The effect of heat-treatment on Ag nanocube surface structures and low-temperature isopropanol dehydrogenations

Ag nanocubes have drawn much attention in catalytic field recently. As poly-vinylpyrrolidone (PVP) molecules were used as capping ligands, the catalytic activities of the as-synthesized Ag nanocubes are low as PVP molecules block contacts of reactants with metallic Ag surfaces. The current work carefully studied the thermal degradation of PVP under different heat-treatment conditions and the effect on the surface structures of Ag nanocubes with UV–vis spectroscopy, X-ray photoelectron spectroscopy, Raman scattering, Fourier transformed infrared spectrometer, and transmission electron microscopy. The result showed that all the atmosphere, time, and temperatures of heat-treatments affected the PVP thermal degradation and Ag nanocube surface structures. The PVP thermal degradation around 200 °C did not generate amorphous graphite carbon, but should form the “ polyuamide-polyene ”- like structures over Ag nanocube surfaces. The heat-treatment in air degraded more PVP and led to exposures of more metallic Ag surfaces. It was seen that the “C-F” XPS signals appeared after heat-treatment in air, which arose from CF 3 COO- groups and their degradation products over metallic Ag nanocube surfaces. Isopropanol dehydrogenations were conducted at near-room temperatures, and it is seen that the activities showed a sharp increase with different heat-treatment conditions; this was closely related with the appearance of “C-F” XPS signals. Therefore, the result also supported that the “C-F” species over the metallic Ag surfaces might be important for isopropanol dehydrogenations, in additional to the exposed metallic surfaces. • The effect of heat-treatment on Ag nanocube surface structures was studied under different conditions. • The “C-F” species were observed on the metallic Ag nanocubes surfaces after heat-treatment in air. • The appearance of “C-F” C1s XPS signals was closely related with the sharp increase of isopropanol dehydrogenations.