Recent advances in developing engineered biochar for CO2 capture: An insight into the biochar modification approaches

Carbon dioxide (CO2) is the primary anthropogenic greenhouse gas with a significant contribution to global warming; this excessive emission needs to be controlled through an effective carbon capture and storage (CCS) approach. Biochar has been considered a cost-effective adsorbent for CO2 capture; however, pristine biochar suffe from poor textural properties and surface chemistry. Here, developing engineered biochar requires careful tuning of the physicochemical properties of the biochar to obtain a high CO2 capture capacity. This work presents a review of recent studies on the synthesis of engineered biochar through various modifications for CO2 adsorption. In this context, the impact of different modification approaches, including physical, chemical, and physicochemical treatments, on the CO2 uptake properties of the engineered biochar are reviewed. Emphasis is given to the mechanisms through which the CO2 adsorption capacity of biochar is enhanced after each modification. This survey of literature stresses the importance of maintaining a balance between the textural (specific surface area and micropore volume) and surface chemical attributes (basicity, mineral content, various functional groups, non-polarity and hydrophobicity) to produce engineered biochar with high CO2 uptake capacity, strong selectivity towards CO2 over other gases and stable performance upon multiple cycles of CO2 adsorption-desorption.