Yolk–Shell Nanocomposites of a Gold Nanocore Encapsulated in an Electroactive Polyaniline Shell for Catalytic Aerobic Oxidation

Abstract

Noble metal nanoparticles (NPs) have been widely applied in nanocatalysis owing to the benefits associated with their miniature size. However, improving their stability and reusability during catalytic applications still remains a great challenge. To this end, monodispersed gold@void@polyaniline yolk–shell nanocomposites (Au@void@PANI YSNs) were synthesized using bottom-up template-assisted methods. Au@SiO 2 NPs, prepared from a modified sol–gel process, were used as templates for the thiol–ene click reaction with 4-vinylaniline (VAn) to immobilize the aniline moieties, which later performed as the initiation sites for the oxidative copolymerization of aniline from the outer surface of the Au@SiO 2 –VAn NPs with an electroactive PANI shell (Au@SiO 2 @PANI NPs). The silica layer sandwiched between the Au core and PANI shell was selectively removed by aqueous hydrofluoric acid to produce Au@void@PANI YSNs with a movable Au core. The electroactive PANI shell not only serves as a physical barrier that prevents the self-association of Au cores and provides a vacant cavity where chemical transformations take place on the Au cores in a controlled manner but also improves the activity and stability of Au cores due to the electrons delocalization and transfer from the Au d orbitals of the nanocores to the π-conjugated ligands of the PANI shell, as proved by the X-ray photoelectron spectroscopy results. The as-synthesized YSNs were found to perform as flexible and reusable heterogeneous catalysts with high catalytic efficiency for the aerobic oxidation of alcohol in aqueous solution. One may find the present study to be a general and effective way to fabricate monodispersed hollow nanomaterials in a controlled and green manner.

Functionalization of Hollow Nanomaterials for Catalytic Applications: Nanoreactor Construction

“…Similarly, M@SiO 2 also could be used to fabricate the metal@polymer yolk–shell structures. Via bottom‐up template‐assisted strategies, monodispersed gold@void@polyaniline yolk–shell nanocomposites (Au@void@PANI YSNs) were obtained, as reported by Li et al The core, Au@SiO 2 NPs prepared from a modified sol–gel process were served as seeds for the following surface growth of polyaniline shell, using the thiolene click reaction with 4‐vinylaniline (VAn) as a bridge to immobilize the aniline moieties and subsequent graft copolymerization. After being treated with hydrofluoric acid, the middle silica layer between the Au core and polymer shell was selectively etched, resulting in the Au core encapsulated into a hollow PANI shell.…”

Fabrication of Smart Hybrid Nanoreactors from Platinum Nanodendrites Encapsulating in Hyperbranched Polyglycerol Hollow Shells

“…The observed M n,GPC of HPGD random copolymers are found to be slightly lower than anticipated, which probably arises out of the lower hydrodynamic volume of hyperbranched polymers with compact structure than that of linear standards and the interaction of peripheral terminal groups with the GPC column fillers. 25,29,30 3.2. Preparation of Pt Nanodendrites and Pt@SiO 2 -MTS Core−Shell Nanospheres.…”

“…In view of a relatively low monomer concentration in the course of polymerization and immediate opening of oxirane rings, anionic ring-opening multibranching polymerization (AROMP) using slow monomer addition of glycidol (GLY) with other oxirane comonomers has been explored for introducing tailored functionalities into hyperbranched polyglycerol (HPG) scaffolds with a broad range of accessible molecular weights, narrow molecular weight distributions, high solubility, thermal stability, chemical resistance and biocompatibility. − However, the limited options for characterization of the grafted polymer brushes and the incompatibility with highly basic catalysts eventually lead to the failure in direct AROMP from silica-mediated nanoparticles. To optimize desirable functionalities and maximize the structural advantages, narrowly distributed hyperbranched poly­(glycerol- co - N , N -diallyl glycidyl amine) (HPGD) random copolymers, prepared a priori via AROMP of GLY and N , N -diallyl glycidyl amine (DAGA) in the presence of sodium methoxide as the catalyst and 1,1,1-tris­(hydroxymethyl)­ethane (TME) as the initiator, was then linked to silica-mediated nanoparticles through thiol–ene photopolymerization, as described in Scheme .…”

“…25,29 The synthesis of Pt@SiO 2 -MTS was performed following the previously reported method (see the Supporting Information for details). 30,31 2.2. Synthesis of Hyperbranched Poly(glycerol-co-N,Ndiallyl glycidyl amine) (HPGD) Random Copolymers via Anionic Ring-Opening Multibranching Polymerization (AROMP).…”

“…GLY and 1,4-dioxane were purified by distillation under reduced pressure prior to use. N , N -diallyl glycidyl amine (DAGA) was prepared following a procedure described elsewhere. , The synthesis of Pt@SiO 2 -MTS was performed following the previously reported method (see the Supporting Information for details). , …”