Taizo Sano

Activation of graphitic carbon nitride (g-C3N4) by alkaline hydrothermal treatment for photocatalytic NO oxidation in gas phase

Photocatalytic activity of graphitic carbon nitride (g-C3N4) was significantly improved by an alkaline hydrothermal treatment. The specific surface area of g-C3N4 obtained by heating melamine at 550 °C was only 7.7 m2 g−1, which was too small for it to be utilized as a catalyst for air purification. By the hydrothermal treatment with NaOH solution at 90–150 °C, the surface area was increased up to 65 m2 g−1, and the oxidation rate of nitrogen oxide (NO) under visible light (380 < λ < 480 nm) was increased by 8.6 times. XRD, ESR, elemental analysis and electron microscopy showed that unstable domains of not-well-ordered carbon nitride were removed by hydrolysis to form a mesoporous structure with a higher surface area. Deactivation of g-C3N4 was not observed during the experimental period, although a small part of carbon nitride was decomposed by self-oxidation.

Preparation of a visible light-responsive photocatalyst from a complex of Ti4+ with a nitrogen-containing ligand

An anatase type of TiO2 photocatalyst containing N atoms was synthesized by a new technique using a complex of Ti4+ with a nitrogen-containing ligand as a precursor. The TiO2-like photocatalyst prepared by calcination of a Ti4+–bipyridine complex exhibited high photocatalytic activity for NOx removal under both ultraviolet and visible-light (λ < 645 nm) illumination. The doping of the N atom into the anatase lattice, which is expected from UV-VIS spectroscopy, XRD, and XPS, is inferred as an important factor for the visible light absorption and NOx removal activity under a wide range of visible light illumination. The bipyridine ligand acted as the source of N and C atoms and additionally inhibited sintering of the photocatalyst during heat treatment.

Effect of Pd-photodeposition over TiO2 on product selectivity in photocatalytic degradation of vinyl chloride monomer

Abstract Effects of metal co-catalysts, Pd and Pt, on photocatalytic degradation of vinyl chloride monomer (VCM) were studied. Pd-photodeposited TiO 2 (Pd-TiO 2 ) did not produce any chlorinated organic compounds into the gas phase, while pure TiO 2 produced monochloroacetylchloride and phosgene. The amounts of CO and formic acid formed by Pd-TiO 2 were much smaller than those by TiO 2 , and the CO 2 production proceeded selectively. However, Pd-TiO 2 decomposed VCM more slowly and produced a larger amount of adsorptive chlorinated organic compound, as compared with TiO 2 . Photodeposited Pd is considered to inhibit the VCM decomposition pathway in which the gaseous byproducts are formed by the aid of Cl − ion adsorbed on the photocatalyst. The electron spin resonance (ESR) suggested that the photodeposited Pd suppress the formation of active species, such as Ti 3+ , O 2 − and OH, which are responsible for the formation of gaseous byproducts.

Kinetic study of the formation of cation-excess magnetite

A cation-excess magnetite Fe3+δO4, has been found to form in the range 0.00 < δ < 0.09, in the course of the H2-reduction of magnetite into α-Fe at 300 °C. The formation of the cation-excess magnetite described by (3 +δ)Fe3O4+ 4δH2→ 3Fe3+δO4+ 4δH2O was studied kinetically. In the temperature range 250–350 °C, the rate constants, k1 and k2, were determined for the forward and reverse reactions, respectively. The rate of formation of the cation-excess magnetite depended on the partial pressure of H2 gas. The rate constant, k1, was estimated to be 10–13.8 at 300 °C and the reaction order was 1.11 with respect to the partial pressure of H2O gas. The rate of reverse reaction depended on the partial pressure of H2O vapour and the excess of cations in magnetite, δ. The reaction rate constant k2 was estimated to be 10–2.45 at 300 °C, and the reaction orders were 0.45 and 0.95 with respect to the partial pressure of H2O vapour and the δ value, respectively. The activation energies of the forward and reverse reactions were evaluated to be 63.8 kJ mol–1 and 25.5 kJ mol–1 from the Arrhenius plots.

Removal of high concentration dimethyl methylphosphonate in the gas phase by repeated-batch reactions using TiO2

The aim of our study is to develop apparatuses that use TiO(2) for effective decontamination of air contaminated by Sarin gas. We performed photocatalytic decomposition of gaseous dimethyl methylphosphonate (DMMP) by TiO(2) and identified the oxidization products. The high activity of TiO(2) (0.01 g) was observed under UV-light irradiation and high concentration DMMP (33.5 microM) was removed rapidly. On the other hand, DMMP was not decreased under UV-light irradiation without TiO(2). This indicates that photocatalytic treatment is very effective for the removal of DMMP. Methanol, formaldehyde, formic acid, methyl formate, CO, CO(2) and H(2)O were detected as the primary products. In the gas phase, no highly poisonous substances were detected. In order to examine the performance of photocatalytic activity during long-term reactions, we performed photocatalytic decomposition by repeated-batch reactions using TiO(2). High photocatalytic activities decreased gradually. Meanwhile, the strong adsorption of TiO(2) against DMMP was observed as photocatalytic activities decreased. During the repeated-batch reactions with the sample scaled up (TiO(2): 0.1g), the total amount of removed DMMP reached 968.5 microM by both photocatalytic decomposition and the strong adsorption of TiO(2). These results suggest the possibility of removing large amounts of DMMP.

Reaction mechanism of H2 generation for H2O/Zn/Fe3O4 system

Abstract Several ideas on the reaction mechanism of H2O/Zn/Fe3O4 water splitting system were considered from the aspect of Zn mobility. The vapor deposition of Zn onto the Fe3O4 surface was confirmed by H2 generation reaction with Zn and Fe3O4 set separately. XPS measurements suggested that the surface of Fe3O4 is covered by Zn before the reaction with steam. The rapid reaction process has been supported by this Zn deposition, which greatly enlarges the number of sites of Zn/Fe3O4 pair that is ready to react with steam. In order to keep the Zn from vaporizing off the system, the Zn/Fe3O4 mixture was covered with additional Fe3O4 to capture the Zn vapor. This resulted in improved H2 yield of 99.5%.

A carbon-bearing nickel(II) ferrite: a tailor-made solid reactant for two-step thermochemical water splitting at 300 °C

Carbon-bearing nickel(II) fernte (CBNF) was prepared by repeated decomposition of CO2 on H2-reduced nickel(II) ferrite, and was used in a two-step thermochemical water splitting at 300 °C Gaseous hydrogen could be generated efficiently by the decomposition of water molecules via the redox pair CBNF*/H2O, (CBNF* denotes activated CBNF). The noble material was also characterized by Mossbauer spectroscopy, X-ray diffraction (XRD) and chemical analysis. A peculiar amorphous surface layer composed of carbon, divalent transition metals and oxide ions (CIO layer) was inferred to be responsible for the water-splitting reactivity

Visible light-induced decomposition of a fluorotelomer unsaturated carboxylic acid in water with a combination of tungsten trioxide and persulfate

Photochemical decomposition of a fluorotelomer unsaturated carboxylic acid, C3F7CFCHCOOH (1), in the presence of WO3 and an electron acceptor (S2O8(2-) or H2O2) in water under visible-light irradiation was investigated. Under an O2 atmosphere, 1 was not decomposed either by TiO2 (P25) or WO3 alone. A combination of WO3 and H2O2 also resulted in almost no decomposition of 1. In contrast, irradiation in the presence of a combination of WO3 and S2O8(2-) (potassium salt) efficiently decomposed 1 to F(-), CO2, C3F7COOH, and C2F5COOH. The decomposition of 1 was affected by the counter cation of S2O8(2-): the decomposition extent was higher with K2S2O8 than with (NH4)2S2O8. The decomposition of 1 was further enhanced when the reaction in the presence of WO3 and K2S2O8 was carried out under an argon atmosphere. Under O2, the amount of H2O2 formed in the reaction solution was an order of magnitude higher than the amount formed under argon. This fact suggests that the decrease in the decomposition of 1 under O2 can be ascribed to the formation of H2O2, which consumed S2O8(2-) and SO4(-).

Photocatalytic Solar Tower Reactor for the Elimination of a Low Concentration of VOCs

We developed a photocatalytic solar tower reactor for the elimination of low concentrations of volatile organic compounds (VOCs) typically emitted from small industrial establishments. The photocatalytic system can be installed in a narrow space, as the reactor is cylindrical-shaped. The photocatalytic reactor was placed vertically in the center of a cylindrical scattering mirror, and this vertical reactor was irradiated with scattered sunlight generated by the scattering mirror. About 5 ppm toluene vapor, used as representative VOC, was continuously photodegraded and converted to CO2 almost stoichiometrically under sunny conditions. Toluene removal depended only on the intensity of sunlight. The performance of the solar tower reactor did not decrease with half a year of operation, and the average toluene removal was 36% within this period.

Photochemical effect on reduction of ultrafine (Ni, Zn) ferrite by CO at 300°C

Reduction of ultrafine ZnII ferrite (ZF), (Ni, Zn) ferrite (NZF) and NiII ferrite (NF) with CO was carried out under ultraviolet (UV) irradiation at 300°C to investigate photochemical effects on the redox reaction of ferrites. The rate of reduction of ZF, NZF and NF was increased (130% at maximum) by irradiating with UV light. The electron–hole pairs formed by absorption of the UV light are considered to diffuse thermally to the surface of the ferrite and to assist the reduction of the ferrite at 300°C. The photochemical reduction rate of NZF was larger than those for NF and ZF. The maximal quantum efficiency of the photochemical reduction of NZF was 0.6%.