Synthesis And Catalytic Properties Of Responsive Polymer/Au Hybrid Microgels

Noble metal nanoparticles (NPs) present excellent catalytic activities due to the quantum size effects and surface effects caused by their small size. However, the small size and highly catalytic surface also induce the noble metal NPs sintering, aggregation or hard to separation when they are used as catalysts. Polymer microgels are three dimensional cross-linked polymer networks that combine the properties of solids and fluids, which give rise to the fluid-like transport properties for the molecules significantly smaller than the gel pore size. Meanwhile, the flexible polymer chains containing rich functional groups can absorb and isolate the encapsulated NPs, protecting them from leaking out of the gel or aggregating into bulk metals. Especially, it’s better to construct smart composite catalytic system by using environment stimuli-responsive polymers, which facilities us to control the reaction process or realize other functions, such as separation of the nanocatalysts. However, designing the composite microgel systems with high catalytic activity, long-time stability, easy to separate and good regulated performance remains a challenging topic nowadays.Herein, we demonstrate three new types of responsive Au@polymer catalytic systems through designing the structure of the microgels and the mophology of Au nanoparticles. Our accomplishments may be summarized as follows:(1) Denoted as "One-pot synthesis of pH-responsive catalytic Au@PVP hybrid nanogels". In this work, we prepare pH-responsive hybrid nanogels comprising a specific shape Au core and a highly porous semi-interpenetrated PVP gel at mild polymerized conditions without the use of harsh azo initiators, which may lead to passivation or even etching of the highly active surface atoms of noble metal NPs. This hybrid system possesses a highly catalytic irregular Au NP and a highly porous semi-interpenetrated nanogel demonstrating both a pH modulated catalytic activity and anti-aggregation abilities upon recycling. (2) Denoted as "Controlled synthesis of thermo-sensitive asymmetric Au@p(NIPAM-MAA) hybrid colloids". Inorganic-organic hybrid asymmetric colloids prepared with a soft, responsive p (NIPAM-MAA) polymer are demonstrated here, which is very different from previously reported hybrid colloids only fabricated with a rigid, morphology easily controlled polymer, such as PS or PAN. Janus colloids consist of a thinner p (NIPAM-MAA) shell on one side of the Au core and a thicker shell on the opposite side. While the thinner shell provides a shorter diffusion pathway for reactants to reach the Au core, the thicker shell endows the nanostructure with long-term stability against dissolution and aggregation. Moreover, this new type of responsive Janus particles presents unique thermo-modulated catalytic process.(3) Denoted as "Responsive Au@polymer hybrid microgels for the simultaneous modulating and monitoring of Au-catalyzed chemical reaction". Hybrid microgels are made of Au NPs covered with a temperature and pH dual-responsive copolymer gel shell of p(PNIPAM-Am). The introduction of smart polymer shell onto Au NPs can not only allow modulating the catalysis of the Au core but also allow label-free in situ localized surface plasmon resonance (LSPR) monitoring of the kinetics and thermodynamics of the catalyzed chemical reaction. Unlike conventional spectroscopic methods that only reflect the overall information occurred in the reaction system, the label free in situ LSPR monitoring gives local information occurred on the catalytic surface and therefore has the potential to advance our understanding of the catalyzed chemical reaction.