Kai Kamada

Electrophoretic deposition assisted by soluble anode

The rate of cathodic electrophoretic deposition (EPD) of silicon monoxide particles was accelerated by using a soluble anode such as stainless steel or zinc in an acetone bath containing iodine. In contrast, the use of an inert anode such as Pt inhibited deposition. In the former cases, anodic dissolution or corrosion of the metal plate occurred due to the presence of iodide ions in the bath. The metal ions produced adsorbed onto surface hydroxyl groups of oxide particles together with protons. As a result, a positive suspension ζ-potential was achieved. Deposition using the Zn anode was about 10 times larger than that for the stainless steel anode, attributable to the difference in the solubility of the substrate. The Zn anode is likely to be more soluble than the stainless steel anode because stainless steel is covered with more protective passive film. The electrophoretic deposition mechanisms are discussed briefly, and the utility of a soluble anode in EPD is demonstrated.

Electrodeposition of titanium(IV) oxide film from sacrificial titanium anode in I2-added acetone bath

Abstract A TiO 2 film was fabricated by a simple electrochemical method using a sacrificial titanium anode as a cationic source in an I 2 -dissolved acetone bath, where the solvent contains iodide ions as a supporting electrolyte but no Ti salt as an electrolyte. At the initial stage of electrolysis, anodic oxidation of Ti anode occurred under the presence of water as an impurity to acetone. Subsequently, TiO 2+ was produced as a result of the dissolution of oxide films under the influence of iodide ions, and was then electrodeposited on the cathode surface. The morphologies of as-deposited films were found to be dependent on the film thickness, which in turn is determined by the voltage applied during the electrolysis. Moreover, the obtained films show photocatalytic activity for decomposition of gaseous acetaldehyde without annealing. In this paper, the electrodeposition mechanism is discussed in detail.

Insertion of SiO2 nanoparticles into pores of anodized aluminum by electrophoretic deposition in aqueous system

The fixation of SiO 2 nanoparticles into nanopores arrays of an anodized aluminum (Al 2 O 3 /Al) substrate was carried out using a sol-gel electrophoretic deposition technique in an aqueous SiO 2 sol. Nanosized SiO 2 particles can be easily incorporated into the pores of anodized aluminum prepared in a H 3 PO 4 solution, but not into the pores prepared in a H 2 SO 4 solution because of the difference in the pore diameters. It was confirmed that the particles in suspension were incorporated without applying an electric field. This result was due to the dissimilarity in the surface charges of the particles and anodic oxide film.

Incorporation of oxide nanoparticles into barrier-type alumina film via anodic oxidation combined with electrophoretic deposition

The incorporation of metal oxide nanoparticles into a barrier-type anodic alumina film on an Al substrate was investigated using a one-step anodic oxidation combined with electrophoretic deposition. Basically, the electrolysis was carried out in an oxide nanoparticle dispersed ammonium pentaborate solution using an Al substrate as the anode. As a result, the TiO2 and SiO2 nanoparticles with a negative surface charge could be introduced into the alumina film grown on the Al anode, and the film thickness increased by the dispersion of the nanoparticles inside the alumina layer. The measurement of the capacitance and corrosion potential demonstrated that the present method was valid for enhancing the characteristics of the barrier-type alumina film.

Magnetically applicable layered iron-titanate intercalated with biomolecules

We have prepared bio-inorganic nanohybrids consisting of magnetic inorganic nanolayers (iron-titanate) and protein molecules via exfoliation–restacking process in solution. It was found that the protein molecules were electrostatically and spontaneously incorporated into the interlayer space of the inorganic layered structure by adjusting the pH of the solution appropriately. The binding studies demonstrated the high affinity of the iron–titanate nanolayers for the proteins, and the immobilized protein preserved its activity after the hybridization. The catalytic activity measurement and magnetic separation experiment indicate the formation of magnetically applicable inorganic layer–biomolecule nanohybrids. The magnetic layer–biomolecule nanohybrid developed here would be a novel conspicuous material which shows different properties from those of conventional biomolecule-immobilized magnetic particles.

Electrochemical design of metal distribution in alkali silicate glass with ion-conducting microelectrodes

Electrochemical design of silver distribution near the surface or in the bulk of alkali silicate glass for use in the preparation of optical devices was carried out using an ion-conducting microelectrode. The fundamental solid-state electrochemical cell consists of an anode (Ag)/Ag-β″-Al2O3/alkali silicate glass/cathode (Ag) system, where the Ag+ conducting Ag-β″-Al2O3 microelectrode was used as a cationic source. Ag+ in Ag-β″-Al2O3 was substituted for alkali metal cations in the glass during electrolysis. Scanning the Ag-β″-Al2O3 microelectrode under an applied electric field resulted in the fine-patterned Ag-distribution in the glass surface so that the contact radius between Ag-β″-Al2O3 and glass was extremely small (about 10 µm). Furthermore, the patterned Ag distribution, which was constructed near the surface in advance, can be encapsulated within the bulk by subsequent Na+ injection.

Pinpoint doping using a β″-Al2O3 microelectrode as one application of the solid oxide electrochemical doping (SOED) method

Abstract Pinpoint metal cation doping was carried out using the solid oxide electrochemical doping (SOED) method, where a microelectrode of M-β″-Al2O3 as the solid electrolyte was used as a cationic source. Two different electrolysis systems were employed. One is the Ag (anode)/M-β″-Al2O3 (microelectrode)/doping target/Na-β″-Al2O3/Ag (cathode) electrolysis system, where the electrosubstitution of Mn+ for the cation in the target occurs under an electric field. The other used an oxide ion conducting solid electrolyte at the cathode side instead of Na-β″-Al2O3, where Mn+ can be injected into the target together with the injection of an oxide ion (electro-bi-injection). The pinpoint doping strongly depends on the conductive properties of the doping target and the valence of the dopant cation. Therefore, the cation doping into the alkali borosilicate glass occurs using only the former system because the glass shows a pure cationic conduction. In contrast, a cation can be doped into the superconducting Bi2Sr2CaCu2Oy ceramics using only the latter system because the electrosubstituion of a cation was difficult in an electron-conducting ceramics. In this case, the migration of the metal cations and the oxide ions primarily proceeds through the defects of ceramics (pore surfaces, grain boundaries, etc.). The monovalent cation can be easily injected into the doping target, while the divalent cation cannot be doped. The fact that the pinpoint distribution of the dopant can be controlled by the contact area between the microelectrode and the doping target indicates the migration of dopant was dominated by the potential distribution in the target materials under an electric field. As a result, we have achieved pinpoint doping on a 102-μm scale using the SOED method.

Temperature-controlled reversible exfoliation-stacking of titanate nanosheets in an aqueous solution containing tetraalkylammonium ions

Exfoliation and stacking of titanate nanosheets dispersed in aqueous solutions containing tetraalkylammonium ions can be reversibly controlled by adjusting the solution temperature as a tunable physical parameter. That is, the transparent colloidal solution of exfoliated titanates is clouded on the basis of spontaneous stacking of multiple nanosheets when heated at a certain temperature, and cooling of the clouded solution causes regeneration of the original exfoliated state. This cycle repeatedly and rapidly occurs according to the temperature fluctuation. The origin of behavior is qualitatively interpreted with a temperature-dependent variation in the Debye screening length of negatively charged nanosheets that affects the dispersibility of nanosheets.

Intense emissions from photoproteins interacting with titanate nanosheets

Bioluminescence of the Ca2+-binding photoprotein aequorin (AEQ) is largely enhanced by the co-presence of titanate nanosheets (TNS). A stable and transparent colloidal solution of TNS with a small hydrodynamic diameter of less than 10 nm is synthesized through a simple hydrolysis reaction of titanium tetraisopropoxide followed by a dialysis against pure water. Huge agglomerates of AEQ formed in an aqueous solution are peptized in the presence of TNS. The deflocculation of AEQ is considered to be because of a weak electrostatic interaction with the TNS, which is indirectly demonstrated by the enhanced thermal stability of AEQ. As a result, the TNS addition causes an excellent affinity of Ca2+ towards the binding sites (so called EF hands) in AEQ and subsequently efficient bioluminescence. A similar phenomenon is also confirmed for the chemiluminescence of luminol catalyzed by an oxidoreductase. These findings support the fact that the TNS addition is useful to simultaneously solve the faint emissions and instability of photoproteins.

Photo-excited electroless deposition of semiconducting oxide thin films and their electrocatalytic properties

The present study demonstrates the beneficial effects of ultraviolet (UV) light irradiation on the electroless deposition of several n-type semiconducting oxide thin films from an aqueous solution. To obtain ceria (CeO2), Ce3+ was oxidized to a higher valence in the presence of dissolved oxygen molecules and was then precipitated as CeO2 on a conductive substrate through a local cell mechanism. Irradiation of the substrate by UV light during the reaction caused the generation of photocarriers (electron and holes) in the surface oxide layer. The resultant photocarriers enabled further electrochemical reactions on the surfaces of the pre-deposited CeO2 nuclei together with the substrate surface. As a result, the deposition rate and crystallinity of the film were significantly improved by UV light irradiation. CeO2 thin films prepared on a Pt substrate by the proposed photoelectroless deposition method showed electrocatalytic activity for methanol oxidation without post-annealing, in contrast to the lower activity of a film deposited in the dark. This discrepancy is discussed on the basis of film morphology and crystallinity. Furthermore, it was confirmed that the electroless deposition of Sn and Pr oxide (hydroxide) was also accelerated by photoirradiation. In this paper, the photoelectroless deposition mechanism is discussed in detail, and the advantages of the proposed techniques are clarified.