Green Activation of Activated Carbons Prepared from Palm Nut Shells: A Green Approach Based on Extracts of Gabonese Plants

This study presents a green approach for the preparation of activated carbons (ACs) from biomass (palm nut shells) using aqueous extracts of Gabonese plants (Hallea ciliata (HC), Ricinodendron heudelotii (RH) and Nauclea latifolia (NL)) as bioactivation agents. The objective was to evaluate the influence of secondary metabolites (plant biomolecules) present in the aqueous extracts on the pore structure and surface chemistry of resulting bioactivated carbons, with a view to applications in water treatment in rural zones. Phytochemical screening and antioxidant analyses revealed that the extracts are rich in secondary metabolites. The HC extract exhibited the highest contents of polyphenols (2418.49 µg GAE/g), tannins (1175.73 µg GAE/g) and proanthocyanidins (2069.24 µg GAE/g), as well as strong antioxidant activity (AAI = 3.47). Activated carbons obtained from green activation showed improved textural properties compared to the water-impregnated reference material (AC-water). In particular, the specific surface area increased from 367 m2/g for AC-water to 385 - 447 m2/g for the activated carbons obtained from green activation, with preferential development of microporosity. The AC-HC sample exhibited the most developed surface properties (SBET = 446.51 m2/g, micropore volume = 0.144 cm3/g) and the highest adsorptive capacity (iodine number = 520 mg/g). These results demonstrate that secondary metabolites from aqueous extracts of Gabonese medicinal plants can act as effective green activation agents for the preparation of microporous activated carbons through an environmentally friendly process under the experimental conditions investigated.