Tailoring of Surface Chirality by Micro-Vortices and Specific Adsorption in Magnetoelectrodeposition

Abstract

Solid surfaces often serve as a reaction field for organic molecules. If a surface has chirality, it could play a significant role as an enantioselective catalyst. Electrodeposition in magnetic fields (magnetoelectrodeposition; MED) has potential to produce enantioselective metal surfaces, however, the exploration of chiral formation conditions has not been sufficient in previous MED experiments. Here we show the chiral behaviors of copper film surfaces prepared by galvanostatic MED. We found that the chiral sign depends on both the deposition current and the polarity of magnetic field. Furthermore, we found that the specific adsorption of chloride ions on the film surfaces brings about drastic influence on the chiral formation in MED. At certain chloride concentrations chiral symmetry breaking was observed for the polarity of magnetic field. These findings imply that magnetohydrodynamic micro-vortices and the rate-limiting steps are responsible for the chiral surface formation.

Surface Chirality in Rotational Magnetoelectrodeposition of Copper Films

“…This means that the peak current of an active enantiomer is two times greater than that of another one. Such large |ee| ratios are surprising results in comparison with those in MED with only vertical MHD flows (|ee| < 0.1) [16]. Thus, the RMED technique could be applicable to the synthetic methods of chiral catalysts.…”

“…The breaking of such odd chirality was observed in the Cu MED with chloride additives [16,17], where the specific adsorption of chloride ions on the film surfaces causes the fluctuation in the self-organized state of micro-MHD vortices. The odd chirality breaking was also observed in the Cu MED at weak magnetic fields [18], where the self-organized rigid state of micro-MHD vortices cannot be well developed.…”

Magneto-Dendrite Effect: Copper Electrodeposition under High Magnetic Field

“…In this sense, how to fabricate chiral catalysts is still an open question with important fundamental and technical interest. Magnetic field provides a powerful tool of fabrication for a new type of chiral electrocatalyst; by means of magnetic field and macroscopic rotation, numerous chiral screw dislocations are formed on electrode surfaces, which can donate various chiral activities to crystal nuclei1234. These catalytic activities appear on flat surfaces.…”

Communication—Visualization of Magnetohydrodynamic Micro-Vortices with Guanine Micro-Crystals

“…Electrodeposition under magnetic fields (magnetoelectrodeposition; MED) induces surface chirality on silver and copper films, [1][2][3][4] and such films could serve as catalytic electrodes distinguishing the enantiomers of glucose, alanine and tartaric acid. In the MED processes, the Lorentz force acting on ionic currents causes the magnetohydrodynamic (MHD) flows.…”

“…8 We have found the enantioselective behaviors of the MED silver and copper films. [1][2][3][4] Aogaki proposed the concept of micro-MHD vortices in the MED processes and observed micro-circle structures on the MED film surfaces, 7 which strongly suggested the existence of micro-MHD vortices. However, the direct observation of micro-vortices has never been conducted, even though they could play significant roles for the chiral surface formation and catalytic properties.…”