Redox-active poly(ionic liquid)-engineered Ag nanoparticle-decorated ZnO nanoflower heterostructure: A reusable composite catalyst for photopolymerization into high-molecular-weight polymers

Abstract

A two-step wet chemical method is described for the preparation of spherical silver nanoparticle-decorated flower-shaped zinc oxide (ZnO@Ag) heteronanostructures using a newly designed redox-active poly(ionic liquid)(PIL), poly(1-vinyl-3-butylimidazolium ascorbate) (P[VBuIm][As]). The first step is the generation of ZnO nanoflower using P[VBuIm][As] in water followed by its decoration with in situ formed Ag nanoparticles (AgNPs) by the reduction of AgNO3 with surface adsorbed ascorbate ion. P[VBuIm][As] plays a triple role as shape-directing-cum-capping agent, mediator for Ag+ reduction and inducing the formation of spherical AgNPs. The composite ZnO@Ag heteronanostructures are thoroughly characterized by FESEM, TEM and XRD. The as-synthesized ZnO@Ag heteronanostructures is found to be excellent composite photocatalyst towards photopolymerization of methyl methacrylate (MMA) to very high-molecular-weight poly(methyl methacrylate) (PMMA) (Ca. ∼2 × 105) with very high (82%) conversion in bulk and in solution without any photoinitiator under UV light irradiation (λmax = 350 nm). The ZnO@Ag composite is also an efficient photocatalyst for styrene polymerization in bulk and N-isopropylacrylamide polymerization in water. The photopolymerization with neat ZnO nanoflower catalyst also produces PMMA, but molecular weights are comparatively low with a low conversion. The ZnO@Ag composite photocatalyst is easily isolable by centrifugation after polymerization, is stable and is reusable for four cycles of polymerization of MMA in bulk condition without losing its original activity.