Straw and wood based biochar for CO2 capture: Adsorption performance and governing mechanisms

Biochar derived from seven kinds of straw and wood biomass were prepared and characterized. Their CO2 adsorption performances and the governing mechanisms were investigated. Wood biochar (WBs) had better developed pore structure than straw biochar (SBs), and the specific surface area (SSA) of WBs was 2.73–4.40 times larger than that of SBs. While all the biochar showed good ability to capture CO2, WBs had higher CO2 adsorption capacities (41.23–45.85 mg/g) than SBs (26.53–41.49 mg/g) for their super pore structure. Among the SBs, soybean straw biochar (SS) had the highest basicity and thus the largest CO2 uptake. More importantly, SS had similar CO2 adsorption capacity to that of WBs despite that its SSA was much lower. These suggest that CO2 adsorption on the biochar was controlled by both SSA and basicity, which was further confirmed by linear correlation analysis. The adsorption kinetics and isotherms of CO2 on the biochar were best fitted by the pseudo-first and Langmuir models, respectively, suggesting the dominance of monolayer adsorption process. The adsorption was overwhelming exothermic process; therefore, increasing temperature from 0 °C to 65 °C decreased CO2 adsorption on the biochar by 71.27%-79.75%. Furthermore, the biochar showed high reusability (96.57%-98.94%) after ten CO2 adsorption–desorption cycles. Findings from this study indicate that biochar derived from straw and wood can be used as promising adsorbents for CO2 capture.