Online headspace monitoring of volatile organic compounds using proton transfer reaction-mass spectrometry: Application to the multiphase atmospheric fate of 2,4-hexadienedial.

Chemical processes in clouds have been suggested to contribute significantly to the mass of organic aerosol particles in the atmosphere. Experimental and theoretical evidence suggest that organic mass production in clouds can be substantial and depends on the concentration of organic precursor compounds available in the gas phase. The present study aims at studying the aqueous phase reactivity of one of these overlooked precursors, i.e. 2,4-hexadienedial, an important and toxic intermediate in the atmospheric oxidation of aromatic species. Cautious synthesis and purification of 2,4-hexadienedial was performed. Its effective Henry's law constant was measured using a new simple and fast method based on online flow-injection analysis. The reactivity of 2,4-hexadienedial in the aqueous phase relevant to atmospheric conditions was studied, including hydrate formation, photolysis, ∙OH- and SO4∙--oxidation as well as reaction with NH3. The results revealed a low hydration constant compared to other dicarbonyls (Khyd1 = 7 × 10-2) and no dihydrate formation, indicating in an intermediate solubility (KH = 1.0 × 104 M atm-1) and high absorption cross sections (σ278nm > 10-16 cm2 molecule-1). Compared to its gas phase photolysis, its aqueous phase photolysis showed low quantum yields (Φ290-380nm = 0.9 %), and a significant red shift of the absorbance maximum, leading to a fast aqueous photolysis kinetics (Jaq,atm = 8.7 × 10-5 s-1) under atmospheric solar radiation, but no triplet state formation was detected. Radical oxidation experiments revealed extremely rapid oxidation kinetics (k∙OH = 1.10 × 1010 M-1 s-1 and kSO4∙- = 1.4 × 109 M-1 s-1) driven by fast addition of the radicals to the unsaturated bonds. In contrast, the reaction with aqueous NH3 (kNH3 = 2.6 × 10-3 M-1 s-1) was found slower than glyoxal and 2-butenedial, likely due to the hyperconjugation of 2,4-hexadienedial. Using these new data complemented with assumed aqueous phase kinetics (for NO3, 3C* and 1O2 reactions) and previous gas-phase kinetic ones, the multiphase atmospheric fate of 2,4-hexadienedial was established under atmospheric conditions reported from previous field measurements and models. The results revealed a short day lifetime (∼1 h) and a long night lifetime (>12 h). It was shown that daytime atmospheric chemistry of 2,4-hexadienedial can be influenced by aqueous-phase reactivity during cloud events, up to ∼50 % under thick cloud conditions (Liquid Water Content >2000 g/m3), indicating that even a compound of intermediate solubility can be strongly affected by condensed-phase reactivity. Besides its fast aqueous phase reactivity towards ∙OH and photolysis, its daytime condensed-phase reactivity may be driven by reactions with dissolved triplet states (3C*), up to 35 %, highlighting the need to study further the kinetics, the nature and concentrations of dissolved 3C* under various atmospheric conditions. In addition, the molecular properties and atmospheric behavior of 2,4-hexadienedial were found different from those of glyoxal and 2-butenedial, highlighting the need for detailed atmospheric reactivity studies of polyfunctional compounds, in particular unsaturated compounds.

Pilot-scale study of UVC-based AOPs towards implementation at the outlet of domestic WWTPs.

The degradation of a mixture of ibuprofen, naproxen, and diclofenac in various effluents by UVC/H2O2 or UVC/S2O82- was studied to assess the impact of the matrix composition and of the oxidant precursor on process efficiency. Experiments were carried out in a 20-L laboratory pilot (a scaled-down version of a full-scale pilot). In effluents collected during dry weather, the rural constructed wetland effluent allowed faster degradation than the urban conventional WWTP effluent, regardless of the nature of the targets or of the oxidant precursor. This was mainly attributed to a three-times higher chemical oxygen demand in the urban effluent, likely to quench the oxidative species. UV fluences to reach 90% degradation of the three compounds were 3,800 and 5,500 mJ cm-2 in the rural effluent, whereas they were 6,600 and 6,100 mJ cm-2 in the urban effluent with H2O2 and S2O82-, respectively. After a rainfall event, the rural effluent composition was not significantly affected compared to that of the urban effluent that underwent the dilution effect. Therefore, the stability of the rural effluent composition allowed comparable degradation efficiency, whereas the dilution effect led to a significant increase in the degradation rate constants in the urban effluent (up to four times higher).

A comparative study on Fe(III)/H2O2 and Fe(III)/S2O82- systems modified by catechin for the degradation of atenolol.

The processes of Fe(III) activated persulfate (PS) and H2O2 modified by catechin (CAT) had been shown to be effective in degrading contaminants. In this study, the performance, mechanism, degradation pathways and products toxicity of PS (Fe(III)/PS/CAT) and H2O2 (Fe(III)/H2O2/CAT) systems were compared using atenolol (ATL) as a model contaminant. 91.0% of ATL degradation was reached after 60 min in H2O2 system which was much higher than that in PS system (52.4%) under the same experimental condition. CAT could react directly with H2O2 to produce small amounts of HO• and the degradation efficiency of ATL was proportional to CAT concentration in H2O2 system. However, the optimal CAT concentration was 5 µM in PS system. The performance of H2O2 system was more susceptible to pH than that of PS system. Quenching experiments were conducted indicating that SO4•- and HO• were produced in PS system while HO• and O2•- accounted for ATL degradation in H2O2 system. Seven pathways with nine byproducts and eight pathways with twelve byproducts were put forward in PS and H2O2 systems respectively. Toxicity experiments showed that the inhibition rates of luminescent bacteria were both decreased about 25% after 60 min reaction in two systems. Although the software simulation result showed few intermediate products of both systems were More toxic than ATL, but the amounts of them were 1-2 orders of magnitude lower than ATL. Moreover, the mineralization rates were 16.4% and 19.0% in PS and H2O2 systems respectively.

Assessing the photodegradation potential of compounds derived from the photoinduced weathering of polystyrene in water.

Benzoate (Bz-) and acetophenone (AcPh) are aromatic compounds known to be produced by sunlight irradiation of polystyrene aqueous suspensions. Here we show that these molecules could react with •OH (Bz-) and •OH + CO3•- (AcPh) in sunlit natural waters, while other photochemical processes (direct photolysis and reaction with singlet oxygen, or with the excited triplet states of chromophoric dissolved organic matter) are unlikely to be important. Steady-state irradiation experiments were carried out using lamps, and the time evolution of the two substrates was monitored by liquid chromatography. Photodegradation kinetics in environmental waters were assessed by a photochemical model (APEX: Aqueous Photochemistry of Environmentally-occurring Xenobiotics). In the case of AcPh, a competitive process to aqueous-phase photodegradation would be volatilisation followed by reaction with gas-phase •OH. As far as Bz- is concerned, elevated dissolved organic carbon (DOC) levels could be important in protecting this compound from aqueous-phase photodegradation. Limited reactivity of the studied compounds with the dibromide radical (Br2•-, studied by laser flash photolysis) suggests that •OH scavenging by bromide, which yields Br2•-, would be poorly offset by Br2•--induced degradation. Therefore, photodegradation kinetics of Bz- and AcPh should be slower in seawater (containing [Br-] ~ 1 mM) compared to freshwaters. The present findings suggest that photochemistry would play an important role in both formation and degradation of water-soluble organic compounds produced by weathering of plastic particles.

Application of Fe(III)-EDDS complexes and soybean peroxidase in photo-Fenton processes for organic pollutant removal: insights into possible synergistic effects.

Photo-Fenton processes activated by biodegradable Fe(III)-EDDS complexes have attracted huge attention from the scientific community, but the operative mechanism of the photo-activation of H2O2 in the presence of Fe(III)-EDDS has not been fully clarified yet. The application of the Fe(III)-EDDS complex in Fenton and photo-Fenton (mainly under UV-B light) processes, using 4-chlorophenol (4-CP) as a model pollutant was explored to give insights into the operative mechanism. Furthermore, the potential synergistic contribution of soybean peroxidase (SBP) was investigated, since it has been reported that upon irradiation of Fe(III)-EDDS the production of H2O2 can occur. SBP did not boost the 4-CP degradation, suggesting that the possibly produced H2O2 reacts immediately with the Fe(II) ion with a quick kinetics that does not allow the diffusion of H2O2 into the bulk of the solution (i.e., outside the solvent cage of the complex). So, a concerted mechanism in which the photochemically produced H2O2 and Fe(II) react inside the hydration sphere of the Fe(III)-EDDS complex is proposed.

Anodic TiO2 Nanotube Layers for Wastewater and Air Treatments: Assessment of Performance Using Sulfamethoxazole Degradation and N2O Reduction.

The preparation of anodic TiO2 nanotube layers has been performed using electrochemical anodization of Ti foil for 4 h at different voltages (from 0 V to 80 V). In addition, a TiO2 thin layer has been also prepared using the sol-gel method. All the photocatalysts have been characterized by XRD, SEM, and DRS to investigate the crystalline phase composition, the surface morphology, and the optical properties, respectively. The performance of the photocatalyst has been assessed in versatile photocatalytic reactions including the reduction of N2O gas and the oxidation of aqueous sulfamethoxazole. Due to their high specific surface area and excellent charge carriers transport, anodic TiO2 nanotube layers have exhibited the highest N2O conversion rate (up to 10% after 22 h) and the highest degradation extent of sulfamethoxazole (about 65% after 4 h) under UVA light. The degradation mechanism of sulfamethoxazole has been investigated by analyzing its transformation products by LC-MS and the predominant role of hydroxyl radicals has been confirmed. Finally, the efficiency of the anodic TiO2 nanotube layer has been tested in real wastewater reaching up to 45% of sulfamethoxazole degradation after 4 h.

Enhanced Degradation of Paracetamol by the Fe(III)-Sulfite System under UVA Irradiation.

The Fe(III)-S(IV) system used for advanced oxidation processes (AOPs) at acidic pH has just been proposed and demonstrated valid for very few contaminants in the last several years. In this work, we investigated the effect of ultraviolet A (UVA) radiation on the degradation efficiency of the Fe(III)/S(IV) system at near-neutral pH. Paracetamol (PARA) was selected as a model contaminant. The influencing factors, such as initial pH and Fe(III)/S(IV) molar ratio on chemical kinetics, and the mechanism of PARA degradation are investigated, with an emphasis on the determination of dominant oxidant species. Our results show that irradiation enhances the PARA degradation by accelerating the decrease of pH to acidic levels, and the optimal pH for the degradation of PARA in the Fe(III)/S(IV)/O2 system was around 4.0. At near-neutral pH, more than 60% of PARA was decomposed within 40 min under irradiation, whereas no significant degradation of PARA was observed using Fe(III)/S(IV) at pH 7.0 without irradiation. Mechanism investigation revealed that sulfate radical (SO4•‒) is the main oxidant species generated and responsible for the PARA degradation under these conditions. This finding may have promising implications in developing a new degradation process for dealing with wastewater at near-neutral pH by the Fe(III)/S(IV)/O2 system under UVA irradiation.

Toward a better understanding of ferric-oxalate complex photolysis: The role of the aqueous/air interface of droplet.

In this work, the photo reactivity of ferric oxalate (Fe(III)-Ox) complex in atmospheric particles was investigated. Raman spectroscopy was used to explore the mechanism and kinetics of Fe(III)-Ox photolysis occurring at the aqueous/gas interface, inside the droplet and in bulk solution. Ferrous carbonate (FeCO3) was detected indicating that carbonate ion (CO32-) formed inside the droplets would compete with oxalate ligands for iron complexation. A higher concentration of photoproduct Fe(II)-Ox was observed at the surface and inside of the droplets than in bulk solution. In particular, Fe(III)-Ox on the droplet surface was quickly reduced with light and Fe(II)-Ox concentration gradually decreased with irradiation time. The evolution of Fe(II)-Ox concentration was similar inside the droplet and in bulk solution with a trend of first increasing and then gradually decreasing during irradiation time. Although FeCO3 would hinder Fenton intermediate reaction, the photolysis rate of Fe(III)-Ox in droplets was almost two orders of magnitude times faster than that observed during bulk experiment. In general, the photolysis mechanism and kinetics of Fe(III)-Ox in aqueous/air interface, inside of droplet and bulk solution were distinct, and the production of oxide species from the atmospheric Fe(III)-Ox droplets was underestimated.

Fe2.5Co0.3Zn0.2O4/CuCr-LDH as a visible-light-responsive photocatalyst for the degradation of caffeine, bisphenol A, and simazine in pure water and real wastewater under photo-Fenton-like degradation process.

This paper outlines the synthesis and application of a sustainable composite for the photo-Fenton-like degradation of caffeine, bisphenol A, and simazine. The phase, morphology, optical and magnetic properties of the samples were evaluated by different characterization techniques. The composite of Fe2.5Co0.3Zn0.2O4 and copper-chromium layered double hydroxide (CuCr-LDH) was determined to be the most favorable photocatalyst in the photo-Fenton-like process when compared with Fe3O4, Fe2.5Co0.3Zn0.2O4, CuCr-LDH, and Fe3O4/CuCr-LDH composite. Studying the efficiency of the photo-Fenton-like degradation process in the presence of the Fe2.5Co0.3Zn0.2O4/CuCr-LDH composite revealed a degradation rate constant of caffeine twice more than the sum of those obtained for the individual processes. This ascribes to the synergistic effect by which the photo-generated electron-hole from the catalyst and the efficient reduction of Fe3+, Cu2+, etc. during the photo-Fenton-like reaction is accelerated. Moreover, under the optimal condition and after 120 min of heterogenous photo-Fenton-like process at natural pH, > 90% of pollutants mixture was decomposed. The experiments fulfilled in near-real conditions demonstrated I) the high stability and magnetically recoverability of the photocatalyst and II) the proper degradation performance of the applied heterogenous photo-Fenton-process in the removal of pollutant mixture in different water bodies and in the presence of chloride and bicarbonate ions.

A Review of Manganese(III) (Oxyhydr)Oxides Use in Advanced Oxidation Processes.

The key role of trivalent manganese (Mn(III)) species in promoting sulfate radical-based advanced oxidation processes (SR-AOPs) has recently attracted increasing attention. This review provides a comprehensive summary of Mn(III) (oxyhydr)oxide-based catalysts used to activate peroxymonosulfate (PMS) and peroxydisulfate (PDS) in water. The crystal structures of different Mn(III) (oxyhydr)oxides (such as α-Mn2O3, γ-MnOOH, and Mn3O4) are first introduced. Then the impact of the catalyst structure and composition on the activation mechanisms are discussed, as well as the effects of solution pH and inorganic ions. In the Mn(III) (oxyhydr)oxide activated SR-AOPs systems, the activation mechanisms of PMS and PDS are different. For example, both radical (such as sulfate and hydroxyl radical) and non-radical (singlet oxygen) were generated by Mn(III) (oxyhydr)oxide activated PMS. In comparison, the activation of PDS by α-Mn2O3 and γ-MnOOH preferred to form the singlet oxygen and catalyst surface activated complex to remove the organic pollutants. Finally, research gaps are discussed to suggest future directions in context of applying radical-based advanced oxidation in wastewater treatment processes.

Impacts of environmental levels of hydrogen peroxide and oxyanions on the redox activity of MnO2 particles.

Despite the widespread presence of hydrogen peroxide (H2O2) in surface water and groundwater systems, little is known about the impact of environmental levels of H2O2 on the redox activity of minerals. Here we demonstrate that environmental concentrations of H2O2 can alter the reactivity of birnessite-type manganese oxide, an earth-abundant functional material, and decrease its oxidative activity in natural systems across a wide range of pH values (4-8). The H2O2-induced reductive dissolution generates Mn(II) that will re-bind to MnO2 surfaces, thereby affecting the surface charge of MnO2. Competition of Bisphenol A (BPA), used as a target compound here, and Mn(II) to interact with reactive surface sites may cause suppression of the oxidative ability of MnO2. This suppressive effect becomes more effective in the presence of oxyanions such as phosphate or silicate at concentrations comparable to those encountered in natural waters. Unlike nitrate, adsorption of phosphate or silicate onto birnessite increased in the presence of Mn(II) added or generated through H2O2-induced reduction of MnO2. This suggests that naturally occurring anions and H2O2 may have synergetic effects on the reactivity of birnessite-type manganese oxide at a range of environmentally relevant H2O2 amounts. As layered structure manganese oxides play a key role in the global carbon cycle as well as pollutant dynamics, the impact of environmental levels of hydrogen peroxide (H2O2/MnO2 molar ratio ≤ 0.3) should be considered in environmental fate and transport models.

Efficient removal of estrogenic compounds in water by MnIII-activated peroxymonosulfate: Mechanisms and application in sewage treatment plant water.

In this paper, the degradation of three endocrine-disrupting chemicals (EDCs): bisphenol A (BPA), 17ß-estradiol (E2) and 17α-ethinylestradiol (EE2) by manganite (γ-MnOOH) activated peroxymonosulfate (PMS) was investigated. Preliminary optimisation experiments showed that complete degradation of the three EDCs was achieved after 30 min of reaction using 0.1 g L-1 of γ-MnOOH and 2 mM of PMS. The degradation rate constants were determined to be 0.20, 0.22 and 0.15 min-1 for BPA, E2 and EE2, respectively. Combining radical scavenging approaches, Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) analyses, we revealed for the first time that about 40% of EDCs degradation can be attributed to heterogeneous electron transfer reaction involving freshly generated Mn(IV), and 60% to sulfate radical degradation pathway. The influence of various inorganic ions on the γ-MnOOH/PMS system indicated that removal efficiency was slightly affected by chloride and carbonate ions, while nitrate and nitrite ions had negligible impacts. The application of γ-MnOOH/PMS system in real sewage treatment plant water (STPW) showed that degradation rate constants of EDCs decreased to 0.035-0.048 min-1 and complete degradation of the three EDCs after 45 min. This study provides new insights into the reactivity of combined γ-MnOOH and PMS, and opens new ways for the application of Mn-bearing species in wastewater treatment technologies.

Significant role of iron on the fate and photodegradation of enrofloxacin.

Enrofloxacin (ENR) belongs to the fluoroquinolone (FQ) antibiotics family, which are contaminants of emerging concern frequently found in effluents. Although many works studying photo-Fenton process for FQ degradation have been reported, there are no reports analysing in deep the effect of iron complexation, as well as other metals, towards FQs' photolysis, which, evidently, also contributes in the overall degradation of the pollutant. Therefore, in this work, we report a comparative study between the photochemical fate of ENR and its complex with Fe(III) under simulated sunlight irradiation. In addition, the effect of dissolved oxygen, self-sensitization process, and H2O2 addition on the studied photochemical systems are also investigated. Results indicate that, for free and iron-complexed ENR, singlet oxygen (1O2) is generated from the interaction of its triplet state with ground state oxygen. Half-life time (t1/2) of ENR under sun simulated conditions is estimated to be around 22 min, while complexation with iron enhances its photostability, leading to a t1/2 of 2.1 h. Such finding indicates that at least the presence of iron, might notably increase the residence time of these pollutants in the environment. Eventually, only with the addition of H2O2, the FQ-iron complex is efficiently degraded due to photo-Fenton process even at circumneutral pH values due to the high stability of the formed complex. Finally, after LC/FT-ICR MS analysis, 39 photoproducts are detected, of which the 14 most abundant ones are identified. Results indicate that photoproducts formation is pH and iron dependent.

Hydrogen peroxide and persulfate activation using UVA-UVB radiation: Degradation of estrogenic compounds and application in sewage treatment plant waters.

In the present work, the degradation of three estrogens (17ß-estradiol (E2), estrone (E1) and 17α-ethinylestradiol (EE2)) was investigated under photoactivation of hydrogen peroxide and persulfate. Lab-scale irradiation experiments showed that both UVA and UVB radiations are able to photoactivate the oxidant precursors, although UVB is more efficient to generate radicals and therefore to degrade the targets. The efficiency of both oxidant precursors was investigated showing higher efficiency in the system with persulfate. The pseudo-first order degradation rate constants and the second order rate constants between the hydroxyl or the sulfate radicals and estrogens were measured. In order to evaluate the process efficiency in real treatment conditions, the degradation of the estrogens spiked into sewage treatment plant effluent was studied. Measurements of second order rate constants between the radical and the effluent organic matter by laser flash photolysis allowed to understand the involved quenching mechanisms. A Yeast Estrogen Screen (YES) assay was used to follow the decrease in estrogenic activity during the estrogen degradation. This assay permitted to ensure that the studied processes are not only able to degrade the estrogens but also to remove their estrogenic activity.

Phenanthrene decomposition in soil washing effluents using UVB activation of hydrogen peroxide and peroxydisulfate.

In this work, the decomposition of phenanthrene (PHE) in mimic and real soil washing (SW) effluents was investigated using UVB light assisted activation of hydrogen peroxide (H2O2) and peroxydisulfate (PDS) oxidation processes. The impact of oxidant concentration, initial pH, and coexisting inorganic anions (Cl-, HCO3- and NO3-) on PHE removal was evaluated. PHE degradation efficiency under UVB irradiation followed the order of UVB/PDS > UVB/H2O2 > UVB. The increase of PHE decomposition efficiency was observed with increasing oxidant dose in the range of 2-30 mM upon the two processes. It was found Cl- played different roles in the two activation systems depending on the solution pH and Cl- concentration. The influence of HCO3- on PHE elimination was negligible in the UVB/PDS process, while an inhibitory effect was observed in the UVB/H2O2 system. Nitrate inhibited the PHE decay in both UVB/H2O2 and UVB/PDS processes at the investigated pH 3.3, 7.1 and 8.6. Finally, the application of the two activation processes to the treatment of real SW effluents indicated that up to 85.0% of PHE degradation could be reached under 6 h UVB irradiation with PDS, indicating UVB/PDS process is a promising alternative for SW effluent treatment.

Degradation of Acetaminophen via UVA-induced advanced oxidation processes (AOPs). Involvement of different radical species: HO, SO4- and HO2/O2.

In this work, UVA radiation that is part of solar light is taken as the irradiation source and radicals (HO, SO4- and HO2/O2-) are generated through activation of hydrogen peroxide (H2O2), sodium persulfate (Na2S2O8) and Bismuth catalyst (BiOCl), respectively. The distinguished performance in removing acetaminophen (ACTP), a model pharmaceutical pollutant, by these three radicals was compared for the first time. Effect of pH, halide ions concentration and interfacial mechanism have been investigated in detail. Interestingly, results show that heterogeneous UVA/BiOCl process has higher degradation efficiency than homogeneous UVA/H2O2 and UVA/Na2S2O8 systems whatever the solution's pH. To explain these results, second order reaction rate constant (kradical, ACTP) have been determined with laser flash photolysis (LFP) or radical scavenging experiments. The strongly interfacial-depended HO2/O2- radicals have the lowest second order rate constant with ACTP but highest steady state concentration. BiOCl is much easier activated by UVA, and outstanding ACTP mineralization can be achieved. Combination of BiOCl and Na2S2O8 exhibits synergistic effects rather than antagonism effects with H2O2. This study highlights the relative effective utilization of solar light through interfacial directed BiOCl photocatalysis and its synergistic effects with traditional oxidants.

Innovative depollution treatment using multi-valent iron species: from fundamental study to application in municipal wastewater.

In this work, a new combination of oxidation treatments for the degradation of bisphenol A (BPA) is investigated. This innovative wastewater (WW) treatment includes the use of ferrate (FeO42-) and its decomposition byproducts under dark and UVA irradiation. The oxidation by ferrate leads to a fast but incomplete degradation of BPA with a degradation extent of 45% after 60 min under adopted experimental conditions. However, the ferrate decomposition byproducts which are constituted by solid iron species can be used to further improve the pollutant degradation efficiency. Indeed, ferrate-mediated heterogeneous photo-Fenton process is employed for the first time to enhance the degradation of BPA. With respect to the application for wastewater treatment, UVA irradiation (which is part of solar light), non-toxic and natural origin compounds such as ascorbic acid (AA) and ethylenediamine-N,N'-disuccinic acid (EDDS), are used to design a sustainable process. Under optimized conditions, the degradation extent of BPA using this newly designed treatment reaches almost 100% with AA and 70% with EDDS. In order to assess the feasibility of this treatment, the ferrate-mediated photo-Fenton process is applied to treat municipal wastewater. The obtained results in WW are highly encouraging since a maximum BPA degradation extent of 63% and 60% is observed after 300 min by using AA and EDDS, respectively.

Photochemistry of the Cloud Aqueous Phase: A Review.

This review paper describes briefly the cloud aqueous phase composition and deeply its reactivity in the dark and mainly under solar radiation. The role of the main oxidants (hydrogen peroxide, nitrate radical, and hydroxyl radical) is presented with a focus on the hydroxyl radical, which drives the oxidation capacity during the day. Its sources in the aqueous phase, mainly through photochemical mechanisms with H2O2, iron complexes, or nitrate/nitrite ions, are presented in detail. The formation rate of hydroxyl radical and its steady state concentration evaluated by different authors are listed and compared. Finally, a paragraph is also dedicated to the sinks and the reactivity of the HO• radical with the main compounds found in the cloud aqueous phase. This review presents an assessment of the reactivity in the cloud aqueous phase and shows the significant potential impact that this medium can have on the chemistry of the atmosphere and more generally on the climate.

Mineralization Enhancement of Pharmaceutical Contaminants by Radical-Based Oxidation Promoted by Oxide-Bound Metal Ions.

While the use of transition metal oxides in catalyzing advanced oxidation reactions has been widely investigated, very few reports have focused on how the preliminary contact of oxides with target compounds may affect the succession of reaction. In this study, we examined the adsorption and electron transfer reactions of two fluoroquinolones, flumequine (FLU), and norfloxacin (NOR), with goethite (α-FeOOH) or manganese (Mn) oxide, and their impact on the subsequent mineralization of target compounds using H2O2 or S2O82- under UVA irradiation. Intriguingly, higher total organic carbon (TOC) removal was achieved when antibiotics and metal oxides were allowed for preequilibration before starting the oxidation reaction. The rate and extent of TOC removal are strongly dependent on the molecule structure and the redox-active mineral used, and much less on the preequilibration time. This high efficiency can be ascribed to the presence of reduced metal ions, chemically or photochemically generated during the first stage, onto oxide minerals. Oxide-bound MnII plays a crucial role in catalyzing oxidant decomposition and then producing greater amounts of radical species through a photoassisted redox cycle, regardless of the underlying surface, MnIVO2 or MnIIIOOH. This finding will be of fundamental and practical significance to Mn-based oxidation reactions and wastewater treatment processes.

Enhancement of iron-mediated activation of persulfate using catechin: From generation of reactive species to atenolol degradation in water.

Persulfate (PS) activation reaction, which forms sulfate radical (SO4-), can be used to degrade organic pollutants in water. However, a drawback of this reaction is that the regeneration of ferrous ions requires a high concentration of hydrogen peroxide (Fenton-like reaction) or use of UV radiation. Catechin (CAT), a non-toxic antioxidant of natural origin from tea, is used in this work to improve the sulfate radical-mediated degradation of atenolol (ATL, a model pollutant) in water using relatively low concentrations of reactive chemical species (less than 100 µM). To the best of the author's knowledge, the direct effect of CAT on the oxidation state of iron, which is promoted by the reduction of ferric into ferrous ions with the enhancement of SO4- formation in the presence of PS, is demonstrated for the first time. The enhancement versus inhibition effect of CAT and the chemical mechanism of the iron-based activation process are explained. Results show that UVA radiation, which is representative of solar light, accelerates the initial degradation of ATL by more than 30% through ferric iron photolysis. Finally, a reaction mechanism leading to the formation of hydroxyl radicals (HO) and SO4- is proposed considering the implication of different activation/reaction chemical steps.