Alotaibi, Badriah M., Rapheima, Soraya, Yu, Po Wei, Chen, Xianjue, Roman, Tanglaw, Gibson, Christopher T., Lib, Tiexin, Chen, Dechao, Dos Santos Antunes, Elsa, Li, Qin, Anderson, Mats R., Darwish, Nadim, and Raston, Colin L. (2025) Vortex Fluidic Mediated Synthesis of Enhanced Hydrogen Producing Magnetic Gold. Small Science, 5 (4). 2400449.

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Abstract

While bulk gold is well known to be diamagnetic, there is growing experimental and theoretical work supporting the formation of nano gold with unconventional magnetic properties. However, access to such magnetic gold nanoparticles at scale is limited. It is established that magnetic gold particles are readily accessible when exposing aqueous solutions of auric acid (H[AuCl<inf>4</inf>]) to UV irradiation (λ = 254 nm) under high shear in a vortex fluidic device (VFD), as a photo-contact electrification process. Thin films of liquid in the VFD down to ≈200 μm thick are generated in a tilted rapidly rotating angled glass tube with induced mechanical energy imparted under high shear, which when exposed to UV, reduces Au³⁺ to elemental gold without the need for adding reducing agents, unlike in the conventional synthesis of nano gold particles. The use of magnetic force microscopy (MFM) is reported to show that VFD-generated 2D gold sheets have magnetic gold nanoparticles embedded in them, with the material electron paramagnetic resonance active. A report is made on theoretical insights into the origin of the magnetism and that the material shows a dramatic enhancement of catalytic activity in the hydrogen generation reaction relative to using traditionally produced gold nanoparticles of comparable size.

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