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 SBET = 738 m2 g−1, Vmi = 0.38 cm3 g−1 and Vme = 0.07 cm3 g−1. KOH activation yielded the top-performing carbon, A-KOH, achieving SBET = 1600 m2 g−1, Vmi = 0.74 cm3 g−1, and Vme = 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.