Abstract
In this study, a layer of a pure and dense phase of FAU-type zeolite was synthesized directly on the surface of α-Al2O3 plane macroporous support. Before hydrothermal synthesis, a step of cleaning of the support by an anionic detergent was performed, a roughness surface is created, allowing the anchoring of the zeolite nuclei and then their growth, favoring in this sense the formation of a homogeneous zeolite layer. The obtained membranes were fully characterized using X-ray diffraction analysis (XRD), nitrogen sorption, scanning electron microscopy (SEM), and mercury porosimetry. After 24 h of thermal treatment at 75 °C, a homogeneous zeolite layer composed of bipyramidal crystals of FAU-type zeolite is obtained with a thickness of about 2.5 µm. No obvious defects or cracks can be observed. It was found that the increase in heating temperature could lead to the appearance of an impurity phase, GIS-type zeolite. Then the ideal zeolite membrane was exchanged with Ag+ or Zn2+ cations to studies their antimicrobial properties. Zeolites membranes exchanged with Ag+ showed an agar-diffusive bactericidal activity against gram negative Escherichia coli (E. coli) bacteria. Zn2+ exchanged zeolite membrane presented a bacteriostatic activity that is less diffusive in agar. As expected, non-exchanged zeolite membrane (in its Na+ form) have no effect on bacterial activity. This process is particularly interesting for the synthesis of a good quality FAU-type zeolite membranes with antimicrobial properties.
Highlights
Zeolites are a microporous crystalline aluminosilicate with a three-dimensional network composed of SiO4 and AlO4 tetrahedrally interconnected by oxygen bridges [1,2]
The treated Synthesis supports ofwere immersed in Membranes the synthesis solution as described in Section 3.3 and subjected to hydrothermal treatment
Inspection of these results reveals that the replacement of Na+ compensating cations by Ag+ and Zn2+ does not affect the morphology of FAU-type zeolites
Summary
Zeolites are a microporous crystalline aluminosilicate with a three-dimensional network composed of SiO4 and AlO4 tetrahedrally interconnected by oxygen bridges [1,2] Due to their excellent textural properties and high thermal (up to 700 ◦ C) and chemical stabilities, zeolite materials offer unique frames for a wide variety of industrial applications (catalysis, molecular decontamination, separation, adsorption, energy storage, etc.). The substitution of Si atoms by Al atoms in the zeolite framework creates negative charge that should be compensated by cations (the most common compensating cations are Na+ ) These cations can be exchanged by silver, copper, or zinc cations to confer to zeolites antibacterial, antiviral, and antifungal activities [3,4,5,6,7,8,9]. They can be considered as a credible alternative to Molecules 2020, 25, 3414; doi:10.3390/molecules25153414 www.mdpi.com/journal/molecules
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