(45e) Improving Biochar Surface Area for CO2 Adsorption through Potassium Hydroxide Chemical Activation

With climate change continuing to worsen, developing low-cost, sustainable adsorbents is critical for implementing carbon dioxide (CO₂) capture on an industrial scale. Biochar is a solid material formed from the thermal decomposition of lignocellulosic biomass in an oxygen-deprived environment. This material can be applied as a low cost, sustainable adsorbent for capturing CO₂ but requires surface area improvement before being used. In this work, loblolly pine biochar created from intermediate pyrolysis was chemically activated with potassium hydroxide (KOH) at different activation temperatures, holding times, and KOH:biochar mass ratios to maximize biochar surface area for CO₂ adsorption. Thermogravimetric analysis (TGA) demonstrated that activation improved biochar thermal stability and removed degraded volatile compounds retained in biochar following pyrolysis. By nitrogen (N₂) physisorption, this evolution of volatiles increased biochar surface area for most activation condition combinations with biochar activated at 800°C for 3 h with a 1:1 KOH:biochar mass ratio having the highest specific surface area of 1080 m²/g. X-ray diffraction (XRD) revealed that biochar aromatic sheet size increased with increasing activation temperature from 16 in biochar to 21-36 Å in activated biochar. Fourier-transform infrared (FTIR) spectroscopy showed that aliphatic and oxygenated biochar functionalities were removed with increasing activation temperature. For CO₂ adsorption, the highest surface area activated biochar reached breakthrough and regeneration later than biochar reflecting its significantly higher surface area. As such, CO₂ adsorption capacity increased from 0.45 to 0.73 mmol/g through activation representing a 62% improvement in carbon capture.