Polycarboxlate-based MOFs And Applications In Formic Acid Dehydrogenation,dye Adsorption And White-light Material Fabrication

In recent years,the construction and application of metal framework frameworks(MOFs)based on polycarboxylic acid ligands have been favored by more and more researchers.These materials not only have fascinating and easily regulated structures,but also show potential applications in many fields,especially,in catalysis,adsorption and luminescence.The decomposition of formic acid(FA)to produce hydrogen is an effective way to solve the energy crisis.Supported Pd-based nanoparticles(NPs)including bimetallic Pd-based NPs,like PdAu,Pd Ag and Pd Pt have shown exceptional catalytic activity and dehydrogenation selectivity for FA decomposition.Currently,considerable effort is still required for further improving the catalytic efficiency and the stability(against deactivation and aggregation of Pd NPs)of the supported Pd-based catalysts,hopefully could well meet the demand of practical application in FA dehydrogenation.Therefore,the choice of an appropriate support and preparation method is crucial for getting a highly active and stable supported Pd-based NPs catalyst for FA dehydrogenation.In virtue of the size-adjustable cages and easily decorated by adjusting the organic linkers,MOFs are extraordinarily suitable to serve as support to load noble metal nanoparticles(NPs)for the dehydrogenation of FA.Based on this,we adopted classical MOF UiO-66 and their derivatives as supports and synthesized a series of supported Pd-based bimetallic nanoparticles by changing the impregnation method,introducing the second metal components and increasing the density of amine groups in this paper.Finally,we systematically discussed the influence factors of supported Pd-based catalysts on hydrogen production from FA.In addition,based on two aromatic polycarboxylic acids as ligands,two novel AMOFs are successfully constructed.Subsequently,their structures analysis and applications are investigated.The detailed contents and conclusions of this thesis are as follows:1.A series of UiO-66 supported PdAu composite NPs with different Pd/Au ratios were prepared by a double-solvent method and their catalytic properties were studied for the hydrogen generation from FA in aqueous solution without any additives.The results reveal that the dehydrogenation of FA can be effectively promoted by proper alloy effect and interaction between metal and support.The optimized catalyst Pd0.8Au0.2/UiO-66-NH2-D can achieve FA dehydrogenation efficiently.Its initial turnover frequency(TOF)value is 722 h^-1 at room temperature and this catalyst can be used at least five times.2.Pd0.8Au0.2/UiO-66-NH2-D and Pd0.8Au0.2/UiO-66-NH2-S catalysts with the same amount and ratio PdAu NPs were prepared by double-solvent method and single-solvent method respectively.Their catalytic performances for FA decomposition were investigated.The results reveal that most of PdAu NPs can be encapsulated into the cages of Zr-MOF by using the double-solvent method.In addition,the metal NPs in Pd0.8Au0.2/UiO-66-NH2-D are tinier and more disperse than those in Pd0.8Au0.2/UiO-66-NH2-S,which significantly improves the activity and stability of supported PdAu catalyst.3.In the process of catalyst preparation and FA dehydrogenation,the amine groups play a key role.During the double-solvent impregnation process,Pd²⁺and Au³⁺dissolved in water solvent can be easily coordinated with the-NH2 groups inside the cages of UiO-66-NH2 due to the similar polarity,which reduces the size of NPs and optimizes their distribution.Furthermore,the amine groups are directly involved in the activation of FA molecules,promoting the breakage of O-H bond,thus improving the activity of supported PdAu catalyst.4.A novel anionic metal organic framework(AMOF)material[(CH3)2NH2]6[Cd3(L1)2]·5DMF·3H2O is successfully obtained,in which3,4-di(3,5-dicarboxyphenyl)phthalic acid(H6L1)is served as ligand and Cd Cl2·1.5H2O is regarded as metal source.Total potential guest accessible void volume in 3-D MOF-1 is found to be 4327A³ based on single crystal diffraction results.Based on its better porous structure and stability,the ability of MOF-1 to adsorb organic dyes is investigated.It has been proved that MOF-1 can selectively adsorb cationic dyes as Azure A(AA⁺)and Methylene Blue(MB⁺);The maximum adsorption capacity is 698.2 mg·g^-1for AA⁺and 573.2 mg·g^-1for MB⁺,respectively;For the adsorption of AA⁺,it can be recycled for at least five rounds.Also,it is utilized to fabricate the while-light emitting material.Based on the blue-light emission of MOF-1,the trace Eu³⁺and Tb³⁺ions are introduced into the pores of MOF-1successfully,obtaining a white-light emitting material Eu³⁺/Tb³⁺@MOF-1(CIE chromaticity coordinates:(0.33,0.32)).Meanwhile,Eu³⁺/Tb³⁺@MOF-1 is found to be a potential fluorescence photochromic material,showing a yellow-white-blue light emission.5.A novel AMOF material[(CH3)2NH2][Cd(L2)·DMA]·0.5DMA·1.5H2O(MOF-2)is successfully obtained through a simple hydrothermal synthesis,in which2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine(H3L2)is served as ligand and Cd Cl2·1.5H2O is regarded as metal source.Single crystal diffraction results reveal that MOF-2 is a 3-D structure with quadruple interpenetration,and pyridine-N atoms does not participate in coordination.After vacuum activation,the new compound MOF-2'retains the same structure as MOF-2 despite the removal of the coordination DMA molecule,and its molecular formula is[(CH3)2NH2][Cd(L2)].Based on this,we investigated the catalytic performance of MOF-2'supported PdAu NPs for FA dehydrogenation and the adsorption capacity of dye.The results reveal that Pd_0.8Au_0.2/MOF-2'catalyst obtained by double solvent method expresses a decent catalytic activity at 333 K,with an initial TOF of 1854 h^-1,in virtue of the synergistic effect of the alloy effect of bimetallic PdAu NPs and the uncoordinated pyridine-N atoms on the surface of MOF-2'to active FA molecules.At the same time,MOF-2'can quickly adsorb the cationic dye MB⁺with the adsorption rate of 0.7×10^-2g·mg^-1·min^-1.The maximum adsorption capacity of MOF-2'for MB⁺is 900 mg·g^-1,among which the adsorption capacity by ion exchange is calculated to be 540 mg·g^-1,and the surface adsorption capacity by the uncoordinated pyridine N atoms on the surface of MOF-2'is found to be 340 mg·g^-1.