Water defluoridation with avocado-based adsorbents: Synthesis, physicochemical characterization and thermodynamic studies

This paper reports the synthesis of novel adsorbents for fluoride removal from water using avocado kernel seeds and pyrolysis with and without physical activation. Avocado-based adsorbents were synthetized at different carbonization conditions where CO2 activation was studied to determine its impact on fluoride adsorption properties. Fluoride adsorption capacities and other physicochemical properties of the adsorbents obtained with and without physical activation were compared and analyzed. The best synthesis conditions to improve defluoridation performance of avocado-based carbons were identified. Results showed that the adsorbent obtained via pyrolysis had the highest adsorption properties, while its counterpart obtained with CO2 activation decreased its defluoridation performance where the carbonization temperature was the main synthesis variable. Physicochemical characterization suggested that fluoride adsorption with the avocado-based adsorbents could be governed by electrostatic interactions and a ligand exchange mechanism involving Si moieties. Avocado-based adsorbents showed better defluoridation properties than those reported for other activated carbons obtained from both inorganic and organic precursors. In summary, this study contributes with new insights for the preparation of tailored adsorbents for fluoride removal from water using an alternative lignocellulosic feedstock.