2019 Volume 17 Pages 32-40
Carbonaceous films, adsorptive for a range of volatile organic compounds (VOCs), were prepared by radio-frequency (rf) sputtering of biomedical-grade polypeptide gelatin crystals. The film was composed of densely packed nitrogen-rich microcolumns, resulting in a groove-poor structure. The gelatin-sputtered quartz crystal resonator was characterized by a high capability to adsorb VOCs, especially for the small, dielectric molecules of ethanol and water. Using the sorption capacities of 17 kinds of 500 ppm VOCs, we modeled the linear solvation energy relationship, which was substantially governed by electrostatic intermolecular interactions. Kelvin force microscopy (KFM) revealed that surface charging of the gelatin-sputtered film increased with the exposure time of the VOCs. Moreover, the dynamic force mode (DFM) in scanning probe microscopy (SPM) was used to elucidate the interaction force between the tip and the sample surface. The retarding phase shift increased with the exposure time of the VOCs. Deviation of the interaction force, induced by adsorption of the VOCs, was higher for hexane than for ethanol. The polar VOCs and the non-polar VOCs were roughly separated by the principal component analysis using the KFM and DFM data.