Synthesis Of Phosphorus-based Porous Aromatic Frameworks And Their Catalytic Properties

Porous aromatic frameworks(PAFs)are an important class of porous materials,which have attracted widespread attention due to their high specific surface areas and excellent stability.PAFs are usually constructed with periodically arranged phenyl units connected by C-C bonds.These phenyl units provide PAFs with a large number of accessible inner surfaces and easy functionalized sites.Based on these characteristics,PAFs are widely used in gas adsorption and separation,metal ion extraction and catalysis.Phosphorus is located in the third period of the VA group in the periodic table.It has a unique electronic structure which induces abundant electronic effects.Therefore,phosphine compounds are often used as protective ligands to prepare stable precious metal catalysts.In this thesis,phosphine-containing aromatic compounds are selected to synthesize functionalized PAFs,so that the porous materials not only have high specific surface areas and high stability,but also give play to the advantage of coordination with precious metals.The resulted PAFs are used as supports for gold nanoparticles(Au NPs),and stable heterogeneous gold nano-catalysts(Au-PAFs)with high-efficiency and reusability are prepared.In this thesis,two different synthetic strategies for phosphine-containing PAFs are proposed.1.With diphenylphosphoric acid as the building monomer andα,α’-dibromo-p-xylene as the crosslinking agent,PAF-92 with high specific surface area and high stability is synthesized via Friedel-Crafts alkylation reaction.The Brunauer Emmett Teller surface area of PAF-92 is 504 m~2/g.Because of the phosphoric acid structure in PAF-92,it has abundant electronic effects,and can create a stable coordinated environment with Au NPs.Au-PAF-92 is prepared by using PAF-92 as the Au NPs supporting platform,and its catalytic performance towards the reduction of aromatic nitro compounds is discussed.Nitrobenzenes which contains o-chloro,m-chloro,p-chloro,methoxy and two chlorines functional group are selected as the reduction substrates of nitroaromatics,and the catalytic reduction reaction experiments are carried out at room temperature.The results show that Au-PAF-92has high catalytic activity for the reduction of aromatic nitro compounds with different substituents.2.Dual P centers building monomers with different carbon chain lengths,including bis(diphenylphosphine)methane,1,2-bis(diphenylphosphine)ethane,1,3-bis(diphenylphosphine)propane and 1,4-bis(diphenylphosphine)butane are selected for the synthesis of a series of PAFs containing double P centers.Via Friedel-Crafts alkylation reaction,BPAF-160,BPAF-161,BPAF-162 and BPAF-163are synthesized with the above-mentioned monomers together with biphenyl as comonomer and dimethoxymethane as diplomatic linker.The dual P centers in PAFs’framework can act as electron donors and form stable coordinated structures with Au NPs.The differences of carbon numbers between the double P centers will regulate the contact areas between the reactants and catalysts.The resulted heterogeneous catalyst Au-BPAFs possess excellent catalytic reduction performance for aromatic nitro compounds containing different functional groups.In the cyclic catalysis experiment,Au-BPAFs maintain the satisfactory catalytic activities and are expected to have good application prospects.