Spectroscopic study of tetradecyltrimethylammonium bromide Pt-C14TAB nanoparticles: structure and stability.

The vibrational spectra of platinum nanoparticles (12 nm) capped with tetradecyltrimethylammonium bromide, C(14)TAB, were investigated by Fourier transform infrared (FTIR) spectroscopy. We have shown that the thermal decay of Pt-C(14)TAB nanoparticles in N(2), H(2), and O(2) atmospheres leads to the release of the hydrocarbon chain of the surfactant and the formation of a strongly bonded layer of ammonium cations on the platinum surface. The platinum atoms accessible to CO chemisorption were not reducible by hydrogen in the temperature range from 30 to 200 degrees C. A FTIR spectrum of C(14)TAB adsorbed on Pt nanoparticles was dramatically perturbed as compared with pure C(14)TAB. New intense and broad bands centered at 1450 cm(-1) and 760 cm(-1) are making their appearance in Pt-C(14)TAB. It may be speculated that new bands are the result of coupling between conducting electrons of Pt and molecular vibrations of adsorbed C(14)TAB, and as a consequence, specific vibrational modes of ammonium cation are transformed into electron-vibrational modes.