Zeolite L is a unique host. It accepts a large number of different guests inside of its one-dimensional nanochannels with largest free diameter of 12.6 Å. The composition of the ideal material is K 6 Na 3 (H 2 O) 21 Al 9 Si 27 O 72 . Cations in different sites have different mobility. Only those in the large channel, where 3.6 potassium cations per pseudo unit cell are located, are exchangeable at room temperature in aqueous environment. The nature of these charge-compensating cations influences the proton activity inside the channels and the optical and chemical properties of guests located there. Crystal morphology and size influence ion exchange and adsorption properties of zeolite L. It is important to understand the influence of alkali cations Li + , Na + , K + , and Cs + located in the main channel on the Ar adsorption isotherms. We prepared corresponding samples, measured the Ar adsorption isotherms of the dried samples at 87 K and analyzed the complete isotherms quantitatively. We report the theoretical background needed for this analysis, the computational information and the resulting parameters, including details regarding the first inflection point of the isotherms. The latter is essential because experimental isotherms measure usually more than one event but several such as monolayer formation, second monolayer adsorption, clustering, and cavity filling. We find that the value of the Langmuir monolayer volume and of the specific surface area decrease steadily from the Li + to the Cs + samples. This correlates with the increase of the ionic radii. Cluster formation takes place on top of a second monolayer. It is remarkable, that the enthalpy of cluster formation at 87 K at the outer surface amounts to approximately – 6.5 kJ/mol for all samples and is similar to the value measured on Stöber type silica particles. This means that the cations located inside of the large channels have no influence on the properties of the outer surface of the samples. • We compare adsorption isotherms of alkali cation exchanged zeolite L (LTL). • The complete isotherms are interpreted quantitatively. • We find that the value of the monolayer volume and of the specific surface area decrease steadily from the Li + to the Cs + samples. • The decrease correlates with the ionic radii of the alkali cations. • Cluster formation takes place on top of a second monolayer at the outer surface. • The enthalpy of cluster formation is −6.5 kJ/mol for all samples and is similar to the value measured for Stöber type silica.
Calzaferri Gion (Fri,) studied this question.