The photoelectrocatalytic oxidation of aqueous nitrophenol using a novel reactor
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This paper reports the oxidation of aqueous 4-nitrophenol solutions in a photo-electrochemical bubble column reactor (BCR) in which mass transfer has been shown not to be rate limiting. The work represents the first steps in the scale-up of active photoanodes and efficient reactors for the disinfection and detoxification of water.
The preparation, optimization and application of two types of electrode are described and the results are compared with those for a TiO2 electrode supplied by Ineos Chlor. Photocurrents measured in tap water and in aqueous methanol were used for the initial characterization of the electrodes. The methanol was employed for diagnostic purposes only, as discussed below; methanol can react either by direct hole transfer or by hydroxyl radical recombination, but the balance of these reactions depends upon the nature of the electrode surface. The most active thermal electrodes were fabricated by heating titanium metal in air at 750 °C for 10 min, whilst the most active sol–gel electrodes were heated at 600 °C for 10 min.
Three of the central achievements of the work were to: (1) show that it is possible to design and fabricate photoelectrochemical reactors capable of effecting the mineralization of strongly absorbing organics; (2) confirm that the photocatalytic decomposition of 4-NP in reactors with a 4 dm3 capacity can be increased by the application of a small positive potential and (3) that the application of such a potential significantly enhances the mineralization of 4-NP.
For the mineralization of 0.25 mM nitrophenol solutions the reactivity sequence is:
Photoelectrocatalytic > Photocatalytic > Photochemical > Electrochemical.
However, even at 3 V applied potential, charge recombination is not eliminated. The order of electrode activity was:
Ineos > Sol Gel > Thermal.
Differences between the activities of different electrodes were attributed to changes in the structure and morphology of the TiO2. It is noteworthy that although, for nitrophenol oxidation, the thermal electrodes were the least active, for photoelectrocatalytic disinfection in the same type of reactor, thermal electrodes were the most active.
Keywordsbubble column reactor electric field enhancement nitrophenol photoelectrocatalytic sol–gel TiO2 electrode thermal TiO2 electrode
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- 1.Mills, A., Le Hunte, S. 1997J. Photochem. Photobiol. A1081Google Scholar
- 2.P.A. Christensen and G.M. Walker Opportunities for the UK in Solar Detoxification, ETSU s/P4/00249/REP 1996.Google Scholar
- 4.Goodeve, C.F., Kitchener, J.A. 1938Trans. Faraday Soc34902Google Scholar
- 6.A.L. Pruden and D.F. Ollis, J. Catal. 82 (1983) 404; C.Y. Hsia, C.Y. Lee and D.F. Ollis, J. Catal. 82 (1983) 418.Google Scholar
- 7.Matsunaga, T., Tomada, R., Nakajima, T., Wake, H. 1985Microbiol. Lett29211Google Scholar
- 8.Sun, L., Bolton, J.R. 1996J. Phys. Chem1004127Google Scholar
- 10.Choi, W., Ko, J.Y., Park, H., Chung, J.S. 2001Appl. Cat. B Environ31209Google Scholar
- 11.Wyness, P., Klausner, J.F., Goswami, D.Y. 1994J. Solar. Eng1168Google Scholar
- 12.Crittenden, J.C., Zhang, Y., Hand, D.W. 1996Water Environ. Res68270Google Scholar
- 13.L.M. Peter, in R.G. Compton and A. Hamnett (Eds), Comprehensive Chemical Kinetics, Vol. 29 (Elsevier, Amsterdam, 1989), p. 353 and references cited therein.Google Scholar
- 14.A. Hamnett, in R.G. Compton (Ed.), Comprehensive Chemical Kinetics, Vol. 27 (Elsevier, Amsterdam, 1987), p. 61.Google Scholar
- 15.Gautron, J., Lemasson, P., Marucco, J.F. 1980Far. Disc. Chem. Soc7087Google Scholar
- 18.Harper, J.C., Christensen, P.A., Egerton, T.A., Curtis, T.P., Gunlazuardi, J. 2001J. Appl. Electrochem31623Google Scholar
- 19.Christensen, P.A., Curtis, T.P., Place, B., Walker, G.M. 2002Water Res362410Google Scholar
- 20.K.A. Grey, P. Kamat, U. Stafford and M. Dieckmann, Abstr. Papers Am. Chem. Soc. 203 (1992) 307-ENVR.Google Scholar
- 21.O’Regan, B., Moser, J., Anderson, M., Gratzel, M. 1990J. Phys. Chem948720Google Scholar
- 22.B.D. Cullity, Elements of X-ray Diffraction (Addison-Wesley, 1959).Google Scholar
- 23.Harper, J.C., Christensen, P.A., Egerton, T.A., Scott, K. 2001Appl. Electrochem31267Google Scholar
- 24.T.A. Egerton and P.A. Christensen, in S. Parsons (Ed.), ‘Advanced Oxidation Processes for Water and Wastewater Treatment’ (IWA Publishing, London, 2004), pp. 167–184Google Scholar
- 25.Douglas, D.L., Van Landuyt, J. 1966Acta Metal14491Google Scholar
- 26.Jiang, D., Zhao, H., Zhang, S., John, R. 2003J. Phys. Chem10712774Google Scholar
- 30.Park, H., Choi, W. 2004J. Phys. Chem. B1084086Google Scholar
- 31.Zhang, H.Z., Banfield, J.F. 1998J. Mater. Chem82073Google Scholar
- 32.Salinaro, E.A., Serpone, N. 2000J. Phys. Chem10411202Google Scholar
- 33.Egerton, T.A., King, C.J. 1979J. Oil Col. Chem. Assoc26386Google Scholar
- 35.J.R. Tinlin, Ph. D. Thesis, Newcastle upon Tyne UK (2003).Google Scholar
- 36.Christensen, P.A., Curtis, T.P., Egerton, T.A., Kosa, S.A.M., Tinlin, J.R. 2003Appl. Cat. B Environ41371Google Scholar