Preparation of functionalized platinum nanoparticles: a comparison of different methods and reagents

A number of methods exist for the preparation of platinum nanoparticles, which have numerous industrial applications, especially as catalysts. In this study, we compared three methods for preparing Pt particles with diameters in the range of 1-3 nm. Method 1 involves base-catalyzed reduction of Pt(IV) in ethylene glycol. Methods 2 and 3 are based on phase transfer of a Pt(IV) precursor from water to toluene containing a phase-transfer catalyst (PTC) followed by reduction by NaBH4 and capping by a stabilizing agent. The latter two methods differ in the sequence of addition of stabilizer and reducing agent, and in the nature of the stabilizer. We compared the resulting mean particle sizes using transmission electron microscopy and dynamic light scattering. Our study included a systematic comparison of seven reaction parameters for Methods 2 and 3: the method (sequence of addition), Pt precursor, stabilizer molecule, stabilizer concentration, PTC, PTC concentration, and solvents for Pt suspension. Our data show that, both qualitatively and quantitatively by means of analysis of variance, three of these parameters are significant: method, stabilizer, and PTC. A linear regression allows for prediction of particle size based on these variables and fits the experimental data well, allowing particle size to be adjusted in the range of 1.6-2.2 nm. A gravimetric determination of the yield of the three methods found that while Methods 1 and 2 convert at least 85 % of the Pt precursor to Pt nanoparticles, for Method 3, the yield was less than 30 %.