The study of the ability of zeolites to adsorb amino acids is significant to improve the knowledge of
the interactions between these molecules and solid surfaces. This is of fundamental importance to
increase the level of understanding of much more complex systems and to select adsorbent materials
able to selectively capture amino acids from aqueous solutions.[1]
Zeolites are aluminosilicate materials characterized by regular crystalline structure with microporous
cavities which confer a high superficial area. The physico-chemical proprieties of zeolites depend on
the composition of their framework that consist of tetrahedral units of SiO4 and AlO4 and, in
particular, their ratio (SAR) characterizes the hydrophilic/hydrophobic behavior of the material.
Moreover, the different conformation and dimension of the internal channels and cages influence the
adsorption selectivity towards host molecules.[2] The ability of zeolites to adsorb biologically active
biomolecules such as amino acids is of particular interest in industrial biotechnology[3] due to the fact
that these adsorbent materials could be used as solid solvents to stabilize the different charged forms
of the amino acids.
In this study we tested the different adsorption capacity of zeolites L and ZSM-5 towards the
amino acid L-lysine. These zeolites were chosen since they present different framework, with 2D and
3D channels structures, and different pore dimensions. Moreover, for the zeolite ZSM-5, two
materials having different SAR were selected to study the effect of zeolite chemical composition on
the adsorption capacity. Kinetic and isothermal experiments were carried out at different L-lysine
initial concentrations to study the adsorption processes. The results show high capacity towards the
adsorption of L-lysine for every zeolite investigated. We found a higher capacity for zeolite L with
respect to ZSM-5. Moreover, zeolite ZSM-5 with greater SAR has shown less adsorption, probably
a cause of different surface charge. [1][4] Moreover, the results obtained by thermal analyses (TGDTG-
DTA) showed different interactions within the amino acid-zeolite adduct and different stability,
depending on the peculiarities of the zeolites studied. Further investigation of the refinements of X
ray powder diffraction patterns showed the adsorption sites, the orientation and the interactions of the
amino acid molecules within the zeolite channels.
This work allowed to improve the understanding of the formation and interactions of the adducts
that originate from the adsorption of amino acids on zeolites. The information obtained are useful for
separation of amino acids from complex mixtures.
[1] G. Beltrami, A. Martucci, L. Pasti, T. Chenet, M. Ardit, L. Gigli, M. Cescon, E. Suard,
ChemistryOpen 2020, 9(10), 978–982.
[2] A. Martucci, L. Pasti, N. Marchetti, A. Cavazzini, F. Dondi, A. Alberti, Micropor. Mesopor. Mat.
2012, 148(1), 174-183.
[3] K. Stückenschneider, J. Merz, and G. Schembecker, J. Phys. Chem. 2014, 118, 5810-5819.
[4] T. Chenet, A. Martucci, M. Cescon, G. Vergine, G. Beltrami, L. Gigli, M. Ardit, M. Migliori, E.
Catizzone, G. Giordano, L. Pasti, Micropor. Mesopor. Mat., 2021, 323, 111183
