Advancing direct air capture via wood-derived biochar: catalytic enhancement of CO2 adsorption performance and regeneration stability

Abstract

Wood-derived biochar offers a sustainable and cost-effective method for direct air capture (DAC) of CO2. This study comprehensively examines the impact of operating temperature, gas flow rate, and prolonged saturation on CO2 adsorption performance. A biochar-packed fixed bed column was subjected to synthetic air (400 ppm CO2 and balanced N2) at various flow rates (35–80 mL/min) and temperatures (5°C to 20°C). The biochar exhibits a highly alkaline nature (pH 10.23), high specific surface area, and a rich microporous structure. Maximum CO2 removal occurred at lower temperatures and flow rates, resulting in a CO2 removal rate of up to 91.8% and an adsorption capacity of 0.014 mmol/g at 5°C. Although higher flow rates enhanced adsorption capacity, they reduced removal efficiency. After 12 hours of continuous exposure, saturation behavior was observed, resulting in a total adsorption capacity of nearly 0.055 mmol/g (2.42 mg/g). Kinetic analysis revealed good agreement with both pseudo-second-order (PSO) and pseudo-first-order (PFO) models, indicating the coexistence of physisorption and chemisorption mechanisms. The adsorbent consistently demonstrated stable performance across several regeneration cycles, highlighting its reusability. These results highlight the promise of wood biochar as a viable, renewable DAC sorbent capable of capturing low-concentration CO2 across different environmental conditions.