Gelation of amino acid-based amphiphiles in water-based mixed solvent systems: reusable catalytic templates for nanostructured silica and silica-zirconia photocatalyst

We describe a gelation study of a series of different fatty acid-amino acid conjugated amphiphiles in various mixed solvent systems with water. Field emission scanning electron microscopy (FESEM), polarized optical microscopy (POM) and X-ray diffraction (XRD) study reveals that the self-organization of the amphiphile molecules in the mixed solvent leads to the formation of crystalline fibers, which form the opaque white gel. This amino acid amphiphile-based gel acts as a catalyst as well as a template for the hydrolysis/condensation of tetraethoxysilane (TEOS) to silica and forms a composite gel. The methanol extraction of the opaque white as-prepared composite gel results in the formation of a transparent nanostructured silica gel. The recovered amphiphilic gelator, after a methanol wash, can be reused for preparing a gel, which can subsequently be used as a catalyst to prepare a nanostructured silica gel again. The FESEM study confirms that the formed nanostructured silica gel is made up of spherical silica nanoparticles. We also extend this gel-based catalysis strategy to prepare silica-zirconia mixed oxide nanostructures. TEM examination reveals the formation of spherical silica-zirconia nanoparticle of high surface area as confirmed through BET surface area measurement. Finally, the photocatalytic activity of silica-zirconia mixed oxide is investigated towards methylene blue degradation. The mixed oxide shows higher photocatalytic efficiency than neat zirconia nanostructures.