Synthesis Of Hierarchical Metal-organic Frameworks For Organic Catalysis

Metal-organic frameworks?MOFs?are highly porous crystalline materials,and have attracted dramatical attention due to their potential applications in gas adsorption separation,molecular sensing,optical devices,and heterogeneous catalysis.Particula-rly,MOFs have been considered as one of most promising heterogeneous catalysts owing to their high specific surface area,tunable pore structure and abundant catalytic activity sites.Three strategies have been developed for the design of MOF-based catalysts:?1?metal nodes serving as catalytic site,for example,the open metal sites in MOFs are potential Lewis acid catalytic site;?2?appended functional groups?e.g.-NH2,-SH,-SO3H,L-proline,etc.?on the organic ligands of MOFs;?3?loaded functio-nal guests,for examplemetal nanoparticles?MNPs?loaded MOFs,MNPs@MOFs.It has been found that the catalytic performance of MOFs is closely related to its structural defects.Compared with the conventional MOFs,hierarchical MOFs possess more accessible catytic sites.Template controlled MOF growth and MNPs loaded MOFs are two efficient methods for the synthesis of hierarchical MOFs.In this thesis,hierarchical HKUST-1 and UiO-67-NH₂ nanoplates were synthesized by the utility of templates.The catalytic performance of hierarchical HKUST-1 and UiO-67-NH₂ were investigated.Moreover,MNPs@MOFs were sysnthesized under mild conditions.The main researches are following:?1?The combination of solvent-induced crystallization and templates?e.g.,hexadecyl trimethyl ammonium bromide,polyvinylpyrrolidone,acetic acid.benoic acid,and pivalic acid?was used to synthesize hierarchical RT-HKUST-1 micro/nano-crystals.By using TEMPO radicals?2,2,6,6-tetramethyl piperidine oxide?as co-catal-yst,RT-HKUST-1 enables selective oxide primary alcohols to their corresponding aldehydes with good conversion and excellent selectivity.Under the same catalytic reaction conditions,RT-HKUST-1 sysnthesized by using CTAB as template show much better catalytic performance than RT-HKUST-1 prepared by using PVP as template.In the case of Knoevenagel condensation reaction,the catalytic activity of RT-HKUST-1 by various conditions under the following oder:RT-HKUST-1_CTAB>RT-HKUST-1>HKUSTsol,where HKUSTsol represent solvothermal synthesis of HKUST-1.?2?Zr-MOFs show excellent water stability and thermal stability.We have synthesized UiO-67-NH₂ octeheda microcrystals and nanoplates with the help of benzoic acid and addition of concentrated hydrochloric acid,respectively.The results showed that when benzoic acid was used as template,the octahedral UiO-67-NH₂ was obtained,and when benzoic acid and concentrated hydrochloric acid were used as template,the layered structural UiO-67-NH₂ containing a large number of defects?mainly the absence of organic ligands?could be obtained.UiO-67-NH₂ synthesized with the two template agents above serves as a base catalyst for the condensation reaction of benzaldehyde and malonitrile knoevenagel reaction,and the octahedral UiO-67-NH₂ is superior to the flaky UiO-67-NH₂.Since UiO-67-NH₂ with flaky structure contains more defect sites,its catalytic performance is theoretically better than that of UiO-67-NH₂ with octahedral morphology.However,the experimental results were contrary to the theoretical results.The catalytic performance of sheet UiO-67-NH₂ did not improve with the increase of defects,but decreased with the increase of concentrated hydrochloric acid content.?3?Four kinds of MNPs loaded MOFscomposites,namely Pt-@HKUST-1,Au@HKUST-1,Pt@UiO-67-NH₂ and Pt@UiO-67-NH₂ were synthesized by solvent-induced crystallization underroom temperature.The feasibility of synthesis of sandwich structure MIL-100?Fe?@Pt-@UiO-66-NH₂ and MIL-100?Fe?@Pt-@UiO-67-NH₂ by coating 25 layers of MIL-100?Fe?integument on the surface of Pt-@UiO-66-NH₂ and Pt-@UiO-67-NH₂ was preliminarily explored by means of layer by layer self-assembly method.TEM results showed that the layered self-assembly method was an effective means to obtain the sandwich structure MOF@MNPs@MOF,which laid a foundation for the subsequent preparation of complex hierarchical structure MOF@MNPs@MOF.