A direct, high yield synthesis for preparing narrow-size silver nanoparticles by decomposition of silver carboxylate precursor under H2 pressure (3 bars) in solution is reported. The method corresponds to that for nanoparticles synthesised by thermal decomposition of carboxylic acid silver salts, but is faster, reproducible, versatile, and easier to control. Most of carboxylate groups are reprotonated upon the presence of dihydrogen and subsequent reduction of Ag+ produces spherical particles of dimensions 4–6 nm. The IR studies indicate that aliphatic carboxylates chemisorb on the nanoparticle surface with the two oxygen atoms coordinated mostly symmetrically and forming bridging bidentate Ag–O bonds. This implies strong interactions between the surfactant and Ag nanoparticle and enhances the stability of Ag colloid. There are some sites yet, probably at vertex or facet atoms of the nanoparticle, which form linkages of chelating bidentate or ionic character. Silver particles can be additionally capped in situ either by aliphatic primary amines or thiols forming mixed carboxylate/amine or carboxylate/thiol protecting monolayer. It is demonstrated that coordination of the second ligand adjusts physicochemical properties of nanoparticles. In the dual passivating system both amine and thiol were found to be tightly bounded to the silver nanoparticle surface.
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