Studies of Muonium Reactivity with Uncapped Gold Nanoparticles and with Surface-Adsorbed Benzene on These NPs in Porous Silica Hosts

• Published in: Journal of physical chemistry. C Vol. 123; no. 45; pp. 27628 - 27642
• Main Authors: Fleming, D. G, MacFarlane, W. A, Xiao, J, Arseneau, D. J, Dehn, M. H, Kiefl, R. F, Zamarion, V. M, Wang, P.-X, Cao, Y, MacLachlan, M. J, Bridges, M. D
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.11.2019
• Subjects: benzene; catalytic activity; encapsulation; hosts; hydrogen; magnetism; nanogold; physical chemistry; porous media; silica
• ISSN: 1932-7447; 1932-7455; 1932-7455
• DOI: 10.1021/acs.jpcc.9b08327

Gold nanoparticles (AuNPs) have been a subject of considerable interest in recent years due to both their magnetic and catalytic properties. This paper reports a two-fold study of the reactivity at 300 K of the isotopic hydrogen atom, muonium (Mu = μ+e–), (i) with bare uncapped AuNPs of different sizes encapsulated in mesoporous (SBA-15) silica hosts, forming a diamagnetic final state in the Mu + AuNP → MuAuNP reaction, and (ii) with surface-adsorbed benzene on these NPs forming the muoniated cyclohexadienyl radical in the Mu + C6H6 → MuĊ6H6 addition reaction. The measured muon-spin relaxation rates, λC, for the chemisorption reaction of Mu with the bare AuNPs show some variation with AuNP size. The Mu + C6H6 addition reaction has been studied over a range of benzene loadings both on bare silica and in the AuNP/silica samples. The measured muon-spin relaxation rates, λTot, exhibit a linear dependence on benzene concentration over the full range of loadings in both cases, in accord with an Eley–Rideal model of surface reactivity. Rate constants, k Bz, were determined from this dependence which exhibit a 2–3-fold faster reaction rate on the AuNPs than on the bare silica, suggesting a catalytic effect due to benzene adsorbed on these NP surfaces.