A B.E.T.-like three sorption stage isotherm
The statistical B.E.T.-treatment of multimolecular sorption is extended to include three distinct sorption stages, viz. (I) the strongly sorbed monolayer, (II) the following h-1 layers, much less strongly sorbed, and (III) the remaining layers, up to infinity, of 'pure liquid' characterist...
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| Formato: | JOUR |
| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_03009599_v85_n7_p1631_Timmermann |
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| Sumario: | The statistical B.E.T.-treatment of multimolecular sorption is extended to include three distinct sorption stages, viz. (I) the strongly sorbed monolayer, (II) the following h-1 layers, much less strongly sorbed, and (III) the remaining layers, up to infinity, of 'pure liquid' characteristics. The new three sorption stages (t.s.s.) isotherm embodies the classical two-parameter B.E.T. equation [stages 1(h = 1)-III] as well as the three-parameter Guggenheim-Anderson-De Boer (G.A.B.) equation [stages I-II (h = ∞)]. The t.s.s. isotherm, which necessarily uses a fourth parameter, retains the mathematical form of the older isotherms with two correction functions determined by the new constant h (extension of stages I and II), functions which become important only at high relative activities of the sorbate. The sorption stage III is evidenced by experimental data in this region: here the G.A.B. isotherm demands that the inverse of the mass sorbed per unit mass of sorbent should be linear in p/p°, while experimentally a deviation downwards is found, which is explained by the t.s.s. isotherm. The four parameters, determined by versatile, easy to apply, graphical methods, show a certain correlation with the type of interactions characterizing the experimental systems. With longer ranged interactions the extent of the sorption stage II increases from h = 8-15 (gas/solids) to h = 15-20 (water/biopolymers) and to h = 20-25 (water/electrolytes-polyelectrolytes). The applicability range of the t.s.s. isotherm extends up to at least p/p° = 0.95. |
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