Nanomaterial-functionalized biochar hybrids for enhanced Pb²⁺ removal: surface engineering and interfacial mechanisms

The removal of lead (Pb) from wastewater has become essential due to its detrimental effects on human health and on the environmental ecosystem. Moreover, rapid industrialization has led to a significant increase in waste generation, contributing to environmental degradation. These two problems can be addressed through a single sustainable solution: converting waste into biochar. Waste-derived biochar (W-BC) is a promising platform for mitigating Pb²⁺ ions due to its cost-effectiveness, high surface area, and adsorption capacity. Moreover, adsorption potency of W-BC can be enhanced through its functionalization with nanomaterials (NMs). In this regard, the present study delves into recent developments in W-BC for the adsorption of Pb²⁺ ions from wastewater. The comprehensive mechanistic insights into the functionalization of W-BC with different NMs (metal, metal-oxides, carbon, and polymer) are critically discussed, with particular emphasis on the enhancement of surface-active sites and adsorption capacity via electrostatic interactions, π-π electron donor-acceptor interactions, hydrogen bonding, surface complexation, and redox processes. This article comprehensively explored the different strategies and favorable experimental parameters (contact time, adsorbent dosage, and pH of solution) for the enhancement of the removal efficiency of W-BC. Additionally, the regeneration approaches for W-BC-based adsorbents have also been discussed, which are crucial for practical and real-time applications. Therefore, the present study provides valuable insights into converting waste materials into an effective lead removal platform for water remediation, thereby contributing to attaining the sustainable development goals (SDGs) and a circular economy.