Thermodynamic characterization of two layers of CO2 on a graphite surface

Abstract

a b s t r a c tWe find by examination of density profiles that carbon dioxide adsorbs on graphite in two distinct layers. We report the activity coefficient, entropy and enthalpy for CO 2 in each layer using a convenient computational method, the Small System Method, thereby extending this method to surfaces. This opens up the possibility to study thermodynamic properties for a wide range of surface phenomena.

A procedure to find thermodynamic equilibrium constants for CO2 and CH4 adsorption on activated carbon

“…A possible route, not much used, is to first find the thermodynamic correction factor, or simply, the thermodynamic factor, s Γ . 33 At constant temperature T and surface area A, 31 for more details:…”

“…The combination of the two layers was also considered as one total layer. 31 The equilibrium between the first and the second layer was next described by the Langmuir equation ( Figure S2). The total layer in equilibrium with the gas was also fitted to a Langmuir type isotherm, as has been done by many authors.…”

“…equation (14). The activity coefficients for the layers were taken from ref 31 , and the simulation results were used to calculate the constant ,…”

“…31 The equilibrium constant was then calculated from equation (14) leading to the enthalpy of adsorption in a similar fashion as before. show that 1/ i Γ decreases non-linearly with the excess adsorption and that the activity coefficient increases with the same.…”

“…The method is next applied to data available in literature for adsorption of CO 2 on two layers of graphite. 30,31 The equilibrium between the first and second gas layers on graphite and the gas, give data that will be fitted to the Langmuir or Henry laws and characterized by the (same) chemical potential. The heats of adsorption from the different techniques will be calculated and compared with experimental data for CO 2 and CH 4 adsorption on activated carbon.…”