Designed Carbide-derived Carbons for Ammonia Filtration

Abstract

A series of carbide-derived carbons were synthesized with specific adsorptive sites to selectively separate ammonia gas from air. Two main strategies were utilized: 1. the inclusion of residual metal sites through the incomplete extraction of a metal atom from a carbide precursor and 2. The addition of acidic functional groups on the surface of a carbide-derived carbon through surface functionalization. The results from the first strategy showed that under certain synthesis conditions, the selection extraction of iron from iron carbide does not follow a traditional layer-by-layer extraction process previously observed for other carbides in literature. Instead, the extraction process is more complex, and allows for a large percentage of residual iron to be retained as well-dispersed iron chloride nanoparticles. These tailored adsorbents were subsequently shown to be active against ammonia in dynamic breakthrough experiments under both dry and humid conditions, and it was proposed that iron chloride ammine complexes are formed. The results from the second strategy highlight that surface functionalization of these highly nanoporous carbonaceous materials significantly improve the dynamic ammonia adsorption capacity of these materials. The acidification of carbide-derived carbons with nitric acid provide a high density of acidic functional groups, and are shown to be very effectively utilized. Findings concerning the type of each functional group are also discussed. Finally, recommendations for future studies and extensions of this work are discussed.