Catalysis is in the core of most chemical processes and one of the principles of Green Chemistry. Several strategies have been used through the last years towards the development of more sustainable catalytic systems. Photocatalysis, for example, consists in harvesting the energy of light and using it to catalyze chemical transformations, leading to a much more effective energy use when compared to traditional thermal-activated processes. Photocatalytic processes rely in the use of photosensitizers (PS), which are species capable of collecting light energy and transferring it to target molecules. Such PS, however, are often based of precious metals, creating the necessity for recovery and reuse. Magnetic recovery is a largely used strategy in the catalytic community, but it has not yet fully reached photocatalysis. Magnetic nanoparticles (MNPs) are intrinsically dark-colored, therefore absorbing visible light and preventing the PS molecules from being activated. Our project proposes to merge photochemistry and magnetic photocatalysis, by developing the first generation of magnetically-recoverable photocatalytic supports. Our strategy consists in coating highly magnetic Fe (0) NPs with silica shells: the iron core provides the magnetic properties, while the silica coating blocks its light absorption and allows the immobilization of PS, which will then not be deactivated by the MNPs. The particles have been successfully made and a fine control of the thickness of the silica layer was achieved (15 to 30 nm of silica on 12 nm iron nanoparticles). Such control was obtained by adding the pre-formed Fe NPs to a reverse microemulsion system, which is then submitted to stepwise additions of a silicon alkoxide. Silica shells are, therefore, allowed to controllably grow due to sol-gel processes that are confined within the aqueous micelles. [Ru(bpy)<sub>3</sub>]<sup>2+</sup> was the PS chosen to be immobilized and preliminary fluorescence tests show the presence of photoactive species on the surface the silica-coated NPs. Magnetic tractability, however, decreases with the increasing amount of silica, so the thickness of the shell is being optimized for maximum photoactivity and minimum loss of magnetic properties. Ongoing experiments also include the evaluation of the catalyst in the photooxidation of citronellol.

Photocatalysis meets magnetic recovery: Silica-coated MNPs as photocatalytic supports

2019 Fall National Meeting

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