Synergetic promotion by oxygen doping and Ca decoration on graphene for CO2 selective adsorption

Abstract

The selective adsorption of CO₂ by alkali earth metal (AEM)-decorated double vacancy graphene (DVG) was investigated with the first principles method. It is found that Be, Ca, Sr and Ba can be anchored stably on the DVG (whereas Mg cannot), and the Ca-decorated sample (Ca_DVG) possesses the strongest CO₂ adsorption with a heat release of −0.45 eV per CO₂. Furthermore, the doping of oxygen atoms on Ca_DVG (denoted as Ca_PyODVG) can remarkably increase the adsorption energy to −0.74 eV per CO₂. This considerable promotion is ascribed to a synergetic effect of Ca decoration and O doping, which boosts extra electrons to transfer from the Ca_PyODVG substrate to the adsorbed CO₂ molecule via the Ca 3p–O 2s hybridization. Notably, the obtained Ca_PyODVG is demonstrated to have a more practical CO₂ desorption temperature, as well as a broader window for the selective adsorption of CO₂ over CH₄ and H₂. Our theoretical results imply that Ca_PyODVG should be a promising candidate for CO₂ capture. Additionally, the adsorption energy of CO₂ is linearly correlated to the work function of a substrate, which may be used to accelerate the experimental screening of promising adsorbents.