Eiichi Abe

Effect of functional group on photochemical properties and photosensitization of TiO2 electrode sensitized by porphyrin derivatives

A series of porphyrin derivatives containing carboxylic-, sulfo- and hydro- groups, 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP), 5,10,15,20-tetrakis(4-sulfophenyl)porphyrin (TSPP) and 5,10,15,20-tetraphenyl-porphyrin (TPP), were examined as sensitizers for porous nanocrystalline TiO2. The difference in the adsorption behavior on the TiO2 electrode surface was discussed. The interaction between the porphyrins and the TiO2 surface was determined and compared using UV–Vis spectra and X-ray photoelectron spectroscopy (XPS). The luminescence spectra of the porphyrins in DMF solution and adsorbed onto TiO2 electrodes were measured. The ionization potentials of the porphyrins in the solid state and adsorbed onto TiO 2 electrodes were determined by a new approach using an apparatus for measuring the emission yield under atmospheric conditions. The importance of the binding states between the dye and TiO2 surface was discussed by comparison of the energy conversion efficiency in a dye-sensitized solar cell. The results indicate that the binding state and the amount of adsorbed dye are important factors affecting the properties of the dye-sensitized solar cell.

Preparation and properties of nanostructured TiO2 electrode by a polymer organic-medium screen-printing technique

An organic-medium screen-printing technique was developed for making porous TiO2 electrodes. The TiO2 pastes were prepared by mixing only 100% polyalkylene glycol and commercial nanocrystalline TiO2 powders. The obtained paste is highly printable and hard to evaporate during printing. The TiO2 electrodes have a very porous structure with large cavities. The dye-sensitized solar cell based on these meso-macroporous TiO2 electrodes exhibits high overall conversion efficiency of 4.3–5.8%, which is comparable to those of prepared by water or terpineol medium.

Photoelectrochemical properties of TiO2 electrodes sensitized by porphyrin derivatives with different numbers of carboxyl groups

Abstract The photochemical and photoelectrochemical properties of two porphyrin derivatives with different numbers of carboxyl groups were investigated. The two porphyrin derivatives are 5-(4-carboxyphenyl)-10,15,20-tritolylporphyrin (H2TC1PP) and 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (H2TC4PP). The interaction between the porphyrin and TiO2 is determined by the UV–vis spectra. Differences in adsorption behavior of the two porphyrin derivatives on the TiO2 electrode surface were observed. The IR data suggest that both of the porphyrins adsorb by bridging or bidentate chelate coordination on the TiO2 surface. Comparing the luminescence spectra of the two porphyrins in solution and the solid state, no spectral difference was observed. However, we found that the variation in the number of carboxyl groups has an influence on the fluorescence spectra of the adsorbed TiO2 electrode. Furthermore, we measured and compared the incident photon-to-current conversion efficiency (IPCE) and the light-to-electrical conversion efficiency of the porphyrin-sensitized solar cell. These results revealed that the number of functional groups influenced the photoelectrochemical properties of the cell.

Coating mass distributions of seed particles in a tumbling fluidized bed coater. Part II. A Monte Carlo simulation of particle coating

Abstract In the preparation of coated particles, a homogeneous distribution of the coating mass is often desired and much effort is made to obtain this. If it is possible to predict the effect of operating conditions on coating mass distributions by computer simulations, some of the experimental difficulties will be reduced. Therefore, in this study, Monte Carlo simulations of coating mass distribution of particles were performed to reproduce a series of experimental results obtained using a tumbling fluidized bed. This method was found to be applicable for reproducing the effect of the operating conditions on the coating mass distributions showing that a more homogeneous distribution was achieved under the following conditions; long coating time; small hold up of core particles; high rate of mixing of the particles, etc. Furthermore, some predictions of the effect of operating conditions on coating mass distributions using this simulation method were performed.

Coating mass distributions of seed particles in a tumbling fluidized bed coater

In order to control the extent of particle coating, it is necessary to clarify how the amount of coating material of each individual seed particle varies with operating condition. The influence of these conditions on the distribution of the mass of coating material, deposited on each single seed particle treated in a tumbling fluidized bed, was experimentally examined in this work. As a result, the coating mass per unit surface area of a single seed particle was proven to obey a normal distribution by number. Moreover, it also became clear that the coefficient of variation of the coating mass distribution, cv, decreased with increasing coating time and size of the seed particle, and with decreasing their holdup. However, the rotational speed of the disk, which forces the aggregative coated particles apart, hardly affected the cv value in the experiment.

Spectroscopic and photoelectrochemical differences between racemic and enantiomeric [Ru(phen)3]2+ ions intercalated into layered niobate K4Nb6O17

Abstract 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 K 4 Nb 6 O 17 . The results were interpreted in terms of a [Nb 6 O 17 ] 4− -chelate and chelate–chelate interactions. The faster luminescence decay and higher photocurrent of the enantiomeric [Ru(phen) 3 ] 2+ –K 4 Nb 6 O 17 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.

Coagulation and dispersion of red mud suspensions

Abstract Red mud is a waste stream the Bayer process for alumina production. This paper deals mainly with the influence of pH on the coagulation and dispersion of red mud suspensions. For the purpose of understanding the coagulation and dispersion phenomena of dilute red mud suspensions, the relationship between zeta potential of red mud and pH is measured, and the phenomena in the case of basic suspensions are analyzed by using the experimental data of zeta potential and the DLVO theory. It is shown that the theory agrees fairly well with the experimental results. Furthermore, measurements of the specific volume of sediment, the zeta potential, the mass fraction of less than 2 μm in red mud and the apparent viscosity of some kinds of slurries, show that in order to entirely disperse red mud suspensions, the addition of a dispersing agent to the suspensions is necessary.

Coagulation of red mud suspensions with an inorganic coagulant

Abstract This paper deals with the coagulation of red mud (a waste product from the Bayer process to produce alumina) in water with an inorganic coagulant (FeCl 3 ·6H 2 O). The coagulative state is evaluated by measuring the transmittance of supernatant liquid and/ or the specific volume of the sediment in suspensions after standing for 24 h. It is found that the most important factor in coagulating red mud is maintaining the pH of solutions in suspensions within the range of 7 to 8 regardless of red mud concentration, because the zeta potential of red mud in this pH range is less than approximately |13| mV, which is already known as the potential range necessary to coagulate fine particles in general.

Fabrication and photoelectrochemical characterization of CdS particles in nanospaces of expandable mica

Abstract Photoelectrochemical properties are investigated for CdS nanoparticles formed in a solution as well as in the nanospaces of expandable mica (EM). The smallest sized CdS particles (≈3 nm in diameter) were obtained in the nanospaces of Cd 2+ exchanged EM (1.2 μm in crystal size) by reacting with H 2 S in the absence of interlayer water. The existence of interlayer water was found to influence the size of CdS particles remarkably. Smaller EM crystals limited the particle growth of CdS along the sheets. Photocurrent was measured for the CdS-EM suspensions/methylviologen system and the CdS-EM film electrode. The variation of the steady state photocurrent value ( i ss ) with pH, showed that i ss increased with the decrease of CdS particle size, while the intersection point (termed as pH 0 ) showed a negative shift with the decrease of CdS particle size. The action spectrum of the CdS-EM film electrode was in good agreement with their absorption spectra of the suspension.

Effect of Microchannel on Improving the Photoelectro- chemical Performance of Nanostructured TiO2 Electrodes Sensitized by Ru Complex

The photoelectrochemical behaviors of the dye-sensitized nanoporous T i 0 2 solar cell with and without microchannels were studied. A remarkably enhancement in the photocurrent of the cell with the microchannels on the T i 0 2 electrode was observed. The resistances of the cells were valuated by measuring the electrical impedance. It was found that the resistances of the cell with the microchannels became smaller than those of the cell without microchannnels. These results suggest that the diffusion of the iodide/triiodide species in the electrolyte was