Preparation of Core—Shell Silver Nanoparticles@Mesoporous Silica Nanospheres with Catalytic Activities

Core-shell silver nanoparticles@mesoporous silica spherical nanoparticles (Ag NPs@MSNs) were prepared by a two-step method. First, Ag NPs were synthesized by chemical reduction using silver nitrate (AgNO₃) as the precursor, cetyl trimethyl ammonium bromide (CTAB) as the stabilizer, and sodium borohydride (NaBH₄) as the reductant. Then, MSNs were obtained by employing CTABstabilized Ag NPs as the template and hydrolyzing tetraethoxysilane (TEOS) precursor in the presence of the alkaline precipitant, triethanolamine (TEOA). The effects of different preparation routes (core-first vs. shell-first), type of reductants as well as extraction methods and agents were studied. The obtained core-shell NPs were characterized by infrared spectroscopy (IR) and transmission electron microscopy (TEM). Our results showed that the core-first route was viable to produce uniform Ag NPs@MSNs with ordered mesostructures. Afterwards, those NPs were used as the catalyst to catalyze the reduction of rhodamine, a model dye compound representing organic pollutants in waste water, in the presence of NaBH₄. It was found that Ag NPs@MSNs not only were efficient catalysts but also participated as coreductants in the reaction. Moreover, they exhibited almost no loss of catalytic efficacy after several reduction cycles, which indicated their promising future use as efficient recyclable catalysts for organic pollutant treatments.