Developing Ag-tercopolymer microgels for the catalytic reduction of p-nitrophenol and EosinY throughout the entire pH range

Abstract

In this study ter-copolymer microgel networks of thermo sensitive N-isopropyl acrylamide (NIPAm), pH sensitive methacrylic acid (MAA) and 2-hydroxyethyl methacrylate (HEMA) monomers were prepared with different MAA content. Ag nanoparticles were stabilized in ter-copolymer microgel networks at pH 3 and 7. The size of microgel particles was studied at different environmental temperature and pH using the Zetasizer Nano and scanning electron microscopy. The thermal stability and metal content in hybrid microgels were confirmed by thermal gravimetric analysis. The hybrid microgels were tested for their catalytic behavior towards the reduction of toxic pollutants p-nitrophenol (pNP) and Eosin Y (EY) with sodium borohydride at the entire pH range (2 to 9, SD ± 0.2). The hybrid microgels prepared at pH 7 showed enhanced catalytic performance because of the high content of Ag nanoparticles, while after the preparation, the catalytic property of the catalysts was found decrease with the increase in environmental pH. It was due to the collapse of the microgel network, which further brings the Ag nanoparticles closer in proximity to each other and enhanced the collision rate of reactants with the surface of catalysts which increased the conversion rate. The composition having high content of MAA showed maximum kapp values i.e. 0.45562 and 0.62537 min−1 towards pNP and EY respectively. The catalysts were recycled and reused for multiple cycles with a negligible decrease in their catalytic rate.