Surface characterization of variously treated Nafion-H, Nafion-H supported on silica and Nafion-H silica nanocomposite catalysts by infrared microscopy Original Research Article

Nafion-H, silica-supported Nafion-H and two types of Nafion-H silica nanocomposites have been studied by Fourier transform–infrared (FT-IR) microscopy working in the reflectance mode. The as received as well as the variously pretreated samples (evacuation at 298, 378 and 423 K) were investigated in the mid-IR range. The IR spectra of rehydrated samples were also studied. For Nafion-H, evacuation at 298 or 378 K resulted in significant but reversible dehydration. Pretreatment at 423 K leads to more extensive changes, i.e. the loss of certain amount of –SO2OH groups through irreversible desulfonation/dehydroxylation. The dehydration–rehydration behavior of the other materials proved to be reversible, irrespective of the temperature of outgassing. Here, (reversible) changes in the OH region were also observed, depending on the temperature of pretreatment. Changes are reflected in splitting and shifting of IR bands. These observations may be explained by the dehydroxylation of silica, during which gradual disruption of the extended hydrogen bonded OH networks occurs.