Abstract
The paper aims to provide new insights into the mechanism of adsorption of nitrogen at 77 K in the submonolayer range, by means of analysis of the isotherm derivative d[N(p)]/dp. For this purpose, a series of isotherms of adsorption on different types of carbons are analyzed. In order to investigate deterministic isotherms, a series of isotherms of adsorption in slit-shaped micropores, calculated by Lastoskie et al., are analyzed by the same method. It is shown that the derivatives can always be fitted to power laws, i.e., d[N(p)]/dp ∝ pν where −2 ≤ ν ≤ 0. For carbons, several regimes, characterized by different ν values are evidenced. In contrast, for silicas, a single power law (−1 ≤ ν ≤ −0.5) is evidenced over a broad range of relative pressures (10-6−0.2). It yields a Freundlich equation after integration, whereas more than one equation is needed to describe adsorption on carbons. Depending on ν, integration yields Henry, Freundlich, or Temkin equations or a new one (“C-type”), involving a negative ex...
Published Version
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