Ligand-capped metal nanoparticles exhibit promising properties as catalysts. Its large surface to volume ratio allows for high catalytic activity, while its ligands dictate the immediate environment around the catalytic surface, allowing for directed catalytic selectivity. Alkanethiolate-capped palladium nanoparticles (PdNPs) have previously been synthesized using a modified Brust-Schiffrin synthesis (using alkyl thiosulfate instead of alkanethiol), in which the nanoparticle core size is established during alkyl thiosulfate ligand passivation of the nanoparticle nucleation-growth initiated by borohydride reduction. Due to the dependence of core size on amount of ligand present, surface ligand density decreases with increasing core size. Herein we present a method in which core size is established independent to ligand addition, allowing the formation of PdNPs with similar core sizes, yet different surface ligand density. In this method, core size is established during the temporary passivation of growing nanoparticles by borohydride and tetraoctylammonium bromide (TOAB), allowing nucleation to reach completion. Various molar equivalents of alkyl thiosulfate are then added, prompting the replacement of borohydride and TOAB and the formation of alkanethiolate-capped PdNP. The resulting PdNPs were characterized via 1H NMR, UV-Vis spectroscopy, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), FT-IR, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Overall enhanced catalytic activity of hydrogenation/isomerization of dienes and alkenes was observed for PdNPs with a lower ligand density, proving the isolated effect of surface ligand density from other variations such as core size and shape.

Synthesis of alkanethiolate-capped palladium nanoparticles through reversed alkyl thiosulfate addition to control core size & tune surface ligand density

256th National Meeting (2018)

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