CO2 capture using biochar derived from municipal residual sludge conditioned with chitosan

To achieve the dual objectives of pollution reduction and carbon mitigation, this study examined the effects of biochar derived from urban residual sludge conditioned with chitosan (SBCC) on the CO ₂ capture capacity. Using raw sludge biochar (RSB) as the control group, and focusing on the preparation temperature of the biochar and the adsorption temperature of CO ₂ as main parameters, the study explored the CO ₂ adsorption performance of modified sludge biochar. The mechanism of CO ₂ adsorption by SBCC was elucidated through the analysis of the surface morphology, elemental composition, functional groups, and surface area of the sludge biochar. Results indicate that the optimal preparation and adsorption temperatures for RSB are 800°C and 30°C, respectively, with a maximum CO ₂ adsorption capacity of 28.36 mg/g. For SBCC, the optimal temperatures are 600°C and 30°C, respectively, achieving a maximum CO ₂ adsorption of 89.88 mg/g. Compared to RSB, SBCC primarily exhibits a chemisorption process, with its adsorption mechanism involving strong dipole-quadrupole interactions between nitrogen atoms and CO ₂ . In the sludge, chitosan undergoes partial hydrolysis through alkalinization, forming carboxyl groups. These carboxylic functional groups facilitate the formation of hydrogen bonds between CO ₂ and the carbon surface, as well as condensation reactions between alkaline functional groups and CO ₂ . Moreover, SBCC also demonstrates good reusability. After five cycles of adsorption and desorption, it still retains up to 75% of its initial CO ₂ adsorption capacity.