Zeolitic Materials Superficially Modified With Cationic Substances

Dear Colleagues,

Zeolites have recently received a great deal of attention from the scientific community thanks to their easy accessibility and their peculiar properties, with a particular focus on their well-known ion exchange capacity.

Natural zeolites are porous minerals that have an anionic structure. Their crystalline structure generally includes silicon (aluminum) and tetrahedron oxygen, while the architecture of their porous networks is formed by the interaction between the different structural tetrahedrons. Thanks to these characteristics, zeolites act as cation exchangers in structures, through the loss or acquisition of water molecules.

Natural zeolites of sedimentary origin are currently employed in many fields, such as environmental protection, agricultural and industrial applications, pharmaceutics, and medicine, taking advantage of their several interesting properties, such as physical adsorption, cation exchange, alkali metals reactivity, expansion tendency and thermal insulation, compressive strength, and durability. More in detail, zeolites can be used in wastewater and gas purification, soil remediation, and controlled drug delivery.

Lately, great attention has been paid to the study of the surface activity exhibited by natural zeolites. In fact, zeolites can superficially interact with large organic molecules, such as surfactants, and are exchangeable if they have a positive charge and/or are adsorbable if polar. Sorption of a cationic surfactant onto a negatively charged surface involves both cation exchange and hydrophobic bonding. The interaction between natural zeolites and surfactant molecules, when a sufficient number of surfactant molecules is present in the system, leads to the formation of a bilayer on zeolite external surfaces. This, in turn, results in a charge reversal on the external zeolite surface, thereby providing sites where anions can be retained and cations repelled, while neutral species can partition into the hydrophobic core. Moreover, an additional cation exchange capacity remains on the internal surfaces of the zeolite. Thus, modification of natural zeolites gives rise to a product that can sorb organic compounds and exchange inorganic cations/anions while retaining favorable hydraulic properties.

This Special Issue of Applied Sciences, titled “Zeolitic Materials Superficially Modified with Cationic Substances”, is intended for a wide and interdisciplinary audience, and the major aim includes, but is not limited to, highlighting the current state of the art in the following areas:

• Surface modification of natural zeolites and their characterization (monolayer or bilayer formation, external cation exchange capacity and anion exchange capacity, sorption properties);
• The study of the anion exchange properties of surface-modified zeolites through batch and dynamic processes;
• Modeling of sorption properties of surface-modified zeolites;
• Applications of surface-modified zeolites as anion exchangers for wastewater treatment (pollutants ions and emerging contaminants);
• Applications of surface-modified zeolites as carriers for drug delivery.

Original articles and reviews dealing with the properties of zeolites superficially modified with cations, as well as their actual and potential applications, are warmly welcome.

Dr. Marco Biondi
Dr. Laura Mayol
Prof. Bruno de Gennaro
Guest Editors

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