Design Of Several Novel Functional Metal-organic Frameworks And Derived Materials For Solar Energy Conversion

As a green and sustainable advanced technology,photocatalytic process,which efficiently convert abundant solar energy into applicable chemical energy,shows great advantages and market prospects in solving current increasingly serious energy and environmental issues of clean water resource.Considering the photosensitizing unit and catalytic active unit as the two main components involving in the photocatalytic systems,a variety of novel MOF-based or-derived photocatalysts that feature outstanding robustness,low cost-efficiency,high solar energy utilization capability,and efficient charge separation were well developed based on the structural diversity of MOFs.Meanwhile,the relationship between structural function and activity were also been studied.The research content of this thesis belongs to the interdisciplinary fields of chemical engineering,inorganic chemistry and environmental chemistry,which has important scientific research value and practical significance.,.The main research achievements are described as follows:1.Formation of willow leaf-like structures composed of NH₂-MIL68(In)on a multifunctional multiwalled carbon nanotube backbone for enhanced photocatalytic reduction of Cr(VI). MWCNT as an electron acceptor was introduced into NH₂-MIL-68(In)by a facile dynamic hydrothermal method,and the willow leaf-like MOF grown along with the MWCNT backbones to form MWCNT/NH₂-MIL-68(In)composite(PL-x),leading to highly efficient transfer of the photogenerated carriers for Cr(VI)photoreduction.The mechanism of enhanced Cr(VI)photoreduction by the incorporation of MWCNT was elaborated.First,the incorporated MWCNT generates new mesopores to facilitate Cr(VI)diffusion.Second,the incorporated MWCNT serves as an excellent photosensitizer to enhance visible light absorption without lowering the conduction band position.Last,the incorporated MWCNT not only accepts the photogenerated electrons from NH₂-MIL-68(In),but also provides an electron migration platform,which ensures efficient charge transfer and retards e^-/h⁺ recombination.2.Encapsulated MWCNT@MOF-derived In₂S₃ tubular heterostructures for boosted visible- light-driven degradation of tetracycline.MWCNT@MOF-derived In₂S₃ hollow tube heterostructure was synthesized via facile MOF sulfidation process,with significantly boosted photocatalytic degradation performance of tetracycline(TC)under visible light irradiation.The 0.3%-MWCNT@MOF-derived In₂S₃ exhibited the highest photocatalytic activity for visible-light-driven TC degradation,achieving?100%degradation efficiency, with apparent reaction rate constants 3-5 times higher than that of the pure MOF-derived hollow In₂S₃ and traditional In₂S₃ bulk.The enhanced performance was attributed to the synergy between electron acceptor MWCNTs and active center of MOF-derived In₂S₃ hollow tube.The shorter transfer distance and enhanced separation of charge carriers not only promote the carrier transfer and inhibit the recombination rate effectively,but also improves the visible light response.3.Metal-organic frameworks significantly enhance photocatalytic hydrogen evolution and CO₂ reduction with Earth-abundant copper photosensitizers.Two multifunctional MOFs, m PT-Cu/Co and m PT-Cu/Re,comprising of cuprous photosensitizers(Cu-PSs)and molecular Co or Re catalysts were synthesized,for photocatalytic hydrogen evolution and CO₂ reduction,respectively.The hierarchical integration of Cu-PSs and Co/Re catalysts in these MOFs facilitates multielectron transfer to drive hydrogen evolution and CO₂ reduction under visible light with a hydrogen evolution turnover number(TON)of 18,700 for m PT-Cu/Co and a CO₂ reduction TON of 1328 for m PT-Cu/Re,which represent 95-fold enhancement over their homogenous controls.Photophysical and electrochemical investigations revealed the reductive quenching pathway in hydrogen evolution and CO₂ reduction catalytic cycles and attributed the significantly improved performances of MOFs over their homogenous counterparts to enhanced electron transfer due to close proximity between Cu-PSs and catalytic centers and stabilization of Cu-PSs and molecular catalysts by the site-isolation effect of MOF framework.4.Metal-organic frameworks integrate Cu photosensitizers and SBU-supported Fe catalysts for photocatalytic hydrogen evolution.A series of MOFs,Fe X@Zr₆-Cu(X=BF₄^-,Br^-,Cl^-,OAc^-),comprising cuprous photosensitizing linkers(Cu-PSs)and catalytically active Fe^? centers supported on SBUs were designed for photocatalytic hydrogen evolution.Close proximity(?1 nm)between Cu-PS and SBU-supported Fe sites and stabilization of low-coordinated Fe sites by periodically ordered SBUs led to exceptionally high hydrogen evolution activity,with TON of up to 33,700 and turnover frequencies of up to 880 h^-1.Photocatalytic hydrogen evolution activities of Fe X@Zr₆-Cu correlate with the lability of X counter anions,suggesting open coordination environments of Fe sites generated by labile X groups facilitate the formation of Fe-hydride intermediates before hydrogen evolution.