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.