Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Provisional)

Abstract

The purpose of this Manual is twofold: first to draw attention to the problems and ambiguities which have arisen in connection with the reporting of gas adsorption (physisorption) data; second to formulate proposals for the standardisation of procedures and terminology which will lead to a generally accepted code of practice. The proposals are based on, and are in general accordance with, the Manual of Symbols and Terminology for Physicochemical Quantities and Units (1979) and Parts I and II of Appendix II (1972 and 1976). The first stage in the interpretation of a physisorption isotherm is to identify the isotherm type and hence the nature of the adsorption process(es): monolayer-multilayer adsorption, capillary condensation or micropore filling. The BET method is unlikely to yield a value of the actual surface area if the isotherm is either Type I or Type III; but both Type II and Type IV isotherms are, in general, amenable to the BET analysis, provided that the value of C is neither too low nor too high and that the BET plot is linear in the region of the isotherm containing Point B.