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The complex of iron and tetra-amido macrocyclic ligand (Fe-TAML), or Collin’s reagent, is a promising catalyst to carry out Fenton-like degradation of contaminants. Previously, the ability of Fe-TAML to activate sulfite and metabisulfite (S2O52-, MBS) other than hydrogen peroxide, was reported, which could lead to cheaper, safer, and almost equally efficient oxidation of contaminants. However, the actual species involved in the Fe-TAML/MBS is not yet clear. Experiments reported here included a combination of tests involving the presence of various scavengers, modified atmospheres (air vs. N2), as well as measurements with electron paramagnetic resonance. Specifically, the tests were designed to positively exclude the presence of various active species and identify the most likely one. Thus, we theorize the involvement of the peroxymonosulfate radical (SO5·-) in the presence of the Collin’s reagent and metabisulfite and provide indirect evidence of the activity of this species. Specifically, we demonstrated that this system triggers a Fenton-like process, able to induce the degradation of phenol. The exploitation of such a reactive species may be favourable, as it may selectively induce the degradation of target contaminants in the presence of excess interfering agents, starting from the cheap, safe, and easily handled metabisulfite, which is an interesting substitute for hydrogen peroxide.

Partitioning between surface waters and the atmosphere is an important process, influencing the fate and transport of semi-volatile contaminants. In this work, a simple methodology that combines experimental data and modeling was used to investigate the degradation of a semi-volatile pollutant in a two-phase system (surface water + atmosphere). 4-Isobutylacetophenone (IBAP) was chosen as a model contaminant; IBAP is a toxic transformation product of the non-steroidal, anti-inflammatory drug ibuprofen. Here, we show that the atmospheric behavior of IBAP would mainly be characterized by reaction with center dot OH radicals, while degradation initiated by center dot NO3 or direct photolysis would be negligible. The present study underlines that the gas phase reactivity of IBAP with center dot OH is faster, compared to the likely kinetics of volatilization from aqueous systems. Therefore, it might prove very difficult to detect gas-phase IBAP. Nevertheless, up to 60% of IBAP occurring in a deep and dissolved organic carbon-rich water body might be eliminated via volatilization and subsequent reaction with gas-phase center dot OH. The present study suggests that the gas-phase chemistry of semi-volatile organic compounds which, like IBAP, initially occur in natural water bodies in contact with the atmosphere is potentially very important in some environmental conditions.

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. Graphical abstract

The formation quantum yields of photochemically produced reactive intermediates (PPRIs) by irradiated CDOM (in this study, Suwannee River Natural Organic Matter and Upper Mississippi River Natural Organic Matter) decrease with increasing irradiation wavelength. In particular, the formation quantum yields of the excited triplet states of CDOM (

Peracetic acid has quickly gained ground in water treatment over the last decade. Specifically, its disinfection efficacy toward a wide spectrum of microorganisms in wastewater is accompanied by the simplicity of its handling and use. Moreover, peracetic acid represents a promising option to achieve disinfection while reducing the concentration of typical chlorination byproducts in the final effluent. However, its chemical behavior is still amply debated. In this study, the reactivity of peracetic acid in the presence of halides, namely, chloride and bromide, was investigated in both synthetic waters and in a real contaminated water. While previous studies focused on the ability of this disinfectant to form halogenated byproducts in the presence of dissolved organic matter and halides, this work indicates that peracetic acid also contributes itself as a primary source in the formation of these potentially carcinogenic compounds. Specifically, this study suggests that 1.5 mM peracetic acid may form around 1-10 μg/L of bromoform when bromide is present. Bromoform formation reaches a maximum at near neutral pH, which is highly relevant for wastewater management.

The carbonate radical CO3•− and the excited triplet states of chromophoric dissolved organic matter play an important role in the photodegradation of some easily oxidized pollutants in surface waters, such as the aromatic amines. Anilines and sulfadiazine are known to undergo back-reduction processes when their degradation is mediated by the excited triplet states of photosensitizers (triplet sensitization). Back-reduction, which inhibits photodegradation, means that phenols or the antioxidant (mostly phenolic) moieties occurring in the natural dissolved organic matter of surface waters reduce, back to the parent compounds, the radical species derived from the mono-electronic oxidation of anilines and sulfadiazine. Here we show that a similar process takes place as well in the case of substrate oxidation by CO3•−. The carbonate radical was here produced upon oxidation of HCO3−/CO32− by either HO•, generated by nitrate photolysis, or SO4•−, obtained by photolysis of persulfate. Back-reduction was observed in both cases in the presence of phenols, but at different extents as far as the details of reaction kinetics are concerned, and the occurrence of additional reductants might affect the efficacy by which phenols carry out the reduction process. In particular, when the carbonate radicals were produced by NO3– photolysis in the presence of HCO3−/CO32−, the numerical values of [PhOH]1/2 (the phenol concentration that halves the photodegradation rate of the substrate) were 2.19 ± 0.23 µM for aniline, 1.15 ± 0.25 µM for 3-chloroaniline, 1.18 ± 0.26 µM for 4-chloroaniline, and 1.18 ± 0.22 µM for 3,4-dichloroaniline. In contrast, when CO3•− was produced by photolysis of persulfate in the presence of HCO3−/CO32−, the corresponding values were 0.28 ± 0.02 µM for aniline and 0.79 ± 0.10 µM for sulfadiazine. Back-reduction has the potential to significantly inhibit photodegradation by CO3•− and excited triplet states in natural waters, and to comparatively increase the importance of HO•-mediated degradation that is not affected by the same phenomenon., Water Research, 209, ISSN:0043-1354, ISSN:1879-2448

The carbonate radical CO

The fungicide tebuconazole (TBCZ) is expected to undergo negligible direct photolysis in surface freshwaters, but it can be degraded by indirect photochemistry. TBCZ mainly reacts with hydroxyl radicals and, to a lesser extent, with the triplet states of chromophoric dissolved organic matter (

In the present work, surface engineering of Ti6Al4V, produced via selective laser melting parts, was carried out with the aim of investigating how surface features of substrate may improve the coupling with AlTiN coatings deposited by physical vapor deposition reactive high-power impulse magnetron sputtering. In particular, the work highlighted how vacuum thermal treatments at 800 °C induced peculiar mesoscale morphology and surface chemical modifications of the Ti6Al4V, which contributed to improve the adhesion of the deposited AlTiN thin films. Chemical composition, crystallographic structure, and surface properties of both substrates and coatings were analyzed by field emission scanning electron microscopy (equipped with energy dispersive spectroscopy), atomic force microscopy, x-ray photoelectron spectroscopy, x-ray diffraction, nanoindentation, and scratch test measurements.

International audience; Magnetic particles (MPs) coated with humic acid (HA) prepared under anoxic atmosphere were tested as heterogeneous photo-Fenton catalyst for the activation of hydrogen peroxide (H 2 O 2) and persulfate (S 2 O 8 2−) using Bisphenol A (BPA) as a model pollutant. The role of HA coating, pH value and H 2 O 2 /S 2 O 8 2− concentration were investigated. A positive contribution of HA coating on H 2 O 2 and S 2 O 8 2− activation was found. The highest BPA degradation rates were achieved at acidic conditions (pH 3) with both H 2 O 2 and S 2 O 8 2− , however persulfate showed a significant efficiency even at pH 6, interesting feature in the light of decreasing the wastewater treatment costs. By the addition of selective quenching agents, % OH and SO 4 %-were identified as the main reactive species involved in the BPA abatement. An important contribution of the S 2 O 8 2− photolysis on the overall BPA transformation was highlighted. The reuse of the catalyst was investigated and similar efficiency using H 2 O 2 and S 2 O 8 2− activation was observed until the third catalytic cycle. Experiments carried out using real wastewater samples, showed a good, even if less efficient compared to pure water, BPA removal.

The photocatalytic activity of graphitic carbon nitride (g-C3N4) is actually a hot topic in the field of photocatalysis, as more than one thousand papers have been published in 2019 regarding the photocatalytic properties of this material. Here, we critically evaluated the state-of-the-art focusing on (i) the photophysical and electrochemical properties of this organic semiconductor; (ii) the proposed methods of synthesis that affect dramatically its properties starting from the stoichiometry and the p- or n-type nature; (iii) the features of the heterojunctions in g-C3N4-based hybrid heterostructures (binary, ternary, or also of higher complexity); (iv) its photocatalytic and photochemical applications; and (v) its uses in processes and technologies beyond (photo)catalysis (e.g., analytical applications). The photocatalytic applications of g-C3N4 are reviewed in the light of its overall semiconducting properties and chemical reactivity, focusing on the water photosplitting, the artificial photosynthesis, and photocatalytic CO2 reduction, its use in advanced oxidation processes for the abatement of (bio)recalcitrant pollutants and for photocatalytic disinfection, and last, as photoactivated catalyst for the synthesis of value-added compounds in organic syntheses. Some conclusions regarding the properties of this material and its more promising applications are drawn, together with some general perspectives of this organic semiconductor in the field of photocatalysis.

Summarization: This work reports for the first time the UVC photodegradation of cilastatin, a renal dehydropeptidase inhibitor co-adminstered with the imipenem antibiotic. Initially, solutions of cilastatin at varying concentrations were prepared in ultra-pure water and the direct photolysis of cilastatin was monitored under 254-nm irradiation. Degradation was slower at higher initial cilastatin concentrations, due to absorption saturation. Of the different eluting photoproducts, only one was tentatively identified as oxidized cilastatin bearing a sulfoxide group. UV-254 photolysis occurred faster at lower pH values, because the protonated forms of the molecule (H3A+, H2A) have both higher absorption coefficients and higher photolysis quantum yields than the non-protonated ones (HA−, A2−). The direct photolysis of cilastatin does not involve •OH, as excluded by experiments in which t-butanol was added as •OH scavenger, whereas the presence of humic acids inhibited photolysis due to competition for radiation absorption. The same explanation partially accounts for the observation that the photolysis kinetics of cilastatin was slower in tap water, river water and treated wastewater samples compared to ultra-pure water. Moreover, the direct photolysis quantum yield was also lower in water matrices compared to ultra-pure water. Similar findings reported for triclosan and the herbicide 2-methyl-4-chlorophenoxyacetic acid in previous studies might suggest that the water matrix components could carry out either physical quenching of cilastatin's excited states or back-reduction to cilastatin of the partially oxidized degradation intermediates. Overall, the present results demonstrate that UVC irradiation is a fast and efficient process for the degradation of cilastatin in natural water and treated wastewater. Presented on: Chemosphere

The Fenton process activated by Zero Valent Iron (ZVI-Fenton) is shown here to effectively remove antibiotics reserved for hospital settings (specifically used to treat antibiotic-resistant infections) from wastewater, thereby helping in the fight against bacterial resistance. Effective degradation of cefazolin, imipenem and vancomycin in real urban wastewater was achieved at pH 5, which is quite near neutrality when compared with classic Fenton that works effectively at pH 3–4. The possibility to operate successfully at pH 5 has several advantages compared to operation at lower pH values: (i) lower reagent costs for pH adjustment; (ii) insignificant impact on wastewater conductivity, because lesser acid is required to acidify and lesser or no base for neutralization; (iii) undetectable release of dissolved Fe, which could otherwise be an issue for wastewater quality. The cost of reagents for the treatment ranges between 0.04 and 0.07 $ m−3, which looks very suitable for practical applications. The structures of the degradation intermediates of the studied antibiotics and their likely abundance suggest that, once the primary compound is eliminated, most of the potential to trigger antibiotic action has been removed. Application of the ZVI-Fenton technique to wastewater treatment could considerably lower the possibility for antibiotics to trigger the development of resistance in bacteria.

The performance of a photocatalytic device for VOC abatement was studied at typical environmental concentrations (C0 at ppb and sub-ppb levels) using urban air in a Continuous-flow Stirred-Tank Reactor (CSTR). The photocatalytic performance was evaluated for 42 VOCs at ppb and sub-ppb concentrations and the photocatalytic kinetic constant for abatement k was measured for each specific compound. An overall value of k was also obtained for the sum of all quantified VOCs. The kinetic constant k allows to predict the time needed to abate the substrate down to the desired residual concentration and to define the correct sanitization protocol. The kinetic constant k depends on the effective concentration in accordance with the basic kinetic model already reported for the photocatalytic process. This model foresees the transformation rate of a substrate as a function of a bundle of microscopic kinetic constants, the concentration of the substrate at the surface and the adsorbed photon flux. From this model it was possible i) to correlate the k value with microscopic catalytic parameters and the VOC concentration; ii) to obtain useful suggestions for the standardization of test methods on gaseous pollutants. Clear indications were also obtained on the actual ability of photocatalytic devices to abate urban VOCs. Since many of them are quickly degradable and some fully halogenated hydrocarbons found in urban air are not, this research can also help to decide which organic compounds are suitable for standardization testing or to use a mixture of a majority of them.

Benzotriazoles are a new class of organic emerging pollutants ubiquitously found in the environment. The increase of their concentration to detectable values is the consequence of the inability of the Conventional Waste Water Plants (CWWPs) to abate these products. We subjected 1H-benzotriazole (BTz), tolyltriazole (TTz), and Tinuvin P (TP, a common UV plastic stabilizer) to photocatalytic degradation under UV-irradiated TiO2 in different conditions. The principal photoformed intermediates, the relationship between the degradation rate and the pH, the degree of mineralization, and the fate of the organic nitrogen were investigated. Under the adopted experimental conditions, all the studied substrates were rapidly photocatalytically transformed (the maximum degradation rates for BTz and TTz were (3.88 &plusmn, 0.05) &times, 10&minus, 2 and (2.11 &plusmn, 0.09) &times, 2 mM min&minus, 1, respectively) and mineralized (the mineralization rate for BTz and TTz was 4.0 &times, 3 mM C min&minus, 1 for both substrates). Different from the 1,2,4-triazole rings that are not completely mineralized under photocatalytic conditions, 1H-benzotriazole and tolyltriazole were completely mineralized with a mechanism that involved a partial conversion of organic nitrogen to N2. The photocatalytic process activated by UV-irradiated TiO2 is an efficient tool to abate 1H-benzotriazole and its derivatives, avoiding their release in the environment.

Superoxide, produced photochemically as well as microbially, is an important reactant present in seawater and a major source of hydrogen peroxide. Superoxide decay may occur through catalyzed or uncatalyzed dismutation forming H2O2 and O2, through oxidation to O2, or through reduction into H2O2. Under definite circumstances, the redox processes that are different from dismutation could produce or consume H+, thereby altering the pH of seawater. In order to alter the pH, these processes have to involve, together with O2•, redox couples that exchange e and H+ in a ratio other than 1:1. This potential pH modification is dependent on several factors, including the extent of H+ imbalance, the rate of formation/transformation of superoxide (which reaches a steady-state concentration in seawater), and the alkalinity of seawater (which varies globally from 2.10 to 2.45 mmol L1 and buffers the pH variations). In the present study, an estimate of the possible pH changes associated with photochemically-produced superoxide in the global ocean has been provided. Among the important approximations that were required to perform the calculations, one was that it was not possible to include the microbially generated O2•, as a geographic distribution of microbial processes is not available. Unfortunately, the microbial production of O2• is comparable to or at certain times even higher than its photochemical production. Despite the above-stated and certain other limitations, it may be inferred that the tropical and equatorial oceans, because of the high O2• photoproduction rates, would be having the highest potential of undergoing pH variations (up to 0.005 pH units in ten years). Along the tropical/equatorial latitude belt, at comparable sunlight irradiance, such variations are expected to be the largest (0.005 pH units) in the Indian Ocean due to a relatively low alkalinity, in the range of 2.2–2.3 mmol L1. The lowest variations (0.003–0.004 pH units) are expected in the Atlantic Ocean, because of a relatively high alkalinity in the range of 2.3–2.4 mmol L1. The main requirement for the O2• chemistry to impact the pH of seawater significantly is that the H+-imbalance reactions should be maintained for a sufficiently long period of time. The pH effect is most probably to be operational in the river-impacted coastal areas (potential candidates are the areas affected by the following rivers: Ganges, Mekong, Irrawaddy, Zambezi, Amazon River, Orinoco, Mississippi, and Rio Grande), which are characterized by a continuous flow of redox-active organic compounds into the seawater.

The light absorption and scattering play a prominent and often underrated role in the overall photocatalytic process and heavily affect the rate. This is particularly important for the choice of the catalyst in addition to other chemical and physical parameters usually considered for their catalytic role. Here we propose an approximated but easy-to-apply method to evaluate the light harvested by the photocatalyst slurry and its scattering/absorption coefficients, which does not require the use of complex spectrophotometric tools and the complicated radiative transport equation. The optical properties are obtained with the lamp and in the experimental setup employed in the photocatalytic batch tests. Among the four TiO2 specimens considered, we characterized Evonik P25 and Hombikat UV100. The obtained scattering and absorption coefficients helped in rationalizing the experimental results on the degradation of formic acid at low concentration. From the rate dependence on the catalyst concentration, this approach allowed further understanding of the role of catalyst-specific properties affecting the overall catalytic performance. This approach is proposed as a starting point for fixing conditions to compare different photocatalysts.

The photochemical fate of the herbicide bentazone was assessed by lab experiments and modeling tools. Experimental and modeling results showed that bentazone is mainly photodegraded by direct photolysis in natural water samples, even in the presence of dissolved organic matter (DOM) that can act as light-screening agent, photosensitizer and scavenger of reactive species. Even when it was dissolved in natural water samples containing different DOM amounts, the phototransformation kinetics of bentazone was unchanged compared to irradiation runs in ultrapure water. This finding suggests that the DOM and the other components of our samples did not affect the direct photolysis of bentazone by light-absorption competition, at least at the experimental optical path lengths, and did not induce significant indirect photodegradation by producing reactive transient species. Photochemical modeling in a lake-water photoreactivity scenario corroborated the observed experimental results, showing the predominant role of direct photolysis in the overall (direct + indirect) photodegradation of bentazone at different water depths and DOM contents. However, the model predicted a minor but non-negligible contribution of indirect photochemistry (i.e., reactions triggered by HO•, CO3•− and 3CDOM*) to the herbicide degradation. This contribution (especially by 3CDOM*) could become crucial in deep and DOM-rich water bodies. Finally, several photoproducts formed by direct photolysis and HO•-induced photodegradation were identified, which should not be particularly toxic for aquatic organisms and Vibrio fischeri bacteria.

The Fenton reaction is an effective advanced oxidation process occurring in nature and applied in engineering processes toward the degradation of harmful substances, including contaminants of emerging concern. The traditional Fenton application can be remarkably improved by using iron complexes with organic ligands, which allow for the degradation of contaminants at near-neutral pH and for the reduction of sludge production. This work discusses the mechanisms involved both in the classic Fenton process and in the presence of ligands that coordinate iron. Cyclohexane was selected as mechanistic probe, by following the formation of the relevant products, namely, cyclohexanol (A) and cyclohexanone (K). As expected, the classic Fenton process was associated with an A/K ratio of approximately 1, evidence of a dominant free radical behavior. Significantly, the presence of widely common natural and synthetic carboxyl ligands selectively produced mostly the alcoholic species in the first oxidation step. A ferryl-based mechanism was thus preferred when iron complexes were formed. Common iron ligands are here proven to direct the reaction pathway towards a selective metal-based catalysis. Such a system may be more easily engineered than a free radical-based one to safely remove hazardous contaminants from water and minimize the production of harmful intermediates.

The complete removal of biorecalcitrant xenobiotics, including most notably the pharmaceutical pollutants, by advanced oxidation processes is often difficult to be reached in urban or industrial wastewater because of the high concentration of organic and inorganic scavengers that compete with the xenobiotics for the oxidizing species. This work investigates a coupled treatment train in which wastewater effluents are pretreated with a negatively charged loose nanofiltration (NF) membrane (HydraCoRe70, made up of sulfonated polyethersulfone) to enhance the removal of xenobiotics with the thermal Fenton process. Carbamazepine (CBZ), a drug prescribed mainly for epilepsy treatment, is used here as a model xenobiotic. After optimizing the conditions for separation and degradation, the NF–Fenton approach was applied to both synthetic wastewater and real samples to assess the overall efficiency of CBZ removal. The Fenton degradation of CBZ was drastically enhanced in nanofiltered samples, thanks to the removal by the membrane of nearly all organic matter that would otherwise consume the reactive oxidizing species (e.g., the hydroxyl radical). On the basis of a preliminary treatment cost analysis, it can be concluded that the combined process is potentially applicable to the treatment of several kinds of wastewaters (e.g., industrial ones) to favor the removal of biorecalcitrant contaminants. Key cost savings of NF–Fenton concern the lower amounts of Fenton reagents needed to degrade CBZ and (even more importantly) the decreased levels of acids and bases for pH adjustment before and after the oxidative process because of the lower buffer capacity of the NF permeate compared to feed wastewater, after the removal by the NF of many inorganic ions and most organic carbon.

International audience; The secondary pollutant 3,4-dichloroaniline (DCA) is produced by the biological degradation of several herbicides, including propanil in paddy fields. The enzymatic hydrolysis of propanil yields DCA with almost quantitative yield. DCA undergoes rather fast photodegradation in paddy water, mostly by direct photolysis. An exception might be represented by the cases (rather rare in paddies) of quite high nitrate concentration (around 50 mg of NO3– L–1), when DCA degradation by CO3•– would play a comparable role to that by direct photolysis. The experimentally measured photoreactivity parameters were used as input data for a photochemical model, which predicted a DCA lifetime of 0.5–1 days in sunlit paddy fields in late May, when propanil is usually applied. The model predictions compare remarkably well with the DCA attenuation data reported in field studies, carried out in paddies in temperate regions. Moreover, a consecutive reaction model based on typical biological (propanil) and photochemical (DCA) lifetimes reproduced quite well the time trends of both compounds in paddies, as reported in the literature. These successful comparisons suggest that photodegradation in general, and direct photolysis in particular, may play a key role in DCA attenuation in paddy water.

Humic substances are poorly known, though they represent a major pool of non-biotic organic carbon on earth. In particular, there is little knowledge on the formation of humic substances by irradiation of organic matter dissolved in waters. Specifically, it is known that humic substances can be formed from proteins by photochemical processes in surface waters, but the role of single amino acids and their transformation pathways are not yet known. Therefore, here we studied the phototransformation of aqueous l-tryptophan under simulated sunlight. Irradiated l-tryptophan solutions were analyzed by absorption, fluorescence, nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopies, chromatography, potentiometry and mass spectrometry (MS). The solutions appeared turbid after irradiation; therefore, nephelometry and dynamic laser light scattering were used to characterize the suspended particles. Results show that about 95% of l-tryptophan was degraded in 8-h irradiation, undergoing deamination and decarboxylation of the amino acidic moieties to release ammonium and formate. The MS signal at m/z 146 suggests the formation of 3-ethylindole, while pH-metric and NMR data revealed the presence of hydroxylated compounds. The phototransformation intermediates of l-tryptophan had fluorescence and absorption spectra similar to those of humic substances, they were able to produce ·OH upon irradiation and tended to aggregate by both ionic and hydrophobic interactions. Overall, our findings reveal for the first time the nature of products formed upon phototransformation of l-tryptophan. Interestingly, the transformation of l-tryptophan is quite different from that of the previously studied l-tyrosine, although both compounds produce humic-like materials under irradiation.

Tannic acid (TA) belongs to the class of hydrolysable tannins that are natural polymers derived from the vegetable kingdom. Although TA is described as a molecule with a central core of glucose esterified with five digallic units, its molecular structure has not yet been completely clarified. Actually, TA is described as a mixture of different compounds. In this work, by using potentiometry, UV-vis and fluorescence spectroscopy, as well as ab initio calculations we identified the protonation properties and spectroscopic features of TA. A preliminary investigation on gallic acid (GA), present as an impurity in the commercial TA mixture, and on methyl 3,4,5-trihydroxybenzoate served as a benchmark for the computational work and gave insight into the contribution of GA to the TA properties. GA principally affects the pH of TA solutions and the fluorescence signals. The data showed the presence of three main types of protogenic groups that can be assigned to the typical TA structure, with pKa values included in the range of 6–8.5, which can be ascribed to the phenolic functions. The least acidic site shows the highest concentrations, and the dissociation of half of the TA phenolic groups takes place at pH ∼ 7.8. The UV-vis spectra of the protonated and deprotonated species were obtained through data elaboration by stoichiometric and chemometric approaches. The results show main absorption maxima (277 and 323 nm, respectively) similar to those obtained using ab initio calculations. Overall, we achieved a remarkable coherence among the outcomes obtained by using different methodologies.

Membrane distillation is a promising technology to desalinate hypersaline produced waters. However, the organic content can foul and wet the membrane, while some fractions may pass into the distillate and impair its quality. In this study, the applicability of the traditional Fenton process was investigated and preliminarily optimized as a pre-treatment of a synthetic hypersaline produced water for the following step of membrane distillation. The Fenton process was also compared to a modified Fenton system, whereby safe iron ligands, i.e., ethylenediamine-N,N′-disuccinate and citrate, were used to overcome practical limitations of the traditional reaction. The oxidation pre-treatments achieved up to 55% removal of the dissolved organic carbon and almost complete degradation of the low molecular weight toxic organic contaminants. The pre-treatment steps did not improve the productivity of the membrane distillation process, but they allowed for obtaining a final effluent with significantly higher quality in terms of organic content and reduced Vibrio fischeri inhibition, with half maximal effective concentration (EC50) values up to 25 times those measured for the raw produced water. The addition of iron ligands during the oxidation step simplified the process, but resulted in an effluent of slightly lower quality in terms of toxicity compared to the use of traditional Fenton.

The interest toward the development of hybrid photocatalytic materials is exponentially grown in the last decade. In this review, we summarize the current research progresses in the production of hybrid materials, with a particular focus on carbon based material coupled with titanium dioxide, photobiocatalysts, and their application in the removal of emerging contaminants from water, i.e. pharmaceutical products. We give some highlights on the key properties and features of these advanced composites, the involved mechanisms and on the potential hazards posed by these nanomaterials.

Different amounts of graphene oxide were chemically reduced with hydrazine in the presence of nanometric TiO 2 and SiO 2 . The photocatalytic performance of the resulting hybrid materials was compared with pristine supports using phenol and methylene blue (MB) under two different irradiation conditions (UV–vis and Vis only light). MB is strongly adsorbed on the hybrid materials. Significant MB degradation rates were observed on pristine TiO 2 and hybrid TiO 2 -reduced graphene oxide (rGO) material under both irradiation conditions. In the presence of the hybrid catalyst, the degradation of MB under Vis is due to the dye-sensitized mechanism, while under UV–vis there is an additional semiconductor-based photocatalytic mechanism. Conversely, the presence of rGO reduces the rate of photocatalytic transformation for the poorly adsorbed phenol under UV irradiation, and a negligible degradation rate was observed under Vis. The UV–vis absorption spectra of aqueous suspensions of hybrid materials with different rGO loading indicate a strong interaction of the two materials and a reduction of the light absorption due to the presence of rGO. Among many mechanisms reported on the role of rGO, it is inferred that the working mechanism involves electron transfer from photoexcited states of rGO onto the titania, and holes migration from titania to rGO, where adsorbed substrates are oxidized. This oxidation is possible only if the substrate HOMO has higher energy (less positive standard redox potential) than the empty states of excited rGO, supposedly for MB and not for phenol. Then, reduced graphene is advantageous when substrates are adsorbed and when the charge separation is possible (coupled with a proper semiconductor like TiO 2 ). Alone, or coupled with low work function oxides like SiO 2 , rGO could be ineffective.

International audience; When irradiated in paddy-field water, propanil (PRP) undergoes photodegradation by direct photolysis, by reactions with •OH and CO3•–, and possibly also with the triplet states of chromophoric dissolved organic matter. Irradiation also inhibits the nonphotochemical (probably biological) degradation of PRP. The dark- and light-induced pathways can be easily distinguished because 3,4-dichloroaniline (34DCA, a transformation intermediate of considerable environmental concern) is produced with almost 100% yield in the dark but not at all through photochemical pathways. This issue allows an easy assessment of the dark process(es) under irradiation. In the natural environment, we expect PRP photodegradation to be important only in the presence of elevated nitrate and/or nitrite levels, e.g., [NO3–] approaching 1 mmol L–1 (corresponding to approximately 60 mg L–1). Under these circumstances, •OH and CO3•– would play a major role in PRP phototransformation. Because flooded paddy fields are efficient denitrification bioreactors that can achieve decontamination of nitrate-rich water used for irrigation, irrigation with such water would both enhance PRP photodegradation and divert PRP dissipation processes away from the production of 34DCA, at least in the daylight hours.

International audience; Phototransformation is important for the fate in surface waters of the pharmaceuticals diclofenac (DIC) and naproxen (NAP) and for clofibric acid (CLO), a metabolite of the drug clofibrate. The goal of this paper is to provide an overview of the prevailing photochemical processes, which these compounds undergo in the different conditions found in freshwater environments. The modelled photochemical half-life times of NAP and DIC range from a few days to some months, depending on water conditions (chemistry and depth) and on the season. The model indicates that direct photolysis is the dominant degradation pathway of DIC and NAP in sunlit surface waters, and potentially toxic cyclic amides were detected as intermediates of DIC direct phototransformation. With modelled half-life times in the month-year range, CLO is predicted to be more photostable than DIC or NAP and to be degraded mainly by reaction with the •OH radical and with the triplet states of chromophoric dissolved organic matter (3CDOM*). The CLO intermediates arising from these processes and detected in this study (hydroquinone and 4-chlorophenol) are, respectively, a chronic toxicant to aquatic organisms and a possible carcinogen for humans. Hydroquinone is formed with only ∼5% yield upon CLO triplet-sensitised transformation, but it is highly toxic for algae and crustaceans. In contrast, the formation yield of 4-chlorophenol reaches ∼50% upon triplet sensitisation and ∼10% by ·OH reaction. The comparison of model predictions with field data from a previous study yielded a very good agreement in the case of DIC and, when using 4-carboxybenzophenone as proxy for triplet sensitisation by CDOM, a good agreement was found for CLO as well. In the case of NAP, the comparison with field data suggests that its direct photolysis quantum yield approaches or even falls below the lower range of literature values.

The prolonged “Millennium” drought affecting Australia in the 2000s had important consequences on surface-water bodies, including the Lower Lakes (Lake Alexandrina and Lake Albert) located at the terminal end of the River Murray system. Shallower water depths, limited solute dilution and altered geochemical processes ensured that the concentration values of several water constituents increased considerably during drought, including the water parameters of photochemical significance (nitrate, bicarbonate, carbonate and the dissolved organic carbon, DOC). The aim of this study was to model the photochemical processes in the Lower Lakes during the drought and post-drought periods, to provide insight into the changes that photoinduced reactions can undergo in periods of water scarcity. Among the photochemical processes involved in the light-assisted transformation of dissolved compounds, an important role is played by indirect photochemistry where degradation is triggered by photogenerated transient species such as hydroxyl ( OH) and carbonate (CO3 −) radicals, and the triplet states of chromophoric dissolved organic matter (3CDOM*). Results of photochemical modelling suggest that the reactions induced by 3CDOM* would be enhanced during drought, while the processes triggered by OH and CO3 − would be less modified. For compounds undergoing efficient degradation with 3CDOM*, enhanced photochemistry during drought could offset the higher concentration values resulting from lower dilution. In contrast, for compounds mainly degraded by OH or CO3 − the drought period could produce a concentration increase not balanced by an increment in the photochemical reactivity of the water body.

International audience