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Per- and Polyfluoroalkyl Substances
Published in Caitlin H. Bell, Margaret Gentile, Erica Kalve, Ian Ross, John Horst, Suthan Suthersan, Emerging Contaminants Handbook, 2019
Ian Ross, Erica Kalve, Jeff McDonough, Jake Hurst, Jonathan A L Miles, Tessa Pancras
The hypothesized functional reductant credited with attack on PFASs is the solvated electron (i.e., hydrated electron or aquated electron) (Park et al. 2009; Song et al. 2013; Mitchell et al. 2014). The solvated electron is typically generated through the disproportionation of the water molecule into hydrogen radical, the solvated electron, and the hydroxyl radical. The large standard reduction potential (–2.9 volts) makes the solvated electron a powerful reductant (Buxton 1988). The solvated electrons attack the α- position C-F bonds instead of C-C bonds, to initiate the defluorination process (Qu et al. 2010; Song et al. 2013). Solvated electrons are nonselective powerful reductants and can be generated through UV-irradiation of reductants, but are readily scavenged by dissolved oxygen and nitrate, suggesting that its application for ex situ water treatment will be challenging, and oxygen and anions, such as nitrate, which will consume the reductants, could impact the treatment efficacy (Schaefer et al. 2017; Ross, McDonough et al. 2018).
Applications of Chemical Kinetics in Environmental Systems
Published in Kalliat T. Valsaraj, Elizabeth M. Melvin, Principles of Environmental Thermodynamics and Kinetics, 2018
Kalliat T. Valsaraj, Elizabeth M. Melvin
There are a variety of transients that have been identified in natural waters. Some of the important ones are (1) solvated electron, (2) triplet and singlet oxygen, (3) superoxide ions and hydrogen peroxide, (4) hydroxyl radicals, and (5) triplet excited state of dissolved organic matter. The level of steady state concentrations of some of these species and their typical half-lives in natural waters are given in Table 4.4. Solvated electron (eaq−) is a powerful oxidant, observed in natural waters during irradiation. It reacts rapidly with electronegative compounds (both organic and inorganic). Its reaction with O2 is the primary pathway for the production of superoxide anions in natural waters. The major source of eaq− is aquatic humic compounds. The quantum yield for their production is approximately 10−5. Dissolved organic matter in natural waters is also known to absorb photons to generate singlet and triplet excited states. These then decay by transferring energy to dissolved oxygen to produce singlet oxygen. Singlet oxygen is an effective oxidant, and the quantum yield for its formation is 0.01–0.03 in UV and blue spectra. Superoxide ions and hydrogen peroxide are found both in lakes and in atmospheric moisture (fog and rain). They are longer lived than other transients and are powerful oxidants for most organics. Algae and other biota are known to quench the action of superoxide ions.
Low and High LET Degradation Studies of Metal-Loaded Organic Phase Ligands in the ALSEP Process
Published in Solvent Extraction and Ion Exchange, 2023
Christian G. Bustillos, Randy O. Ngelale, Mikael Nilsson
The solvated electron () will mostly react with the solvent rather than the ligand and is not expected to play a significant role in ligand radiolysis despite being a reducing agent.[60] The production of the n-dodecane radical during irradiation (•[C12H26]+) will react with the ligands with fast reaction kinetics and will predominantly contribute to ligand degradation.[31,36,50,52,58,61] Due to the first-order kinetics of T2EHDGA degradation, the dodecane radical cation charge transfer occurs directly with T2EHDGA, and due to the zero order degradation, through an intermediate or multi-step reaction with HEH[EHP].[31,58] Radiolytic degradation of T2EHDGA and HEH[EHP] of the ALSEP solvent is therefore expected to occur through electron or proton transfer induced by the n-dodecane radical, and all discussion of ligand degradation will presume radiolysis generally occurs through this charge transfer.
Synthesis and characterization of low-melting ferrocenyl salts: a study of thermal and photochemical redox reactions
Published in Journal of Coordination Chemistry, 2018
Carlos Díaz, Guillermo Ferraudi, A. Graham Lappin, Allen Oliver, Mauricio Isaacs
The prospect that photolysis of these ferrocene derivatives at wavelengths below 350 nm results in production of the solvated electron, may be tested. The photoredox processes of 1 and 2 were investigated using the flash photolysis technique under various media conditions. Solutions containing either [FcCH2N(CH3)3]+ or [(FcCH2)2Im]+ in CH3OH deaerated with streams of N2 were flash-photolysed at 351 nm. Transient spectra photogenerated by the flash irradiation of the respective complexes exhibited new absorption bands in the 600–700 nm region and λob ≤ 450 nm, consistent with the formation of e–sol and [FcCH2N(CH3)3]+2 or [(FcCH2)2Im]+2 (Equations (6) and (7)). An example of the transient spectrum photogenerated in the photolysis of [(FcCH2)2Im]2+ is illustrated in Figure 10. On the basis of the pulse radiolysis experiments, the spectra are consistent with the convolution of the e–sol and [FcCH2N(CH3)3]2+ spectra in one case and the e−sol with [(FcCH2)2Im]+2 spectra in the other.
Gamma Radiolysis of TODGA and CyMe4BTPhen in the Ionic Liquid Tri-n-Octylmethylammonium Nitrate
Published in Solvent Extraction and Ion Exchange, 2020
Peter Zsabka, Karen Van Hecke, Andreas Wilden, Giuseppe Modolo, Michelle Hupert, Vincent Jespers, Stefan Voorspoels, Marc Verwerft, Koen Binnemans, Thomas Cardinaels
In contrast, the samples irradiated under neutral conditions yielded nitrosylated organic compounds. Based on the above considerations, the source of the NO functional group is not nitrate radicals, but another reaction mechanism. These are obtained most probably as a result of several successive radical reactions. At higher pH, the most abundant radiolysis product in water is the solvated electron. The solvated electrons can be attracted by the cations of the ionic liquid or react with NO3− ions and generate nitrite radicals and nitrite anions (reactions 4–6). The reaction between solvated electron and nitrate anion is known to have a very fast reaction rate k = 9.7 × 109 mol L−1 s−1).[54] The reaction rate of dinitrogene tetraoxide with water is relatively slow (k = 1.5 × 103 mol L−1 s−1) suggesting that under the conditions of the irradiation, nitrite radicals should be abundant, while solvated electrons are probably present at low concentrations. Nitrite anions can also scavenge solvated electrons (reaction 7) and eventually result in the formation of nitroso-compounds (reaction 8).[55,56] However, based on the considerations of abovementioned known reaction rates, it is probably the reaction of nitrite radicals with the cations of the quaternary ammonium cations that generate nitrosylated compounds (reaction 9).