Adsorption of SO2 and NH3 onto copper/graphene nanosheets composites: Statistical physics interpretations, thermodynamic investigations, and site energy distribution analyses

Copper/graphene nanosheets composites (CGCs) were adopted as multi-gas adsorbents to remove two harmful gases (i.e., ammonia and sulfur dioxide) in the atmospheric environment, respectively. Methods such as N2 adsorption/desorption, scanning electron microscopy, and X-ray diffraction were selected to fully characterize CGCs. Under laboratory conditions, the adsorption isotherms of NH3 and SO2 onto CGCs at three different temperatures (298.15 K, 308.15 K, and 318.15 K) and different pressures (0 ∼ 1.8 bar) were quantitatively tested. A multilayer model with saturation (M5) was adopted as the best suitable model to explore the adsorption mechanism for SO2-CGCs and NH3-CGCs adsorption systems from a molecular level. The numerical simulation results demonstrated that the adsorption of NH3 by CGCs is a multi-anchorage process and a pure parallel adsorption position (298.15 K), a multi-linking process and a mixed adsorption orientation (308.15 K and 318.15 K). In contrast, SO2-CGCs adsorption system at 298.15 K, 308.15 K, and 318.15 K, there will be a multi-molecule process and a pure non-parallel adsorption position. Overall, from statistical physical, thermodynamic and SED analyses, the adsorption mechanism of SO2 and NH3 on CGCs, which was mainly governed by the density of receptor sites (Dm), was a spontaneous exothermic reversible adsorption process driven by physical interaction forces for which van der Waals interactions were responsible, while the high temperature is detrimental to the occurrence of high adsorption capacity.