Journal of Porous Materials 8, 49–59, 2001 c  2001 Kluwer Academic Publishers. Manufactured in The Netherlands. Application of Comparative Method for Estimating Microporosity of Porous Solids in Adsorption from Solutions ANDRZEJ DABROWSKI AND ZYGMUNT FEKNER Faculty of Chemistry, Maria Curie-Sklodowska University, Lublin 20-031, Poland IMRE D ´ EK ´ ANY Department of Colloid Chemistry and Nanostructured Materials Research Group of the Hungarian Academy of Sciences, Attila J ´ ozsef University, H-6720 Szeged, Hungary Received May 13, 1999; Revised December 7, 1999 Abstract. The concept of a comparative method in terms of the liquid adsorption on solids is presented. This method is based on comparison of the excess adsorption isotherm on a porous solid with that measured on a reference nonporous adsorbent. It is proved that proposed approach gives the possibility for separating a total excess adsorption isotherm into partial isotherms, proper for micro- and mesopores. Several experimental systems are analyzed to illustrate the usefulness of the comparative method for evaluating the surface phase capacity, which presents an important quantity in the study of adsorption from solution in the whole concentration region. The comparative method examined for adsorption systems of microporous active carbons seems to be useful for investigating other porous materials as silica gels, zeolites or metal oxides. Keywords: adsorption from solutions, microporous structure, surface phase capacity, comparative method, structural heterogeneity Introduction A great number of adsorbents applied on laboratory and commercial scales possesses a strongly developed microporous structure. The micropores, characteristic for adsorbents of large specific area are a source of a substantial increase in the adsorption capacity because their whole accessible volume may be regarded as the adsorption space. And the result is that effectiveness of adsorption on porous solids largely depends on mi- cropore percentage contribution in the entire porous structure. In contrast to gas adsorption on microp- orous solids [1–5], the theoretical description of ad- sorption from liquid mixtures on these solids is still unsatisfactory [6–14]. On the other hand, adsorption at solid/liquid interface is very important both for general studies (e.g. adsorption liquid chromatography) [15] and for creating new, effective technological pro- cesses [16, 17]. In this paper a theoretical description is developed to assess the microporous structure in the porous solids by means of the excess solid/liquid adsorption isotherms. The so-called comparative method is reexamined and its physical foundations are discussed [10, 11, 18]. Another aim is to present an independent approach to estimate the surface phase capacity in micro- and mesopores which leads to a new method for determin- ing the total surface phase capacity formed in microp- orous solids. The third goal deals with the possibility of sep- aration of the total excess adsorption isotherm into partial excesses, proper for micro- and macropores. Owing to analysis of the excess isotherms correspond- ing with micropores an easy method comes up for