Specific and non-specific interactions between ammonia and activated carbons

Abstract

It is shown that the adsorption of NH 3 by activated carbons at different temperatures follows Dubinin's theory and, as in the case of water, for carbons with high oxygen contents one observes an upward deviation in the initial section of the DR plot. This indicates a strong primary adsorption, due to specific interactions. At higher relative pressures, this adsorption is followed by a classical micropore filling mechanism, where NH 3 conforms to the pattern of non-specific adsorption. The affinity coefficient b 1 (NH 3 ) associated with primary adsorption varies between 0.4 and 1.2. It depends on the characteristic energy E 0 and on the ratio between the amount of oxygen present on the surface and the limiting amount of ammonia adsorbed in the micropores. This behaviour had been reported earlier for the adsorption of short alcohols, but with a single DR plot, due to the fact that specific and non-specific interactions were similar. For carbons with little oxygen on the surface, NH 3 adsorption leads to a single DR plot, irrespective of the average pore-size.

The effect of the physical and chemical characteristics of activated carbons on the adsorption energy and affinity coefficient of Dubinin equation

“…Therefore, the effect of adsorbent surface chemistry on β (i.e., E/E 0 ) is canceled out. It has been also demonstrated that Dubinin theory can be applicable to some polar compounds (e.g., water vapor and ammonia) that are capable of having specific interactions with carbon surface [10][11][12].…”

Adsorption of ammonia on activated carbon from aqueous solutions

“…The former was assigned to physisorption process while the latter was adsorption on chemical groups. Stoeckli et al [13] indicated that the adsorption of ammonia by activated carbons at different temperatures followed Dubinin theory. For carbons with high oxygen contents an upward deviation was observed in the initial section of the DR plot while for carbons with little oxygen on the surface NH 3 adsorption led to a single DR plot, irrespective of the average pore-size.…”

Complexity of ammonia interactions on activated carbons modified with V2O5

“…So far, researchers have explored different types of adsorbents such as zeolites, alumina and activated carbons [3][4][5][6][7][8][9][10][11], with a special interest granted to the latter ones. Indeed, activated carbons, due to their high surface area and pore volume, are considered as the most efficient adsorbents in pollutant removal [12].…”