Synthesis And Catalytic Study Of Carbonized And Functionalized Hypercrosslinked Hollow Nanospheres

Porous organic polymers are popular materials which have been widely used and studied.Compared with inorganic porous materials,they have the advantages of high specific surface areas,light skeleton,multi-pore structure,good thermal stability and strong chemical modification.Therefore,they play irreplaceable roles in gas adsorption,fluorescence detection,drug transport and multiphase catalysis.However,as the newly developed materials,organic porous polymers have some problems,such as complex synthetic strategy,poor controllability of structure and incomplete development of applications.Therefore,it is the focus of current research to design a relatively simple and stable synthetic route of porous organic polymer materials and to excavate their unique properties to make full use of them.This thesis will focus on the development of a variety of polymer porous materials with specific functions and study their catalytic acid-base one-pot reactions,oxidation,reduction,coupling reactions and applications in the field of photothermal conversion under relatively mild conditions.And through the continuous optimization of the performance of porous polymer catalyst materials,the design of the current green chemistry and sustainable development requirements of the catalytic system,so that the catalysis develops toward low energy consumption,no pollution and environmentally friendly direction.Firstly,copolymers（PS-b-PLA）are prepared by ring-opening polymerization（ROP）and reversible addition-fragmentation chain-transfer radical polymerization（RAFT）using Z-type chain transfer agent.Subsequently,the hollow porous organic nanosphere networks（H-PONNs）containing rich initiator sites of trithiester are obtained by the method of Friedel-Crafts alkylation hypercrosslinking induced self-assembly reaction,which could continue to initiate polymerization in the cavity of the hollow spheres.Based on the unique structure,it is possible to introduce incompatible small acid molecular（PVBS）and small base molecular（VBMAP）into the interior of the hollow sphere by polymerization,respectively.One end of the synthesized polymer（PPVBS/PVBMAP）is anchored inside the hollow sphere（like a heterogeneous catalyst）,while the other end is free to move（like a homogeneous catalyst）.Subsequently,the catalytic effect on acid-base one-pot reaction is investigated.The experimental results show that the synthesized acid catalyst and base catalyst have good catalytic activity and cyclic stability.On the basis of the hollow microporous nanospheres,magnetic nanoparticles（Fe₃O₄）and palladium nanoparticles（Pd）are introduced into the cavity of the hollow nanospheres respectively by impregnation method to form a unique yolk shell structure（Pd@MPONs）.Therefore,the catalyst is endowed with high catalytic activity and fast magnetic responsing ability.The study on the adsorption properties of Pd@MPONs shows that the yolk shell structure can rapidly enrich the substrate into the cavity of the hollow sphere,thus greatly promoting the contact between the substrate and the active site,which is the key to the high catalytic activity of Pd@MPONs for the oxidation of alcohol at room temperature.Experiments show that Pd@MPONs has excellent catalytic activity,good cyclic stability and excellent magnetic recovery performance for alcohol oxidation and Heck reaction.The prepared PLA-B-PS block copolymer was cross-linked with small molecule pyrrole to obtain hollow nanospheres（PPy-HHNs）with polypyrrole shell.Polypyrrole has strong near-infrared photothermal conversion ability,and PPy-HHNs have a unique hollow sphere structure that enables multiple reflection of light in the cavities,thus greatly improving the utilization rate of light.Hence,under the irradiation of near-infrared light,the internal temperature of PPy-HHNs could be up to 80℃.Besides,the photothermal conversion ability of PPy-HHNs was indirectly proved by driving the thermal activation D-A reaction.Through the comparison of HHNs without pyrrole and PPy-PS without hollow structure,the doping of pyrrole and the existence of hollow structure are the key of photothermal conversion.Then,a near-infrared controlled catalytic platform is designed to control the process of thermal activation D-A reaction by switching on and off the near infrared light.N-doped hollow porous nanospheres（N-HPNs）are prepared from copolymer（PNVC-b-PLA）with two blocks of polyn-vinylcarbazole（PNVC）and polylactic acid（PLA）,respectively,and crosslinked with small molecule melamine.Subsequently,both palladium and iron salts are impregnated on N-HPNS.Finally,the nitrogen-doped magnetic hollow carbon spheres supported Pd Fe alloy catalyst（Pd Fe@N-MHCNs）is obtained by in-situ carbonization reduction reaction.Through a series of characterization,it is proved that iron and palladium exist in the form of alloy.In order to study the synergistic catalytic effect of Pd Fe@N-MHCNs,catalysts with different palladium-iron ratios are prepared and their catalytic performance is tested.Experiments show that Pd Fe@N-MHCNs can catalyze the hydrogenation of levulinic acid and N-alkylation of alcohols and amines efficiently under relatively mild conditions,and it shows good cyclic stability.Based on the Friedel-Crafts alkylation hypercrosslinking reaction,a triazine framework polymer（C-CTMP）with high nitrogen content is obtained by cross-linking small molecules carbazole and melamine directly.By utilizing the strong complexation between rich nitrogen and metal elements on the carrier,the precious metal palladium salts are subsequently impregnated on C-CTMP.In situ growth of Pd nanoparticles on nitrogen-doped carbon materials by high temperature carbonization reduction reaction（Pd@N-PCM）.The results show that Pd@N-PCM can catalyze suzuki-Miyaura coupling reaction under mild conditions（room temperature,non-toxic solvent and air atmosphere）and has excellent catalytic activity and cyclic stability.