Electrochemical Scanning Tunneling Microscopy Observation of Ordered Surface Layers on an Anionic Clay-Modified Electrode

Abstract

Electrochemical scanning tunneling microscopy (STM) observations have been performed on a highly ordered pyrolytic graphite (HOPG) electrode modified with a cast film of hydrotalcite (HT) crystal ([Mg6Al2(OH)16]3/4CO3·1/2Cl·2H2O). The electrode was in contact with an aqueous solution of 5 mM Na3[Fe(CN)6] and 0.1 M Na2SO4 at 600 mV (vs Ag/AgCl). The STM image of the electrode showed a two-dimensional lattice with a = 1.40 ± 0.04 nm, b = 1.85 ± 0.04 nm, and α = 63 ± 3°. One bright spot in the image was present at every 3.4 [Mg6Al2(OH)16]2+ units, leading to the conclusion that the spot represented a [Fe(CN)6]3- ion adsorbed on a crystal surface. At 81 mV (vs Ag/AgCl), the STM image exhibited a two-dimensional lattice with a = 1.74 ± 0.04 nm, b = 1.83 ± 0.04 nm and α = 60 ± 3°. This was ascribed to the lattice made by a mixture of [Fe(CN)6]3- and [Fe(CN)6]4- on a HT surface. At −200 mV (vs Ag/AgCl), the STM image showed a two-dimensional lattice with a = 1.94 ± 0.04 nm, b = 1.90 ± 0.04 nm and α = 60 ± 3°, which was ascribed to the lattice made by reduced [Fe(CN)6]. - These results confirmed that an ordered molecular adsorption layer changed dynamically during the electrochemical processes.

The mechanisms of reduction of hexavalent chromium by green rust sodium sulphate: Formation of Cr-goethite

“…Indeed, experiments with X-ray photoelectron spectroscopy showed that green rust behaves as a semi-conductor and with scanning tunnelling microscopy (STM), that electrons tunnel in response to a slight potential difference between tip and sample (unpublished results). Yao et al (1998) have established the possibility for such electron transfer across interlayers for similar layered double hydroxides (LDHs). They were able to tunnel electrons between hydrotalcite crystals on a graphite substrate and a tungsten tip, using STM.…”

Electrocatalytic Oxidation and Determination of Cysteine at Oxovanadium(IV) Salen Coated Electrodes

“…However, our attempts failed and VO 2+ -S could not be incorporated/adsorbed on MCM-41 type silica materials due to unknown reasons. Similarly, clay film [48,49] and Nafion film [31,32,38] coated electrodes were also examined to ion-exchange/incorporate VO 2+ -S into the respective films as per our previous procedures [50]. Surprisingly, VO 2+ -S could not be ion-exchanged/incorporated on clay and Nafion films also.…”

Facile synthesis of Zn-Al layered double hydroxide from aqueous suspension of zinc oxide and aluminum hydroxide

“…8)- 10) In addition to the studies on the mechanism of the LDH formation and their structures, the introduction of guest species into the interlayer space of LDHs has been reported for such applications as catalysts, 11)-16) controlled photochemical reactions, 17), 18) electrodes, 19)-21) bioactive nanocomposites, 22)-26) and polymer additives, 27)-29) and so on. The wide range of application of LDHs and their intercalates motivates researchers to develop a simple, economically viable synthetic method.…”