Kayo Nohara

Processes of formation of NH4+ and NO3− ions during the photocatalyzed oxidation of N-containing compounds at the titania/water interface

Nitrogen-containing substrates such as amino acids, amides, succinimide, imidazole, hydroxylamine and urea were photodegraded in illuminated TiO2 suspensions, and the temporal course of formation of NH4+ and NO3− ions was monitored. The hydroxylated nitrogen moiety in a molecule was predominantly converted to NO3− ions, whereas a primary amine and/or an amide were exclusively transformed to NH4+ ions under the prevailing conditions. Heterocyclic nitrogen groups in imidazole were converted to both NH4+ and NO3− ions via the intermediates whose structures were the primary amine and hydroxylamine, respectively. The influence of chemical structure on formation of NH4+ and NO3− ions is discussed from the view point of adsorption behaviours of substrates onto the TiO2 surface.

Photo-oxidative degradation of the pesticide permethrin catalysed by irradiated TiO2 semiconductor slurries in aqueous media

Abstract The organochlorine pesticide permethrin can be photodegraded into Cl− and CO2 with TiO2 semiconductor catalyst. The aromatic moiety in permethrin is easily cleaved approximately via apparent first-order kinetics. The aromatic ring opening rate (1.73 × 10−3 min−1) is nearly identical with the dechlorination rate (1.82 × 10−3 min−1). The presence of the TiO2 catalyst, UV irradiation and oxygen gas are essential for photo-oxidation at a reasonable rate. The insoluble permethrin (in water) can be efficiently photodegraded in a TiO2 slurry of hexane-water mixture under solar exposure with high conversion (more than 90%), even at high concentration (17 000 ppm), in 8 h on a sunny day. The hydrophobic TiO2 catalyst (T-805 modified by octyltrimethoxyl silane gives more effective photocatalytic activity than the naked TiO2 (P-25).

Dependence on chemical structure of the production of NH 4 + and/or NO 3 −3 ions during the photocatalyzed oxidation of nitrogen-containing substances at the titania/water interface

The dependence of the formation of NH4+ and/or NO3− ions on chemical structure has been examined in TiO2 photocatalyzed oxidations of various amino acids, amides, and nitrogen-heterocyclic compounds. The primary amino groups and the amide moiety are converted photocatalytically and predominantly to NH4+ ions, whereas the hydroxylamino group in N-hydroxysuccinimide is photoconverted predominantly to NO3− ion. Results show that the nitrogen at the 1-position in imidazole is mainly photoconverted to NH4+ ion by analogy with the equivalent nitrogen atom in pyrrole; the nitrogen at the 3-position is transformed into NO3− ion. Formation of ammonium ions is faster than formation of nitrate ions in all but the N-hydroxysuccinimide substrate.

Photodegradation of surfactants XIV. Formation of NG4+ and NO3− ions for the photocatalyzed mineralization of nitrogendashcontaining cationic, nondashionic and amphoteric surfactants

The photo-oxidation of cationic, nondashionic and amphoteric nitrogendashcontaining surfactants (ndashdodecylpyridinium chloride (DPC) and benzyl-tetradecyldimethyl-ammonium chloride (BTDAC); dodecanoyl-ndash(2-hydroxyethyl) amide (ndashDHA) adn dodecanoyl-N,ndashbis(2 hydroxyethyl) amide (N,ndashDHA); dodecyl-β-alanine (C12-β-Ala) and ndash(2-hydroxydodecyl)-ndash(2-hydroxyethy)- β-alanine (C12-βHAA)) was examined in UV-illuminated, air-equilibrated aqueous titania suspensions. Variations in the surface tension of the photo-oxidized surfactant solutions were monitored as a function of the irradiation time. The formation of ammonium and nitrate ions, together with the evolution of carbon dioxide, was investigated for the various surfactant chemical structures to obtain mechanistic information on the mineralization pathways. The yield of NH4+ ions was 4–13 times greater than yield of NO3+ ions. The amount of NH4+ ions formed depends on the structures of the surfactants. Mechanistic details of the photocleavage of the alkyl chains were inferred by probing the oxidation of sodium dodecanoate. The intermediates formed during the temporal photomineralization of the surfactant species were identified by high-frequency Fourier transform (FT) proton nuclear magnetic resonance (NMR) spectroscopy.

Photodegradation of surfactants IX: The photocatalysed oxidation of polyoxyethylene alkyl ether homologues at TiO2-water interfaces

Abstract The photocatalysed mineralization of the non-ionic surfactants polyoxyethylene alkyl ethers (CnEm, n = 10, 12, 14, 16 and 18 and m = 5, 6, 7, and 8) has been investigated in an UV-illuminated heterogeneous TiO2 suspension under aerated conditions. The temporal course of the photo-oxidation of these surfactants was monitored by a dye extraction spectroscopic procedure. The formation of peroxide and carbonyl intermediates and their ultimate mineralization of CO2 were also examined. As the ethoxyl chain length of C12Em homologues increases, the degradation rate which occurs via pseudo-first-order kinetics decreases in the order C12E5 > C12E6 > C12E7 > C12E8. The CnE8 homologues (n = 10, 12, 14, 16 and 18) exhibit the same degration tendencies irrespective of the alkyl chain length. In the competitive photodegration of the polyethoxyl moiety and the long alkyl chain, the ethoxyl chain is more easily cleaved than the alkyl group. Complete mineralization of the surfactants was evidenced by monitoring the stoichiometric evolution of CO2 originating mostly from the ethoxyl moiety of C12Em after irradiation for 20 h. The initial photo-oxidation occurs sequentially one by one from the terminal position of the ethoxyl chain. The participation of ·OH radicals in the photo-oxidation process was determined using 5,5-dimethyl-1-pyrroline-1-oxide spin-trapping electron spin resonance measurements.

Photocatalyzed degradation of polymers in aqueous semiconductor suspensions. I. Photooxidation of solid particles of polyvinylchloride

The photocatalyzed oxidative decompositions of solid particles of polyvinylchloride (PVC; size about 100 to 200 μm), of the polyvinylidene chloride copolymer (95% PVC/5% PVLC; size ∼ 400–600 μm), and a PVC film have been examined in suspensions of titania and zinc oxide illuminated by UV light and/or by natural sunlight. Dechlorination and evolution of carbon dioxide were monitored, the latter occurring by the intermediacy of acetic and formic acids. The photodegradation of polymer specimens was enhanced in TiO2/water media by such added oxidants as hydrogen peroxide and potassium persulfate. Photocorrosion of these particulates was also examined by scanning electron microscopy.

A mechanistic study of the photoelectrochemical oxidation of organic compounds on a TiO2/TCO particulate film electrode assembly

The photo-oxidative degradation of sodium benzene sulfonate, 2-phenoxyethanol, ethyleneglycol, diethyleneglycol, acetic acid and formic acid, was examined on a TiO2 particulate film immobilized on a transparent conductive oxide (TCO) glass electrode assembly. The photocurrents generated during the photodegradation of these organic compounds were monitored. Formation of intermediate species (acetic acid and formic acid) during the temporal course of the photo-oxidative process(es) appears to have a direct effect on the photocurrents.

Photocatalytic degradation of the hydrophobic pesticide permethrin in fluoro surfactant / TiO2 aqueous dispersions

The hydrophobic permethrin can be easily photodecomposed into CO2 and Cl− ions in a fluoro surfactant / TiO2 aqueous dispersion, since permethrin can be solubilized in the micellae of non-photodegradable fluoro surfactants. The aromatic cleavage, dechlorination and CO2 evolution rates in the degradation of permethrin with the pure TiO2 (P-25) catalyst increase in the order of cationic surfactant < water < anionic surfactant system. Those with the modified TiO2 (T-805) catalyst increase in the order of anionic surfactant < water < cationic surfactant system.

Photodegradation of surfactants. XV: Formation of SO42− ions in the photooxidation of sulfur-containing surfactants

Abstract Three types of surfactants and related reference compounds containing sulfonate (-SO 3 Na), sulfate (-OSO 3 Na) or thioether carboxylate (-S-Cn-COOK) group were photodecomposed in an aqueous heterogeneous dispersion system. The photomineralization to SO 4 2− ions was examined for the surfactants with different chemical structures. The photocatalytic activities of TiO 2 and ZnO were compared for the sulfonates of dodecylbenzene sulfonate (DBS) and polystyrene sulfonate (PSS), the sulfates of sodium dodecyl sulfate (SDS), and the potassium salts of S-dodecylthioglycol acid (TGA), S-dodecylthiopropionic acid (TPA) and S-dodecylthiomalic acid (TMA). ZnO catalyst exhibited higher activity in the formation of SO 4 2− ion than TiO 2 catalyst.

Photocatalyzed mineralization of nitrogen-containing compounds at TiO2/H2O interfaces

Abstract The photodegradation of two compounds containing multi-nitrogen atoms, azobisformamidoacetic acid (AFAA) and trihydrazinotriazine (THTA), was examined in aerated aqueous TiO 2 dispersions under UV irradiation. The photocleavage of the conjugated double bond in AFAA and of the ring containing heteronitrogen atoms in THTA was monitored by UV/Vis spectroscopy and the mineralization products (CO 2 , N 2 , NH + 4 and NO − 3 ) in the photodegradation processes were determined by gas chromatography and ion liquid chromatography. The photocatalytic kinetics and a possible mechanism for the partial degradation are also discussed on the basis of the experimental results.