Surface energetics of graphene oxide and reduced graphene oxide determined by inverse gas chromatographic technique at infinite dilution at room temperature

Graphene is of great interest for many far-reaching applications that involve interparticle interactions in adsorbents, coatings, and composites. A deep understanding of the surface components has been crucial but achieving the most accurate and reliable values of these, unaffected by experimental conditions or the analytical techniques used, remains a major challenge. To this end, we have proposed in this paper a novel approach for the first time, to the best of our knowledge, to determine London dispersive and specific (polar) components including the Lewis acid-base character of the surface free energy of graphene materials (graphene oxide (GO), reduced graphene oxide (rGO), and graphite) using inverse gas chromatography (IGC) technique at an infinite dilution. We have estimated the London dispersive surface energy values of graphite, GO, and rGO as van der Waals interaction to be 156-179, 89-106, and 110-119 mJ m^-2, respectively, in the temperature range of 320-360 K. These are attributable to the surface properties impacted by the oxygen moieties, defects, and micropores on the carbon frameworks. Further, the acceptor (K_A) and donor (K_D) parameters of GO were found to be 0.71 and 0.96, respectively, while those of rGO were 0.54 and 1.05. Notably, the GO is more of the Lewis acid character that could be amphoteric, while the Lewis base characteristics of both GO and rGO are not significantly changed. These results provide foundational knowledge to understand the physicochemical properties of graphene surfaces, which should be helpful to designing interface engineering in various applications.