Advanced biochar hybrid systems for adsorptive removal of water contaminants: Progress, mechanisms, and future directions

Abstract Contamination of aquatic systems by organic materials, heavy metals, pharmaceuticals, dyes, pesticides, and emerging pollutants is a pressing problem not only for aquatic systems but also for human health. Among the various treatment technologies, adsorption is among the most effective, economical, and environmentally friendly water decontamination technologies. In this context, biochar has garnered considerable attention for its widespread availability, tuneable porous structure, surface functionality, and low production cost. However, the adsorption, selectivity and regeneration properties of biochar are not always desirable. To overcome the issues, metal and metal oxide nanoparticle based advanced biochar hybrid systems, carbon based nano materials, and other functional materials have been developed to enhance the physicochemical properties and adsorption efficiency. This review aims to critically evaluate recent advances in biochar‐based hybrid adsorbents for water purification, with a particular focus on adsorption. Different biochar hybrid systems are critically reviewed, covering the synthesis approaches, structure and physicochemical characteristics, and the mechanisms of contaminant removal by adsorption, including electrostatic attraction, ion exchange, surface complexation, pore filling, hydrogen bonding, hydrophobic interactions, and π – π interactions. The adsorption efficiency of the biochar hybrids to various contaminant types (heavy metals, dyes, pharmaceutical residues, and pesticides) are systematically evaluated. Besides that, the factors influencing the adsorption behaviour, the regeneration and reusability, the environmental safety and feasibility is also examined. Finally, the existing problems and future research opportunities are presented, including multifunctional biochar hybrids, modelling, scaling up biochar production, and application in complex water matrices. This review further maps dominant removal mechanisms directly to specific hybrid material features and outlines the design and optimization of second‐generation biochar‐based hybrid adsorbents for sustainable and efficient water purification.