Coconut Shell-Derived Activated Carbons: Preparation, Physicochemical Properties, and Dye Removal from Water

Valorizing coconut shell waste as a renewable lignocellulosic precursor offers a sustainable route to produce high-performance activated carbons for wastewater treatment. In this study, coconut shells were transformed into activated carbons through physical activation (air, CO₂, steam) and chemical activation (H₃PO₄, ZnCl₂, KOH), allowing direct comparison of how each method influences porosity and surface chemistry. Among the physically activated samples, steam activation produced the best material, A-ST, with S_BET = 738 m² g^-1, V_mi = 0.38 cm³ g^-1 and V_me = 0.07 cm³ g^-1. KOH activation yielded the top-performing carbon, A-KOH, achieving S_BET = 1600 m² g^-1, V_mi = 0.74 cm³ g^-1, and V_me = 0.22 cm³ g^-1. Adsorption tests with methylene blue, methyl orange, and orange G showed a clear link between physicochemical features and dye uptake. A-ST and A-KOH exhibited the highest capacities due to their wide micro-mesoporosity and favorable surface charge at the adsorption pH. In both cases, methylene blue was most strongly retained, confirming that large aromatic cations benefit from π-π interactions with graphene-like layers and easy micropore access. Overall, the results demonstrate that coconut-shell valorization is maximized when activation enhances both porosity and surface chemistry, enabling the production of tailored sorbents for the efficient removal of organic contaminants.