Photocatalysis Meets Magnetism: Designing Magnetically Recoverable Supports for Visible-Light Photocatalysis

Abstract

While magnetic supports have been widely used to immobilize homogeneous catalysts in organic chemistry, this strategy has so far found very little application in photocatalysis. Indeed, magnetic supports are dark colored, and thus compete for photon absorption with photocatalysts themselves. We have developed a series of core–shell Fe(0)-silica nanoparticles as supports for immobilizing the photosensitizer Ru­(bpy)3 2+, featuring various silica shell thicknesses16–34 nm SiO2on 9 nm Fe cores. The supports and the resulting photocatalytic systems were studied for their magnetic, optical, and catalytic properties in the context of the photooxidation of citronellol, and we found that thicker silica shells lead to higher catalytic activity. We correlated this effect as well as Ru­(bpy)3 2+ fluorescence and singlet oxygen generation to the absorption properties of the supports. We were able to reuse our optimal system three times with minimal loss of activity and achieved turnover numbers largely surpassing the performance of homogeneous Ru­(bpy)3 2+. This work highlights the role of material design in the conception of new supports for applications in heterogeneous photocatalysis.

Performances of Homogeneous and Heterogenized Methylene Blue on Silica Under Red Light in Batch and Continuous Flow Photochemical Reactors

“…This experiment is in agreement with an adsorption/desorption equilibrium occurring in between the solid and liquid phases. We have previously shown (Terra et al, 2020) that the excited state lifetime of Ru (bpy) 3 Cl 2 was not affected by immobilization on silica or on magnetic iron/silica nanoparticles and believe that, the excited state properties of MB remain the same whether in solution or immobilized on silica nanoparticles.…”

“…To counter such sustainability issues, our group and others have developed recyclable photocatalytic systems, such as heterogenized solid PCs (Mori et al, 2010;Mori and Yamashita, 2016;Tambosco et al, 2018;Choi et al, 2020;Gisbertz and Pieber, 2020;Soria-Castro et al, 2020;Materna and Hammarström, 2021). In particular, we investigated the straightforward non-covalent immobilization of PCs on silica particles which resulted in an improved reactivity and stability (Tambosco et al, 2018), and provided additional physical properties such as magnetism (Terra et al, 2020) or plasmonic resonance (Gellé et al, 2021). We also developed a continuous flow photochemical process with a fixed photocatalytic bed reactor to leverage productivity issues (Blanchard et al, 2020).…”

Synthetic strategies of phenazine derivatives: A review

“…In recent years, with the exhaustion of fossil energy and the increasing of environmental issues, searching, and utilizing renewable and clean new energy sources have become a hot topic. Visible light is a typical inexhaustible clean energy, used as driving force for the organic transformation [11,[146][147][148][149][150][151]. Therefore, it is urgent to design efficient visible-light-driven photocatalysts to maintain environmental sustainability.…”

Applications of Sensitized Semiconductors as Heterogeneous Visible-Light Photocatalysts in Organic Synthesis

“…Note that attention will be given only to visible-light photocatalysts activation where the semiconductor and the sensitizer share the redox activity, and when this synergic interaction triggers the photoreactivity. Systems where inert supports are used to immobilize soluble photocatalysts will not be taken into account. − …”