Synthesis of nanostructured magnetic photocatalyst by colloidal approach and spray–drying technique

Nanostructured particles with a magnetic core and a photocatalytic shell are very interesting systems for their properties to be magnetically separable (and so reusable) in photocatalytic water depuration implant. Here, a robust, low time-consuming, easily scale up method to produce Fe3O4/SiO2/TiO2 hierarchical nanostructures starting from commercial precursors (i.e. Fe3O4, SiO2) by employing a colloidal approach (i.e. heterocoagulation) coupled with the spray–drying technique is presented. In particular, a self-assembled layer-by-layer methodology based on the coagulation of dissimilar colloidal particles was applied. First, a passive layer of silica (SiO2, amorphous) was created on magnetite in order to avoid detrimental phenomena arising from the direct contact between magnetite and titania, then the deposition of titania onto silica-coated-magnetite was promoted. TiO2, SiO2 and Fe3O4 nanosols were characterized in terms of zeta potential, optimized and a self-assembled layer-by-layer approach was followed in order to promote the heterocoagulation of silica onto magnetite surface and of titania onto silica coated magnetite. Once optimized the colloidal route, the mixture was then spray-dried to obtain a granulated powder with nano-scale reactivity, easier to handle and re-disperse in comparison to starting nanopowders with the same surface properties. The nanostructured particles have been characterized by different techniques such as SEM, TEM, XDR and their magnetic properties have been investigated. Moreover, preliminary photocatalytic texts have been performed.

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► TiO2/SiO2/Fe3O4 nanostructured particles.
► Magnetic – UV light photocatalyst.
► Colloidal approach coupled with spray–drying.
► Cost-effective industrially scalable approach.