Lignin waste-based low-cost porous carbon for efficient and stable CO2 capture

• Synthesis of low-cost porous carbon CO 2 adsorbents from lignin waste via one-step carbonization/activation method. • Utilization of K 2 CO 3 activator and high calcination temperature enabled the formation of numerous micropores below 2 nm and mesopores in the range of 2–4 nm. • Optimal porous carbon demonstrates exceptional CO 2 capture capacity up to 3.75 mmol/g at 1 bar and 25 °C. • Excellent CO 2 /N 2 selectivity of 57.2, low regeneration energy Q st of 15.9–23.8 kJ/mol and excellent stability over multiple adsorption/desorption cycles highlight application potentials. Developing a low-cost and renewable porous carbon-based CO 2 adsorbent with excellent CO 2 capture capacity, selectivity, stability and low regeneration energy is a contemporary research subject worldwide, especially in the context of a circular and carbon neutral economy. Herein, we report the synthesis of novel low-cost porous carbon materials for highly efficient CO 2 capture prepared from abundant lignin waste via a one-step direct activation/carbonization method. Upon optimization of the activation temperature and activator concentration, the optimal carbon adsorbent material L-K-2–750 with K 2 CO 3 as activator, K 2 CO 3 /lignin mass ratio of 2/3 and activation temperature of 750 °C, exhibited a high specific surface area (797 m 2 /g) and high total pore volume (0.33 cm 3 /g). It demonstrated an excellent CO 2 adsorption capacity of 3.75 mmol/g at 25 °C and 1 bar, which is comparable to or better than the CO₂ adsorption capacities reported in the literature (1.1–4.4 mmol/g). Adsorption/desorption cycling experiments revealed excellent stability over five cycles with <2 % loss of adsorption capacity. CO 2 /N 2 selectivity experiments showed an excellent selectivity of 57.2 in a CO 2 /N 2 mixture (15:85). The Isosteric Adsorption Heat (Q st ) level of 15.9–23.8 kJ/mol confirmed low regeneration energy, thus making this material highly promising for practical applications.