Highly selective and reversible adsorption of trace gaseous ammonia by a stable nanoporous carboxylic acid-functionalized silica aerogel

Gaseous ammonia (NH 3 ), a highly corrosive and toxic pollutant, poses significant risks to human health and the environment. This study addresses the challenge of trace NH 3 removal by synthesizing carboxylic acid-functionalized silica aerogels (CMSA-X) through a simple, cost-effective two-step grafting approach. The fabricated CMSA-4 aerogel exhibited a high -COOH group content (4.13 mmol·g −1 ) and a stable nanoporous structure, enabling reversible and highly selective adsorption for trace gaseous ammonia. It demonstrated exceptional adsorption capacity (3.90 mmol·g - 1 at 0.1 bar and 7.30 mmol·g -1 at 1.0 bar) and outstanding adsorption selectivity (selectivity coefficients of ∼43031 for NH 3 /N 2 and ∼2200 for NH 3 /CO 2 , respectively). The NH 3 -saturated CMSA-4 can be easily regenerated by low temperature treatment (393 K), and maintained 94% adsorption capacity after ten adsorption-desorption cycles. The superior dynamic adsorption capacities of 3.36 mmol·g - 1 under dry condition and 3.28 mmol·g - 1 under humid condition outperformed previously reported adsorbents. Field tests further confirmed its efficacy in removing trace NH 3 (2 ppm), achieving removal rates 1.6-3.8 times higher than commercial alternatives. In-situ diffusion infrared spectroscopy revealed that proton transfer caused OCO - NH 4 + formation is the key adsorption mechanism. This study provides a promising method to develop high-performance adsorbent for efficient trace NH 3 removal in environmental and industrial applications.