Photoinduced reactivity of titanium dioxide

Ozonation of drinking water: part I. Oxidation kinetics and product formation.

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Water Analysis: Emerging Contaminants and Current Issues

Evaluation of advanced oxidation processes for water and wastewater treatment - A critical review.

The degradation of acid red 14 (AR14), commonly used as a textile dye, can be photocatalysed by ZnO. Using advanced oxidation processes (AOPs), zinc oxide appears to be a suitable alternative to TiO2 for water treatment. In this study, a detailed investigation of photocatalytic degradation of acid red 14 is presented. Photodegradation efficiency was small when the photolysis was carried out in the absence of ZnO and it was also negligible in the absence of UV light. The semi-log plot of dye concentration versus time was linear, suggesting first order reaction (K=0.0548 min−1). The effects of some parameters such as pH, amount of photocatalyst, hydrogen peroxide and ethanol concentration were also examined. The addition of proper amount of hydrogen peroxide improved the decolorization, while the excess hydrogen peroxide could quenched the formation of hydroxyl radicals ( OH). As our results indicated that ethanol inhibited the photodegradation of dye, we concluded from the inhibitive effect of ethanol that hydroxyl radicals played a significant role in the photodegradation of dye. This should not undermine direct oxidation caused by positive holes.

Photocatalytic degradation of azo dye acid red 14 in water on ZnO as an alternative catalyst to TiO2

Acetone is a significant pollutant in contaminated groundwaters and industrial effluents. It can be treated by the UV/H2O2 process but only slowly. This study aims to understand the degradation mechanism and hence the reasons for slow treatment. The degradation of acetone was carried out in a UV reactor in the presence of ∼16 mM H2O2 such that most of the UV was absorbed by H2O2. The decay of acetone was followed by gas chromatography, and the generation of intermediates (identified as acetic, formic, and oxalic acids) was followed by ion chromatography. Measurement of the total organic carbon indicated a complete carbon balance throughout the reaction ending in mineralization. A kinetic model, based on an assumed mechanism, was developed that generated a profile of reactants and intermediates in agreement with the experimental data, including the pH profile. The initial concentrations of acetone and hydrogen peroxide strongly affect the initial rate of acetone degradation, but no pH effect was observed i...

Kinetics and mechanism of the degradation and mineralization of acetone in dilute aqueous solution sensitized by the UV photolysis of hydrogen peroxide

Methyl tert-butyl ether (MTBE) is a pollutant often found in groundwaters contaminated by gasoline spills or from leaking underground storage tanks. The common techniques often used for the remedia...

UV/H2O2 Treatment of Methyl tert-Butyl Ether in Contaminated Waters

1,4-Dioxane is an EPA priority pollutant often found in contaminated groundwaters and industrial effluents. The common techniques used for water purification are not applicable to 1,4-dioxane, and the currently used method (distillation) is laborious and expensive. This study aims to understand the degradation mechanism of 1,4-dioxane and its byproducts in dilute aqueous solution toward complete mineralization, by using the UV/H2O2 process in a UV semibatch reactor. The decay of 1,4-dioxane generated several intermediates identified and quantified as aldehydes (formaldehyde, acetaldehyde, and glyoxal), organic acids (formic, methoxyacetic, acetic, glycolic, glyoxylic, and oxalic) and the mono- and diformate esters of 1,2-ethanediol. Measurement of the total organic carbon (TOC) during the treatment indicated a good agreement between the experimentally determined TOC values and those calculated from the quantified reaction intermediates, ending in complete mineralization. A reaction mechanism, which accoun...

Mechanism of the Degradation of 1,4-Dioxane in Dilute Aqueous Solution Using the UV/Hydrogen Peroxide Process

The quantum yield (QY) of the iodide–iodate chemical actinometer (0.6 M KI–0.1 M KIO3) was determined for irradiation between 214 and 330 nm. The photoproduct, triiodide, was determined from the increase in absorbance at 352 nm, which together with a concomitant measurement of the UV fluence enabled the QY to be calculated. The QY at 254 nm was determined to be 0.73 ± 0.02 when calibration was carried out against a National Institute of Standards and Technology traceable radiometer or photometric device. At wavelengths below 254 nm the QY increased slightly, leveling off at ∼0.80 ± 0.05, whereas above 254 nm the QY decreases linearly with wavelength, reaching a value of 0.30 at 284 nm. In addition, the QY was measured at different iodide concentrations. There is a slight decrease in QY going from 0.6 to 0.15 M KI, whereas below 0.15 M KI the QY drops off sharply, decreasing to 0.23 by 0.006 M KI. Calibration of the QY was also done using potassium ferrioxalate actinometry to measure the irradiance. These results showed a 20% reduction in QY between 240 and 280 nm as compared with radiometry. This discrepancy suggests that the QY of the ferrioxalate actinometer in this region of the spectrum needs reexamination.

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Quantum Yield of the Iodide–Iodate Chemical Actinometer: Dependence on Wavelength and Concentration¶

The quantum yields for two actinometers have been determined using a tunable laser light source at the National Institute of Standards and Technology (NIST) in Gaithersburg, MD. The power of this light source has been calibrated against an absolute cryogenic radiometer, considered accurate with an uncertainty better than 0.1% at a coverage factor k = 2. The quantum yield at 253.7 nm for the ferrioxalate actinometer was found to be 1.38 ± 0.03, which compares favorably with the value 1.40 ± 0.03 determined by Goldstein and Rabani. The quantum yield at 253.7 nm for the KI/KIO3 actinometer was found to be 0.69 ± 0.02 at 23.5 °C. Again this compares favorably with 0.72 ± 0.03 determined by Goldstein and Rabani and 0.73 ± 0.02 determined by Rahn et al. Based on the determinations to date, including the present investigation, the recommended values for the quantum yields at 253.7 nm are 1.39 ± 0.02 (temperature independent) for the ferrioxalate actinometer and [(0.71 ± 0.02) + (0.0099 ± 0.0004)(t − 24)] for the KI/KIO3 actinometer, where t is the temperature (°C) of the actinometer solution. Finally, a protocol is recommended for the use of the KI/KIO3 actinometer to calibrate radiometer detectors at 253.7 nm.

Determination of the quantum yields of the potassium ferrioxalate and potassium iodide–iodate actinometers and a method for the calibration of radiometer detectors

Mihaela I. Stefan

Papers

Kinetics and mechanism of the degradation and mineralization of acetone in dilute aqueous solution sensitized by the UV photolysis of hydrogen peroxide

UV/H2O2 Treatment of Methyl tert-Butyl Ether in Contaminated Waters

Mechanism of the Degradation of 1,4-Dioxane in Dilute Aqueous Solution Using the UV/Hydrogen Peroxide Process

Quantum Yield of the Iodide–Iodate Chemical Actinometer: Dependence on Wavelength and Concentration¶

Determination of the quantum yields of the potassium ferrioxalate and potassium iodide–iodate actinometers and a method for the calibration of radiometer detectors