Production of activated carbon from urban pruning residues of Cojoba arborea and Mangifera indica and its application in the removal of pharmaceuticals from aqueous media

Abstract

The production of activated carbon (AC) from urban tree pruning waste represents a sustainable alternative for the valorization of lignocellulosic residues. In this study, residues from Mangifera indica (mango) and Cojoba arborea (indian-earring-tree) were used, with chemical activation employing zinc chloride (ZnCl₂). The residues were air-dried (25 ± 5 °C) for 30 days, ground, and subjected to carbonization in a muffle furnace at 310 °C for 1 hour. Activation was optimized using a Central Composite Rotational Design (CCRD), varying pyrolysis temperature and ZnCl₂ to charcoal ratio (ZnCl₂/char), with the response variable being the amount of acidic functional groups (mEq g⁻¹). The optimal conditions were 331 °C and a ratio of 2.4 for mango-derived AC (MG-T1), and 239 °C and a ratio of 2.7 for indian-earring-tree-derived AC (BI-T2). After optimization, adsorption tests were performed with six pharmaceuticals (tetracycline, chloramphenicol, sulfaclopyridazine (SCP), metformin, ciprofloxacin) in aqueous media at pH 2.5, 5.5, and 8.5. The activated carbons were characterized for point of zero charge (pH_ZPC), morphology (SEM), and structure (XRD), showing porosity and composition suitable for adsorption. The best performance was observed for BI-T2, which achieved 82.6% removal of SCP at pH 5.5. The results indicate that the produced ACs have potential for application in the treatment of pharmaceutical-contaminated water.