Carbon materials with porous skeleton and specific chemical functionality have shown great potentials in the applications of gas adsorption, storage, separation and sensing. While a variety of literature have demonstrated that pore structure and chemical environment of carbon materials possess synergistic effects on these applications, there is still much to learn regarding structure-activity relationships, especially individually determining the role of chemical functionality or porosity in gas adsorption. Oxygen-containing groups widely exist in carbon materials and profoundly influence gas molecule adsorption on carbon surface, the complexity of carbon source and post-treatment methods, however, modify not only the surface chemistry of carbons but also their porous structure, making it considerably difficult to exclusively determine the effect of O-species. To this end, edge carboxyl group decorated graphene nanoplatelets (OGnPs) with different oxygen contents were prepared to investigate the effects of O-species on gas adsorption using SO2 as probe molecule. The OGnPs were obtained employing a simple ball milling method with dry ice assistance by which the oxygen content can reach as high as 14.06 wt-%, endowing 21 times increase in SO2 adsorption capacity as compared with oxygen-free graphene nanoplatelets. Both temperature-programmed desorption (TPD) experiments and DFT calculation were used to elucidate the nature of enhanced SO2 adsorption including adsorption types, adsorption energy and carbon-SO2 interactions. The adsorbed SO2 molecules on OGnPs can desorb easily at temperature lower than 100 oC, indicating their physisorption nature. Based on adsorption energy data, DFT calculation further demonstrate that the enhanced SO2-carbon adsorption by carboxyl groups doping is in the form of physisorption but not chemisorption. This means that the role of oxygen doping is to remodel the local electronic density, the polarity of carbon atoms as well as charge distribution of carbon surface, which induces the enhanced SO2 physisorption on whole carbon surface, but not the site-to-site chemisorption. This work not only demonstrates a new route for the controllable introduction of oxygen functional groups into carbon framework, but also shed new insights into the role of oxygen doping in enhancing gas molecule physisorption, challenging the traditionally held chemisorption view.
5:00 PM–7:00 PM Apr 23, 2019 (US - Arizona)
PCC North, 300 Level, Exhibit Hall C-E