Modified biochar and its nanocomposites for efficient removal of aqueous Hg species from contaminated water

Abstract

Mercury contamination in aqueous systems has emerged as a severe threat to the environment and human beings because of the toxicity of this heavy metal in different chemical forms and its persistent nature, leading to bioaccumulation followed by biomagnification. Efficient removal of all types of aqueous mercury species from the contaminated water can be done by different methods. Modified biochar and its nanocomposites are promising and sustainable adsorbents for this purpose, due to their low cost preparation and precursor abundance. This review presents the significant potential of modified biochar and its nanocomposites for effective recovery of aqueous mercury species to mitigate mercury pollution worldwide. This review comprehensively examines recent developments in the preparation and modification of biochar-based adsorbents for their specific application of aqueous mercury sequestration from the contaminated environment. Various methods of biochar preparation, modification, and biomass pretreatment techniques are discussed in correlation with the enhancement of physicochemical properties. Biochar-mercury binding mechanisms indicate complex interactions during the adsorption process, including electrostatic attraction, ligand exchange, redox transformations facilitated by metal nanoparticles, complexation with S-containing functional groups, charge shielding, cation bridging, etc. Biochar modification substantially improves mercury adsorption capacities by enhancing the selectivity, while preparation of nanocomposites demonstrates fast adsorption kinetics with high regeneration potential during several cycles. Major advantages like recyclability and low environmental impact make the modified biochar nanocomposites a potential candidate for scalable water treatment applications. However, it comes with the challenges of large-scale production processes, environmental safety issues, and comprehensive toxicity assessment. More scientific attention is required to optimize the regeneration strategies in order to facilitate a sustainable real-world mercury remediation technology.