Reactions Of Carbonate Radical Research Articles

Efficient organic pollutants conversion and electricity generation for carbonate-containing wastewater based on carbonate radical reactions initiated by BiVO4-Au/PVC system

In this paper, we propose an efficient simultaneous refractory organics degradation and electricity generation method for carbonate-containing wastewater based on carbonate radical reactions initiated by a BiVO4-Au/PVC (PVC: photovoltaic cell) system. In the system, nanoporous BiVO4 film and Au modified PVC were used as photoanode and photocathode, respectively. HCO3− was used as the electrolyte. Carbonate radicals, which have lower recombination rates than hydroxyl radicals and strong oxidation abilities, can be generated easily by the capture reaction of hydroxyl radicals with HCO3−, which is one of the most abundant anions in the aquatic environment. The results show that the removal ratios of rhodamine b, methyl orange and methylene blue in the system increased sharply to 77.98 %, 89.15 % and 93.2 % from 18.23 %, 21 % and 23.14 % (BiVO4-Pt/ SO42-), respectively, after 120 min. Meanwhile, the short-circuit current density is up to 2.19–2.41 times larger than the traditional system. Other common ions in natural water minimally affected the properties of the new system. The excellent performance could be ascribed to large amounts of carbonate radicals in the system, which have great potential for efficient carbonate-containing wastewater treatment and energy recovery.

Serum electrolytes can promote hydroxyl radical-initiated biomolecular damage from inflammation

Chronic inflammatory disorders are associated with biomolecular damage attributed partly to reactions with Reactive Oxygen Species (ROS), particularly hydroxyl radicals (•OH). However, the impacts of serum electrolytes on ROS-associated damage has received little attention. We demonstrate that the conversion of •OH to carbonate and halogen radicals via reactions with serum-relevant carbonate and halide concentrations fundamentally alters the targeting of amino acids and loss of enzymatic activity in catalase, albumin and carbonic anhydrase, three important blood proteins. Chemical kinetic modeling indicated that carbonate and halogen radical concentrations should exceed •OH concentrations by 6 and 2 orders of magnitude, respectively. Steady-state γ-radiolysis experiments demonstrated that serum-level carbonates and halides increased tyrosine, tryptophan and enzymatic activity losses in catalase up to 6-fold. These outcomes were specific to carbonates and halides, not general ionic strength effects. Serum carbonates and halides increased the degradation of tyrosines and methionines in albumin, and increased the degradation of histidines while decreasing enzymatic activity loss in carbonic anhydrase. Serum electrolytes increased the degradation of tyrosines, tryptophans and enzymatic activity in the model enzyme, ketosteroid isomerase, predominantly due to carbonate radical reactions. Treatment of a mutant ketosteroid isomerase indicated that preferential targeting of the active site tyrosine accounted for half of the total tyrosine loss. The results suggest that carbonate and halogen radicals may be more significant than •OH as drivers for protein degradation in serum. Accounting for the selective targeting of biomolecules by these daughter radicals is important for developing a mechanistic understanding of the consequences of oxidative stress.

Degradation of pharmaceuticals in UV (LP)/H2O2 reactors simulated by means of kinetic modeling and computational fluid dynamics (CFD)

UV/H2O2 treatment is a well-established technique to degrade organic micropollutants. A CFD model in combination with an advanced kinetic model is presented to predict the degradation of organic micropollutants in UV (LP)/H2O2 reactors, accounting for the hydraulics, fluence rate, complex (photo)chemical reactions in the water matrix and the interactions between these processes. The model incorporates compound degradation by means of direct UV photolysis, OH radical and carbonate radical reactions. Measurements of pharmaceutical degradations in pilot-scale UV/H2O2 reactors are presented under different operating conditions. A comparison between measured and modeled degradation for a group of 35 pharmaceuticals resulted in good model predictions for most of the compounds. The research also shows that the degradation of organic micropollutants can be dependent on temperature, which is relevant for full-scale installations that are operated at different temperatures over the year.

Predicting pharmaceutical degradation by UV (MP)/H2O2 processes: A kinetic model

A kinetic model for the degradation of organic micropollutants (OMPs) by MP UV lamps has been developed. The model includes (photo)chemical reactions of hydrogen peroxide and nitrate; reactions with the most important water matrix components; changes in pH; and transient radical concentrations. Three pathways of organic micropollutant degradation are involved: direct photolysis, hydroxyl radical reactions and carbonate radical reactions. The model was validated using collimated beam experiments for a group of 35 pharmaceuticals in synthetic and natural water matrices. For MP UV with 10mg/L H2O2, good agreement between the modelled and measured degradation rates was found. For MP UV without H2O2, most of the pharmaceuticals were well predicted, except for the sulphonamides. A sensitivity analysis on different water matrix constituents was performed for MP UV with H2O2, NO3- and both H2O2 and NO3-. Also, the most important chemical reactions for the degradation of OMPs are identified for different water matrices.

Predicting pharmaceutical degradation by UV (LP)/H2O2 processes: A kinetic model

Abstract Pharmaceuticals and other organic micropollutants are increasingly found in water sources. The UV/H2O2 process is a suitable technology to degrade these pharmaceuticals. A kinetic model is presented to predict pharmaceutical degradation during UV/H2O2 treatment. Reactions with background constituents in the water matrix, such as (bi)carbonate, nitrate and NOM were considered as well as hydroxyl radical and carbonate radical reactions with the pharmaceuticals. The kinetic model is validated by collimated beam experiments. In several water matrices a good agreement between measured and modelled degradation was found, for direct photolysis as well as advanced oxidation. For only 5 of the 36 compounds, the model over or under predicted the measured results. Possible explanations are: pH effects during photolysis and radical scavenging by NOM. The influence of each reaction incorporated in the kinetic model was studied by a sensitivity analysis. The sensitivity study showed that nitrate reactions can also be relevant in UV (LP) applications when there is no hydrogen peroxide and low concentrations of NOM.

Absolute kinetics and reaction efficiencies of hydroxyl-radical-induced degradation of methyl isothiocyanate (MITC) in different quality waters

Methyl isothiocyanate (MITC), a toxic and corrosive skin and respiratory irritant, is a common soil fumigant byproduct which has become an atmospheric, aqueous, and soil contaminant. The work described here examines the degradation and potential removal of MITC from contaminated waters via free radical reactions. We have measured the oxidizing hydroxyl radical ( ·OH) reaction rate constant with MITC over a range of temperatures relevant to wastewater treatment conditions, determining a room temperature value of (5.69 ± 0.56) × 10 8 M −1 s −1 and a corresponding Arrhenius activation energy of 12.90 ± 0.82 kJ mol −1. Hydroxyl radical reaction efficiencies with MITC in pure water, an associated matrix of model real-world waters, and a reverse osmosis permeate water have also been determined. While solutions containing these constituents had significantly decreased MITC removal efficiencies (5.5–14.7%) as compared to pure water (54.4 ± 3.4%), relative rate calculation corrections showed that the ·OH radical efficiencies for solutions containing DOM were the same as in pure water. However, the slightly higher efficiencies for carbonate-containing solutions indicated that some additional MITC degradation occurred from carbonate radical reactions.

Oxidation of Cu(II) aminopolycarboxylates by carbonate radical: A flash photolysis study

Reactions of carbonate radical (Co3−) generated by photolysis or by radiolysis of a carbonate solution, with Cu(II) complexes of aminopolycarboxylic acids viz., Cu(II)ethylenediamine tetraacetate [CuIIEDTA]2− and Cu(II)-iminodiacetate [CuIIIDA] were studied at pH 10. 5 and ionic strength 0.2 mol·dm−3. Time-resolved spectroscopy and kinetics for the transients were studied using flash photolysis and stable products arising from the ligand degradation of the complex were ascertained by steady-state radiolysis experiments. From the kinetic data it is observed that CO3−, radical reacts initially with CuII-complex to form a transient intermediate having maximum absorption at 335 nm and 430 nm. From the subsequent reactions of this intermediate it was assigned to be CuIII. species. This Cu(III) species undergoes intermolecular electron transfer with the CuII-complex to give a radical intermediate which again slowly reacts with CuII-complex to give a long lived species containing Cu−C bond. This long lived species, however, slowly decomposed to give glyoxalic reaction between CuIII-complex and a suitable donor, the one electron reduction potential for [CuIIIEDTA]1−/[CuIIEDTA]2− and [CuIIIIDA]+1/CuIIIDA was determined.

Temperature Effects on the Kinetics of Carbonate Radical Reactions in Near-Critical and Supercritical Water

Pulse radiolysis was used to generate the carbonate radical (CO3-•) in subcritical and supercritical water. The effect of the charge of the reaction partner on the kinetics of the reaction with aqueous carbonate radical was examined over the temperature range 30−400 °C, at 4150 ± 75 psia, pH 10.55. The rate constant for oxide transfer between two CO3-• radicals was insensitive to temperature below 200 °C, but increased by a factor of 300 from 1.61 × 107 to 2.90 × 109 M-1 s-1 between 200 and 400 °C. The rate constants for the one-electron oxidation of aniline, p-aminobenzoate, N,N-dimethylaniline, and p-N,N-dimethylaminobenzoate by CO3-• under the same conditions all displayed a negative temperature dependence at temperatures below 320 °C. Above 320 °C, the rate constants for the oxidation of the anionic aminobenzoates by CO3-• increased sharply, whereas those for the oxidations of the corresponding neutral anilines did not increase until 360 °C.

One electron oxidation of Ni(II)-iminodiacetate by carbonate radical

Reactions of carbonate radical (CO3−), generated by photolysis or by radiolysis of a carbonate solution with nickel(II)-iminodiacetate (Ni(II)IDA) were studied at pH 10.5 and ionic strength (I)==0.2 mol·dm−3. The stable product arising from the ligand degradation in the complex is mainly glyxalic acid. Time-resolved spectroscopy and transient kinetics were studied using flash photolysis. From the kinetic data it was suggested that the carbonate radical initially reacts with Ni(III)IDA with a rate constant (2.4±0.4)·106 dm3·mol−1·s−1 to form a Ni(II)IDA species which, however, undergoes a first-order transformation (k=2.7·102·s−1) to give a radical intermediate of the type Ni(II)RNHCHCO 2 − ) which rapidly forms an adduct containing a Ni−C bond. This adduct decays very slowly to give rise to glyoxalic acid. From a consideration of equilibrium between Ni(II)IDA and Ni(III)IDA, the one electron reduction potential for the Ni(III)IDA/Ni(II)IDA couple was determined to be 1.467 V.

Reactions of carbonate radical with cobalt(II) aminopolycarboxylates

Reactions of carbonate (CO3−·) and bicarbonate (HCO3·) radicals generated by photolysis of a carbonate or bicarbonate solution at pH 11.2 and 8.5, respectively, with Co(II) complexes of iminodiacetic acid (IDA) and ethylenediaminetetraacetic acid (EDTA) have been studied. The rate constants for the reactions were in the order of 106–107 dm3mol−1s−1. From the time-resolved spectroscopy of the products formed after reaction of CO3·−· or HCO3·, it is observed that CO3−· or HCO3· oxidize the metal center to its higher oxidation state.