Comparative adsorption behavior of ibuprofen and clofibric acid onto microwave assisted activated bamboo waste

Abstract

The adsorption behavior of two representative pharmaceutically active compounds and widespread used drugs (ibuprofen and clofibric acid) were evaluated using a relatively abundant and inexpensive material, bamboo waste, as adsorbent prepared via ZnCl2 activation process followed by microwave heating. The Langmuir, Freundlich, Dubunin-Raushkevich, and Temkin models were applied to describe the adsorption isotherm for the two systems. The goodness of curve fitting in the various models was done in accordance with linear regression coefficients and various error functions. The Langmuir isotherm model was applicable for describing the binding data for both ibuprofen (IBP) and clofibric acid (CA) onto activated bamboo waste (ABW) with the following order of adsorption capacity: IBP (278.55 mg·g-1) > CA (229.35 mg·g-1). The Gibbs free energy of -6.15 and -5.56 kJ mol-1 estimated for IBP and CA onto ABW unravelled the spontaneous nature of this adsorbent toward these adsorbates. Both pH and temperature exhibited a remarkable effect on the adsorption of IBP and CA. Adsorption kinetic data for IBP and CA showed that the processes obeyed pseudo-second-order kinetic expression and diffusion in micropore and mesopore was the potential rate-controlling step. The desorption of IBP using methanol was very effective with more than 96% of IBP desorbed from ABW within 10 min to allow the reusability of the adsorbents. In contrast, methanol was less effective for CA as only 60% desorption was possible with the solvent. Certain physicochemical and spectroscopic characterization, viz., macro- and microanalysis, Bohem titration, pHpZC, Drift method, SEM-EDS, surface area, porosity, and FTIR were analyzed in an attempt to better understand the adsorption process. © 2014 American Chemical Society.