Abatement of an Azo Dye on Structured C-Nafion/Fe-Ion Surfaces by Photo-Fenton Reactions Leading to Carboxylate Intermediates with a Remarkable Biodegradability Increase of the Treated Solution

A novel C-Nafton/Fe-ion structured fabric capable of mediating Orange II decomposition in Fenton-immobilized photoassisted reactions is presented. The catalyst preparation requires the right balance between the amount of the Nafion necessary to protect the C-surface and the minimum encapsulation of the Fe-cluster catalytic sites inside the Nafion to allow the photocatalysis to proceed. The C-Nafion/Fe fabric can be used up to pH 10 under light to photocatalyze the disappearance of Orange II in the presence of H2O2. The photocatalysis mediated by the C-Nafion/Fe-ion fabric increased with the applied light intensity and reaction temperature in the reaction needing an activation energy of 9.8 kcal/mol. This indicates that ion- and radical-molecule reactions take place during Orange II disappearance. The build up and decomposition of intermediate iron complexes under light involves the recycling of Fe2+ and was detected by infrared spectroscopy (FTIR). This observation, along with other experimental results, allows us to suggest a surface mechanism for the dye degradation on the C-Nafion/Fe-ion fabrics. The C-Nafion/Fe-ion fabric in the presence of H2O2 under solar simulated light transforms the totally nonbiodegradable Orange II into a biocompatible material with a very high BOD5/COD value. X-ray photoelectron spectroscopy (XPS) and sputtering by Ar+-ions of the upper surface layer of the C-Nafion/Fe-ion fabric allow us to describe the intervention of the photocatalyst down to the molecular level. Most of the Fe clusters examined by transmission electron microscopy (TEM) showed particle sizes close to 4 nm due to their encapsulation into the Gierke cages of the Nafion thin film observed by scanning electron microscopy (SEM) and optical microscopy (OM)

Photocatalytic Storing Of O2 As H2o2 Mediated By High Surface Area Cuo. Evidence For A Reductive-oxidative Interfacial Mechanism

CuO powders with a high specific surface area are shown to be able to produce H2O2 in aqueous solution under simulated light irradiation. The highest rate of peroxide production was observed under mild experimental conditions using O2 and a large surface area photocatalyst CuO irradiated with a solar simulator having light intensities between 60 and 90 mW/cm2. The CuO employed had a specific surface area (SSA) of 64.8-70.1 m2/g and was prepared in a tubular furnace by controlled thermal decomposition of precipitated copper oxalate. The CuO particles produced were 1 μm cubes with primary particles around 15 nm. No peroxide was produced under the same conditions with commercial CuO, with SSA 200 times lower. The CuO synthesized during this work was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), specific surface area [Brunauer-Emmett-Teller (BET)], porosity, and X-ray photoelectron spectroscopy (XPS). From XPS, it was observed that only CuII was present in the unused and used CuO. This indicates that the redox transient species involving other Cu oxidation states disappear very fast during the reaction, regenerating CuII during H2O2 production. Diverse experiments provided some evidence for the possible interfacial reaction mechanism leading to H2O2, following the initial step of O2 - formation on the CuO surface under irradiation with photons, with energies exceeding the band gap of CuO. A photocatalyzed degradation of a concentrated 4-chlorophenol (4-CP) solution was observed under solar-simulated light in the presence of CuO. © 2005 American Chemical Society.211885548559Karlin, D.K., Gulneth, Y., (1987) Progress in Inorganic Chemistry, 35, pp. 220-237. , Lippard, S., EdTolman, B.W., (1997) Acc. Chem. Res., 30, pp. 227-240Lockwood, A.M., Blubaugh, J.T., Collier, M.A., Lovell, S., Mayer, M.J., (1999) Chem. Int. Eng., 38, pp. 225-227Puzari, A., Baruah, J., (2002) J. Mol. Catal. A: Chem., 187, pp. 149-162Agterberg, F., Driessen, W., Reedjik, J., Buijs, W., (1994) New Developments in Selective Oxidation II, 82, pp. 6396-16346. , Cortés, V., Bellon, S., Eds.Elsevier Sci.: Amsterdam, The NetherlandsLouloudi, M., Mitopoulou, K., Evagelou, E., Delihiannakis, Y., Hadjiliadis, N., (2003) J. Mol. Catal. A: Chem., 198, pp. 231-240Meunier, B., (1992) Chem. Revs., 92, pp. 1411-1417Schweigert, N., Acero, J., Von Gunten, U., Canonica, S., Zehnder, A., Eggen, R., (2000) Environ. Mol. Mutagen., 36, pp. 5-12Pate, J.E., Cruse, R.W., Karlin, K.D., Solomon, E.I., (1987) J. Am. Chem. Soc., 109, pp. 2624-2630Pate, J.E., Ross, P.K., Thamann Th, J., Reed, C.A., Karlin, K.D., Sorrell Th, N., Solomon, E.I., (1989) J. Am. Chem. Soc., 111, pp. 5198-5209Clerici, M., Ingallina, P., (1998) Catal. Today, 41, p. 351Kohler, A.M., Curry-Hyde, A.E., Hughes, B.A., Sexton, N.W., (1997) J. Catal., 108, pp. 323-332Toyir, J., Ramirez, P., Fierro, J., Homs, N., (2001) Appl. Catal. B, 29, pp. 207-215Zhou, J., Kang, C.Y., Chen, A.D., (2003) J. Phys. Chem. B, 107, pp. 6664-6667Sun, K., Liu, J., Browning, N., (2002) Appl. Catal. B, 38, pp. 271-281Bandara, J., Kiwi, J., Pulgarin, C., Peringer, P., Pajonk, H.-G., Elalui, A., Albers, P., (1996) Environ. Sci. Technol., 30, pp. 1261-1267Barret, P., Joyner, L., Halenda, P., (1951) J. Am. Chem. Soc., 73, pp. 1371-1380Wagner, C.D., (1989) Handbook of X-ray Photoelectron Spectroscopy, , Perkin-Elmer Corp.: Eden Pairie, MNWagner, C.D., (1990) Practical Surface Analysis, 1, p. 597. , Briggs, D., Seah, P., Eds.Wiley-Interscience: Chichester, U.KShirley, D.A., (1972) Phys. Rev. B, 5, pp. 4709-4714Hardee, K., Bard, A., (1977) J. Electrochem. Soc., 124, pp. 215-224Crompton, R.T., (1997) Toxicants in the Aqueous Ecosystem, , John Wiley and Sons: New YorkBielski, J.B., Cabelli, D., Arudi, R., Ross, A., (1985) J. Phys. Chem. Ref. Data, 14, pp. 1041-1061Goldstein, S., Czapski, G., Meyerstein, D., (1990) J. Am. Chem. Soc., 112, pp. 6489-6493Titus-Pera, M., Molina-Garcia, V., Banos, M., Gimenes, J., Esplugas, S., (2004) Appl. Catal. B, 47, pp. 219-246Sabhi, S., Kiwi, J., (2001) Water Res., 35, pp. 1994-2002Kiwi, J., Lopez, A., Nadtochenko, V., (2000) Environ. Sci. Technol., 34, pp. 3277-3284Graetzel, J., Kiwi, J., Morrison, C., Davidson, S., Tseung, A., (1985) J. Chem. Soc., Faraday Trans. 1, 81, pp. 1883-189

Evolution of toxicity during melamine photocatalysis with TiO2 suspensions

The fate of melamine has been studied under UV light irradiation (medium pressure mercury arc) in the presence of TiO2 and H2O2. The increase in the concentration of aromatic and aliphatic photo-products were determined in solution concomitantly with the decrease observed for the melamine concentration. The main intermediate products occurring during photodegradation were identified by liquid chromatography coupled mass spectrometry (LC-MS) with the MS detection in positive and negative ions. The oxidation of melamine under UV-irradiation in the presence of H2O2 proceeds step by step leading to ammeline, ammelide, and finally to cyanuric acid. The mineralization of melamine was not observed due to the formation of cyanuric acid as intermediate photo-product. The adsorption of melamine on TiO2 was found to vary with the pH of the suspension increasing at pH > 5 due to the charge-exchange transfer between the adsorbent and the adsorbate. Two different bioassays using Vibrio fischeri and Daphnia magna have been used to test the evolution of toxicity during the UV/TiO2/H2O2 treatment. The toxicity of the initial melamine solution seems to increase due to the intermediates generated in solution. (C) 2004 Elsevier B.V. All rights reserved

Photocatalytic Storing of O2 as H2O2 Mediated by High Surface Area CuO. Evidence for a Reductive-Oxidative Interfacial Mechanism

CuO powders with a high specific surface area are shown to be able to produce H2O2 in aqueous solution under simulated light irradiation. The highest rate of peroxide production was observed under mild experimental conditions using O2 and a large surface area photocatalyst CuO irradiated with a solar simulator having light intensities between 60 and 90 mW/cm2. The CuO employed had a specific surface area (SSA) of 64.8-70.1 m2/g and was prepared in a tubular furnace by controlled thermal decomposition of precipitated copper oxalate. The CuOparticles produced were 1 μmcubes with primary particles around 15 nm. No peroxide was produced under the same conditions with commercial CuO, with SSA 200 times lower. The CuO synthesized during this work was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), specific surface area [Brunauer-Emmett-Teller (BET)], porosity, and X-ray photoelectron spectroscopy (XPS). From XPS, it was observed that only CuII was present in the unused and used CuO. This indicates that the redox transient species involving other Cu oxidation states disappear very fast during the reaction, regenerating CuII during H2O2 production. Diverse experiments provided some evidence for the possible interfacial reaction mechanism leading to H2O2, following the initial step of O2-‚ formation on the CuO surface under irradiation with photons, with energies exceeding the band gap of CuO. A photocatalyzed degradation of a concentrated 4-chlorophenol (4-CP) solution was observed under solar-simulated light in the presence of CuO

Photocatalytic storing of O-2 as H2O2 mediated by high surface area CuO. Evidence for a reductive-oxidative interfacial mechanism

CuO powders with a high specific surface area are shown to be able to produce H2O2 in aqueous solution under simulated light irradiation. The highest rate of peroxide production was observed under mild experimental conditions using 02 and a large surface area photocatalyst CuO irradiated with a solar simulator having light intensities between 60 and 90 mW/cm(2). The CuO employed had a specific surface area (SSA) of 64.8-70.1 m(2)/g and was prepared in a tubular furnace by controlled thermal decomposition of precipitated copper oxalate. The CuO particles produced were mu m cubes with primary particles around 15 nm. No peroxide was produced under the same conditions with commercial CuO, with SSA 200 times lower. The CuO synthesized during this work was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), specific surface area [Brunauer-Emmett-Teller (BET)], porosity, and X-ray photoelectron spectroscopy (XPS). From XPS, it was observed that only Cu-II was present in the unused and used CuO. This indicates that the redox transient species involving other Cu oxidation states disappear very fast during the reaction, regenerating Cull during H2O2 production. Diverse experiments provided some evidence for the possible interfacial reaction mechanism leading to H2O2, following the initial step of O-2(-). formation on the CuO surface under irradiation with photons, with energies exceeding the band gap of CuO. A photocatalyzed degradation of a concentrated 4-chlorophenol (4-CP) solution was observed under solar-simulated light in the presence of CuO.21188554855