Jürg Hoigné

Photometric method for the determination of low concentrations of hydrogen peroxide by the peroxidase catalyzed oxidation of n n diethyl p phenylenediamine dpd

The concentration of hydrogen peroxide (H2O2) in distilled water, drinking water and in different types of surface and rain waters can be easily determined by a photometric method in which N,N-diethyl-p-phenylenediamine (DPD) is oxidized by a peroxidase catalyzed reaction. DPD is available as a commercial reagent. In all waters its oxidation occurs with a stoichiometric factor of 2.0 and leads to an absorbance (at 551 nm) of 21,000 ± 500 M−1cm−1 per H2O2. In the presence of other hydroperoxides H2O2 can be determined by comparison with a blank in which the H2O2 is destroyed with sulfite, and the sulfite residual masked with formaldehyde. The detection limit is 0.2 μg l−1 in distilled water and about 0.3 μg l−1 in most types of natural waters when 10 cm cells and a spectrophometer are used. We consider the DPD method to be a candidate for a standard method for drinking water analysis because it is easy to perform and to calibrate for absolute determinations.

Photolysis of Fe (III)-hydroxy complexes as sources of OH radicals in clouds, fog and rain

Abstract Photolysis of the monohydroxy complex of Fe(III), Fe(OH)2+, has been proposed as a major source of OH radicals in rain. It is also a significant source of OH radicals in clouds and fog, and probably in some acidic surface waters. Fe(OH)2+ is the dominant monomeric Fe(III)-hydroxy complex between pH 2.5 and 5, based on currently available equilibrium constants for Fe(III)-hydroxy complexes. Quantum efficiencies for the photolysis of Fe(OH)2+ are 0.04±0.04 at 313 nm and 0.017±0.003 at 360 nm (293 K, ionic strength = 0.03 M). The measured rate constant for midday June sunlight photolysis of Fe(OH)2+ is 6.3 × 10−4s−1 (half life = 18 min). Model calculations based on measured quantum yields and absorption spectra are in satisfactory agreement with measured sunlight photolysis rates of monomeric Fe(III).

Rate constants of reactions of ozone with organic and inorganic compounds in water—III. Inorganic compounds and radicals

Abstract Second-order rate constants for reactions of ozone with 40 inorganic aqueous solutes are reported. Included are compounds of sulfur (e.g. H2S, H2SO3, HOCH2SO3H), chlorine (e.g. Cl−, HOCl, NH2Cl, HClO2, ClO2), bromine (e.g. Br−, HOBr), nitrogen (e.g. NH3, NH2OH, N2O, HNO2) and oxygen (e.g. H2O2), as well as free radicals (e.g. O2−, OH•). Most of these compounds exhibit an increase in rate constant with increasing pH corresponding to their degree of dissociation. Rate constants are based on ozone consumption rates measured by conventional batch-type or continuous-flow methods (10−3-10+6 M−1 s−1 range) and determinations of stoichiometric factors. Also listed are data determined by pulse-irradiation techniques using kinetic spectroscopy (1010 M−1 s−1 range). Additional literature data are reviewed for completeness. Results are discussed with respect to water treatment and environmental processes.

Chemistry of Aqueous Ozone and Transformation of Pollutants by Ozonation and Advanced Oxidation Processes

Ozonation is widely and successfully applied for many types of oxidative water treatments. Its chemical effects can be described by considering the sequences of highly selective direct reactions of molecular ozone and the reactions of the more reactive but less selective OH radicals which are always produced from decomposed ozone in aqueous systems. These radicals also control the ozone based AOPs (Advanced Oxidation Processes). In some cases even formation and reactions of additional secondary oxidants, such as carbonate radicals, hypobromite, and hydrogen peroxide have to be accounted for.

Activated Carbon and Carbon Black Catalyzed Transformation of Aqueous Ozone into OH-Radicals

Abstract In an ozone-containing water a suspension of a few milligrams per liter of activated carbon (AQ or carbon black (CB) initiates a radical-type chain reaction that then proceeds in the aqueous phase and accelerates the transformation of O3 into secondary radicals, such as hydroxyl radicals (°OH). This results in an Advanced Oxidation Process (AOP) that is similar to an O3-based AOP involving application of H2O2 or UV-irradiation. We have studied these phenomena by observing the effect of suspensions of AC and CB on the rate of transformation of O3 in lakewater and in well-characterized solutions. In addition, the stoichiometric yield factor of the AC-catalyzed conversion of O3, into °OH has been shown to be comparable to that which is achieved by a slower process in the absence of AC. This comparison has been based on the measured depletion of an O3-resistant organic °OH probe that was added as a trace reference compound and that competed with a kinetic excess of solutes that controlled the lifetim...

Photo-sensitized oxidation in natural water via OH radicals

A method is presented for determining production and consumption rates of .OH radicals produced photochemically in natural surface waters. It is based on the determination of the kinetics by which the concentration of a specified trace compound decreases during irradiation. In samples from Lake Greifensee (Switzerland) low production rates for .OH limit its possible effects. In addition, fast consumptions by the natural dissolved organic solutes and by the bicarbonate protect organic micropollutants from oxidation by .OH. Neither direct nor indirect H2O2 photolysis was a significant source of .OH in the lakewater studied lacking iron, whereas nitrate photolysis could have been a source. Comparison with reaction kinetic formulations allows generalizations for other types of waters.

Kinetics of reactions of chlorine dioxide (OClO) in water—I. Rate constants for inorganic and organic compounds

The kinetics of chlorine dioxide consumption by a wide range of inorganic and organic compounds, including a comprehensive series of phenols, have been determined using conventional batch-type and stopped-flow methods. In all cases, the rate law was first-order in chlorine dioxide and first-order in substrate. The methods allowed us to determine second-order rate constants over a range from 10−5 to 105 M−1s−1. Measured rate constants were high for nitrite, hydrogen peroxide, ozone, iodide, iron (II), and, whenever the pH was not very low, for phenolic compounds, tertiary amines, and thiols. Bromide, ammonia, structures containing olefinic CC double bonds, aromatic hydrocarbons, primary and secondary amines, aldehydes, ketones and carbohydrates were unreactive under conditions of water treatment. For substrates that are weak acids, such as phenols, or weak bases, the effect of pH on the reaction rate showed that the rate constants for the deprotonated compounds are much higher than those for the protonated species.

The role of copper and oxalate in the redox cycling of iron in atmospheric waters

During daytime, the redox cycling of dissolved iron compounds in atmospheric waters, and the related in-cloud transformations of photooxidants, are affected by reactions of Fe and Cu with hydroperoxy (HO2) and superoxide (O2−) radicals and the photoreduction of Fe(III)-oxalato complexes. We have investigated several of the important chemical reactions in this redox cycle, through laboratory simulation of the system, using γ-radiation to produce HO2/O2−. At concentrations comparable to those measured in atmospheric waters, the redox cycling of Fe was dramatically affected by the presence of oxalate and trace concentrations of Cu. At concentrations more than a hundred times lower than Fe, Cu consumed most of the HO2/O2−, and cycled between the Cu(II) and Cu(I) forms. Cu+ reacted with FeOH2+ to produce Fe(II) and Cu(II), with a second order rate constant of approximately 3 × 107 M−1s−1. The presence of oxalate resulted in the formation of Fe(III)-oxalato complexes that were essentially unreactive with HO2/O2−. Only at high oxalate concentrations was the Fe(II)C2O4 complex also formed, and it reacted relatively rapidly with hydrogen peroxide (k = (3.1 ± 0.6) × 104 M−1s−1). Simulations incorporating measurements for other redox mechanisms, including oxidation by ozone, indicate that, during daytime, Fe should be found mostly in the ferrous oxidation state, and that reactions of FeOH2+ with Cu(I) and HO2/O2−, and to a lesser degree, the photolysis of Fe(III)-oxalato complexes, are important mechanisms of Fe reduction in atmospheric waters. The catalytic effect of Cu(II)/Cu(I) and Fe(III)/Fe(II) should also significantly increase the sink function of the atmospheric liquid phase for HO2 present in a cloud. A simple kinetic model for the reactions of Fe, Cu and HO2/O2−, accurately predicted the changes in Fe oxidation states that occurred when authentic fogwater samples were exposed to HO2/O2−.

Rate constants for reactions of singlet oxygen with phenols and other compounds in water

Abstract Rate constants for some environmentally important organic model compounds reacting with singlet oxygen in water have been determined in laboratory experiments using rose bengal as a sensitizer. Dimethylfuran, furfuryl alcohol, 2,3-dimethyl-2-butene and diethylsulfide react about three times faster in water than in non-aqueous solutions. Phenolic compounds react faster at higher pH values. Their rate constants exactly increase with their degree of dissociation. Rate constants for the ionized species of these phenolic compounds are greater than 10 8 M −1 s −1 . In natural surface water under solar irradiation reaction with singlet oxygen is important only for a few classes of especially reactive organic compounds.

Inter-calibration of OH radical sources and water quality parameters

OH radicals are the key oxidants that control most Advanced Oxidation Processes (AOPs) currently applied in water technology and that also occur in some natural systems such as cloud waters. The efficiencies of the various OH radical sources can be experimentally quantified and compared when they are calibrated by following the oxidation of inter-calibrated reference compounds that react during the process only with OH radicals. To apply and generalize the results, however, water quality parameters controlling the lifetime of OH radicals via OH-scavenging reactions by pollutants and further solutes must also be quantified by methods that allow for calibrations.