Ag nanoparticle-entrapped hydrogel as promising material for catalytic reduction of organic dyes

A granular hydrogel based on chitosan (CTS) and acrylic acid (AA) was prepared using Fenton's reagent as the redox initiator and N,N'-methylenebisacrylamide as the crosslinker under ambient conditions. The resulting three-dimensional (3D) networks can serve as micro-or nano-reactors for the production of highly stable silver nanoparticles by the in situ reduction of silver nitrate (AgNO3) with sodium borohydride (NaBH4) as reducing agent and Al3+ as surface crosslinking agent. The as-prepared Ag-entrapped hydrogel was successfully confirmed by means of Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA), and then tested to catalyze the NaBH4 reduction of two organic dyes: methylene blue (MB) and Congo red (CR). The catalytic results indicate that within 30 min, MB and CR with an initial concentration of 20 mg L-1 can be reduced completely, and the catalytic activity is independent of initial pH and ion strength. In addition, the Ag-entrapped hydrogel shows excellent reusability for ten successive cycles, with no appreciable decrease in the catalytic effects.