Local heterogeneity function, h(q), for Fowler-Guggenheim (FG; mean-field non-specific lateral interactions) and Kiselev (Kis; specific associative interactions) compared with Langmuir equation (in the absence of heterogeneity).
© A.W.Marczewski 2002
A Practical Guide to Isotherms of ADSORPTION on Heterogeneous Surfaces
Global Heterogeneity, H:
local heterogeneity function h(q): FG, Kis
(see global heterogeneity calc. plot)
Local heterogeneity function, h(q), for Fowler-Guggenheim (FG; mean-field non-specific lateral interactions) and Kiselev (Kis; specific associative interactions) compared with Langmuir equation (in the absence of heterogeneity).
Similarity of FG and Kiselev equations - with respect to the behaviour of their isotherms) is visible. FG and Kiselev isotherms also behave similarly to Langmuir for low and high coverages:
hint(q → 0) = hint(q → 1) = hL(q) = 1
However - in the absence of surface heterogeneity - we always have:
hint(q) ≤ hL(q) = 1.
q=1 is reached for p→∞ or [p/(1-x)]→∞ (for vapors x=p/ps) or for solute adsorption c→∞ or [c/(1-x)]→∞ (for weakly soluble solutes; x=c/cs).
NOTE.
Replace p with c for dilute solute adsorption.
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