Hydrochar-derived activated carbons from poplar and spruce sawdust: synthesis, characteristics and carbon adsorption performance

The escalating demand for energy across various sectors has led to a significant increase in greenhouse gas emissions, primarily due to the extensive use of fossil fuels. This study addresses the critical need for effective carbon capture adsorbents to mitigate environmental impacts. Bio-based activated carbons, known for their high surface area and pore volume, were synthesized from poplar and spruce sawdust through hydrothermal carbonization (HTC) followed by simultaneous carbonization and activation. HTC, aimed at enriching precursors with oxygen-rich surface functional groups, was conducted at temperatures of 180, 200, and 220 °C for 90 min. This process produced hydrochars that were subsequently activated at 800 °C in the presence of KOH under a nitrogen atmosphere. Remarkably, the activated carbons derived from poplar sawdust hydrochar (at a HTC temperature of 200 °C) and spruce sawdust hydrochar (at a HTC temperature of 220 °C) demonstrate superior specific surface areas of 1680.59 and 1231.57 m 2 /g, along with total pore volumes of 0.87 and 0.62 cm 3 /g, respectively. Moreover, both poplar and spruce hydrochar-based activated carbons exhibit high CO 2 adsorption capacities of 3.75 and 3.43 mmol/g, respectively, at 24.85 °C and 1 atm. Their CH 4 adsorption capacities are 1.52 and 1.42 mmol/g, respectively, under the same conditions. This work highlights the potential of bio-based activated hydrochars in applications such as indoor air quality improvement and industrial flue gas treatment, emphasizing the importance of pretreatment and activation conditions in optimizing adsorbent performance.