Zr,Fe-based Metal-Organic Frameworks Photocatalysts: Design,Derivation And Properties

Compared with traditional inorganic photocatalysts,metal-organic framework?MOF?photocatalysts have huge specific surface area,regular and open channels,andfacile tunability,having received considerable attentions.However,some unfavorable features of most MOF photocatalysts such as severe recombination of charge carriers,low light absorption,lack of active sites and etc.,greatly restrain their photocatalytic applications.On the other hand,due to the uniform structure and porosity,MOFs are ideal templates to derive various inorganic nanomaterials.MOFs can be easily derived to monometallic compounds,however,they are still difficult to be applied for the preparation of bimetallic solid-solution materials.To address above challenges,the following works have been attempted in this thesis.Firstly,for reducing severe recombination of charge carriers,we encapsulated small cocatalyst inside MOF pores to form heterojunctions so as to separate the electron-hole pairs.Carbon dots?CDs?have wide light absorption and fast electron transfer rate.When coupled with MOF photocatalysts,CDs can work as electron acceptors and photosensitizers.We chose a typical MOF?i.e.,NH₂-UiO-66?as main photocatalyst and CDs as cocatalyst for photocatalytic CO₂ reduction.We found that CDs encapsulated in MOFs exhibit better photocatalytic performance than CD-decorated MOFs.The exploration of photocatalytic mechanism suggested that placing small CDs cocatalyst near the internal metal-oxo clusters of MOFs can help efficient charge transfer and separation in the hybrid catalysts,due to the formation of many small heterojunctions among MOFs.Meanwhile,CDs could also act as photosensitizers and broaden the light absorption range of catalysts to improve their photocatalytic performance.The developed CD-hybridized MOFs catalysts have been characterized in detail and their working mechanism has been explored.Secondly,considering that the CB position of some MOF photocatalysts is not negative enough for targeting photocatalytic reactions,we employed the dye-sensitization strategy to elevate the CB position of these MOFs,and use Fe-based MOFs for photocatalytic CO₂ reduction as an example.In previous reports,there's only liquid HCOOH product has been obtained and no valuable gaseous products were observed,due to the low CB position of Fe-MOFs.Given that Fe site is a good active site for catalytic CO₂ reduction to CO,we employed the dye-sensitization strategy to elevate the CB positions of Fe-based MOFs and successfully obtained CO as gas product.We revealed that Fe-based MOFs exhibit excellent activity toward CO production under[Ru?bpy?₃]Cl₂-sensitization due to the utilization of numerous Fe sites among Fe-MOFs.The working mechanism of above dye-sensitized photocatalytic system have also been explored and proposed.Thirdly,for deriving bimetallic solid-solution photocatalysts with MOFs,we proposed to facile strategy to utilize bimetallic MOFs as templates and regulate their compositions by varying the metal ratio among MOF precursor.Aiming to photocatalytic H₂ and O₂ production,we present a metal-organic framework derived route to prepare bimetallic Fe-Ni-P nanotubes using Fe-Ni-MIL-88 nanorods as templates.When integrated with different dyes,these Fe-Ni-P nanotubes can serve as efficient catalysts for photocatalytic H₂ and O₂ production,respectively.Additionally,catalytic activities of such dye-sensitized systems can be conveniently regulated by tailoring the metal compositions in Fe-Ni-P nanotubes.The roles of different components in the system have been explored and corresponding working mechanism is proposed.