Water adsorption on carbons - Critical review of the most popular analytical approaches

The purpose of the current study is to present the state of art in the field of analytical description of water sorption on carbons. We discuss the most important and promising models proposed recently (for example by Mahle; Talu and Meunier; and Malakhov and Volkov) as well as some older theoretical models inspired by the pioneering ideas proposed in the papers of Dubinin, Serpinsky, Barton, D'Arcy, Watt, Do and Do and others. The applicability, advantages, and defects of all these analytical formulas are pointed out and some new approaches in this field are presented. The special attention is paid to the finite adsorption space and the possible involvement of partial chemisorption, i.e. the existence of various types of the hydrophilic centres. Since the calculation of isosteric enthalpy from an adsorption equation, and the comparison of theoretical enthalpy plot with the values measured calorimetrically, is the fundamental condition for the verification of the correctness of an adsorption model, for all considered models we show the corresponding adsorption enthalpy equations. The validity of all mentioned above models is verified for the data measured for five water-activated carbon systems. Finally, a summary of obtained results and some perspectives and suggestions for the description of experimental data are presented. From the analysis of experimental data it is seen that developed recently- the heterogeneous Do and Do model is probably the most successful for the simultaneous description of water adsorption and enthalpy of adsorption results. (c) 2007 Elsevier B.V. All rights reserved.