Energetics of water adsorption and immersion on carbons

The equations of adsorption of water proposed by Dubinin and Serpinsky (DS) , Barton et al, and D'Arcy and Watt are being analysed; and the isosteric e nthalpy of adsorption and the enthalpy of immersion equations are developed where possible. It is proven that the derivation of the adsorption enthalp y formula from DS equation proposed by Kraehenbuehl, Stoeckli and co-worker s is incorrect; the reason is that it neglects the temperature dependence o f the maximum adsorption. If one takes this into account, it leads to some decrease in the enthalpy of adsorption with coverage and not-as it was sugg ested by those authors-to the constant enthalpy of adsorption. The new adso rption equation is bring proposed which takes into account the energetic he terogeneity of carbon adsorption centers and postulates the physical adsorp tion of water. All analysed equations of adsorption can simultaneously gene rate the observed experimentally water isotherm shapes as well as the heat plots obtained from calorimetry. Moreover, for D'Arcy and Watt and for bimo dal DS equations as well the shape of adsorption enthalpy changes with the number of adsorption centers. On the contrary, DS and Barton's equations ge nerate only one type-convex to adsorption axis-of enthalpy of adsorption pl ot. (C) 1999 Elsevier Science B.V. All rights reserved.