.The specific research contents are as follows:(1)A series of aromatic aldehydes were reacted with amino groups in NH2-MIL125(Ti)to improve the photocatalytic oxidation efficiency of alcohols.The composition,morphology and crystal structure of catalytic materials were tested by XRD,XPS,SEM and TEM,and the visible light response performance and band structure of photocatalytic materials were tested by UV-vis spectrum,UPS,Mottchottky test,fluorescence spectrum and fluorescence life,so as to optimize the titanium MOF photocatalytic materials.In order to reveal the mechanism of enhanced photocatalytic efficiency of materials,DFT theoretical calculations were used to determine the HOMO and LUMO electron cloud distribution in specific regions of MOF,and the relationship between band gap and catalytic performance was verified experimentally.(2)COF-TpPa with ketone-enol tautomerism was prepared by hydrothermal method and showed good activity in photocatalytic oxidation of benzylamine.At the same time,COF-LZU1,which has similar structure and molecular composition,was compared with COF-TpPa,so as to recognize the superiority of keto-enol structure in the photocatalytic oxidation of benzylamine.In addition,the effects of COF-TpPa and COF-LZU1 on the photocatalytic,adsorption and structural properties of both aerobic and anaerobic oxidation of benzylamine were discussed,and the photocatalytic mechanism was also studied.(3)Building a core-shell type Ⅰ heterojunction structure of MOF nanostructures with accelerated photo-induced electrons and charge-carrier separation between semiconductors could enhance the photocatalytic performance.The introduction of nano-sheet polymer PMTPA with conjugated groups,enables the variation of the intrinsic electronic properties.The electrons and holes inside the material can move to the interface in an orderly manner,thus oxidation reaction proceeds more efficiently.In addition,a possible mechanism to elucidate the process of photocatalysis was explored.Therefore,the MOF-based photocatalysts possesses great potentials in future green organic synthesis.