Jincai Zhao

Photodegradation of surfactants: Part vi complete photocatalytic degradation of anionic, cationic and nonionic surfactants in aqueous semiconductor dispersions

Abstract Various kinds of anionic ( e.g ., C 12 -DBS, C 12 -DS, C 12 -LES-3, C 14 -AOS, and C 12 -DG), cationic ( e.g ., C 16 -HTAB and C 12 -BDDAC) and nonionic ( e.g ., NPE n (n = 7, 9, 17, 50), C 18 -PEA-15, C 12–14 -BHA, C 12–14 -PAE-10, C 12–14 -NOE and C 14–16 -NOE) surfactants have been photodegraded in a heterogeneous dispersion of TiO 2 semiconductor particles under UV illumination. These surfactants are ultimately converted to CO 2 . A relationship between the structure of surfactants and the photodegradation rate is indicated in a comparison of the results with literature studies of biodegradation. CO 2 evolution from the photooxidation of anionic surfactants is faster than that observed from cationic surfactants in the initial stages of irradiation (2h). The nonionic surfactants photodegrade more slowly, evolving CO 2 at about 20% mineralization yield. UV-illuminated titanium dioxide affords strongly oxidizing catalytic sites, irrespective of the structure of surfactant.

Fate of amino acids upon exposure to aqueous titania irradiated with UV-A and UV-B radiation Photocatalyzed formation of NH3, NO3−, and CO2

Abstract The fate of nitrogen in various amino acids was examined following their photooxidative (and/or reductive) transformation catalyzed by UV-A and UV-B illuminated aqueous TiO 2 dispersions. The nitrogens in the amino acids are photoconverted predominantly into NH 3 (analyzed as NH 4 + ) and to a lesser extent into NO 3 − ions; NH 4 + /NO 3 − ratios span the range 3–12 after ca. 8 h irradiation. Extensive evolution of CO 2 is also observed; in some cases it is quantitative. Variations in the NH 4 + /NO 3 − ratio in the transformation of amino acids are dependent on the substrates molecular structure. Some of the steps in an otherwise complex mechanism of the heterogeneous photocatalyzedmineralization are described.

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).

Heterogeneous photocatalytic degradation of cyanide on TiO2 surfaces

Abstract A reagent KCN solution and an industrial wastewater containing CN − can be efficiently degraded photocatalytically in aqueous TiO 2 semiconductor dispersions. The disappearance of CN − , consumption of O 2 , formation of OCN − an intermediate and ultimate mineralization to CO 2 and N 2 were quantitatively determined. A large-scale photoreactor (5 l) was also manufactured, which is an excellent device for the photodecomposition of a large amount of cyanide.

Photodegradation of surfactants catalyzed by a TiO2 semiconductor

Abstract The photo-oxidation of surfactants catalyzed by a TiO2 semiconductor, which is one of the methods suggested to solve the problem of water pollution, is reviewed on the basis of our earlier reported experimental results. The photodegradation rates of different kinds of surfactants and of various moieties (aromatic, oxyethylene and alkyl groups) in the surfactant structure are discussed. A possible photo-oxidation mechanism at the TiO2/water interface is proposed.

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.

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.

Photodegradation of surfactants X. Comparison of the photo-oxidation of the aromatic moieties in sodium dodecylbenzene sulphonate and in sodium phenyldodecyl sulphonate at TiO2H2O interfaces

Abstract Two isomers of sodium dodecylbenzene sulphonate (DBS) and sodium 12-phenyldodecyl sulphonate (PDS) were photodegraded in heterogeneous TiO 2 dispersions. Aromatic opening rate, CO 2 evolution, and pH variation were examined in the photodegradation process. The photo-oxidation of the aromatic moiety in DBS was faster than that in PDS. Although the photodegradation kinetics can be modelled in terms of the Langmuir—Hinshelwood equation, it was shown earlier that the kinetics data are silent as to surface vs . solution reaction. This notwithstanding, it is agreed here that pre-adsorption precedes the photo-oxidation. The participation of . OH radicals generated at the irradiated TiO 2 ue5f8H 2 O interface in the photo-oxidation process was confirmed by spin-trapping electron spin resonance measurements.