Schottky junction/ohmic contact behavior of a nanoporous TiO(2) thin film photoanode in contact with redox electrolyte solutions.

The nature and photoelectrochemical reactivity of nanoporous semiconductor electrodes have attracted a great deal of attention. Nanostructured materials have promising capabilities applicable for the construction of various photonic and electronic devices. In this paper, a mesoporous TiO(2) thin film photoanode was soaked in an aqueous methanol solution using an O(2)-reducing Pt-based cathode in contact with atmospheric air on the back side. It was shown from distinct photocurrents in the cyclic voltammogram (CV) that the nanosurface of the mesoporous n-TiO(2) film forms a Schottky junction with water containing a strong electron donor such as methanol. Formation of a Schottky junction (liquid junction) was also proved by Mott-Schottky plots at the mesoporous TiO(2) thin film photoanode, and the thickness of the space charge layer was estimated to be very thin, i.e., only 3.1 nm at -0.1 V vs Ag/AgCl. On the other hand, the presence of [Fe(CN)(6)](4-) and the absence of methanol brought about ohmic contact behavior on the TiO(2) film and exhibited reversible redox waves in the dark due to the [Fe(CN)(6)](4-/3-) couple. Further studies showed that multiple Schottky junctions/ohmic contact behavior inducing simultaneously both photocurrent and overlapped reversible redox waves was found in the CV of a nanoporous TiO(2) photoanode soaked in an aqueous redox electrolyte solution containing methanol and [Fe(CN)(6)](4-). That is, the TiO(2) nanosurface responds to [Fe(CN)(6)](4-) to give ohmic redox waves overlapped simultaneously with photocurrents due to the Schottky junction. Additionally, a second step photocurrent generation was observed in the presence of both MeOH and [Fe(CN)(6)](4-) around the redox potential of the iron complex. It was suggested that the iron complex forms a second Schottky junction for which the flat band potential (E(fb)) lies near the redox potential of the iron complex.

Photoelectrochemical conversion of NO3(-) to N2 by using a photoelectrochemical cell composed of a nanoporous TiO2 film photoanode and an O2 reducing cathode.

Photoelectrochemical conversion of nitrate anions into dinitrogen was successfully achieved by using a photoelectrochemical cell composed of a nanoporous TiO2 film photoanode and an O2 reducing cathode in the presence of NH3, which can be regarded as a model of denitrification and is of importance for environmental cleaning.

Wide range ammonia concentration analyzer utilizing a new principle of photoelectrochemical reaction at a nanoporous TiO2 photoanode.

It was successfully demonstrated that ammonia concentration in water can be determined easily with a remarkably wide dynamic range of 5 orders of magnitude by measuring the photocurrent generated by ammonia in a photoelectrochemical cell composed of a nanoporous TiO(2) photoanode, an O(2)-reducing Pt cathode and a UV-LED (ultra-violet light-emitting-diode) light source.

Direct electrical power generation from urine, wastes and biomass with simultaneous photodecomposition and cleaning.

Electric power was for the first time generated directly from urine, wastes, and biomass with simultaneous photodecomposition and cleaning by using a biophotofuel cell (BPFC) composed of a nanoporous TiO2 film semiconductor photoanode and an O2-reducing cathode. Human urine exhibited a PFC characteristics with J(sc) 0.086 mA cm(-2), Voc 0.56 V, and fill factor (FF) 0.50 under irradiation by a solar simulator with AM 1.5 G and 100 mW cm(-2) incident light intensity. Both the soluble and residual parts of waste paper partially solubilized by a H3PO4 aqueous solution were also photodecomposed with simultaneous electrical power generation. As trials of various biomass materials, Coca-Cola (to test colored sample), Japanese rice wine (to test alcohol aqueous solution), and grated radish (to test slurry state sample) also generated effectively electrical power during photodecomposition by a solar simulator.

Visible light decomposition of ammonia to N2 with Ru(bpy)3(2+) sensitizer.

Visible light decomposition of aqueous NH3 to N2 was investigated using a photocatalyst aqueous solution based on molecular photoelectron relay systems of either sensitizer (tris(2,2'-bipyridine)ruthenium(II), (Ru(bpy)3(2+))/potassium peroxodisulfate(K(2)S(2)O(8)) or Ru(bpy)3(2+)/methylviologen dichloride(MV2+)/O2, capable of using visible light instead of UV-driven semiconductors such as TiO2. It was confirmed by using an in situ visible absorption spectral change under irradiation that the Ru(II) complex is oxidized to the Ru(III) complex by K(2)S(2)O(8), and that the Ru(III) complex formed is stable without NH3, while the added NH3 was oxidized by the Ru(III) complex to produce the Ru(II) complex. In the presence of 1 mM NH3 aqueous solution, the Ru(III) complex was the predominant species under the photostationary state, but in the presence of 100 mM NH3, Ru(II) predominated. Gas-chromatographic analysis of the gaseous phase in the presence of 8.1 M NH3 showed that the photochemical oxidation of ammonia yielded N2. It was also demonstrated by using the in situ visible absorption spectrum under irradiation of the NH3 (1 M)/Ru(bpy)3(2+) (0.1 mM)/MV2+ (10 mM) system under Ar that MV+* is accumulated, showing that NH3 works as an electron donor for MV+* accumulation with simultaneous formation of the oxidized product of ammonia ((NH3)ox) without producing N2. It was suggested that the reduced product (MV+*) and the oxidized product ((NH3)ox) are in a kind of dynamic equilibrium prohibiting further oxidation of (NH3)ox by Ru(bpy)3(3+) to N2. In the O2 atmosphere, the oxidation of MV+* to MV2+ takes place to accumulate Ru(III) complex, so that (NH3)ox was further oxidized to N2. The high activity of IrO2 as a cocatalyst in this system was demonstrated.

Detection of Cryptosporidium parvum oocysts using a microfluidic device equipped with the SUS micromesh and FITC-labeled antibody.

Development of a microfluidic device equipped with micromesh for detection of Cryptosporidium parvum oocyst was reported. A micromesh consisting of 10 x 10 cavities was microfabricated on the stainless steel plate by laser ablation. Each cavity size, approximately 2.7 microm in diameter, was adopted to capture a single C. parvum oocyst. Under negative pressure operation, suspensions containing microbeads or C. parvum oocysts flowed into the microchannel. Due to strong non-specific adsorption of microbeads onto the PDMS microchannel surface during sample injection, the surface was treated with air plasma, followed by treatment with 1% sodium dodecyl sulfate (SDS) solution. This process reduced the non-specific adsorption of microbeads on the microchannel to 10% or less in comparison to a non-treated microchannel. This microfluidic device equipped with the SUS micromesh was further applied for the capture of C. parvum oocysts. Trapped C. parvum oocysts were visualized by staining with FITC-labeled anti-C. parvum oocyst antibody on a micromesh and counted under fluoroscopic observation. The result obtained by our method was consistent with that obtained by direct immunofluorescence assay coupled with immunomagnetic separation (DFA-IMS) method, indicating that the SUS micromesh is useful for counting of C. parvum oocysts. The newly designed microfluidic device exploits a geometry that allowed for the entrapment of oocysts on the micromesh while providing the rapid introduction of a series of reagents and washes through the microfluidic structure. Our data indicate that this microfluidic device is useful for high-throughput counting of C. parvum oocysts from tap water sample.

Direct counting of Cryptosporidium parvum oocysts using fluorescence in situ hybridization on a membrane filter.

This report describes the development of a direct and rapid detection method for the pathogenic protozoan, Cryptosporidium parvum, from environmental water samples using fluorescence in situ hybridization (FISH) on a membrane filter. The hydrophilic polytetrafluoroethylene (PTFE) membrane filter with FISH-stained oocysts yielded the highest signal to noise (S/N) ratio of the different membrane filters tested. PTFE membranes retained 98.8+/-0.4% of the concentrated oocysts after washing, simultaneous permeabilization and fixation with a hot ethanol solution, and hybridization with a fluorescently labeled oligonucleotide probe. This procedure eliminates subsequent time-consuming recovery steps that often result in a loss of the actual oocysts in a given environmental water sample. Furthermore, C. parvum was successfully distinguished from Cryptosporidium muris and other species in environmental water samples with the addition of formamide into the hybridization solution. In tap water samples, the S/N ratio was heightened by washing the membrane filter prior to FISH with a 1 M HCl solution in order to reduce the large amounts of impurities and background fluorescence from the non-specific adsorption of the fluorescently labeled oligonucleotide probe.

Visible light decomposition of ammonia to dinitrogen by a new visible light photocatalytic system composed of sensitizer (Ru(bpy)(3)2+), electron mediator (methylviologen) and electron acceptor (dioxygen).

Visible light decomposition of aqueous ammonia to dinitrogen was successfully achieved by using a new photocatalytic system based on a molecular photoelectron relay composed of a sensitizer (Ru(bpy)(3)2+), an electron mediator (methylviologen) and an electron acceptor (dioxygen), which can be used as a visible light-driven photocatalyst instead of UV-driven semiconductors.

Development of an automated water toxicity biosensor using Thiobacillus ferrooxidans for monitoring cyanides in natural water for a water filtering plant.

An on-line biosensor consisting of immobilized Thiobacillus ferrooxidans and an oxygen electrode was developed for automated monitoring of acute toxicity in water samples. T. ferrooxidans is an obligatory acidophilic, autotrophic bacterium and derives its energy by the oxidation of ferrous ion, elemental sulfur, and reduced sulfur compounds including metal sulfides. The assay is based on the monitoring of a current increase by addition of toxicoids, which is caused by the inhibition of bacterial respiration and decrease in oxygen consumption. Optimum cell number on the membrane was 5.0 x 10(8) cells. The steady-state current was obtained when concentration of FeSO4 was above 3.6 mM at pH 3. The sensor response of T. ferrooxidans immobilized membrane for 5.0 microM KCN was within an error of 10% for 30 membranes. A linear relationship was obtained at KCN concentration in the range of 0.5-3.0 microM in a flow-type monitoring system. Minimum detectable concentrations of KCN, Na2S, and NaN3 were 0.5, 1.2, and 0.07 microM, respectively. The monitoring system contained two biosensors and these sensors were cleaned with sulfuric acid (pH 1.5) twice a day. This treatment could remove fouling on microbial immobilized membrane by natural water and ferrous precipitation in the flow cell. This flow-type monitoring sensor was operated continuously for 5 months. Also, T. ferrooxidans immobilized membrane can be stored for one month at 4 degrees C when preserved with wet absorbent cotton under argon gas.