Design And Synthesis Of Phosphine-based Porous Aromatic Frameworks And Their Catalytic Properties

Porous aromatic frameworks(PAFs)have attracted great attentions due to their low skeleton density,high surface area and ultra-high thermal and chemical stability.Benefitting from the various synthesis methods and easy-modifiable frameworks,PAFs have been widely applied in gas adsorption,separation and catalysis.Phosphorus(P),located in the 3rd period and the V A group in the periodic table of elements,has unique electronic structure and effect.Therefore,phosphine compounds are commonly used as metal ligands to prepare homogeneous catalysts.However,compared to the stable and recyclable heterogeneous catalytic system,homogeneous catalytic system is prohibited from many practical applications because of the rapid deactivation of accessible active sites and difficulty in catalysts separation.In order to combine the advantages of homogeneous catalysis and heterogeneous catalysis,supported metal catalysts have attracted more and more attentions.In this thesis,phosphine compounds were effectively introduced into PAFs’ skeletons,and a series of phosphine based PAFs were designed and synthesized successfully.The obtained phosphine based PAFs were employed as support materials of gold nanoparticles(AuNPs)to prepare AuNPs heterogeneous catalysts,which exhibited highly efficient catalytic activities and recyclable property.In addition,different synthetic strategies were also proposed to produce phosphine based PAFs with high surface areas.The advantages of permanent porosity,excellent stability of PAFs as well as the coordination character of P with metals would enrich the types of support materials for AuNPs immobilization.1.Triphenylphosphine and dipheny-2-pyridylphosphine were selected as building units,and PAF-93 and PAF-94 with high surface areas and good stabilities were synthesized by simple and economic Friedel-Crafts alkylation reaction.The supported AuNPs catalysts Au-PAF-93 and Au-PAF-94 were prepared by utilizing the interactions between P,N atoms in PAFs’ skeletons and AuNPs.In Au-PAF-94,higher content of AuNPs with smaller sizes were detected because of the stronger interactions induced by the synergistic effect of P and N donors with AuNPs.Compared to Au-PAF-93 with single P sites,Au-PAF-94 exhibited more excellent catalytic performance.2.Porous materials with high surface area are conductive to the AuNPs immobilization and transportation and separation of reactants in the catalytic process.In order to synthesize phosphine based PAFs with higher specific surface area,another synthetic strategy different from that used in the synthesis of PAF-93 was investigated.In this work,based on the selection of triphenylphosphine and dipheny-2-pyridylphosphine as building monomers,biphenyl and dimethoxymethane were introduced into the reaction system as external linkages.Under the catalysis with anhydrous Fe Cl3,PAF-95 and PAF-96 were synthesized using Friedel-Crafts alkylation reaction.The obtained PAF-95 and PAF-96 possessed higher specific surface area than PAF-93 and PAF-94,indicating the good effect of improved synthetic method.The heterogeneous nano-catalysts Au-PAF-95 and Au-PAF-96 showed great activities and high selectivity in the reduction of nitroarenes as well as good stabilities and recyclability.After five catalytic cycles,Au-PAF-95 and Au-PAF-96 still maintained high catalytic activity.3.In order to obtain PAFs with more abundant metal coordination sites,a series of monomers containing dual P centers such as bis(diphenylphosphino)methane,1,2-bis(diphenylphosphino)ethane and 1,3-bis(diphenylphosphino)propane were selected.Upon the employment of Friedel-Crafts alkylation reaction,PAF-160,PAF-161 and PAF-162 with dual coordination sites were successfully prepared.These PAFs were served as porous supports for AuNPs immobilization to produce heterogeneous Au nano-catalysts(Au-PAF-160,AuPAF-161 and Au-PAF-162).The different lengths of alkyl chains between two P centers would regulate the distance of catalytic active sites in Au-PAFs,so the distribution of catalytic centers were relatively dispersed.The heterogeneous catalysts Au-PAF-160,Au-PAF-161 and AuPAF-162 exhibited excellent catalytic performance for the reduction of nitroarenes with diverse functional groups as well as double nitro groups.Furthermore,they displayed satisfactory catalytic performance in the continuous column catalytic experiments and were potential candidates in the industrial applications.