Honeycomb-like nitrogen-doped ultramicroporous biochar for efficient and robust CO₂ capture

Honeycomb-like nitrogen-doped ultramicroporous biochar for CO₂ capture is synthesized through various methods utilizing biomass, urea, and KOH as raw materials, nitridation agent, and porogen, respectively. The resulting materials meticulously undergo comprehensive characterization, revealing densely packed ultramicropores arranged in honeycomb-like patterns. The biochar predominantly exists in a graphite state of carbon with sufficient defects and abundant functional groups, along with a high nitrogen content, thereby providing numerous CO₂ sorption sites. High CO₂ sorption capacities are observed of 4.15 mmol/g (at 1 bar and 298 K) and 5.45 mmol/g (at 1 bar and 273 K) with sorption heat around 23 kJ/mol. The Sips model fitting displays satisfactory results at 298 K, indicating a maximum sorption capacity around 5.45 mmol/g, with regression correlation coefficients exceeding 0.9942. The sorption selectivity between CO₂ and N₂ is notably influenced by the surface nitrogen content present in the materials. These sorbents exhibit exceptional cyclic robustness during vacuum pressure swing cycles, with an attenuation rate as low as 13.98% over 20 cycles. The abundant availability and cost-effectiveness of biomass, combined with a straightforward synthesis procedure and excellent CO₂ sorption performance, position honeycomb-like N-doped ultramicroporous biochar synthesized through the one-pot carbonization-activation method as promising candidates for CO₂ capture applications.