Silver nanoparticles stabilized by bundled tungsten oxide nanowires with catalytic and antibacterial activities
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n in situ redox reaction was developed to synthesize bundled tungsten oxide (WO3@W18O49) ultrafine nanowires (BUNs) loaded with Ag nanoparticles using weakly reductive W18O49 and oxidative silver nitrate as precursor. However, due to the weak activation between the two reactants, redox just happened on the surface of W18O49, resulting in the formation of W18O49 coated with WO3 (here, we refer this structure to WOx simply), and the bulk phase of the composites retained the same pattern. Ag nanoparticles (,5 nm) with a narrow size distribution were obtained and immobilized onto WOx BUNs without any aggregation. The paper presented a systematic investigation on the Ag-WOx nanocomposite used as a catalyst for the reduction of p-nitrophenol and as an antibacterial agent against Escherichia coli. The remarkably enhanced performance may be ascribed to the moderate interaction of the small Ag-NPs and WOx BUNs with high specific surface area. I. INTRODUCTION
Different considerably from their bulk properties, metal nanoparticle (M-NP) catalyst systems have aroused wide concern in many different areas including, but not limited to, environmental science, chemistry, and medical applications.1–4 As to the synthesis of metal nanoparticle colloids, the most common methods involve wet chemical “bottom-up procedures,” particularly the chemical reduction of metal salts. Normally, it is in aqueous or organic media that the chemical reduction of transition metal salts is performed to generate zerovalent metal colloids.5 However, metal nanoparticles (NPs) tend to aggregate during their catalytic process and can cause loss while separation after the end of reaction. These problems cause severe restrictions in using costly metal NPs as catalysts for the above-mentioned large-scale applications.6 Hence, stabilizers are employed to provide stability of the NPs when they are formed. Domingos et al. report an approach for effectively combining a high-throughput method using linear polyethylene imine (LPEI) with in situ screening and multivariate optimization of the synthesis conditions to produce highly catalytically stable Ag-NPs.7 The most commonly used stabilizer is a surfactant or a polymer matrix, which may form a layer of organic compounds present at the interface and need the further heat treatment at high temperature. Tungsten oxide and WO3x-based materials are intensively investigated due to their interesting properties, such as tunable electronic and electrochemical properties, etc.8 Studies on WO3xsupported metal particles have proved that the support
can enhance the catalytic performance of the metal nanoparticles.9–11 Up to now, tungsten oxide with various morphologies, such as rods, wires, and mesoporous structure, has been obtained.12 However, there are few reports on the preparation of high-quality tungsten oxide BUNs and metal/WO3x BUNs heteronanocomposites. In particular, monoclinic W18O49 BUNs with the largest oxygen deficiency in the WO2.625–WO3 range have been reported as the only oxide that can be isolated in a pure for
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