Sustainable biochar synthesis via synergistic H2O2-KOH modification for enhanced CO2 physisorption

• A synergistic improvement of biochar by H 2 O 2 -KOH modification is proposed; • H 2 O 2 facilitates biochar deoxygenation, while KOH enhances its pore structure; • The biochar with a fine hierarchical microporous structure is fabricated; • Biochar with a BET surface area of 3522.7 m 2 /g is successfully synthesized; • CO 2 uptake capacity of biochar is 6.6 mmol·g -1 at 30°C with excellent cyclic stability. Excessive CO 2 emissions lead to a gradual increase in global average temperatures and an increased frequency of extreme weather events. Exploiting advanced materials for CO 2 capture has become a key issue of concern to all countries. In this study, a new biomass carbonization strategy, co-modification by H 2 O 2 and KOH, is proposed to prepare microporous biochar from pine sawdust with high CO 2 adsorption capacity. Results indicate that the co-modification strategy can produce biochar with a specific surface area as high as 3522.7 m 2 /g (with a micropore ratio of 90.3%), which increases by 56.7% compared to the biochar produced by biomass carbonization without H 2 O 2 treatment. The adsorption properties of the co-modification-derived biochar are investigated by CO 2 -TPD and TG, and the biochar exhibits a maximum CO 2 adsorption capacity of 6.60 mmol/g at 30°C and retains over 91.2% of this capacity after 10 cycles. It is revealed that H 2 O 2 -KOH modification can significantly promote the physisorption capacity of the biochar, highlighting the enhanced CO 2 capture efficiency due to alkaline hydrogen peroxide treatment on the biochar and its enhancement in CO 2 capture.