Enhancing the adsorption capacity of lignin-based super activated carbon for trace toluene under highly humid conditions through [2 + 1] cycloaddition reactions

Continuous adsorption removal of trace VOCs under humid conditions, especially when the relative humidity (RH) is ≥50 %, faces great challenges in indoor air purification. Herein, we synthesized super-activated carbons (LSACs) using alkali lignin extracted from black liquor via potassium hydroxide (KOH)-assisted chemical activation. The LSAC-3 with ultra-high specific surface area ( S BET : 2535 m 2 /g) and microporosity (92.4 %) was then covalently grafted with the CF 2 groups onto its surface through a [2 + 1] cycloaddition reaction to significantly enhance humidity resistance. After modification, the LSAC-3-CF 2 preserved adsorption sites to the greatest extent, with a minimal loss of S BET , at only 4.9 %. Moreover, LSAC-3-CF 2 , which contained a trace fluorine element (0.55 %), exhibited excellent hydrophobic performance, with a water contact angle (WCA) of 153.7°. The dynamic adsorption experiments further demonstrated that LSAC-3-CF 2 exhibited superior trace toluene adsorption capacity, with 145.9 mg/g at 50 RH% and 46.0 mg/g at 80 RH%, respectively, superior to many reported adsorbents. In addition, LSAC-3-CF 2 displayed excellent regeneration performance after three dynamic adsorption cycles. The adsorption mechanism of toluene on LSAC-3-CF 2 could be attributed to (1) the improved π-π stacking interaction between toluene molecules and the adsorbent surface, and (2) the reduced hydrogen bond interaction between water molecules and oxygen-containing groups onto the adsorbent surface due to the covalent grafting of CF 2 group. This study provides valuable insights and design references for developing adsorbents that can effectively adsorb trace VOCs under high humidity conditions, offering potential solutions for improving indoor air quality.