Analysis of the chemical and physical factors affecting reactive adsorption of ammonia on graphene/nanoporous carbon composites

Adsorption of ammonia was studied on composites of graphene and nanoporous carbon (5 and 20 wt.% graphene). The breakthrough curves were measured in three consequent adsorption–desorption runs in either dry or wet conditions. The mechanism of ammonia retention was evaluated from the point of view of either reactive or physical adsorption. The important finding is the insensitivity of the ammonia adsorption on the composites on the water content in the challenge gas. An about 50% decrease in the surface area and volume of micropores compared to nanoporous carbons does not affect the amount of physically adsorbed ammonia. It is governed by the volume of ultramicropores (pore width <0.7 nm), density of groups on the surface, hydrophobicity level, and the electronic conductivity. The surface acidity level and thus the amounts and strength of oxygen groups being able to react with ammonia at ambient conditions are of paramount importance for the reactive adsorption process.