Tuning the Acid/Base Surface Character of Carbonaceous Materials by Means of Cold Plasma Treatments

Carbonaceous materials, in the form of flat graphite slabs and carbon black granules, are surface-modified in radio frequency (RF, 13.56 MHz) glow discharges fed with NH3/O-2 mixtures at different power values, in order to graft oxygen-containing and/or nitrogen-containing chemical groups. In this way, it is possible to adjust the acid/base character of the material surfaces in a predictable way, as a function of the feed composition and of the power. A plasma reactor equipped with a rotating vacuum chamber and internal glass wings is used to keep the granular materials homogeneously stirred and to modify the surface of both graphite slabs and carbon black granules. The chemical modifications have been evaluated using X-ray photoelectron spectroscopy. Water contact angle measurements have been carried out on flat graphite, with water solutions at different pH, in order to study the acid/base character imparted to the functionalized surface. Scanning electron microscopy analysis has been performed to check the effects of plasma treatments on the morphology of the substrates.