The one-pot synthesis of monolayer-protected metal nanoparticles derived from sodium S-dodecylthiosulfate (Bunte salt) in aqueous solution is described. Silver nanoparticles, which were produced by the borohydride reduction of silver nitrate in H2O, were stabilized by the adsorption of S-dodecylthiosulfate followed by the removal of the SO3- moiety. Temporary stabilization of silver sols by the adsorption of borohydride and borate prevented aggregation of silver nanoparticles in H2O. The syntheses of other metal nanoparticles, including gold, copper, and palladium particles in H2O, were less successful. Gold and copper particles were completely aggregated and precipitated out immediately after the addition of NaBH4, yielding only insoluble clusters. Stable and soluble palladium nanoparticle could be prepared, but the presence of Pd-thiolate complex was also observed. These nanoparticles were characterized using 1H NMR, UV-vis spectroscopy, FT-IR spectroscopy, and transmission electron microscopy.

This paper shows that an introduction of thiosulfate anions in place of bromide anions greatly improves both chemical and thermal stability of tetraoctylammonium-protected gold nanoparticles. Tetraoctylammonium thiosulfate [(Oct)4N+-O3SS]-protected gold nanoparticles are synthesized by the reduction of (Oct)4N+-AuCl4 to Au(I)-SSO3-, followed by the addition of sodium borohydride. The presence of thiosulfate anions instead of bromide anions on the surface of gold nanoparticles results in a significant dampening of the surface plasmon band of gold at 526 nm due to the strong interaction between thiosulfate and the gold nanoparticle surface. Cyanide decomposition and heating treatment studies suggest that (Oct)4N+-O3SS-protected nanoparticles have much higher overall stability compared to (Oct)4N+-Br-protected gold nanoparticles.

We present a systematic study on the synthesis of mixed monolayer-protected clusters (MMPCs) from mixtures of alkanethiols. Our results show that solvation-driven thermodynamic preferential adsorption of precursor ligands governs monolayer composition of MMPCs. In the mixed system HO(CH2) n SH/ CH3(CH2) m SH (n = m or n ≠ m) in toluene, adsorption of the polar component is largely favored because of the poorer solvation of polar tail groups in toluene compared to tetrahydrofuran (THF). When MMPCs are generated from the mixed system HO(CH2) n SH/CH3(CH2) m SH (n = m) in THF, the tail group effect is much less. The MMPC synthesis in THF solutions containing HO(CH2) n SH/CH3(CH2) m SH (n ≠ m) shows large thermodynamic control, which promotes a preferential adsorption of the thiols with a longer alkyl chain onto the surface of clusters. Transmission electron microscopy (TEM) and UV−vis spectroscopy data suggest that the average core dimension of MPCs generated from alkanethiols in THF is slightly smaller than that of MPCs generated from alkanethiols in toluene under the same conditions.

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