Removal of zinc from water using graphene-like biochar produced from palm seed shells

Water pollution by trace metals poses a serious threat to both human health and the environment, making their removal from contaminated water a critical issue. Recent research has focused on identifying efficient and sustainable adsorbents. In this study, oil palm seed shells (Elaeis guineensis) were used to synthesize graphene-like biochar (BGp), which was then partially oxidized to obtain oxidized biochar (BOGp), aimed at removing zinc from aqueous solutions via adsorption. Characterization of the materials revealed low moisture content and high ash content for both BGp and BOGp. Their bulk densities were 0.76 g/cm³ (BGp) and 0.71 g/cm³ (BOGp), while the point of zero charge (pHₚzc) values were 7.3 and 4, respectively. X-ray diffraction (XRD) analysis showed distinct peaks at 2θ ≈ 10° and 2θ ≈ 26.03°, characteristic of oxidized graphitic carbon. BOGp exhibited a higher BET specific surface area (340.32 m²/g) compared to BGp (228.20 m²/g). Infrared (FTIR) spectroscopy confirmed the oxidation of BOGp through intensified C=O stretching vibrations. Both materials demonstrated high zinc removal efficiencies. Using 0.1 g of adsorbent in 50 mL of a 1 mg/L zinc sulfate solution, removal rates of 73.4% (BGp) and 90.11% (BOGp) were achieved. The adsorption processes followed pseudo-second-order kinetics and were characterized as chemisorption. The Freundlich and Temkin isotherm models, indicating multilayer and exothermic adsorption, confirmed the effectiveness of both materials. This study underscores a sustainable and value-added approach to utilizing agricultural waste for water treatment applications.