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

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-), with i) bare uncapped AuNPs of different sizes, 8 nm, 10 nm and 38 nm 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 = MuC6H6 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 on both 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 w...