A new facile strategy for higher loading of silver nanoparticles onto silica for efficient catalytic reduction of 4-nitrophenol

Abstract

A new “seed mediated” strategy was designed and demonstrated for the higher loading of silver nanoparticles (Ag NPs) onto silica (SiO₂) to obtain a Ag NPs enriched SiO₂ (designated as Ag(E)–SiO₂) catalyst. Simplified two steps were utilized for the preparation of Ag(E)–SiO₂. In the first step, SiO₂ was functionalized with a negatively charged p-toluene sulfonic acid ion and embedded with a few Ag NPs(seed) and obtained as Ag(seed)–SiO₂(p-TSA⁻). In the subsequent step, excessive Ag⁺ ions were pre-concentrated onto the SiO₂ surface using the negative charges on the SiO₂ surface and reduced to Ag NPs. The pre-existing Ag NPs(seed) and pre-concentrated Ag⁺ ions enabled the growth of a further layer of Ag NPs to obtain Ag(E)–SiO₂. Results from FTIR spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements clearly supported our strategy of simultaneous functionalization of SiO₂ and Ag(seed) formation through the first step. Detailed FESEM, TEM and XPS analysis revealed higher loading (∼80 weight% (wt%)) of Ag NPs in Ag(E)–SiO₂ with a metallic valence state. The catalysts, Ag(seed)–SiO₂(p-TSA⁻) and Ag(E)–SiO₂, containing low Ag (∼10 wt%) and higher Ag loading (∼80 wt%) of Ag NPs, respectively, were tested for the reduction of toxic organic compounds such as 4-nitrophenol (4-NP) and methylene blue (MB). The Ag(E)–SiO₂ catalyst exhibited superior catalytic performance for 4-NP/MB reduction as compared to Ag(seed)–SiO₂(p-TSA⁻) (conventional) as well as over several other Ag NPs supported catalysts reported in the literature. The enhanced catalytic performance of Ag(E)–SiO₂ for 4-NP and MB reduction suggests that our new strategy is promising for the preparation of efficient supported catalysts for water purification and related applications.