Preparation and characterization of zinc-exchanged montmorillonite and its effectiveness as aflatoxin B1 adsorbent

A zinc-exchanged montmorillonite (Zn-MONT) was prepared from a natural montmorillonite (MONT) and the adsorption of aflatoxin B-1 (AFB(1)) was investigated at pH 3 and 7. Characterization of Zn-MONT was done by determination of chemical composition, the point of the zero charge (pH(pzc)), thermal (DTA/TGA/DTG) and X-ray powder diffraction (XRPD) analysis. Adsorption of AFB(1) (C-0 = 4 ppm) by Zn-MONT, at different solid/liquid ratios (10, 1 and 0.5 g L-1), at pH 3 or 7, showed that its adsorption was high (over 96%) and independent of pH, similar to MONT. No desorption of AFB(1) from MONT-AFB(1) and Zn-MONT-AFB(1) complexes occurred at pH 6.5, suggesting strong binding of AFB(1) by both adsorbents. Furthermore, AFB(1) adsorption by Zn-MONT followed a nonlinear (Langmuir) type of isotherm at pH 3 with a calculated maximum capacity of 60.17 mg g(-1). The stability of MONT-AFB(1) and Zn-MONT-AFB(1) complexes was evaluated by calculating the binding energies between AFB(1) and metal cations using quantum chemical methods. The evaluated interaction energies of AFB(1) with hydrated Zn2+, Mg2+, and Ca2+ cations showed that the strongest interaction was the interaction of the Zn2+ system, -70.2 kcal mol(-1), whereas energies for Mg-2 and Ca2+ systems were -68.8 and -62.9 kcal mol(-1), respectively. The results indicate that Zn-MONT can be suitable for potential practical application as both, an antibacterial and an aflatoxin binding agent. (C) 2012 Elsevier B.V. All rights reserved.