Abstract
Abstract Nickel (Ni) contamination in water systems presents serious environmental and human health concerns due to its toxicity and persistence. This study evaluated the potential of activated orange peel powder (OPP), sugarcane bagasse (SCB), and their activated composite form (OPP:SCB) for the bio-adsorption of Ni(II) from aqueous solution. The bio-sorbents were thermally activated at 450 °C and batch adsorption studies were conducted to optimise pH, contact time, adsorbent dosage, and initial metal ion concentration. Under optimum conditions, activated OPP and SCB achieved Ni(II) adsorption capacity of 39.8 mg/g and 39.7 mg/g respectively, while the activated OPP:SCB composite (5:5 ratio) achieved adsorption capacity of 40.0 mg/g. Adsorption kinetic studies revealed that pseudo-second-order was the suitable kinetic model describing data hence denoting chemisorption while adsorption isotherm revealed the removal of Ni(II) fitted the Langmuir adsorption isotherm. Characterization results revealed porous and heterogeneous surfaces containing oxygenated functional groups such as hydroxyl, carboxyl, and carbonyl groups that enhanced Ni(II) bio-adsorption. Energy dispersive X-ray spectroscopy result confirms the presence of Ni(II) in activated material after bio-adsorption. Morphological and spectral changes after bio-adsorption confirmed successful interaction between Ni(II) ions and the bio-sorbents. Regeneration studies further demonstrated good stability and reusability up to six adsorption–desorption cycles. The findings highlight activated OPP, SCB, and their composite form (OPP:SCB) as efficient, low-cost, and environmentally friendly bio-sorbents for remediation of Ni-contaminated water systems.