Photocatalytic oxidation in the presence of microwave irradiation: observations with ethylene and water (original) (raw)
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Microwaves in advanced oxidation processes for environmental applications. A brief review
Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 2010
This review article focuses, albeit non-exhaustively, on the influence of microwave radiation on photoassisted processes often referred to as Advanced Oxidation Processes. In particular, we describe and illustrate the possible advantages of microwaves in TiO 2 -assisted photodegradations and photomineralizations of various organic pollutants such as herbicides and endocrine disruptors, among others. Described are also various reactor configurations involving UV/visible radiation and microwaves, with the former being supplied either by traditional Hg lamps or alternatively by electrodeless lamps activated by microwaves. To place the use of microwaves on processes occurring in aqueous TiO 2 dispersions in perspective regarding environmental applications, we first introduce the various sources of pollutants and subsequently describe in brief the various advanced oxidation processes such as UV/peroxidation, UV/ozonation and the photo-Fenton process(es) in addition to direct photolysis either by sunlight or by artificial light sources.
Chemical Physics Letters, 2003
Formation of Å OH radicals during TiO 2 photocatalyzed oxidations driven by simultaneous UV and microwave radiation was probed by the electron spin resonance technique employing a novel setup in which the ESR sample (contained the DMPO spin-trap agent and P-25 TiO 2 or pure anatase or pure rutile in aqueous media) could be irradiated by both UV light and microwave radiation; the microwave generator was coupled through an N connector to the ESR sample cavity and to a photoreactor in which phenol was photooxidized by simultaneous irradiation with UV light and microwaves to assess whether the photooxidative process correlated with the concentration of Å OH radicals formed.
Journal of Chemical Technology & Biotechnology, 2009
BACKGROUND: A continuous-flow microwave photocatalytic reactor was set up consisting of a glass tube equipped with microwave powered mercury electrodeless discharge lamps (EDLs) coated with thin films of nanoporous titanium(IV) oxide. The effect of operational parameters on photocatalytic degradation of aqueous mono-chloroacetic acid (MCAA) by a TiO 2 /UV/MW process was investigated. RESULTS: Studies were carried out at a relatively high concentration of MCAA (0.1 mol L −1), and revealed that reaction temperature and light intensity of the EDLs depend inversely on the flow rate, but that the 366 nm line intensity of EDL is directly proportional to the reaction temperature. The photodegradation of MCAA was enhanced by heating and significantly enhanced by air bubbling of the reaction mixture in the glass reservoir at laboratory temperature. The photocatalytic efficiency increased with the number of titania-coated EDLs inserted in the glass tube reactor. CONCLUSIONS: It was found that the operational parameters (i.e. flow rate, reaction temperature, number of titania-coated EDLs, and air bubbling) had important effects on degradation efficiency. The photocatalytic degradation of MCAA on thin films of titanium(IV) oxide in the continuous-flow microwave photoreactor can be enhanced in the TiO 2 /UV/MW system.
Environmental Science & Technology, 2004
The photocatalyzed degradation (PD) of the cationic rhodamine-B (RhB) dye was examined in aqueous TiO 2 dispersions using UV/Vis illumination assisted by microwave radiation (PD/MW). The initial degradation by the PD/ MW method is compared to the PD method and to the thermally assisted PD method using conventional heating (PD/ TH). Total organic carbon (TOC) assays show that the efficiency of complete mineralization of the dye follows PD/ MW > PD/TH > PD > MW. In all cases, microwave radiation alone had no effect on the loss of TOC. The degradation involving microwave radiation was especially efficient when coupled to UV irradiation. By contrast, the extent of degradation of RhB involving suitable excited states through visible irradiation of the dye was rather inefficient when coupled to microwave radiation. Contact angle measurements on the TiO 2 photocatalyst particles indicate that microwave radiation also causes an increase in the hydrophobic character of the TiO 2 surface, with consequences on the adsorption mode of the dye substrate and thus on the overall mechanism of degradation. Deethylated RhB intermediates were identified by an electrospray ESI ionization mass spectral technique in the positive ion mode and subsequently confirmed by HPLC/ absorption spectroscopy. Computer simulations led to estimates of frontier electron densities of all atoms of the RhB structure, affording inferences as to the position of radical attack on RhB. The nitrogen atoms of the dye were all converted to NH 4 + ions. The major difference between the thermally assisted PD/TH method and the microwaveassisted PD/MW method showed that nonthermal effects from the microwave radiation impact significantly on the nature of the photocatalyst surface. These effects led to a more efficient photodegradation and mineralization of the dye substrate.
Photocatalytic oxidation of acetone vapor on TiO2/ZrO2 thin films
Applied Catalysis B: Environmental, 1999
The photocatalytic oxidation of acetone vapor on TiO 2 /ZrO 2 thin films is presented in this study. Acetone conversion data collected using a non-circulating tubular reactor are analyzed using a general power law model and a Langmuir-Hinshelwood-Hougen-Watson (LHHW) model; the LHHW model provides a slightly better fit than the 1/2 order power law model. The effects of reaction temperature and relative humidity on the rate of reaction are presented. Using either kinetic model, increasing the reaction temperature from 30 to 77 • C (in a dry feed stream) significantly increases the reaction rate constant at a 95% confidence level; however, increasing the temperature from 77 to 113 • C does not have a significant effect. The addition of water vapor (50% relative humidity) to the feed stream at 77 • C significantly increases the reaction rate constant at a 95% confidence level. Also, at three different temperatures and a single reaction condition, the conversion of acetone is enhanced in the presence of water vapor. No byproducts are detected in the effluent stream of the photocatalytically active reactor.
Journal of Chemical Technology & Biotechnology, 2012
BACKGROUND: Mercury electrodeless discharge lamps (Hg-EDLs) coated with titania in the form of thin films were used to generate UV/Vis radiation when placed in a microwave field. Effects of additional operational parameters (i.e. initial MCAA concentration, reaction temperature, and the presence of inorganic anions) on the photocatalytic degradation of aqueous mono-chloroacetic acid (MCAA) in a microwave field are discussed. RESULTS: Studies were carried out in atmospheric or low-pressure batch type microwave photocatalytic reactors. The photocatalytic process was monitored by the change in concentration of Cl − in the solution. Coupled UV/MW irradiation led to effective photodegradation at higher MCAA concentration at an optimum value of 0.15 mol L −1. Photocatalytic reaction of MCAA was favoured at higher temperature mainly owing to thermal dependence of the Hg-EDL light intensity on the 366 nm line. Inhibition of MCAA photodegradation was observed in the presence of CO 3 2− and SO 4 2− anions, whereas the effect of NO 3 − was negligible. CONCLUSIONS: It was found that additional operational parameters had important effects on photocatalytic efficiency in a microwave field. The MCAA photodegradation process with titania-coated Hg-EDLs can be enhanced in the TiO 2 /UV/MW system.
Kinetics and Catalysis, 2005
The results of studies on the effect of the preparation procedure on the properties of TiO 2 -based photocatalysts and the kinetics and mechanism of the photocatalytic oxidation of organic water pollutants are surveyed. The effects of calcination temperature, surface modification with platinum, and acid-base treatment of the surface of titanium dioxide on its activity in model gas-phase and liquid-phase reactions are considered. Optimal catalyst preparation conditions were found in order to achieve maximum activity, and conceivable reasons for the effects of the above factors on the activity were revealed. The intermediate products and mechanisms of the photocatalytic and dark reactions of solutes that simulated chemical warfare agents in water are considered. All of the test simulants can undergo complete oxidation to form inorganic products in an aqueous TiO 2 suspension under irradiation with UV light. It was found that, in addition to oxidation, the dark steps of hydrolysis also play an important role in the degradation of these substances. The low-frequency ultrasonic treatment (20 kHz) of a photocatalyst suspension in the course of the photocatalytic oxidation of dimethyl methylphosphonate can accelerate the reaction because of the facilitated transport of reactants to the surface of photocatalyst particles.