Tannin-derived micro-mesoporous carbons prepared by one-step activation with potassium oxalate and CO₂

Micro-mesoporous carbons (MMCs) were successfully prepared using natural polyphenolic compounds, condensed tannins, and glyoxal, a nontoxic aldehyde, in lieu of synthetic phenolic compounds like formaldehyde and resorcinol as carbon precursors. Such MMCs were fabricated by a soft-templating strategy under mild conditions. Porosity development was achieved by varying the amount of potassium oxalate as an in-situ activator coupled with one-step CO₂ activation at 700 °C. This strategy allowed for the enhancement of microporosity as well as retention of the uniform mesoporous structure of the carbons. The CO₂ uptakes of 5.2 mmol/g at 0 °C and 3.6 mmol/g at 25 °C were achieved at 1 bar pressure for the tannin-derived activated MMC sample with a surface area of 1192 m²/g, a volume of fine micropores (sizes below 1 nm) of 0.33 cm³/g, and a mesopore volume of 0.49 cm³/g. This study opens new opportunities for a facile and green synthesis of MMCs from less toxic precursors with tailored porosity by synergistic effects of chemical and physical activation. The resulting MMCs exhibit the potential applicability not only as CO₂ sorbents but also in other environmental applications such as adsorption of organic volatile compounds and dye molecules, which require slightly larger pores.