Electrochemical Characterization of Bromine Reduction to Tribromide in Individual Nitrobenzene-in-Water Emulsion Droplets

Abstract

We report an electrochemical study of bromine reduction to tribromide in a single nitrobenzene (NB) droplet during a single collision event. The feasibility of this study is based on the favorable distribution of Br2 in NB rather than in water, which was demonstrated by voltammetry at the NB/water interface. The NB-in-water emulsions containing the ionic liquids trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)amide (ILPA) as the supporting electrolyte and sodium dodecyl sulfate (SDS) as the surfactant were prepared by a high-power ultrasonication. Its single droplet as an attoliter reactor, colliding on a 25 μm Pt UME, was monitored by chronoamperometry. The spike-type current transients of Br2 reduction can elucidate the size and size distribution of NB, and measure the diffusion in the droplet as analyzed by a bulk electrolysis model. The frequency of collisions can provide diffusion coefficient of the droplets to the UME. Moreover, the i-t decay behavior can be simulated, which fits well with the experimental one.

Mapping Solvent Entrapment in Multiphase Systems by Electrogenerated Chemiluminescence

“…Single-entity electrochemistry is a blooming field where the collision of single micro- and nanodroplets is often studied. ,− During these experiments, it is often assumed that a circular contact area forms upon the collision of a droplet with a polarized electrode interface . This assumption has significant ramifications, as the geometry and size of the contact area are critical to a kinetic and mechanistic evaluation of the electrochemical signal. ,, Here, we present an optical method to investigate the contact area for droplets larger than the diffraction limit of light (i.e., microdroplets), finding that a significant portion do not form circular contact areas and/or contain discrete solvent pockets, effectively forming an adsorbed double emulsion.…”

Ultrasensitive Electrochemistry by Radical Annihilation Amplification in a Solid–Liquid Microgap

“…When droplets irreversibly collide with an ultramicroelectrode, the electrochemistry within the droplet can be observed in amperometry 16−22 and, more recently, voltammetry. 23,24 This type of experiment has been used to elucidate mechanistic insight of reactions in droplets 25 and the nucleation and growth properties of single nanoparticles in nanodroplets. 26,27 These experiments conventionally require more than 10 mM analyte species be dissolved in the droplet to observe an appreciable signal in the amperometric or voltammetric measurement.…”

“…Droplets (radii from hundreds of nanometers to micrometers) can be generated by ultrasonicating a dispersed phase into a continuous phase. , Based on solubility, it is possible to selectively dissolve molecules of interest into the dispersed phase. When droplets irreversibly collide with an ultramicroelectrode, the electrochemistry within the droplet can be observed in amperometry − and, more recently, voltammetry. , This type of experiment has been used to elucidate mechanistic insight of reactions in droplets and the nucleation and growth properties of single nanoparticles in nanodroplets. , These experiments conventionally require more than 10 mM analyte species be dissolved in the droplet to observe an appreciable signal in the amperometric or voltammetric measurement.…”

Electrochemistry under confinement

“…If either a less hydrophilic anion N À or a less hydrophobic cation X + can enter or leave the droplet, the electroneutrality can be maintained and a current response is observable. across the oil/water interface were recently presented for bromide 204 and acetate. 187 In contrast to this, Peng et al presented a quasi-reversible Fc/Fc + redox process for Fc confined in toluene nanodroplets, maintaining electroneutrality through the surfactant Tween20.…”