Tsuyoshi Ochiai

Antibacterial performance of a novel photocatalytic-coated cordierite foam for use in air cleaners

n Abstractn n A novel titanium dioxide-coated cordierite foam (TiO2/cordierite foam) was developed for use in air cleaners. By a simple impregnation procedure, TiO2 nanoparticles were immobilized firmly onto the surface of a cordierite foam substrate through high-temperature (500°C) calcination. The strong bactericidal performance of the fabricated foam was evaluated by a newly developed test method for complex three-dimensional through-pore structures. This method could trace 5–6log units of decrease in bacterial cell numbers in an air environment, thus meeting the criteria of both the JIS and ISO standard test methods. With 0.25mWcm−2 of UV-A irradiation for 24h, the bactericidal rate of the TiO2/cordierite foam exceeded 99.9% for five types of airborne or droplet-based infectious pathogens: Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa), Legionella pneumophila (L. pneumophila), Klebsiella pneumoniae (K. pneumoniae), and methicillin-resistant Staphylococcus aureus (MRSA). The results of repeat testing, where the same sample was used three times, revealed that the bactericidal rate for E. coli was maintained at 99.9% in the second and third use, indicating that the TiO2/cordierite foam possesses a long-term bactericidal action. The TiO2/cordierite foam also exhibited a high photocatalytic degradation capability on gaseous acetaldehyde, which is associated with sick building syndrome, and volatile organic compounds to generate CO2 and H2O. The results demonstrated that TiO2-coated cordierite foam has great potential for use in air-cleaning filters with not only high bactericidal performance to remove pathogens in the air and in droplets, but also strong decontaminating and deodorizing functionality.n n

Fabrication of a TiO2 nanoparticles impregnated titanium mesh filter and its application for environmental purification

A novel photocatalytic filter, titanium-mesh sheet modified with TiO2 (TMiP), was fabricated and applied for environmental purification. The high flexibility of TMiP allows for an easy to design and fabricate photocatalytic reactor. Moreover, TMiP provides an excellent air or water pass-through while maintaining a high level of surface contact with UV irradiation.

Polymeric Adsorption of Methylene Blue in TiO2 Colloids—Highly Sensitive Thermochromism and Selective Photocatalysis

The polymeric adsorption of methylene blue (MB) on a TiO(2) surface is reported. The MB molecule on the TiO(2) surface mainly exists as the H-trimeric adsorption state, which results in the MB@TiO(2) polymeric sol. The trimeric adsorption leads to a remarkable blueshift of visible-light adsorption of MB. Electrostatic attraction is important for trimeric adsorption of MB on TiO(2) surfaces. The trimer-monomer equilibrium is highly sensitive on temperature changes, showing an interesting reversible thermochromism. The MB@TiO(2) polymeric sol can be photodegraded under UV illumination without destroying the equilibrium of trimer-monomer. Compared with anionic methyl orange, the TiO(2) colloid hydrosol shows highly selective photocatalysis of MB and other cationic dyes, including crystal violet, methylene green, and victoria blue B. The MB@TiO(2) polymeric sol is stable under visible-light illumination because interfacial transfer of electrons does not exist between MB and TiO(2).

Development of an O3-assisted photocatalytic water-purification unit by using a TiO2 modified titanium mesh filter

An ozone-assisted photocatalytic water-purification unit using a TiO2 modified titanium-mesh sheet (TMiP) was investigated. Significant decomposition of biological and chemical contaminants has been achieved by highly active intermediates formed by catalytic decomposition and photocatalysis.

Electrochemical inactivation kinetics of boron-doped diamond electrode on waterborne pathogens

A boron-doped diamond (BDD) electrode was constructed as a water disinfector for the inactivation of water borne pathogens. The bactericidal effect of the disinfector was evaluated on artificially contaminated waters containing, respectively, Escherichia coli, Pseudomonas aeruginosa and Legionella pneumophila at high density. By treating the bacterial suspensions with 4 V of constant voltage between the BDD and the counter-electrode for 50 min, the population of E. coli and P. aeruginosa decreased from (10E + 7-8 colony-forming unit mL(-1)) to below the detection limits of the colony-formation method. Meanwhile, L. pneumophila were reduced to virtually zero when analyzed by fluorescence-based staining. The influences of production parameters (voltage, NaCl concentration and flow rate) on the disinfection kinetics of the BDD disinfector were examined with respect to operational conditions. Voltage was the most significant factor for adjusting the extent of electrolysis, followed by NaCl concentration and flow rate, to influence the disinfection efficiency. The disinfection of natural river water samples containing numerous microbes was performed for a practicability investigation of the BDD electrode. Approximately 99.99% bactericidal efficiency was confirmed by viability detection for E. coli and common germs in treated water. The results showed that the BDD electrode is a promising tool for various wastewater disinfections to combat waterborne diseases.

Compact and effective photocatalytic air-purification unit by using of mercury-free excimer lamps with TiO2 coated titanium mesh filter

A photocatalyst–excimer–lamp hybrid reactor was investigated using a mercury-free xenon chloride excimer lamp wrapped with a TiO2 modified titanium-mesh sheet (TMiP). Significant decomposition of 6 ppm of methylmercaptane gas has been achieved by the reactor in a 36 L box within 3 h.

Field performance test of an air-cleaner with photocatalysis-plasma synergistic reactors for practical and long-term use.

A practical and long-term usable air-cleaner based on the synergy of photocatalysis and plasma treatments has been developed. A field test of the air-cleaner was carried out in an office smoking room. The results were compared to previously reported laboratory test results. Even after a treatment of 12,000 cigarettes-worth of tobacco smoke, the air-cleaner maintained high-level air-purification activity (98.9% ± 0.1% and 88% ± 1% removal of the total suspended particulate (TSP) and total volatile organic compound (TVOC) concentrations, respectively) at single-pass conditions. Although the removal ratio of TSP concentrations was 98.6% ± 0.2%, the ratio of TVOC concentrations was 43.8% after a treatment of 21,900 cigarettes-worth of tobacco smoke in the field test. These results indicate the importance of suitable maintenance of the reactors in the air-cleaner during field use.

Application of Boron-Doped Diamond Microelectrodes for Dental Treatment with Pinpoint Ozone-Water Production

Ozone is known to act as a powerful antimicrobial agent against bacteria, fungi, and viruses. The strong oxidation ability of ozone induces the destruction of bacterial cell walls, cytoplasmic membranes, and biomolecules on the bacterial cell surface. Recently, ozone has received growing attention as a useful tool for dental treatment. Ozone has a severely disruptive effect on cariogenic bacteria, resulting in the elimination of acidogenic bacteria. However, while laboratory studies suggest a promising potential of ozone in dentistry, this has not been fully realised in clinical studies to date. In this study, a novel pinpoint ozone-water production unit for dental treatment using boron-doped diamond (BDD) microelectrodes was developed. The application of BDD electrodes is promising for electrolyzing water to produce ozone, because of their superior chemical and dimensional stability, as well as their large overpotential for the oxygen-evolution reaction. 9] Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) were used as test bacteria to assess the disinfection efficiency of the units. The BDD microelectrodes were prepared by method reported previously which has already been established for applications in in vivo detection. The BDD thin film was deposited on a prepared tungsten wire using a microwave-plasma-assisted chemical-vapor deposition system. Prior to BDD deposition, the tungsten wire was shaped by electrochemical etching to achieve a very small wire diameter. The as-prepared BDDcoated tungsten wires can then be used to fabricate microelectrodes with very small wire diameters (500 mm). A scanning electron microscopy (SEM) image of such a fabricated BDD microelectrode shows that the wire diameter is small (500 mm) with the polycrystalline diamond grain size being approximately 2 mm (Figure 1 a). The Raman spectrum (excitation wavelength: 532 nm) of the BDD microelectrode

Effective Photocatalytic Hydrogen Evolution by Cascadal Carrier Transfer in the Reverse Direction

Visible-light-responsive photocatalysts used in the highly efficient hydrogen production exhibit several disadvantages such as photocorrosion and fast recombination. Because of the potential important applications of such catalysts, it is crucial that a simple, effective solution is developed. In this respect, in this study, we combined SiC (β modification) and TiO2 with CdS to overcome the challenges of photocorrosion and fast recombination of CdS. Notably, we found that when irradiated with visible light, CdS was excited, and the excited electrons moved to the conduction band of TiO2, thereby increasing the efficiency of charge separation. In addition, by moving the holes generated on CdS to the valence band of SiC, in the opposite direction of TiO2, photocorrosion and fast recombination were prevented. As a result, in the sulfide solution, the CdS/SiC composite catalyst exhibited 4.3 times higher hydrogen generation ability than pure CdS. Moreover, this effect was enhanced with the addition of TiO2, giving 10.8 times higher hydrogen generation ability for the CdS/SiC/TiO2 catalyst. Notably, the most efficient catalyst, which was obtained by depositing Pt as a cocatalyst, exhibited 1.09 mmol g–1 h–1 hydrogen generation ability and an apparent quantum yield of 24.8%. Because water reduction proceeded on the TiO2 surface and oxidative sulfide decomposition proceeded on the SiC surface, the exposure of CdS to the solution was unnecessary, and X-ray photoelectron spectroscopy confirmed that photocorrosion was successfully suppressed. Thus, we believe that the effective composite photocatalyst construction method presented herein can also be applied to other visible-light-responsive powder photocatalysts having the same disadvantages as CdS, thereby improving the efficiency of such catalysts.