Theoretical perspectives and recent advances in palm-based adsorbents for sustainable heavy metal removal from aqueous systems

Heavy metal contamination in water systems remains a pressing environmental and public health issue due to the persistence and toxicity of metals such as Pb²⁺, Cd²⁺, Cr⁶⁺, and As³⁺. Increasing global attention on environmental protection has spurred the scientific community to focus on developing strategies for addressing heavy metal contamination. Among various remediation strategies, adsorption using palm-based biosorbents has emerged as a sustainable and cost-effective solution. This review synthesizes the major theories and conceptual frameworks that explain the behavior and efficiency of palm-derived materials in heavy metal removal from aqueous solutions. Key adsorption isotherm models, including Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, and Redlich–Peterson were examined to evaluate their applicability across monolayer, multilayer, and heterogeneous adsorption processes. Kinetic models, such as pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion, were analyzed to unravel adsorption kinetics and rate-limiting steps. Thermodynamic principles were also discussed, offering insights into spontaneity, energy changes, and molecular disorder during adsorption. In addition, this review highlights surface chemistry and material science theories, particularly the role of functional groups, zeta potential, and textural properties characterized via BET theory. The novelty of this work lies in its integrative approach, which combines surface chemistry, material science theories, and emerging approaches such as machine learning and molecular modeling to develop a unified conceptual framework. The review critically examines current limitations, model inconsistencies, and challenges related to scale-up, offering strategic directions for future research and industrial application. By integrating chemical engineering insights with advanced theoretical frameworks, this work aims to inform the rational design, optimization, and deployment of palm-based biosorbents for next-generation water purification technologies.