Straw-derived porous biochars by ball milling for CO2 capture: Adsorption performance and enhanced mechanisms

In order to break the limitation of straw biochar adsorption capacity, this study evaluates the feasibility of enhancing CO 2 adsorption capacity in straw-derived biochars via ball milling (BM) and explores the underlying mechanisms. Biochars were prepared from corn straw, banana stalk, and cotton stalk employing a two-step process comprising pyrolysis followed by the BM process. The ball-milled biochars demonstrated CO 2 adsorption capacities of 45.38, 49.88, and 42.60 mg·g −1 at 30 °C, corresponding to increases of 23.52 %, 9.50 %, and 8.93 % in comparison to untreated biochars. The adsorption process was found to be highly exothermic, with CO 2 adsorption capacity decreasing by 49.69–65.87 % as the temperature was raised from 0 to 70 °C. Kinetic studies and adsorption isotherms demonstrated that the BM process primarily enhanced physisorption in corn straw biochar and chemisorption in banana stalk and cotton stalk biochars. Correlation analysis indicated that CO 2 adsorption was influenced by pore volume, total basicity, and ash composition. The biochars' high adsorption capacity was attributed to pore filling, van der Waals forces, H bonding, and acid-base interactions. Furthermore, after 10 adsorption-desorption cycles, the biochars retained 92.16–98.01 % of their initial CO 2 adsorption capacity, demonstrating high stability and reusability. Overall, the findings highlight the potential of the BM process as an effective method for enhancing the CO 2 adsorption performance of straw-derived biochar. • Porous straw biochar was prepared by two steps of pyrolysis and ball milling. • Ball milling increased the CO 2 adsorption capacity of straw biochar by 20 %. • Pore filling, H-bonding, and acid-base interactions drived CO 2 adsorption. • The CO 2 adsorption capacity of biochar remained above 90 % after 10 cycles. • Ball milling boosted straw biochar's physical and chemical adsorption.