Synthesis Cerium-Based MOFs And Studies On The Visible-Light Mediated Decarboxylative Oxygenation

Two-dimensional metal-organic framework nanosheets（2D MOFs nanosheets）are an emerging class of ultrathin,porous,organic/inorganic hybrid crystalline materials.Compared with three-dimensional metal-organic framework（3D MOFs）,2D MOFs nanosheet is an ideal heterophase catalyst with the advantages of high density and accessible catalytic sites,short reactant/product diffusion path and fast electron transfer.In this paper,cerium ammonium nitrate（CAN）and Ce₆ clusters are used as metal nodes,direct chain dicarboxylic acid with C_2vsymmetry and tricarboxylic acid with D_3h symmetry as organic ligands,and acetic acid（HOAc）,formic acid（FA）and benzoate（BA）are used as modulators to regulate the morphology and structure of Ce-UiO MOFs and Ce-BTB nanosheets;The Ce-UiO-type MOFs and two-dimensional Ce-BTB nanosheets were used as photocatalysts to investigate the visible light-mediated decarboxylation oxidation properties,and investigate the photocatalytic properties and the size,morphology and efficiency of Ce-MOFs and crystal structure.The research content of this paper is mainly divided into the following two parts:（1）Study of visible light-mediated decarboxylation of Ce-UiO-type MOFsWith ceric ammonium nitrate and Ce₆ clusters as metal nodes,terephthalic acid（H₂bdc）,4,4’-biphenyl dicarboxylic acid（H₂bpdc）,2-aminoterephthalic acid（H₂bdc-NH₂）and 2-amino-4,4’-biphenyl dicarboxylic acid（H₂bpdc-NH₂）was used as an organic ligand to construct Ce-UiO-type MOFs and amino-functionalized Ce-UiO-NH₂-type MOFs.By controlling the amount of HOAc,FA or BA,the morphology and crystal structure of Ce-MOFs can be regulated.The above catalyst can be converted into p-fluorobane formaldehyde and p-fluorobane methanol by decarboxylation oxidation under room temperature,oxygen atmosphere and visible light irradiation;After 3 h reaction,the conversion rate of CAN-UiO-66 and CAN-UiO-67synthesized with cerium nitrate as metal salt can reach 95%,but the catalytic performance of introducing BA or HOAc into the reaction system is reduced;Ce₆-UiO-66 and Ce₆-UiO-67 were synthesized using Ce₆ clusters as metal salts.Under the same catalytic conditions,the conversion of p-fluorophenylacetic acid was 92%and 83%,respectively.However,amino-modified Ce₆-UiO-66-NH₂ and Ce₆-UiO-67-NH₂ can hardly catalyze the decarboxylation of p-fluorophenylacetic acid,and the reason of amino-inhibition needs to be further studied.（2）Synthesis of 2D Ce-BTB nanosheets and study on visible light-mediated decarboxylation propertiesTwo-dimensional Ce-BTB nanosheets were constructed using ammonium cerium nitrate and H₃BTB as metal salts and organic ligands,and HOAc,FA and BA as regulators.HOAc and BA play a decisive role in the morphology and crystallinity of Ce-MOFs,and the acid-free Ce-BTB₀ nanosheets were small and highly agglomerated into microspheres with lower crystallinity and specific surface area(103.5m~2·g^-1);The Ce-BTB-H₆₀ regulated by HOAc was a dispersed nanosheets with large size.The interlaced and crimped nanosheets had larger space,higher crystallinity and larger specific surface area(197.2m~2·g^-1).The Ce-BTB-BA₆₀ regulated by BA was highly dispersed nanosheets with large size and hexagonal shape,and the thickness was about 45 nm,but the specific surface area was small(12.4 m~2·g^-1).The effect of the structure and morphology of Ce-BTB two-dimensional nanosheets on the photocatalytic oxidative performance of p-fluorophenylacetic acid was investigated by using the oxidative reaction of p-fluorophenylacetic acid as a model.Under the same reaction conditions,the catalytic performance of Ce-BTB-H₆₀ and Ce-BTB-BA₆₀ were better than that of Ce-BTB₀.The high catalytic efficiency mainly came from the dispersed nanosheet structure and higher crystallinity.Finally,the mechanism of visible light-catalyzed decarboxylation based on Ce^IV/III-Oxo redox couple was proposed.