Nano Metal/MOFs Composites Construction And Photocatalytic Organic Synthesis

As a relative new type of crystalline porous material,metal-organic framework materials（MOFs）have received extensive attention and wide application in the field of catalysis due to their high specific surface area,structural diversity and customizability.The permanent porosity of MOFs makes them own advantages in the field of loading restricted guest species（such as metal nanoparticles（MNPs））to improve the catalytic performance.In recent years,MOFs have been widely used in photocatalysis such as hydrogen production,CO₂ photoreduction,and organic pollutant decomposition.However,MOFs based photocatalytic materials were rarely utilized in the field of organic synthesis.This work focused on the design and construction of MOFs-based nanocomposites and explored their applications in photocatalytic organic conversion.（1）MOFs with different crystal sizes,morphologies and structures were constructed by changing the ligand structure and adjusting the coordination of 2-methylimidazole（2-MI）.With MOFs as the carrier,the noble metal Pd was loaded in MOFs by double-solvent method.The"quasi-MOF"structure was formed by calcination at 300℃under nitrogen,and the Pd NPs were prepared by in situ photoreduction.SEM characterization showed that 2-MI could adjust the morphology of NH₂-MIL-101（Fe）crystal,and the morphology was stable during calcination at300℃.FT-IR,Raman,XRD and XPS results showed that calcination at 300℃could partially decompose the organic ligands of MOFs to form"quasi-MOF"structure,and"quasi-MOF"structure could promote the interaction between Pd NPs and organic nodes.TEM results displyed that Pd NPs were uniformly dispersed on MOFs.UV vis-DRS and transient photocurrent results indicated the significant improvement in visible light absorption and electron-hole pair separation transmission with"quasi-MOF".Compared with Pd/NH₂-MIL-101（Fe）,2-MI assisted synthesis of needle like Pd/NH₂-MIL-101（Fe）-2MI increased the nitrobenzene conversion from 82%to 100%and the N-alkylation chemoselectivity from 64%to 86%in one pot multi-step hydrogenation and N-alkylation under visible light.The chemoselectivity of N-alkylation increased from 86%to 96%after the strong interaction formation between Pd NPs and inorganic nodes.After centrifugation,the conversion and chemoselectivity of the photocatalyst could be well maintained in five cycles.In situ diffuse reflectance infrared Fourier transform spectroscopy（DRIFTS）was used to analyze the reaction mechanism.（2）Three kinds of classical Fe-MOFs were synthesized by hydrothermal or solvothermal methods.Pd NPs with average particle size of about 4.5 nm were loaded in Fe-MOFs by two-solvent and photoreduction method.The similar Pd NPs average particle size avoided the influence of metal particle size on the photocatalytic performance.The SEM,TEM,FT-IR,XRD and XPS results showed that the three Fe-MOFs had different morphology and microstructure,and the Pd NPs were uniformly dispersed on the Fe-MOFs;PL,UV vis-DRS,EIS,and transient photocurrent indicated that the difference in microstructure and the introduction of Pd would affect the light absorption capacity and the efficiency of electron-hole pair separation and transmission.Pd/MIL-101（Fe）nanocomposites had good photocatalytic activity and recycling performance under visible light.The conversion of amine and aldehyde oxidative amination reaction to form amide could reach 94.2%;the conversion of C-H arylation of thiazole and bromobenzene was as high as 93.1%;with K₂HPO₄,the conversion of decarboxylation cross-coupling between iodobenzene and cinnamic acid could reach93.7%,E/Z=99/1,and Z-type product was the main product with K₂CO₃.The reaction mechanism was proposed with various control experiments and research methods.In summary,we have designed and synthesized series of highly efficient,stable and well dispersed Pd/MOFs composite photocatalysts.The developed photocatalysis showed excellent photocatalytic performance in several novel photocatalytic organic reactions.In addition,the corresponding photocatalytic reaction mechanism was analyzed with various research methods.This dissertation expanded the application of MOFs based photocatalytic materials in the field of photocatalytic organic conversion.