Biochar Modification Methods for Augmenting Sorption of Contaminants

Biochar is a stable carbonaceous material obtained on pyrolysing biomass. Although it possesses crucial properties of high surface area, porosity, surface functionality, and sorption capacity, there is immense scope to augment these properties for effective contaminant sorption. Physical and chemical modifications enhance surface area, porosity, and contents of oxygen-containing functional groups. While acidic modifications augment surface functional groups and cation exchange capacity, alkaline modifications increase aromaticity, hydrophobicity, and π-π interactions. Impregnation with metals amplifies magnetic properties, availability of active sites, chemisorption, electrostatic attraction, and complexation. These modifications assist in sorption of cationic and anionic contaminants. Accordingly, the present study reviews modified biochars which promote eco-friendly contaminant removal. Moreover, various biomass and modification methods utilised for modified biochar production have been elaborated along with the changes in physico-chemical properties. Importantly, mechanistic insights into the functional role of modified biochars for removal of contaminants have been provided. Further, the impact of ageing on modified biochars and their contaminant adsorption performance have been discussed. Lastly, the feasibility and limitations of various biochar modification methods in addition to different research gaps have been presented to create a road map for future investigations. Waste management and contaminant remediation are the need of the hour for planet survivability, which could be achieved by precise biochar modification.Graphical abstract