Linking Experimental and Theoretical Studies of CO₂ Binding for Insight into the Structure of Activated Carbon

Five different physically motivated analytic isotherm models are fit to experimental $(P,V)$ data from seven different sources reporting studies of the adsorption of CO₂ by activated carbon. The model behavior upon parameter optimization suggests that multi-layer adsorption does not play a dominant role in CO₂ uptake by activated carbon. Only by explicitly modeling two distinct types of binding sites in the first adsorption layer does the model fully capture the nuances of the data. The values of the best-fit parameters provide good support for a widely used structural model of activated carbon: that it may be represented by nanoscopic flakes of hexagonally bonded carbon, the edges of which are terminated by functional groups. This conclusion is confirmed by comparison of the fitting parameter values to published results of first-principles calculations of the interaction of CO₂ with systems having chemical features representative of this structural model.