KOH-Activated Carbons Derived from Plum Stones, Date Stones, and Walnut Shells for the Adsorption of Anionic Surfactant

Water contamination with surface-active agents, such as sodium lauryl sulfate (SLS), represents a serious environmental concern, driving the need for efficient and low-cost alternative adsorbents as a step toward sustainable waste valorization. In this study, waste biomass derived from plum stones, date stones, and walnut shells was successfully transformed into activated carbons via chemical activation using potassium hydroxide (KOH) at 850 °C with a 1:1 impregnation ratio. The synthesized materials underwent comprehensive physicochemical characterization utilizing TG-DSC, elemental analysis, Boehm titration, SEM, TEM, and nitrogen physisorption (BET), whereas their adsorption performance was evaluated against aqueous SLS solutions across various concentrations. The obtained results reveal a predominantly microporous structure with a high specific surface area, reaching up to 1059.01 m2/g for ACdate. The equilibrium adsorption data were well described by the Langmuir isotherm model, which yielded model-estimated asymptotic adsorption capacities (qm) of 219.70 mg/g for ACwalnut, 178.25 mg/g for ACdate, and 57.80 mg/g for ACplum. These values represent Langmuir-derived model parameters rather than experimentally attained adsorption capacities within the investigated concentration range. Notably, despite having a lower specific surface area than ACdate, ACwalnut exhibited the highest Langmuir-estimated qm, which may be associated with its structural balance and well-developed mesoporous network (0.210 cm3/g), facilitating the intraparticle transport of SLS molecules. These findings highlight that high efficiency originates from a synergistic combination of accessible porosity, a mesoporous transport network, hydrophobic character, and specific surface functional groups, demonstrating the exceptional potential of these activated carbons for anionic surfactant wastewater remediation.