Environmental remediation by an integrated microwave/UV illumination technique: IX. Peculiar hydrolytic and co-catalytic effects of platinum on the TiO2 photocatalyzed degradation of the 4-chlorophenol toxin in a microwave radiation field

Abstract The photocatalyzed degradation of the 4-chlorophenol toxin (4-CP) in aqueous naked TiO 2 and platinized TiO 2 suspensions simultaneously subjected to UV light and microwave radiation was revisited to examine the fate of this toxin in the microwave-assisted photocatalytic process by monitoring loss of total organic carbon (TOC; mineralization), formation of chloride ions (dechlorination of 4-CP), and identification of intermediates using HPLC and electrospray mass spectral (LC–MSD) techniques. Attempts are made to delineate microwave thermal and nonthermal factors that impinge on the degradation by comparing experimental results from microwave-generated heat versus results from a conventional (externally heated) thermally-assisted process, and from results in which the thermal factors were minimized by examining the degradative process at constant ambient temperature (25 °C). Possible microwave radiation effects on the Pt co-catalyst supported on TiO 2 were also probed through comparison of the degradation of 4-CP occurring on Pt/TiO 2 and on naked TiO 2 photocatalysts. Results suggest that, in a microwave radiation field, naked TiO 2 and Pt/TiO 2 particle surfaces interact with the microwaves. The degradation pathway exhibited characteristics of hydrolysis of reactants and intermediates. Nonthermal microwave effects play a role in the overall degradative process occurring in platinized TiO 2 dispersions. The possible nature of these unusual microwave effects is briefly discussed.

[1]  F. Marken,et al.  Microwave activation of electrochemical processes: enhanced electrodehalogenation in organic solvent media. , 2002, Journal of the American Chemical Society.

[2]  A. Emeline,et al.  Spectral Dependence and Wavelength Selectivity in Heterogeneous Photocatalysis. I. Experimental Evidence from the Photocatalyzed Transformation of Phenols , 2000 .

[3]  R. C. Richter,et al.  Peer Reviewed: Microwave-Enhanced Chemistry , 2001 .

[4]  H. Kamada,et al.  ESR Study of Active Oxygen Radicals from Photoexcited Semiconductors Using the Spin-Trapping Technique , 1992 .

[5]  D. Clark,et al.  Microwaves: Theory and Application in Materials Processing , 1991 .

[6]  S. Horikoshi,et al.  Environmental remediation by an integrated microwave/UV illumination technique: VI. A simple modified domestic microwave oven integrating an electrodeless UV-Vis lamp to photodegrade environmental pollutants in aqueous media , 2004 .

[7]  M. Kang,et al.  Enhanced photodecomposition of 4-chlorophenol in aqueous solution by deposition of CdS on TiO2 , 1999 .

[8]  Y. Nosaka,et al.  Properties of O2.- and OH. formed in TiO2 aqueous suspensions by photocatalytic reaction and the influence of H2O2 and some ions , 2002 .

[9]  W. Jenks,et al.  Photocatalytic Degradation of 4-Chlorophenol. 1. The Hydroquinone Pathway , 1999 .

[10]  A. Emeline,et al.  Spectral Selectivity of Photocatalyzed Reactions Occurring in Liquid−Solid Photosystems , 2002 .

[11]  A. Loupy.  Microwaves in organic synthesis , 2002 .

[12]  S. Horikoshi,et al.  Environmental remediation by an integrated microwave/ UV-illumination method. 1. Microwave-assisted degradation of rhodamine-B dye in aqueous TiO2 dispersions. , 2002, Environmental science & technology.

[13]  Keiichi Tanaka,et al.  Photocatalytic degradation of organochlorine compounds in suspended TiO2 , 1990 .

[14]  R. W. Matthews,et al.  Photo-oxidation of organic material in aqueous suspensions of titanium dioxide , 1986 .

[15]  P. Kamat,et al.  Radiolytic and TiO2-Assisted Photocatalytic Degradation of 4-Chlorophenol. A Comparative Study , 1994 .

[16]  C. Minero,et al.  Photodegradation of dichlorophenols and trichlorophenols in TiO2 aqueous suspensions: kinetic effects of the positions of the Cl atoms and identification of the intermediates , 1993 .

[17]  S. Horikoshi,et al.  Environmental remediation by an integrated microwave/UV illumination method. V. Thermal and nonthermal effects of microwave radiation on the photocatalyst and on the photodegradation of rhodamine-B under UV/Vis radiation. , 2003, Environmental science & technology.

[18]  S. Horikoshi,et al.  Environmental remediation by an integrated microwave/UV-illumination method II.: Characteristics of a novel UV–VIS–microwave integrated irradiation device in photodegradation processes , 2002 .

[19]  J. Lemaire,et al.  Photochemistry and environment , 1984 .

[20]  K. Gray,et al.  Probing photocatalytic reactions in semiconductor systems: Study of the chemical intermediates in 4 -chlorophenol degradation by a variety of methods , 1994 .

[21]  R. W. Matthews.  Purification of water with near-U.V. illuminated suspensions of titanium dioxide , 1990 .

[22]  S. Horikoshi,et al.  Environmental remediation by an integrated microwave/UV illumination technique. 3. A microwave-powered plasma light source and photoreactor to degrade pollutants in aqueous dispersions of TiO2 illuminated by the emitted UV/visible radiation. , 2002, Environmental science & technology.

[23]  Nicholas J. Turro,et al.  A New Method To Determine the Generation of Hydroxyl Radicals in Illuminated TiO2 Suspensions , 1997 .

[24]  Specific activation by microwaves: myth or reality? , 1992 .

[25]  P. Gaillard,et al.  MICROWAVE HEATING AS A NEW WAY TO INDUCE LOCALIZED ENHANCEMENTS OF REACTION RATE. NON-ISOTHERMAL AND HETEROGENEOUS KINETICS , 1996 .

[26]  T. Kitamura,et al.  Microwave-Assisted Hydrogenation of Chlorinated Phenols for Complete Dechlorination , 2000 .

[27]  S. Horikoshi,et al.  Environmental remediation by an integrated microwave/UV-illumination technique: IV. Non-thermal effects in the microwave-assisted degradation of 2,4-dichlorophenoxyacetic acid in UV-irradiated TiO2/H2O dispersions , 2003 .

[28]  W. Jenks,et al.  Photocatalytic Degradation of 4-Chlorophenol. 2. The 4-Chlorocatechol Pathway , 1999 .

[29]  D. Martin,et al.  Microwave-enhanced dechlorination of chlorobenzene , 2003 .

[30]  M. Hoffmann,et al.  Chemical and Physical Characterization of a TiO2-Coated Fiber Optic Cable Reactor , 1996 .

[31]  A. Hiskia,et al.  Comparison of the photoredox properties of polyoxometallates and semiconducting particles , 2001 .

[32]  P. Kamat,et al.  Electrochemically Assisted Photocatalysis. 2. The Role of Oxygen and Reaction Intermediates in the Degradation of 4-Chlorophenol on Immobilized TiO2 Particulate Films , 1994 .

[33]  D. Bahnemann,et al.  Photocatalytic Degradation of 4-Chlorophenol in Aerated Aqueous Titanium Dioxide Suspensions: A Kinetic and Mechanistic Study , 1996 .

[34]  R. Abramovitch,et al.  decomposition of PCBs in soil using microwave energy , 1999 .

[35]  M. Hoffmann,et al.  Mathematical Model of a Photocatalytic Fiber-Optic Cable Reactor for Heterogeneous Photocatalysis , 1998 .

[36]  A. Bard,et al.  Heterogeneous Photocatalytic Preparation of Supported Catalysts. Photodeposition of Platinum on TiO2 Powder and Other Substrates , 1978 .

[37]  E. Papaconstantinou,et al.  On the mechanism of photocatalytic degradation of chlorinated phenols to CO2 and HCl by polyoxometalates , 1996 .

[38]  Y. Nosaka,et al.  Photocatalytic ˙OH radical formation in TiO2 aqueous suspension studied by several detection methods , 2003 .

[39]  S. Horikoshi,et al.  Hydroxyl radicals in microwave photocatalysis. Enhanced formation of OH radicals probed by ESR techniques in microwave-assisted photocatalysis in aqueous TiO2 dispersions , 2003 .

[40]  Nick Serpone,et al.  Environmental remediation by an integrated microwave/UV illumination method: VII. Thermal/non-thermal effects in the microwave-assisted photocatalyzed mineralization of bisphenol-A , 2004 .

[41]  R. Abramovitch,et al.  Decomposition of PCB's and other polychlorinated aromatics in soil using microwave energy , 1998 .

[42]  Junichi Nishino,et al.  Primary Passages for Various TiO2 Photocatalysts Studied by Means of Luminol Chemiluminescent Probe , 1999 .

[43]  Y. Zhang-Steenwinkel,et al.  Dielectric heating effects on the activity and SO2 resistance of La0.8Ce0.2MnO3 perovskite for methane oxidation , 2004 .