Platinum nanoparticles functionalized with acetylene derivatives and the influence of ligand length on their electrocatalytic activity

Platinum nanoparticles were prepared by sodium borohydride reduction of Pt(II) precursors and stabilized by the self-assembly of acetylene derivatives of different lengths (phenylacetylene, 4-ethylphenylacetylene, and 4-butylphenylacetylene). Transmission electron microscopic measurement showed that these nanoparticles exhibited similar average core sizes of 2.22 ± 0.83 nm, 2.09 ± 0.91 nm, and 2.18 ± 0.77 nm, respectively. FTIR study confirmed that the Pt cores were capped by these acetylene ligands with the breaking of the terminal CH vibrational stretch and a substantial red-shift of the CC vibration. X-ray photoelectron measurements showed that platinum is in the metallic form. Pt nanoparticles all exhibited typical exponential decay profiles with some difference in small absorption peaks before 360 nm in UV-vis measurements. In (αhv)1/2 versus hv plot, band gap decrease is related with the increase of ligand chain length. The Pt nanoparticles all showed apparent photoluminescence with a clear red-shift of the excitation and emission peak positions as compared to those of the free monomers, due to intraparticle charge delocalization between the particle-bound acetylene moieties. Electrochemical measurements showed that the nanoparticles exhibited electrocatalytic activity towards the oxidation of methanol and hydroquinone oxidation, and the activity was found to increase with increasing ligand chain length.