Synthesis of Silver Nanoparticles Loaded onto Polymer-Inorganic Composite Materials and Their Regulated Catalytic Activity.

We present a novel approach for the preparation of polymer-TiO₂ composite microgels. These microgels were prepared by the in situ hydrolysis and condensation of titanium tetrabutoxide (TBOT) in a mixed ethanol/acetonitrile solvent system, using poly(styrene---isopropylacrylamide)/poly(-isopropylacrylamide--methacrylic acid) (P(St-NIPAM/P(NIPAM--MAA)) as the core component. Silver nanoparticles (AgNPs) were controllably loaded onto the polymer-TiO₂ composite microgels through the reduction of an ammoniacal silver solution in ethanol catalyzed by NaOH. The results showed that the P(St-NIPAM)/P(NIPAM--MAA)-TiO₂ (polymer-TiO₂) organic-inorganic composite microgels were less thermally sensitive than the polymer gels themselves, owing to rigid O⁻Ti⁻O chains introduced into the three-dimensional framework of the polymer microgels. The sizes of the AgNPs and their loading amount were controlled by adjusting the initial concentration of [Ag(NH₃)₂]⁺. The surface plasmon resonance (SPR) band of the P(St-NIPAM)/P(NIPAM--MAA)-TiO₂/Ag (polymer-TiO₂/Ag) composite microgels can be tuned by changing the temperature of the environment. The catalytic activities of the polymer-TiO₂/Ag composite microgels were investigated in the NaBH₄ reduction of 4-nitrophenol. It was demonstrated that the organic-inorganic network chains of the polymer microgels not only favor the mass transfer of the reactant but can also modulate the catalytic activities of the AgNPs by tuning the temperature.