Green fabrication of hydrogel-immobilized Au@Ag nanoparticles using tannic acid and their application in catalysis

Abstract

Highly catalytically active core–shell nanoparticles (NPs) have attracted great attention towards applications. Herein, core–shell Au@AgNPs were simply obtained via a green and cheap one-step method using tannic acid (TA) as both a reductant and a stabilizer. TA was used to cross-link poly(vinyl alcohol) (PVA), forming a PVA/TA hydrogel with the repeated freezing–thawing method. The gelation mechanism was confirmed by urea-treatment experiment, UV-vis, IR, TG, and DSC. The freezing–thawing treatment endows TA and PVA with better conditions to form hydrogen bonds, and the intensive hydrogen bond interactions and weak crystallization interactions work in synergy to maintain the three-dimensional network of the PVA/TA hydrogel. Owing to favorable mechanical properties and suitable pore size, the PVA/TA hydrogel further served as a support for the immobilization of Au@AgNPs that exhibited excellent and recyclable catalytic degradation ability for 4-nitrophenol, 2-nitrophenol, methylene blue, and Congo red.