A dimeric titanium planar structure conventionally explains surface reactions of TiO2 photocatalysis. Although it has been assumed to be planar, we found that the hydroxyl-terminated cluster model (Ti2O6H4) essentially has a non-planar structure calculated with B3LYP/6-311G. The hydrogen atom positions shift the HOMO and LUMO energy levels, relating to photocatalytic oxidation and reduction abilities. The results indicate that settling a new larger model to fit many phenomena quantitatively is highly required since the planar structure potentially involves a severe electronic problem.

We investigate optimized structures of a cyclic methanol cluster (CH3OH)(4) by starting different-sized planar symmetric structures, where all the H atoms of the OH groups direct to the next O atom, and all the COH parts are in-plane. At the HF/STO-3G level, initial O-O distances at 2.7 angstrom and more lead to the most stable structure, whereas those less than 2.7 angstrom result in two other stable conformers. The border distance indicates the efficient range of hydrogen bonding forces of the OH groups. HF/6-31G (d) results in a planar structure with negative frequencies, whereas B3LYP/6-31G (d) gives a conformer whose methyl groups face the same direction. These structures result from the balance between the stabilization due to the orbital broadening of unshared electron pairs of O and the repulsive force of the methyl groups, reflecting the tendency for transformation among the conformers. To calculate force constants with the calcall option is effective in obtaining the most stable structure regardless of the initial O-O distance.

Polysulfide anions play crucial roles in the liquid phase, but they are difficult to describe in theoretical calculations. We have investigated diffuse functions dependent total energy, bond length, and molecular orbitals for disulfide dianion (S-2(2-)) in water using conventional ab initio unrestricted Hartree-Fock method (UHF/6-311G+(d)) with a polarizable continuum model (PCM, epsilon = 78.39) by changing sigma value of diffuse functions. S-2(2-) in water turns out to be more stable than S-2 and S-2(-), though it is too unstable to exist in vacuum so that the excess electrons will auto-detach. The optimal sigma value that gives a local minimum of total energy for S-2(2-) in water is found to be 0.12. These new findings will contribute toward using more appropriate diffuse functions for other polysulfide anions as well.

Modification of graphitic carbon nitride (g-C3N4) with silver metal significantly improved the adsorption capacity and the photocatalytic degradation activity for methyl mercaptan, which is a typical sulfurous compound, under visible light. These improvements were easily obtained by the shear mixing method. The ultrafine crystallites of metallic silver were formed on surface of carbon nitride by shear mixing of HT-g-C3N4 (Hydrothermal treated g-C3N4) in aqueous solution of silver acetate. One atom of the silver captured ca. 0.6 molecule of methyl mercaptan on average, while a silver atom deposited on TiO2 captured only 0.03 molecule. The migration of silver crystallites over the g-C3N4 surface and the formation of silver thin-layer during the adsorption of methyl mercaptan were observed by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The silver crystallite on g-C3N4 seemed to have higher mobility than that on TiO2 to form the coordination suitable for the adsorption of methyl mercaptan. This coordination of Ag also enhanced the photocatalytic degradation of methyl mercaptan to dimethyl disulfide. (C) 2016 Elsevier B.V. All rights reserved.

Electron impact ionization mass spectrometry enables detection of cluster ions from a water-alcohol binary mix-ture, by which it was previously reported that a pure alcohol solution gave only small cluster ions, while the addition of water in a small amount (ca. 20wt%) resulted in the appearance of much larger cluster ions. We have theoretically examined the effect of existing water on the formation of alcohol clusters, by taking a typical cyclic cluster composed of three ethanol and one water molecules. The calculations were carried out with the Hartree-Fock method with 6-31G** basis set. As a result, we showed that the ionization of alcohols is followed by proton (H + ) donation by the water close to the ionized alcohol via energy transfer. The excess ionization energy is taken by the dissociation of the water molecule so that the alcohol-rich cluster ions will be stabilized. In the absence of water, the excess energy is distributed through-out the cluster, so that large cluster ions, not possible to observe, will be fragmented into small pieces in a vacuum.

We examined Chlorella cells exposed to several kinds of oxidative stress, namely photocatalysis, UV light, heat, and H2O2. After these oxidative treatments, the Chlorella cells were stained with neutral red, methylene blue, eosin Y, or fluorescein diacetate (FDA). The results of FDA staining were generally the most consistent with those of colony-forming unit assays. In addition, chlorophyll autofluorescence was responsive to photocatalytic oxidation and may be useful as a simple, rapidly obtained index of the viability of Chlorella cells exposed to photocatalysis. We also discussed differences in the stainability of cells in terms of external and internal cellular damage. Photocatalytic oxidation resulted in the greatest degree of cellular damage, including lipid peroxidation and cell deformation.

In order to determine whether natural attenuation of chlorinated ethenes by microbial activity occurs in aquitards, sediments at a site contaminated with tetrachloroethene were vertically studied by drilling. The distribution of microbes (Dehalococcoides group and anaerobic hydrogen producers) and the ability of the sediments to sustain microbial dechlorination were determined in an aquitard as well as in an aquifer. Close-spaced sampling revealed the existence of large populations of Dehalococcoides and H(2)-producing bacteria, especially in the organic-rich clayey aquitard rather than in the aquifer. The vinyl chloride reductase gene was also detected in the clay layer. Furthermore, incubation experiments indicated that the clay sediment could sustain transformations of tetrachloroethene at least to vinyl chloride. In contrast, no significant transformation was observed in the aquifer sand. Our results indicate that dechlorination of tetrachloroethene by bacteria can take place in an organic-rich clayey aquitard, and that organic-rich clay may also be important in the natural attenuation in an adjacent aquifer, possibly supplying a carbon source or an electron donor.

The photocatalytic degradation of malachite green (MG) dye molecules in aqueous solution was investigated by using palladium (Pd) modified tungsten trioxide (WO3) under simulated solar light. The optimum values for Pd content vs. WO3 and catalyst concentration in solution for MG (5.0 μmol L−1) degradation were 0.5 wt.% and 150 mg L−1, respectively. The MG concentration change followed the pseudo first order kinetics of the Langmuir-Hinshelwood model. Since MG was also degraded under visible light (λ > 470 nm), which was not absorbed by WO3, the mechanism involved both the photocatalytic degradation and self-sensitized degradation of MG. Pd modified WO3 would be useful as an efficient tool for the decolorization of wastewater under solar light.

We have discovered that HNO3 and related species are released from the TiO2 surface into air in the TiO2 photocatalytic oxidation of NO2 (1 ppm) under continuous UV light illumination (1 mW cm(-2)) by dehumidifying the outlet gas of the reaction and analyzing the recovered condensate liquid by ion chromatography. The origin of the HNO3 recovered in the dehumidifier could not be explained by a simple desorption of HNO3 overproduced on the TiO2 surface. The produced HNO3 must be activated on the TiO2 surface and causing the unidentified reaction.

We have discovered that Cu2+-loaded TiO2 films (1.5μm thick) exhibit a high activity of selective reduction of NO2 to NO in air under UV light illumination (1mWcm−2). This effect is associated with a reduced NO oxidation to HNO3. For an increasing amount of Cu2+ ions the NO reductions become more stable. Cu2+ ions are responsible for the high redox property, playing an important role in adsorption of NO2/NO2−, electron transfer from the TiO2 to NO2/NO2−, and recombination center for positive holes.

We showed that the photocatalytic effect of a coating of TiO(2) greatly reduces the formation of a biofilm by Phormidium tenue (P. tenue), a filamentous cyanobacterium, on glass plates. Sample plates were immersed in P. tenue culture solution (OD(730)=0.3) under concurrent illumination with white fluorescent (WF) and UV light (0.3 mW cm(-2), each) for 11 days. TiO(2)-coated glass plates showed greatly reduced adhesion of P. tenue over 11 days compared to bare plates. The number of P. tenue adhering to bare glass plates increased to over 10(6) cells cm(-2) in 6 days. The photocatalytic anti-biofilm effect was also observed under WF light, although it was small and lasted only a few days. The addition of 1 mM mannitol, a scavenger for the hydroxyl radical (·OH), suppressed the effect. The surface of TiO(2)-coated plates was maintained in a highly hydrophilic state for 11 days, regardless of the addition of mannitol. Therefore, we conclude that the photocatalytic oxidation of P. tenue is effective in preventing the formation of a biofilm.

We have discovered that HNO 3 and related species are released from the TiO 2 surface into air in the TiO 2 photocatalytic oxidation of NO 2 (1 ppm) under continuous UV light illumination (1 mW cm −2 ) by dehumidifying the outlet gas of the reaction and analyzing the recovered condensate liquid by ion chromatography. The origin of the HNO 3 recovered in the dehumidifier could not be explained by a simple desorption of HNO 3 overproduced on the TiO 2 surface. The produced HNO 3 must be activated on the TiO 2 surface and causing the unidentified reaction.

An apparent deactivating behavior of TiO2 photocatalysts in NO (1ppm) oxidation in air was examined using TiO2 nanoparticulate thin films (0.5–1.4μm thick) under continuous UV light illumination (1mWcm−2). The rate of NO oxidation decreased with HNO3 accumulation on the TiO2 surface. At the final steady state, the rate of NO oxidation was one-third of the initial one, and NO2 was released into air at the equivalent rate. The amount of HNO3 trapped on the TiO2 film was increased and finally saturated, at which the largest amount of HNO3 was proportional to the thickness of the film, and then the maximum density of HNO3 on the TiO2 surface was estimated to be ∼0.5moleculenm−2. The value was much smaller than the previously reported one in the NO2 oxidation (∼2moleculenm−2). The discrepancy is explained by the consumption of HNO3 during the photocatalytic reaction, thus HNO3 reacts with NO and produces NO2 on the TiO2 surface under UV light illumination. On the basis of the results, we concluded that the maximum surface density of HNO3 on TiO2 in the NO oxidation is determined by the balance between the accumulation amount and the consumption amount of HNO3 on the TiO2 surface.

Objective: Clean intermittent catheterization (CIC) requires a large number of disposable catheters or a large amount of water and disinfectant. We made titanium dioxide (TiO2)-coated catheters for CIC using technology we have developed previously, and examined the photocatalytic antibacterial effect of this catheter using only light energy and the safety of this type of catheter for practical clinical use.Methods: TiO2-coated catheters were filled with bacterial cell suspensions and illuminated with a 15-W black-light lamp for testing antibacterial potency. Next, we soaked control toxic materials (zinc diethyldithiocarbamate) and the tips of TiO2-coated catheters in M05 medium, and evaluated cell toxicity from the numbers of V79 colonies in these dilutions. Then, bodyweight curves and histological tissue changes were observed over a period of time in mouse-transplanted TiO2-coated catheters and control catheters. Finally, we investigated the use of these TiO2-coated catheters in 18 patients by questionnaire and bacterial culture of TiO2-coated catheters and control catheters.Results: The survival rate of Escherichia coli in the liquid inside the TiO2 catheter decreased to a negligible level within 60 min under ultraviolet (UV)-A illumination. The survival rate of Staphylococcus aureus, Pseudomonas aeruginosa and Serratia marcescens also decreased to a negligible level within 60 min. V79 cells showed no cytotoxicity of this catheter, and there was no difference in bodyweight or foreign body reaction between mouse-transplanted TiO2-coated catheters and control catheters. In a preliminary clinical analysis of 18 patients who voluntarily used this catheter, the rate of positive bacterial culture of the tips of TiO2-coated catheters was 20% versus 60% for conventional catheters after 4 weeks of use.Conclusion: TiO2-coated silicone catheters were easily sterilized under certain light sources and were shown to be safe in an experiment using cultured cells and in animal experiments. Sterilizing catheters with TiO2 photocatalyst thin films are expected to be used clinically for clean intermittent catheterization after proper modification based on this study.

The electrochemical behaviour of TiO2 under X-ray irradiation was studied. Under X-ray irradiation a current, a negative shift in the rest potential, and electrochemical oxidation and decomposition of [FeII(CN)6]4− were clearly observed. The incident photon-current conversion efficiency and energy conversion efficiency was 400–2000% and 0.2–2%, respectively, depending on sample conditions. These results show that the photoelectrochemical reactions were promoted by X-rays with a high incident photon-current conversion efficiency. The photocurrent and photopotential were observed above 4.965keV, which corresponds to the Ti–K edge, indicating that electron-hole pairs are formed during the relaxation process of the excited Ti atoms.

Ag/titanium dioxide (TiO(2))-coated silicon catheters were easily fabricated with Ag nanoparticles deposition on both the inside wall and the outside wall of TiO(2)-coated catheters by TiO(2) photocatalysis. This is an application of the silicon catheters coated with TiO(2), which possess a self-sterilizing and self-cleaning property combining with UV light illumination (Ohko et al., J Biomed Mater Res: Appl Biomater 2001;58:97). Ag/TiO(2)-coated silicon catheters exhibited a strong bactericidal effect even in the dark. When the 2-5 x 10(5) of colony-forming units of Escherichia coli, Pseudomonas aeruginosa, or Staphylococcus aureus were respectively applied to the surface of the Ag/TiO(2) catheters, which were loaded with approximately 15 nmol cm(-2) of Ag, 99% effective sterilization occurred in a very short time: 20 min for E. coli, 60 min for P. aeruginosa, and 90 min for S. aureus. Additionally, the Ag/TiO(2)-coated catheters possessed a strong self-cleaning property. Using UV illumination, the photocatalytic decomposition rate of methylene blue dye representing the self-cleaning capability, on an Ag/TiO(2) catheter which was loaded with 2 nmol cm(-2) of Ag, was approximately 1.2 times higher (at maximum) than that on TiO(2) coating alone. Furthermore, the Ag nanoparticles can be pre-eminently and uniformly deposited onto the TiO(2) coating, and the amount of Ag was easily controllable from a few nanomoles per square centimeter to approximately 70 nmol cm(-2) by changing the UV illumination time for TiO(2) photocatalysis. This type of catheter shows a great promise in lowering the incidence of catheter-related bacterial infections.

In the multicolor photochromism of TiO2 nanoporous films loaded with photocatalytically deposited Ag nanoparticles, visible light-induced electron transfer from Ag to oxygen molecules plays an essential role. Here we examined the effect of TiO2 on the electron transfer. We found that not only photocatalytically deposited Ag, but also electrodeposited Ag and commercially available Ag nanoparticles in a nanoporous TiO2 film exhibit the multicolor photochromism. The electrodeposited Ag exhibits the multicolor photochromism also in a nanoporous ZnO film, but not in nanoporouns indium-tin oxide (ITO) and SiO2 matrices. Photoelectrochemical measurements for the Ag-TiO2 nanocomposite elucidated that some of the photo-excited electrons on Ag are transferred to oxygen molecules via TiO2 and non-excited Ag. Thus, an n-type semiconductor plays an important role in the charge separation between the excited electrons and Ag+. Non-excited Ag on TiO2 also plays an important role in the charge separation and/or catalysis of oxygen reduction. Replacement of the non-excited Ag with Pt accelerated the electron transport from the photo-excited Ag to oxygen molecules and the photochromic behavior.

The photochromism and rewritability of Ag-TiO2 films were deactivated by modification with thiols to make it possible to retain color images displayed on the films (for more than 3 days under white fluorescent lamps), while the deactivated properties were fully reactivated by UV-irradiation.