• O'Neill, M.; Raghuwanshi, V.S.; Wendt, R.; Wollgarten, M.; Hoell, A.; Rademann, K.: Gold Nanoparticles in Novel Green Deep Eutectic Solvents: Self-Limited Growth, Self-Assembly & Catalytic Implications. Zeitschrift für Physikalische Chemie 229 (2015), p. 221-234


In this article, we are reporting the catalytic activity of gold nanoparticles (AuNPs) dispersed in a novel eco-friendly Deep Eutectic Solvent (DES; choline chloride and urea) at room temperature. A low energy sputter deposition method is employed to synthesize AuNPs on the DES surface. This is a simple, economical and clean method for producing monodisperse gold nanoparticles by a self-limited growth mechanism. Detailed Small Angle X-ray Scattering (SAXS), UV–Vis and Transmission Electron Microscopy (TEM) investigations show the formation of spherical AuNPs of 5 nm in diameter. Moreover, these particles have a strong tendency to self-assemble at the DES surface as well as into the bulk. This is a new addition to a novel generation of gold based catalysts. The catalytic activity of Au nanoparticles in DES is revealed quantitatively by analyzing the apparent conversion reaction rate constant 𝑘app of para-nitrophenol to paraaminophenol in the presence of sodium borohydride. Catalytic activity reported in the present article ismuch faster (𝑘app = 0.34 s−1) than the rate reported earlier (𝑘app = 0.030 min−1) by Chirea et al. for gold nanowire networks [Langmuir, 2011, 27, 3906]. In agreement with the literature, we explain the higher catalytic activity in terms of a larger surface area of AuNPs in a non-self-assembled state. Keywords: Catalysis, Para-Nitrophenol Reduction, Reaction Kinetics, Gold, Nanoparticles, Self-Limited Growth, Self-Assembly.