Adsorption of Bovine Serum Albumin on Magnetic Material Montmorillonite: Isotherms, Kinetic, Thermodynamic, and Mechanism Studies

Abstract

The adsorption of a model protein such as bovine serum albumin (BSA) on a magnetic material based on montmorillonite (MtMag) was studied. Kinetic data, equilibrium isotherms, and thermodynamic calculations were performed and analyzed to obtain information about the rate-limiting step of the adsorption process and propose a possible adsorption mechanism. Equilibrium studies showed optimal adsorption around pH 4.5, the maximum adsorption capacity being around 231.9 mg g-1 at 25 °C. The latter behavior may be ascribed to the most packed protein conformation at pH conditions near the BSA isoelectric point. In addition, the BSA adsorption capacity decreased with the ionic strength (10–3−10–1 M) and increased with the temperature (15–30 °C). In all cases, the Sips model yielded the best fit to the experimental results. The thermodynamic analysis revealed an isosteric heat dependence on the coverage, which allowed ruling out the Langmuir model. The kinetic data were adequately fitted by the IPD model, which suggests that the rate-limiting step of the adsorption process is the diffusion of BSA molecules into the internal sites.