Catalytic Reduction of 4‑Nitrophenol Using\nSilver Nanoparticles with Adjustable Activity

Abstract

We report on the development of ultrasmall\ncore–shell silver\nnanoparticles synthesized by an upscaled modification of the polyol\nprocess. It is foreseen to use these thoroughly characterized particles\nas reference material to compare the catalytic and biological properties\nof functionalized silver nanoparticles. Small-angle X-ray scattering\n(SAXS) analysis reveals a narrow size distribution of the silver cores\nwith a mean radius of <i>R</i>_c = 3.0 nm and\na distribution width of 0.6 nm. Dynamic light scattering (DLS) provides\na hydrodynamic radius of <i>R</i>_H = 10.0 nm\nand a PDI of 0.09. The particles’ surface is covered with poly­(acrylic\nacid) (PAA) forming a shell with a thickness of 7.0 nm, which provides\ncolloidal stability lasting for more than 6 months at ambient conditions.\nThe PAA can be easily exchanged by biomolecules to modify the surface\nfunctionality. Replacements of PAA with glutathione (GSH) and bovine\nserum albumin (BSA) have been performed as examples. We demonstrate\nthat the silver particles effectively catalyze the reduction of 4-nitrophenol\nto 4-aminophenol with sodium borohydride. With PAA as stabilizer,\nthe catalytic activity of 436 ± 24 L g^–1 s^–1 is the highest reported in the literature for silver\nnanoparticles. GSH and BSA passivate the surface substantially, resulting\nin a catalytic activity of 77.6 ± 0.9 and 3.47 ± 0.50 L\ng^–1 s^–1, respectively.