Bio-based composites of alginate, cellulose, and Moringa oleifera for heavy metal removal in water purification: a comprehensive and critical review of mechanisms, fabrication, and performance

Abstract

The escalating prevalence of heavy metal contamination in aquatic ecosystems, driven by industrialisation, urbanisation, and population growth, has necessitated the development of sustainable and efficient water purification technologies. This review critically evaluates recent advances in developing and applying bio-based composites comprising sodium alginate, cellulose, and Moringa oleifera (M. oleifera) to remove heavy metals from aqueous systems. The review examines the physicochemical characteristics, adsorption mechanisms, and synergistic properties of these biopolymers, emphasising the role of the active compounds in each. The deduction from the comparative study of this review reveals cellulose-based composites demonstrating the highest overall adsorption performance, with several systems exceeding 1000 mg g⁻¹ across different heavy metals. Although alginate composites achieve the highest single reported capacity, 1742 mg g⁻¹ for Pb²⁺, their performance is more dependent on chemical or nanoparticle functionalisation. M. oleifera biosorbents show moderate adsorption capacities, with improvements mainly observed after chemical modification. Overall, cellulose composites exhibit the most consistent and versatile adsorption behaviour among the three materials. This review identifies potential applications, highlights key research gaps, and outlines future directions for advancing bio-based composite materials as viable solutions for sustainable water treatment.