Diclofenac removal from water by adsorption on Moringa oleifera pods and activated carbon: Mechanism, kinetic and equilibrium study

Abstract

The productive chain of Moringa oleifera can generate by-products such as pods and bark, which can become large environmental liabilities. In the search for cleaner production processes, which tend to value by - products, this work evaluated the potential application of the Moringa oleifera pod as a low cost adsorbents in the removal of diclofenac. Babassu coconut activated carbon was used for comparison purposes. The biosorbent characterization revealed a variety of functional groups on its surface, so that electrostatic attractions, π-π interactions and hydrogen bondings between diclofenac molecules and biosorbent may be involved in the adsorption mechanism. Moreover, activated carbon showed a highly microporous surface, in which the internal diffusion controlled the process, resulting in a slower adsorption. At equilibrium, the Freundlich model was the most accurate to represent the experimental data for both adsorbents, indicating a multilayer adsorption. Thermodynamic parameters showed that adsorption on biosorbent were an exothermic and chemosorptive process. On the other hand, on activated carbon it was an endothermic process accompanied by weak interactions. The maximum adsorption capacities obtained for both adsorbents, were, under the conditions analyzed, very close in values (60.805 mg g−1 and 71.150 mg g−1 for biosorbent and activated carbon, respectively). Therefore, this study demonstrated that Moringa oleifera pods, due to its high great efficiency in the removal of diclofenac, can be a low cost and promising alternative to conventional adsorbents in water treatment.