Tuning microporosity and surface chemistry: The synergistic effect of KOH and urea on CO₂ capture performance of sucrose-derived activated carbons

The optimization of activated carbons (ACs) for CO₂ adsorption is a critical challenge in carbon capture technologies, and a precise control over porosity and surface chemistry is needed to develop high-performance ACs. This study explores the effects of activation conditions on the microporosity and surface chemistry of ACs derived from sucrose, highlighting the synergistic role of KOH and urea in a one-step activation process. The combined use of KOH and urea significantly enhances CO₂ uptake (up to 7.36 mmol g−1 at 0 °C and 740 Torr) by promoting the formation of ultra-micropores (<0.7 nm) and incorporating N- and K-based adsorption sites. Furthermore, urea plays a crucial role in preventing the formation of residual potassium carbonate occurring for activation temperature ≤ 700 °C, thereby improving the efficiency of KOH activation at low activation temperature and ensuring a well-developed porous network favourable for CO₂ capture. KOH/urea activated carbons show a CO₂:N₂ selectivity of up to 61 at 20 °C in a 15:85 CO₂:N₂ mixture, outperforming the materials activated using KOH-only in post-combustion conditions. These findings provide fundamental insights into the mechanisms governing KOH/urea co-activation and offer a scalable, cost-effective strategy for designing high-performance ACs in industrial CO₂ capture applications.