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Films of redox active Ni–Al–Cl layered double hydroxides (LDHs) lost mass on oxidation and gained mass on reduction. The size of the mass changes depended on the composition and on the pH of the electrolyte solutions. In pH 8 potassium borate or phosphate buffers, the decreases in mass on oxidation were small. An apparent mass per mole of electrons transferred (MPE) of only 4–6 g/mol was obtained. This suggests that compensation for the positive charge generated by oxidation of the Ni(II) sites occurred by loss of protons from the LDH lattice accompanied by the loss of some water from the LDH interlayer spaces. The mass changes were two to three times larger when sodium was present in the buffers. For example, the MPE in a pH 8 potassium borate buffer containing 4 mM sodium increased to 19 g/mol. This was attributed to a contribution from the expulsion of sodium ions adsorbed in the LDH films to the charge neutralization mechanism. The MPE increased when the pH of the electrolyte increased. At pH 10 the mass loss was also no longer reversible. This was attributed to the decomposition of the Ni–Al LDH when it was subjected to potential scanning in the more basic solutions. In non-buffered potassium acetate or sodium acetate solutions, the MPEs were found to decrease with decrease in the scan speed, from 20 to 22 g/mol at 50 mV/s to as little as 6 g/mol at 5 mV/s in potassium acetate.

We performed the photodeposition of Ag clusters onto a TiO 2 nanosheet hybridized with an amphiphlic Ru(II) complex (denoted by TiO 2 –Ru/Ag). Firstly a floating monolayer of [Ru(phen) 2 (dC18bpy)](ClO 4 ) 2 (phen = 1,10-phenanthroline, dC18bpy = 4,4 ′ -dioctadecyl-2,2 ′ -bipyridyl) was formed on an aqueous dispersion of exfoliated layered titanate, (TBAOH) x Ti 2− x /4 □ x /4 O 4 · H 2 O ( x ∼0.7;□, vacancy; TBAOH = tetrabutylammonium hydroxide) (denoted as TiO 2 nanosheet). The monolayer acted as the organic part for the hybridization of TiO 2 particles in an aqueous phase. A hybrid film of TiO 2 nanosheet and an amphiphilic metal complex (denoted by TiO 2 –Ru) was transferred onto an indium tin oxide substrate by the vertical dipping method. Thereafter the electrode was immersed in 1.0 M AgNO 3 for 10 min and rinsed with water. The electrode was irradiated for 30 min by a Xe-lamp (150 W). Atomic force microscope, X-ray photoelectron spectra and cyclic voltammometry showed the formation of silver nanoparticles with a radius of 20–150 nm. The photocurrent response was measured in the potential range of 0.2–1.2 V (vs. Ag|AgCl|KCl(sat)) under the illumination of light (>350 nm). The current increased 1.7 times when the layer number of hybrid films increased from one to two. It should be emphasized that such an increase of photocurrent with a layer number was not observed in the absence of Ag particles.

An ITO electrode modified with a hybrid film of chiral metal complex (Λ-[Os(phen)3]2+) and a clay (montmorillonite) has been prepared for the purpose of chiral sensing. As a first step, a floating monolayer of amphiphilic Os(II) complex, [Os(phen)2(dC18bpy)](ClO4)2 (phen=1,10-phenanthroline, dC18bpy=4,4′-dioctadecyl-2,2′-bipyridyl), was formed on an aqueous dispersion of sodium montmorillonite. The monolayer acted as an organic part for the hybridization of clay particles in an aqueous phase. The hybrid film of clay and amphiphilic metal complex was transferred onto an indium tin oxide (ITO) substrate by the vertical dipping method. The next step was to immerse the electrode in chloroform, during which the amphiphilic Os(II) complex was removed from the clay surface. Thereafter the electrode was immersed in an aqueous solution of 0.5 mM Λ-[Os(phen)3](ClO4)2 and rinsed with water. Cyclic voltammetric measurements were performed at each step of the above procedures. When the observed curves were simulated on the basis of a double-layered modified electrode, the electron transfer rate constant (k1) for Λ-[Os(phen)3]2+/Λ-[Os(phen)3]3+ was determined to be 0.25 s−1. This OsII/OsIII redox couple was found to mediate the electrochemical oxidation of chiral 1,1′-2-binaphthol in a stereoselective way: i.e., the S-isomer was oxidized at a 1.4 times higher rate than the R-isomer.

Chirality effects have been observed in the intercalation, spectroscopic and photoelectrochemical behavior when enantiomeric and racemic [Ru(phen)3]2+ complexes were intercalated in the interlayer spaces of K4Nb6O17. The results were interpreted in terms of a [Nb6O17]4−-chelate and chelate–chelate interactions. The faster luminescence decay and higher photocurrent of the enantiomeric [Ru(phen)3]2+–K4Nb6O17 compounds than the racemic ones suggest that the emission of adsorbed [Ru(phen)3]2+ ions was not only quenched by adsorbed complexes (or concentration quenching) but also by the semiconductive host lattices.

The electrochemical STM method has been applied to a hydrotalcite clay-modified electrode with the aim of obtaining evidence for the formation of a surface layer of the [Fe(CN) 6 ] 3−/4− couple. As a result, ordered surface layers of [Fe(CN) 6 ] 3−/4− ions on a hydrotalcite-modified electrode have been observed with an in-situ electrochemical STM instrument: the initial lattice of [Fe(CN) 6 ] 3− with a =1.40±0.04 nm, b =1.85±0.04 nm and α =63±3° changed to an expanded lattice of [Fe(CN) 6 ] 4− with a =1.94±0.04 nm, b =1.90±0.04 nm and α =60±3° due to the electrochemical reduction.

A quartz crystal microbalance (QCM) has been used to investigate mass transfer coupled with electron transfer through a hydrotalcite clay film. The electrode was prepared by casting an aqueous suspension of hydrotalcite (denoted as Mg–Al–HT) or hydrotalcite ion-exchanged with [Fe(CN) 6 ] 3− (denoted as Mg–Al–HT–[Fe(CN) 6 ]) 3− . Adsorption studies using QCM and UV-visible spectroscopic measurements revealed that [Fe(CN) 6 ] 3− was incorporated as an ion-paired species with a counter cation. The adsorbed species on an electrode in contact with a 0.1 M NaCl solution was identified as a divalent ion-pair (Na[Fe(CN) 6 ] 2− ) while the adsorbed species in contact with a 0.1 M Na 2 SO 4 or Na 2 CO 3 solution was a monovalent ion-triplet (Na 2 [Fe(CN) 6 ] − ). Electrochemical QCM measurements on an electrode modified with Mg–Al–HT–[Fe(CN) 6 ] 3− revealed that one Na[Fe(CN) 6 ] 2− or Na 2 [Fe(CN) 6 ] − ion was leached from a film when one or two [Fe(CN) 6 ] 3− ions were reduced, respectively. The leaching of these anions took place in order to compensate the excess negative charge generated in a film.

In phosphate solution at pH 4.6, in situ STM images on Au(111) were different in the potential regions where the Au(111) interface is taken to be free from phosphate adsorption and where the upd Zn is formed. In the former region, the observed STM image was Au(111)(1×1), and in the upd region, the image was taken to be (√3×√3)R30°. As the phosphate is expected to adsorb on upd Zn by oxidative reaction, it is suggested that the latter image is due to the adsorbed phosphate species formed on upd Zn at Au(111) by upd induced adsorption.

The electrochemical quartz crystal microbalance (EQCM) has been employed to investigate the mass transport processes on a clay-modified electrode. The systems investigated were the redox couples of [Ru(bpy) 3 ] 2 − 6 (bpy = 2,2′-bipyridine), [Ru(NH 3 )] 6 2+/3+ and [Fe(CN) 6 ] 4 −/3− . A clay-modified electrode was prepared by depositing synthetic saponite onto a gold coated quartz crystal. An electrode was allowed to swell for more than 50 h in 0.01 M Na 2 SO 4 or NaCl or NaClO 4 prior to the adsorption and electrochemical measurements. The EQCM results revealed that the charge balancing during a redox reaction was accomplished by leaching or incorporating mobile ions in the clay film. For the [Ru(bpy) 3 ] 2+/3 couple, one [Ru(bpy) 3 ] 3− molecule was eliminated from the clay film when three [Ru(bpy) 3 ] 2+ ions were oxidized. For the [Ru(NH 3 ) 6 ] 2+ 3+ couple, one SO 4 2 ion, which was co-adsorbed with the ruthenium complex, was removed from the clay film when two [Ru(NH 3 ) 6 ] 3+ molecules were reduced. For the [Fe(CN) 6 ] 4−/3− couple, a part of the excess charge generated by the initial oxidation of [Fe(CN) 4 ] 4− was canceled out by the elimination of a sodium ion bound by a clay layer. No mass transfer was detected during the oxidation at the later stage. This was probably because sodium ions in the aqueous medium within a clay film carried excess charge. The results are discussed in relation to the reported electrochemical behavior of these metal complexes.

A quartz crystal microbalance (QCM) has been applied to study the adsorption of [Ru(bpy)3]2+ (bpy=2,2′–bipyridyl) and [Ru(NH3)6]3+ by a clay-modified electrode. An electrode was prepared by depositing an aqueous suspension of synthetic sodium saponite onto a gold-coated quartz crystal and drying it under air. After the electrode was swelled for 20 to 120 h in an aqueous 0.01 M Na2SO4 solution, a metal complex was injected into the electrolyte solution. The resistance of the electrode did not change during the adsorption process so that the mass change of the electrode was monitored in terms of the change of resonance frequency. In case of [Ru(bpy)3]2+, the saturated adsorption of racemic [Ru(bpy)3]2+ caused the mass increase of 0.49±0.03 g per 1 g of clay, while that of enantiomeric [Ru(bpy)3]2+ caused the mass increase of 0.29±0.02 g per 1 g of clay. On the basis of these values, it was concluded that racemic [Ru(bpy)3]2+ was exchanged with hydrated sodium ion ([Na(H2O)4]+) in a clay film as a monovalent ion-paired species ([Ru(bpy)3]2+·1/2SO42−), while enantiomeric [Ru(bpy)3]2+ was exchanged with [Na(H2O)4]+ partly as a divalent ion and partly as a monovalent ion-paired species. Under the similar conditions, the saturated adsorption of [Ru(NH3)6]3+ caused the mass increase of 0.17±0.01 g per 1 g clay. The results indicated that [Ru(NH3)6]3+ was replaced with [Na(H2O)4]+ in a clay film as a monovalent ion-paired species ([Ru(NH3)6]3+·SO42−). These results were compared with the adsorption experiments of the same complexes by colloidally dispersed sodium saponite.

The thin film of an ion-exchanged adduct of a clay and tetra-n-decylammonium cations ((n-decyl)4N+) was formed at an air|water interface. A clay-modified electrode was prepared by depositing the film onto a glassy carbon substrate with the Langmuir-Blodgett method. When the electrode was soaked in an aqueous solution of hexa-ammineruthenium(III) chloride ([Ru(NH3)6]Cl3), (n-decyl)4N+ cations were replaced with [Ru(NH3)6]3+ ions. The electrochemical behavior of [Ru(NH3)6]3+ in the ultra-thin film was studied by measuring the cyclic voltammetry and coulometry on the clay-modified electrode. The atomic force microscope images of a saponite film deposited on a microglass plate and saponite-(n-decyl)4N+ transferred on a microgalss plate were compared.