Structural analysis of naproxen-intercalated bentonite (Unye)

Abstract

The difference in the basal spacing (8.79 angstrom) and a higher mass loss (6.2%) in the temperature range of 200-750 degrees C of naproxen-bentonite (N-bentonite) comparing to that of Unye bentonite (UB) signified the existence of thermally stable organic species in the interlamellar space of the bentonite clay. The asymmetric OCO- stretching band (1607 cm(-1)) of N-bentonite became stronger in the temperature interval of 100-400 degrees C as a result of binding via the C=O group of the ligand to exchangeable cation and/or water molecule whereas the OH bending peak of water (1633 cm-1) and the C=C stretching vibration of aromatic ring (1531 cm(-1))became weaker on thermal treatment. The effect of ionic strength on the desorption of naproxen species and the related kinetic data revealed that the release mechanism at pH = 7.4 is unrestricted diffusion controlled and governed by the repulsive interactions between the bentonite surface and the negatively charged species. The pore structure characteristics of the bentonite samples corresponding to the surface area, pore volume and pore size were determined by using the conventional analysis of the nitrogen adsorption-desorption isotherms. (C) 2011 Elsevier B.V. All rights reserved.