Chemical and thermal stability of Pt nanocubes synthesized with various surface-capping agents.

Pt nanocubes with a size of below 10 nm were synthesized by using various surface-capping agents of polyvinylpyrrolidone (PVP), tetradecyltrimethylammonium bromide (TTAB), and oleylamine with high shape purity. TGA and XPS data revealed the amount and characteristics of the residual organic molecules on the surface of Pt nanocubes. Chemical and thermal stability of these nanoparticles were examined by observing the change of cubic shape upon heating under different chemical environments of N2, H2 and air. The shape change such as rounding of the vertexes or aggregation depended on the type of surface-capping agent and chemical environments. The cubic shape generally started to deform at 200 degrees C and the nanoparticles were mostly fused together at 300 degrees C. The thermal treatment under air produced more PtO layer on the surface with less shape deformation or aggregation when compared with H2 or N2 treatments. Among three surface-capping agents used in this study, oleylamine-capped Pt nanocubes show the highest shape stability with no shape change or aggregation even at 300 degrees C under air.