Construction And Properties Of Temperature-Responsive Polymer Decorated Metal Nanohybrid Catalysts Based On Mussel-Inspired Chemistry

Noble metal nanoparticles?NPs?have gained wide attention owing to their nano-structural morphologies,large surface area and high chemical activity,which led to broad applications in catalysis,optoelectronic devices and biomedicine.However,the catalytic activity of metal NPs may be hindered due to their self-aggregation and instability,which greatly limits the development prospect of metal NPs.A large number of studies show that the efficient catalysis can be achieved by using graphene oxide?GO?,Fe3O4 and other materials as support of metal NPs.Two-dimensional GO material is considered as an attractive candidate for catalyst supports due to their large surface area,good electronic property,chemical stability and mechanical strength.It is worth noting that there is an intense synergistic interaction between carbon supports and PdNPs,which can enhance the catalytic activity and stability of PdNPs.Owing to excellent magnetic properties,Fe₃O₄ NPs are favored for their magnetic separation and reuse of hybrid nanomaterials,satisfying the concept of green chemistry.However,there is poor dispersion and stability for GO or Fe₃O₄supported metal NPs in the water-phase catalytic system.Therefore,introducing hydrophilic polymer to modify catalyst carrier is an effective method to solve the above-mentioned shortcomings.Environmentally responsive polymers can induce a series of physical and chemical changes in polymer components when external stimuli?temperature or pH?are applied.Metal nanocatalysts stabilized by temperature-responsive polymers have attracted extensive attention due to their special properties and potential application prospects.In this thesis,we fabricated temperature-responsive coordination polymer functionalized nanohybrid materials based on mussel-inspired chemistry and used them as catalyst supports of metal NPs.The episulfide group as ligand in block copolymer chain can well control and stabilize the in situ generated metal NPs,thus realizing efficient catalytic reduction process and intelligent temperature-responsive catalysis.The detailed content of this thesis includes the following two parts:In the first part,the temperature-responsive block copolymer brush grafted reduced graphene oxide nanohybrid?BPrGO?was successfully constructed using the principle of mussel-inspired chemistry,and was applied as the support carrier of highly active ultra-fine palladium NPs to achieve highly efficient heterogeneous catalytic reduction.We first synthesized a novel temperature-responsive episulfide-containing double-hydrophilic diblock copolymer,poly?poly?ethylene glycol?methyl ether methacrylate-co-2,3-epithiopropyl methacrylate?-block-poly?N-isopropylacrylamide??P?PEGMA-co-ETMA?-b-PNIPAM?from a thermo-sensitive hydrophilic monomer NIPAM and another hydrophilic monomer PEGMA as well as ETMA coordination monomer,through a reversible addition-fragmentation chain transfer?RAFT?polymerization utilizing a chain-transfer agent with a catechol unit as the end group.Then the block copolymer was successfully grafted onto the surface of rGO by mussel chemistry reaction to prepare polymer brush-modified nanohybrid sheet?BPrGO?,which was used as catalyst carrier to prepare Pd nanoparticles-loaded nanohybrid catalyst?PdNPs@BPrGO?via the in situ reduction of palladium precursors with the episulfide ligands of the block copolymer as a stabilizer.The resulting PdNPs@BPrGO nanohybrid catalyst had good water dispersibility and stability.The results showed that compared with the PdNPs@GO catalyst without polymer modification,the low dose PdNPs@BPrGO catalyst exhibited excellent catalytic effect in the reduction of methylene blue and nitrophenol,and could be used for at least five times without significant loss of catalytic activity.PdNPs@BPrGO catalysts also possessed an interesting temperature-responsive catalytic property due to the reversible“coil-to-globule”phase transition behaviour in aqueous solution for PNIPAM blocks onto the surface of catalyst.In the second part,RAFT polymerization was used to prepare P?NIPAM-co-ETMA?copolymer with catechol end group,which was grafted onto superparamagnetic Fe3O4nanoparticles by coordination adhesion based on mussel chemistry,and used as the carrier of metal nanocatalyst.With carbon dots?CDs?as reducing agent and stabilizer,a kind of high efficiency magnetic recoverable nanohybrid catalyst?PFe3O4@CDs@PdNPs?was prepared by using in situ reduction Pd²⁺to Pd NPs with the episulfide groups as ligands on the copolymer brushes.Because CDs can act as electron donors and/or receptors,they have strong synergistic catalysis with PdNPs and can significantly promote the catalytic activity of PFe3O4@CDs@PdNPs.Compared with the CDs-free modified catalyst PdNPs@PFe3O4,the as-prepared nanocatalyst had higher catalytic reduction activity for p-nitrophenol and different dyes,including methylene blue?MB?,methyl orange?MO?,rhodamine B,Congo red?CR?,rhodamine 6G?R6G?and resin azure?RZ?,which is attributed to the better water dispersion stability of the catalyst and the synergistic catalysis of CDs.In addition,the PFe3O4@CDs@PdNPs catalyst can be easily recycled by external magnetic field,and reused at least six repeated cycles,and at the same time,also has a temperature responsive catalytic behavior.