FRACTIONAL STATISTICAL THEORY OF FINITE MULTILAYER ADSORPTION

ANDRÉS TAKARA; EVELINA QUIROGA; NELIO ARIEL OCHOA; DANIEL MATOZ-FERNANDEZ; ANTONIO JOSÉ RAMIREZ-PASTOR

Cartagena

Congreso; 2° Congreso Iberoamericano de adsorción; 2015

Universidad de Los Andes

In thiswork, a new theoretical frame to treat finite multilayer adsorption as afractional statistics problem was presented. The formalism, based on ageneralization of the fractional statistics thermodynamic theory of adsorption(FSTA) [1], is capable of including the main models of adsorption as particularcases. In this scheme, the Helmholtz free energy and its derivatives arewritten in terms of an exclusion parameter g, whichrelates to the configuration of the molecules in the adsorbed state. The well-knownLangmuir [2] and Brunauer-Emmett-Teller (BET)[3] theories are obtained for g = 1 and g =0, respectively. For values of g between0 and 1, FSTA allows us to describe intermediate cases between simple monolayeradsorption and generalized multilayer adsorption.Thetheoretical results were compared with experimental data. For that, proteinadsorption assays were performed using bovine serum albumin (BSA) onto an ionexchange resin (Amberlyst 15) for different values of pH (4, 7.5 and 9.5) and temperature(25, 37 and 45° C). A nonlinear regression technique was used in fitting theexperimental data, where the isotherms were fitted with two free parameters:exclusion parameter g andequilibrium constant Ke. An excellent agreement between theory and experiments was found. Thevalues obtained for the fitting parameters indicate the occurrence of finitemultilayer adsorption, and show that the statistical exclusion parameter g results highly sensitive to the configuration of the molecule in theadsorbed state. Thestudy presented here shows that the FSTA model provides a framework and compactequations to consistently model experimental data ranging from monolayer toinfinite multilayer adsorption.