Spectroscopic Study of the Thermal Degradation of PVP-Capped Rh and Pt Nanoparticles in H2 and O2 Environments

Poly(N-vinylpyrrolidone (PVP)-capped platinum and rhodium nanoparticles (7-12 nm) have been Studied with UV-vis, FTIR, and Raman spectroscopy. The absorption bands in the region of 190-900 nm are shown to be sensitive to the electronic structure of surface Rh and Pt atoms as well as to the aggregation of the nanoparticles. In-situ FTIR-DRIFT spectroscopy of the thermal decay of PVP-stabilized Rh and Pt nanoparticles in H-2 and O-2 atmospheres in temperatures ranging from 30 to 350 degrees C reveals the decomposition of PVP above 200 degrees C; PVP transforms into a polyamide-polyene-like material that is, in turn, converted into a thin layer of amorphous carbon above 300 degrees C. Adsorbed carbon monoxide was used as a probing molecule to monitor changes of the electronic structure of surface Rh and Pt atoms and accessible surface area. The behavior of surface Rh and Pt atoms with ligated CO and amide groups of pyrrolidones resembles that of surface coordination compounds.