Construction Of Thermo-responsive Coordination Polymer-stabilized Gold Nanohybrids And Their Applications In Catalysis

Nanohybrid materials have aroused great interest of researchers in the optoelectronics,energy,environment and catalysis fields because they integrated the properties of various materials in one.Especially,the gold nanoparticles?Au NPs?have also been widely introduced into the nanohybrid materials due to its special performance.However,it is well known that one of the main problems of gold nanoparticles is its colloidal stability in solution media.A large number of studies have shown that the method using polymer to stabilize nanoparticles can effectively improve the colloidal stability of Au NPs in solution.The Au NPs hybrid materials can be prepared by modifying the gold nanoparticles with different materials,and taking the advantage of the possible synergies between them to improve the existing properties of nanohybrid materials and to endow them with new functionality and to improve some deficiencies in nature of the materials,which can play a greater role in practical applications.In recent years,the nanohybrid materials constructed by integrating Au NPs with graphene oxide?GO?and magnetic Fe₃O₄ are much favored by everyone.In addition,the “environmentally responsive” material,which has been widely concerned in recent years,has also been introduced into nanohybrid materials.The “environmentally responsive” material refers to a class of materials that can alter their physical or chemical properties by making intelligent responses to external stimuli?temperature,pH,magnetic fields,light,etc?and this kind of materials has a very good application prospect in both performance and practical application.In this thesis,gold nanoparticles were selected as one of the building units,and the episulfide-containing thermo-responsive polymer ligand was used as the stabilizer.And integrated with reduced graphene oxide and magnetic Fe₃O₄ magnetic materials,we successfully constructed a new type of gold nanohybrids with controllable self-assembled morphology and multifunctional integration of thermo-responsive and recyclable properties,and studied their applications in catalysis.The detailed content of this thesis includes the following two parts:In the first part,we firstly designed and prepared the temperature-responsive block copolymer P?NIPAM-co-ETMA?-b-P?PEGMA??P?from episulfide-containing 2,3-epithiopropyl methacrylate?ETMA?as ligand and N-isopropylacrylamide?NIPAM?with thermo-responsive properties as well as water-soluble poly?ethylene glycol?methylether methacrylate?PEGMA?via reversible addition fragmentation chain transfer?RAFT?polymerization.And the micellar assembly behavior of this block copolymer was also studied.Gold nanoparticles?Au NPs@P?with different sizes and morphologies were prepared by in-situ reduction method in the coordination micelles using the episulfide group in the block polymers as ligand.We also investigated the effect of the polymer on the size and morphology of Au NPs obtained by in situ synthesis route,and the catalytic performance of the resulting Au NPs@P hybrids was studied by using a model reaction of catalytic reduction of p-nitrophenol by NaBH4.The effects of the size of Au NPs and the amount of reducing agent and catalyst on the catalytic reaction were mainly studied.The results showed that the introduction of polymer ligand P improved the stability of Au NPs@P hybrid catalyst which exhibited excellent catalytic activity for the reaction of p-nitrophenol,and the catalytic activity increased with the increase size of Au NPs in the hybrid catalyst.In addition,the use of thermo-sensitive polymer ligands also imparted the intelligent controllable properties to Au NPs with thermal “switching” when catalyzing the reduction of nitrophenol.In the second part,we developed a new method to construct the temperatureresponsive polymer functionalized reduced graphene oxide?RGO?@Fe₃O₄@Au NPs magnetic nanocomposites?AuNPs@GFDP?for organic catalytic reaction.We first synthesized superparamagnetic Fe₃O₄ nanoparticles?NPs?on reduced graphene oxide?RGO@Fe₃O₄?via one-pot chemical functionalization method,and then a polydopamine?PDA?layer was formed on the surface of RGO@Fe₃O₄ to obtain RGO @ Fe₃O₄ @ PDA composite?GFD?using the self-polymerization of dopamine?DA?in the weak alkaline aqueous solution by mussel-inspired chemistry.The thermo-responsive copolymer ligand of poly?N-isopropylacrylamide-co-2,3-epithiopropyl methacrylate?P?NIPAM-co-ETMA??P?was also synthesized via a reversible addition fragmentation chain transfer?RAFT?polymerization and was grafted onto the surface of GFD?GFDP?via a simple Michael addition reaction.Finally,the episulfide groups in the copolymer were used as ligands to fabricate Au NPs functionalized GFDP nanocomposites through in situ reduction of HAuCl4 in GFDP solution.Au NPs@GFDP nanocomposite exhibited excellent dispersibility and stability in aqueous solutions.We studied the catalytic reduction of different nitrophenols by Au NPs @ GFDP.The results showed that Au NPs@GFDP as a catalyst during the reaction of reduction nitrophenol by Na BH4 had a higher catalytic performance.More importantly,due to the presence of magnetic Fe₃O₄ nanoparticles,the Au NPs @ GFDP nanocomposite materials were easily separated and recycled by magnetic separation and the efficiency of catalyst reuse was also very ideal.The catalytic reduction reaction also exhibited excellent temperature-responsive behavior due to the presence of thermo-sensitive PNIPAM segments on the surface of Au NPs@ GFDP catalyst.The method of constructing temperature-responsive nano hybrid materials developed by this work may be of great potential for various industrial catalytic applications.