Description of different solid adsorbent surfaces adsorption mechanisms based on a sequential decomposition isotherms

PABLO D. HÚMPOLA; HÉCTOR S. ODETTI ; FLORES ETHEL SUSANA; VICENTE JOSÉ LUIS

SURFACE REVIEW AND LETTERS

WORLD SCIENTIFIC PUBL CO PTE LTD

Lugar: London, UK; Año: 2013 vol. 20 p. 1 - 12

0218-625X

In order to analyze the adsorption capacities of di®erent solid substrates, we present a multi-step method to separately study the isotherm at di®erent pressure ranges (steps). The method is based on simple gas isotherm measurements (nitrogen, methane, carbon dioxide, argon, and oxygen) and is tested to describe the adsorption process and characterize a graphitized surface (GCB) and two di®erent granular activated carbons (GAC). The GCB isotherms are described as a sum of Fowler- Guggenheim-Langmuir shifted curves; isotherm behaviors are quite similar at di®erent temperatures, but change below a certain threshold. In GAC the ¯rst steps show the same adsorption characteristics at low pressures (Dubinin´s description), but this behavior changes at higher pressure regimes, which allows one to elucidate how heterogeneous the surfaces are or how strong the interactions between adsorbed molecules are for this marginal adsorption to occur. We tested different approaches (from BET multilayer to Aranovich) and found quite di®erent features. We ¯nally conclude that if the description of the adsorption on complex substrates, such as those presented here, is carried using only one model, e.g. Dubinin in case of GACs, the resulting characteristics of the adsorbent would be very biased.