Search

We present a photoactive composite material for water decontamination consisting of non-purified commercial multiwalled carbon nanotubes (CNT(NP)s) supported on an electrospun polymeric mat made of core–sheath polyacrylonitrile–polypyrrole nanofibers. This is the first system that specifically exploits the superior photocatalytic activity of CNT(NP)s compared with the purified carbon nanotubes usually employed. A CNT(NP) still contains the catalytic metal oxide nanoparticles (NPs) used for its synthesis, embedded in the nanotube structure. Under UV-visible irradiation, these NPs generate highly reactive ˙OH radicals capable of degrading the organic molecules adsorbed on the nanotube. Photocatalytic tests on the composite material show that CNT(NP)s act mostly as a source of photogenerated charge carriers. The adsorption of target substrates occurs preferentially onto the polypyrrole sheath, which shuttles the reactive carriers from CNT(NP)s to the substrates. In addition, UV-visible irradiation of semiconducting polypyrrole generates radical species that directly react with the adsorbed substrates. All synthetic procedures reported are scalable and sustainable. This mechanically resistant and flexible composite overcomes one of the weakest aspects of water treatments that employ suspended nanocatalysts, namely the expensive and poorly scalable recovery of the catalyst through nanofiltration. All these features are required for large-scale photocatalytic treatments of polluted water., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Efficient solar water photosplitting is plagued by large overpotentials of the HER and OER. Even with a noble metal catalyst, the hydrogen evolution reaction can be limited by the strong M-H bonding over some metals, such as Pt, Pd, and Rh, inhibiting hydrogen desorption. H absorption is regulated by the potential at the metal nanoparticles. Through controlled periodic illumination of a Pt/TiO2 suspension, we hypothesized a fast variation of the photopotential that induced catalytic surface resonance on the metal, resulting in more than a 50% increase of the efficiency at frequencies higher than 80 Hz.

Understanding the correlation between the morphological and functional properties of particulate materials is crucial across all fields of physical and natural sciences. This manuscript reports on the investigation of the effect of polyethylene glycol (PEG) employed as a capping agent in the synthesis of SrTiO3 crystals. The crucial influence of PEG on both the shape and size of the strontium titanate particles is revealed, highlighting the effect on the photocurrents measured under UV&ndash, Vis irradiation.

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.

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.

Photocatalytic building materials, asphalts for road paving, pigments and coatings have been shown to be a promising remediation technique for air pollutants such as NOx and VOC’s. An open issue is the durability of the air cleaning characteristic in time of deployed material. Current ISO standards for photocatalytic activity testing are time consuming and cannot be used directly on-site to follow the activity of the material surface in time. The present work describes a new portable system for assessing the photo-catalytic activity of the surface of a material. The system is composed of a continuously stirred continuous flow photoreactor with a very low volume chamber (15 mL) including a 4 cm diameter opening. This opening is equipped with a gasket system that assure very good seal when the reactor lay on the surface to be tested. The gaseous phase is mixed with a UV transparent turbine. The surface is uniformly irradiated with an adjustable LED source. A gaseous stream containing a substrate (e.g. NO) is fluxed in the photoreactor. The outflow from the reactor is monitored with the proper sensor (Photoionization detector for VOC, electrochemical sensor for NOx). The portability and the low volume of the reaction chamber allow to carry out very fast measurements (few minutes) on-site, with several advantages in terms of time, costs, making very easy the durability control of deployed photocatalytic materials, also on rough surfaces. Here we report the description of the photoreactor and its characterization by using anatase TiO2 films as active materials and NO as substrate.

p-Type organic semiconductors are attractive to develop new photo- and photoelectro-catalytic systems, particularly if the conduction band is located at negative redox potentials. An easy synthetic route to produce carbon-doped carbon nitride (Cn>3N4) with a stable p-type semiconducting character was optimized. The precursors used were melamine and triaminopyrimidine. The p-type Cn>3N4 exhibited a remarkable photoactivity under visible light compared with pristine C3N4, which is a stable n-type organic semiconductor deeply studied as heterogeneous photocatalyst for many environmental applications. The photoelectrochemical features of the synthesized p-type materials and pristine C3N4 were deeply investigated with chronopotentiometry and cyclic voltammetry, in the dark and under different illumination conditions, and then compared with the photocatalytic activity using 2-fluorophenol as substrate and different radiation sources. The p-doping with carbon of C3N4 reduces the band gap, slightly moves the potential of the valence band, and increases the conduction band to more positive potentials, thus precluding the application of these materials when large negative redox potentials are needed.

International audience

Hydrogen production via formate photoreforming on TiO2 is characterized by marked dependence on the ratio between {101} and {001} surfaces for anatase nanoparticles. We observed higher rates of hyd...

Carbon nitride nanoparticles (CNNPs) have been employed as fluorescent sensing tools owing to their unique features, e.g. low cost production, high stability in water and high photoluminescence quantum yield. Here, an easy and versatile synthetic approach was exploited to design fluorescent nanoparticles with surface functionalities suitable for covalent binding to bioligands. High hydrophilic, brightly fluorescent CNNPs, rich of superficial amines, were obtained from the thermal condensation of urea and lysine (CNNPLys) and by tuning the precursor ratio and the heating time. Structure and size of the functionalized nanoparticles were characterized through infrared (IR) spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS). Their optical properties were studied by ultraviolet-visible (UV-Vis) and fluorescence spectroscopy. The superficial primary amino groups, furnished by the lysine co-precursor, enabled for covalently linking CNNPLys to model proteins. The CNNPLys-protein conjugates excited under UV irradiation emit in the 400–450 nm visible range (quantum yield 24%). The applicability of CNNPLys as novel fluorescent probes was demonstrated by a fluorescence quenching assay, in which gold nanoparticles (GNPs) were attached to Staphylococcal protein A and employed to quench the CNNPLys fluorescence by resonant energy transfer (FRET). The quenching occurred upon formation of the specific binding between the GNP-linked protein A and CNNPLys-tagged immunoglobulins, while the inhibition of the binding resulted in the recovery of CNNPLys luminescence. The synthetic strategy, based on combining a “conjugated polymer”-forming unit (urea) and a co-precursor able to provide the desired functional group (lysine), allows designing innovative materials for the development of new generation fluorescence biosensors in which easily functionalized fluorophores are needed.

It has been often reported that an efficient and green photocatalytic dissociation of water under irradiated semiconductors likely represents the most important goal for modern chemistry. Despite decades of intensive work on this topic, the efficiency of the water photolytic process under irradiated semiconductors is far from reaching significant photocatalytic efficiency. The use of a sacrificial agent as hole scavenger dramatically increases the hydrogen production rate and might represent the classic “kill two birds with one stone”: on the one hand, the production of hydrogen, then usable as energy carrier, on the other, the treatment of water for the abatement of pollutants used as sacrificial agents. Among metal oxides, TiO2 has a central role due to its versatility and inexpensiveness that allows an extended applicability in several scientific and technological fields. In this review we focus on the hydrogen production on irradiated TiO2 and its fundamental and environmental implications.

The photocatalytic performance of pristine and rare earth elements (La, Ce, Pr, Er, Yb) doped zinc oxide was tested toward the abatement of a model pollutant in MilliQ water and wastewater matrices. ZnO doped with Ce, Er and particularly with Yb exhibited photoactivity higher than bare zinc oxide and the benchmark TiO2 P25, especially in wastewater matrix. Several electrochemical investigations were performed via chronopotentiometry and cyclic voltammetry aimed to shed light on the reasons why the diverse materials behaved differently. From the overall data a complex picture emerged, where there is not a single property of the materials evidently outperforming the others. Nonetheless, from the analysis of whole data a limited role of doping emerged for La and Pr, doping with Er improved the photocurrent, doping with Yb favored a better accumulation of photoelectrons, and doping with Ce promoted a faster electron transfer.

International audience; By a combination of transient absorption spectroscopy and steady-state irradiation experiments, we investigated the transformation of phenol and furfuryl alcohol (FFA) sensitised by irradiated 4-carboxybenzophenone (CBBP). The latter is a reasonable proxy molecule to assess the reactivity of the excited triplet states of the chromophoric dissolved organic matter that occurs in natural waters. The main reactive species for the transformation of both phenol and FFA was the CBBP triplet state, despite the fact that FFA is a commonly used probe for 1O2. In the case of FFA it was possible to develop a simple kinetic model that fitted well the experimental data obtained by steady-state irradiation, in a wide range of FFA concentration values. In the case of phenol the model was made much more complex by the likely occurrence of back reactions between radical species (e.g., phenoxyl and superoxide). This problem can be tackled by considering only the experimental data at low phenol concentration, where the degradation rate increases linearly with concentration. We do not recommend the use of 1O2 scavengers/quenchers such as sodium azide to elucidate CBBP photoreaction pathways, because the azide provides misleading results by also acting as a triplet-state quencher. Based on the experimental data, we propose a methodology for the measurement of the CBBP triplet-sensitisation rate constants from steady-state irradiation experiments, allowing for a better assessment of the triplet-sensitised degradation of emerging contaminants.

The photodegradation of gaseous perchloroethylene (PCE) was investigated on titanium dioxide under UV light at 365 nm at the gas/solid interface in a CSTR photo-reactor (Continuous Stirred Tank Reactor). The rate and products are strongly affected by oxygen presence. Gaseous products of PCE degradation agree with literature. The production of active chlorine (sum of Cl2, HClO, ClO and ClO2) was investigated both in the presence of oxygen and in anoxic conditions. At low O2 concentration no gaseous active chlorine was determined, while a significant amount was measured in the presence of oxygen. By considering that in the absence of O2 the only possible form of active chlorine is Cl2, this highlights that Cl is not produced, and that chain reactions promoted by the chlorine radical do not occur on the TiO2 surface. The photocatalytic transformation of C2Cl4 was investigated at different concentrations. The rate follows a first order kinetic that is rationalized with a photocatalytic kinetic model in which the substrate is able to react simultaneously with both photogenerated holes and electrons. In anoxic conditions adsorbed halogenated organic compounds with molecular weights higher than that of PCE were produced and chloride ions accumulated at the surface. Reductive pathways have a key role in PCE degradation. The water vapor has a detrimental role on the PCE transformation rate due to the competition with PCE adsorption on reactive sites with 2:1 stoichiometry. The addition of chloride ions on TiO2 surface slows down the PCE degradation rate and the production of gaseous CCl4 but increments that of C2Cl6 in anoxic conditions. This is rationalized by a mechanism in which direct hole transfer to substrate occurs followed by chloride anion addition to the carbocation.

The kinetic of photocatalytic degradation of 2,4-DCP and 1-naphthol on hybrids TiO2/reduced-Graphene Oxide (TiO2/rGO) obtained with two commercial TiO2 specimens and different % rGO loadings was investigated under different irradiation conditions (UV only, UV + Vis and Vis only). 2,4-DCP adsorbs strongly on the rGO phase. With the increment of the rGO loading no increment on the overall reaction rate under UV and UV + Vis irradiation is observed, while a very low but not null photoactivity that increases with the increment of %rGO is observed under Vis only irradiation. It is here proposed for the first time a quantitative kinetic model able to predict the photocatalytic rate of hybrid photocatalysts composed of two phases (whatever the nature of the phases is) with different light absorption and intrinsic reactivity, diverse ability to adsorb the substrate and to partition charge carriers depending on their band alignment. The model is able to decouple the adsorption effect from the kinetic ones. From the analysis of the adsorption and kinetic data at different rGO loadings emerges that: 2,4-DCP partitions preferentially on the rGO phase; the operational photocatalytic mechanism is based on the band-to-band transition promoted by the UV absorption of the semiconductor; rGO shows a negligible but not null visible photoactivity toward 2,4-DCP; the photo-promoted TiO2 conduction band electrons are not injected into rGO where 2,4-DCP is mainly adsorbed. In this light some hypothesis are proposed to justify the negative effect of rGO on the overall oxidative photoactivity.

International audience; Irradiated nitrophenols can produce nitrite and nitrous acid (HONO) in bulk aqueous solutions and in viscous aqueous films, simulating the conditions of a high-solute-strength aqueous aerosol, with comparable quantum yields in solution and viscous films (10–5–10–4 in the case of 4-nitrophenol) and overall reaction yields up to 0.3 in solution. The process is particularly important for the para-nitrophenols, possibly because their less sterically hindered nitro groups can be released more easily as nitrite and HONO. The nitrophenols giving the highest photoproduction rates of nitrite and HONO (most notably, 4-nitrophenol and 2-methyl-4-nitrophenol) could significantly contribute to the occurrence of nitrite in aqueous phases in contact with the atmosphere. Interestingly, dew-water evaporation has shown potential to contribute to the gas-phase HONO levels during the morning, which accounts for the possible importance of the studied process.

Particle aggregation and agglomeration influence the optical properties of materials and therefore their ability to absorb and scatter the incoming radiation, also affecting their photocatalytic activity [1] , [2] , [3] , [4] , [5] , [6] , [7] . We have studied the correlation between aggregation and photocatalytic activity for titanium dioxide by means of experimental measurements of extinction and photocatalytic activity and calculations of their optical properties (extinction, absorption and scattering cross-sections). This approach can be adopted to quantitatively assess the quantum yields of the heterogeneous photocatalytic systems. The study was performed on TiO2 PC105 Cristal ACTiV™, made of aggregated (and agglomerated) primary particles of anatase. The size of the aggregates has been reduced with ultra-sonication. Aqueous suspensions of the obtained materials were characterized by measuring the optical properties (UV–vis extinction), the sizing properties (DLS) and the photocatalytic activity (degradation of phenol under standard conditions). The extinction and absorption spectra of the suspensions were derived from the calculated coefficients, considering also the size distributions measured with DLS, and revealed that light absorption is maximized when particle aggregation and agglomeration are avoided, while diffusion of the incoming radiation dominates when large aggregates and agglomerates are present. The present paper represents a valuable approach to the accurate and reproducible measurement of the photocatalytic activity of TiO2 nanoparticles suspensions, thus allowing a more reliable comparison of the properties of different materials.

The photochemical reactivity of three ionic liquids (1-ethylpyridinium tetrafluoroborate, 1-butyl-4-methylpyridinium tetrafluoroborate, and 1-(3-cyanopropyl)pyridinium chloride) was studied by combining laboratory experiments and photochemical modeling, to get insight into the possible behavior in surface-water environments. Among the studied compounds, phototransformation in sunlit surface waters could be an important attenuation pathway for 1-butyl-4-methylpyridinium tetrafluoroborate (BMPOTFB). In this case the reaction with the carbonate radicals (CO3-) would prevail at low values of the dissolved organic carbon (DOC), while the direct photolysis would be important at intermediate to high DOC values. The sensitization by the triplet states of chromophoric dissolved organic matter could play a significant role at high DOC, especially in the presence of a considerable fraction of highly photoreactive pedogenic organic matter derived from soil runoff. The main processes that account for the phototransformation of BMPOTFB and produce the main detected transformation products (TPs) are hydroxylation, detachment/shortening of the butyl chain and double bond formation. Interestingly, there is a considerable overlap between the TPs formed by direct photolysis and those produced by indirect photochemistry. Some of the TPs formed from BMPOTFB are more toxic than the parent compound towards Vibrio fischeri bacteria, and account for the increase in toxicity of the irradiated mixtures. Differently from BMPOTFB, in the case of the other two studied ionic liquids the photodegradation would play a negligible role in environmental attenuation, with the possible exception of very shallow waters with low DOC.

Titanium dioxide/reduced graphene oxide (TiO2-rGO) composites were synthesized at different loadings of carbonaceous phase, characterized and used as anode materials in Lithium-ion cells, focusing not only on the high rate capability but also on the simplicity and low cost of the electrode production. It was therefore chosen to use commercial TiO2, GO was synthesized from graphite, adsorbed onto TiO2 and reduced to rGO following a chemical, a photocatalytic and an in situ photocatalytic procedure. The synthesized materials were in-depth characterized with a multi-technique approach and the electrochemical performances were correlated i) to an effective reduction of the GO oxidized moieties and ii) to the maintenance of the 2D geometry of the final graphenic structure observed. TiO2-rGO obtained with the first two procedures showed good cycle stability, high capacity and impressive rate capability particularly at 10% GO loading. The photocatalytic reduction applied in situ on preassembled electrodes showed similarly good results reaching the goal of a further simplification of the anode production.

The corrosion inhibitor 1H-benzotriazole (pKa = 8.4) can exist in two different forms in natural waters, and photochemical transformation is a potentially significant attenuation pathway for both of them. Depending on conditions, the modelled half-life times range from some days/weeks to several months. In sunlit water bodies, the acidic (neutral) form would undergo direct photolysis (accounting for up to 7% of total phototransformation) and, most notably, reaction with the hydroxyl radicals (·OH) and the triplet states of chromophoric dissolved organic matter (3CDOM*). The basic (anionic) form would undergo significant transformation with ·OH and 3CDOM*. The ·OH reactions would be more important at low dissolved organic carbon (DOC) and the 3CDOM* processes at high DOC. In the presence of highly reactive triplet-state model compounds, the two benzotriazole forms react with similar rate constants. In this case, they would show comparable half-life times in surface-water environments. With less reactive triplet states, the rate constant of the anionic form can be a couple of orders of magnitude higher than that of the neutral one. Under these circumstances, the neutral form could be considerably more photostable than the anionic one at high DOC. Therefore, depending on 3CDOM* reactivity, the solution pH may or may not play an important role in the photoattenuation kinetics of 1H-benzotriazole in sunlit natural waters, especially at high DOC. Both forms of benzotriazole yield hydroxyderivatives as their main transformation intermediates under all the relevant photochemical reaction pathways. These intermediates could be formed via ·OH-induced hydroxylation, or upon electron abstraction followed by reaction with water. Differently from UVC irradiation data reported in previous studies, the concentration of aniline upon excitation of 1H-benzotriazole under environmentally significant UV wavelengths was always below the detection limit of the analytical method used in this work (5 μmol L− 1).

International audience; The vulnerability of Zero-Valent Iron (ZVI) to passivation, which significantly decreases its surface reactivity, limits its use as a reducing agent in environmental remediation applications (e.g., permeable reactive barriers). Passivation of ZVI occurs rapidly in ambient environments due to the presence of oxygen and water, as well as during the reduction of contaminants (e.g. chlorinated and nitrated organic compounds) even in anoxic conditions. Passivated zero-valent iron (pZVI) particles are typically covered by an iron (hydr)oxide layer that entails a loss of the typical properties of this material, prevents the reductive activity to take place, and could made pZVI a waste to be disposed of. This work shows that pZVI has considerable Fenton (oxidizing) reactivity in the presence of H2O2 at acidic pH. The pZVI-Fenton process likely involves reaction between H2O2 and the pZVI surface or near-surface species, because the detected levels of leached Fe in the solution bulk were insufficient to account for the observed degradation processes. Still, leached Fe in the solution at pH 2 and 3 would be too concentrated for some possible applications (e.g. wastewater treatment, which would require an additional precipitation step to remove excess Fe). In such a case, operation at pH 4 would be preferred to maintain reasonable reactivity without measurable Fe leaching. The pZVI-Fenton process was inactive above pH 4, but reactivity could be extended up to pH 5 by UVA irradiation. Surprisingly, a pZVI sample that underwent an additional 78 day aging in aqueous solution exhibited a considerable ability to photochemically remove phenol despite a slower initial stage. These properties account for the possible use of a potential waste in decontamination reactions. © 2016 The Royal Society of Chemistry.

The shallow lakes located in Terra Nova Bay, Antarctica, are free from ice for only up to a couple of months (mid December to early/mid February) during the austral summer. In the rest of the year, the ice cover shields the light and inhibits the photochemical processes in the water columns. Previous work has shown that chromophoric dissolved organic matter (CDOM) in these lakes is very reactive photochemically. A model assessment is here provided of lake-water photoreactivity in field conditions, based on experimental data of lake water absorption spectra, chemistry and photochemistry obtained previously, taking into account the water depth and the irradiation conditions of the Antarctic summer. The chosen sample contaminants were the solar filter benzophenone-3 and the antimicrobial agent triclosan, which have very well known photoreactivity and have been found in a variety of environmental matrices in the Antarctic continent. The two compounds would have a half-life time of just a few days or less in the lake water during the Antarctic summertime, largely due to reaction with CDOM triplet states ((3)CDOM*). In general, pollutants that occur in the ice and could be released to lake water upon ice melting (around or soon after the December solstice) would be quickly photodegraded if they undergo fast reaction with (3)CDOM*. With some compounds, the important (3)CDOM* reactions might favour the production of harmful secondary pollutants, such as 2,8-dichlorodibenzodioxin from the basic (anionic) form of triclosan.

Nitrobenzene (NB) would undergo photodegradation in sunlit surface waters, mainly by direct photolysis and triplet-sensitized oxidation, with a secondary role of the *OH reaction. Its photochemical half-life time would range from a few days to a couple of months under fair-weather summertime irradiation, depending on water chemistry and depth. NB phototransformation gives phenol and the three nitrophenol isomers, in different yields depending on the considered pathway. The minor *OH role in degradation would make NB unsuitable as *OH probe in irradiated natural water samples, but the selectivity towards *OH could be increased by monitoring the formation of phenol from NB+*OH. The relevant reaction would proceed through ipso-addition of *OH on the carbon atom bearing the nitro-group, forming a pre-reactive complex that would evolve into a transition state (and then into a radical addition intermediate) with very low activation energy barrier.

Analytical methodologies for the determination of total dissolved nitrogen (TDN) in waters are based on a conversion step able to transform selectively all the nitrogen species into a compound that is then quantified. A crucial requirement to meet accuracy is the quantitative recovery of all organic and inorganic nitrogen species during the conversion step. In this work, the N recoveries of two widely employed methodologies that use different conversion steps (high temperature catalytic oxidation (HTCO) and persulfate digestion (PD)) were assessed on a set of organic nitrogen compounds, representative of the structures of both dissolved organic matter (DOM) and anthropogenic contaminants. Low recoveries are due to poor selectivity during the conversion step, with the formation of nitrogen compounds other than nitrogen oxide (HTCO) and nitrate (PD). The results show that in many instances the TDN measurements give systematically low results depending on N speciation. PD could give lower results than HTCO even for samples containing only DOM of biological origin. In particular (i) low N recovery was always observed with compounds having two or more contiguous N atoms; (ii) the HTCO method is very effective for TDN quantification in the presence of s-triazine rings while PD method did not yield satisfactory N recovery; (iii) a full N recovery was observed with compounds having amido or amino groups or nitrogen atoms in imidazole, indole and pyrimidine rings; and (iv) the N recoveries for purine derivatives are almost complete with HTCO, but give systematically low results by PD. Finally, the estimation of dissolved organic nitrogen (DON) fluxes and pools from TDN measurements can be affected by uncertainties larger than previously thought as a consequence of (i) the lower N recovery for some nitrogen compounds and (ii) the differences in the N recovery as a function of the adopted analytical methods.

The photoinduced transformation of 2,4,6-triamino-1,3,5-triazine (melamine) was studied by using different advanced oxidation technologies under a variety of experimental conditions. The systems involving homogeneous hydroxyl radicals, as generated by H2O2/hν, Fenton reagent, and sonocatalysis are ineffective. However, melamine is degraded under photocatalytic conditions or by SO4 − (S2O82−/hν). The time evolution of long-living intermediates, such as 2,4-diamino-6-hydroxy-1,3,5-triazine (ammeline) and 2-amino-4,6-dihydroxy-1,3,5-triazine (ammelide), has been followed, being 2,4,6-trihydroxy-1,3,5-triazine (cyanuric acid) the final stable product. During both photocatalytic and S2O82−/hν experiments, in the early steps, a fairly stable intermediate evolving to ammelide is observed in a large extent. This intermediate was identified as 2,4-diamino-6-nitro-1,3,5-triazine. This indicates that the primary photocatalytic event is the oxidation of the amino-group to nitro-group through several consecutive fast oxidation steps, and that a hydrolytic step leads to the release of nitrite in solution. To elucidate the nature of the oxidant species hole scavengers such as methanol and bromide ions were added to the irradiated TiO2. They completely stop the degradation, whereas chloride and fluoride ions decrease the degradation rate. The study of the photocatalytic degradation rate of melamine at increasing concentrations using two different commercial titanium dioxides, such as P25 and Merck TiO2, showed an intriguing behavior. A drastic abatement of the melamine transformation rate was observed when coagulation of the P25 slurry occurs due both to the pH change and melamine concentration effect that increase melamine adsorption. In the presence of TiO2 (Merck) the melamine initial degradation rates are significantly lower than those observed in the presence of P25 but are not depressed at larger concentrations. The experimental evidences (e.g., absence of melamine adsorption onto TiO2 surface at low concentrations or at acidic pH or due to the catalyst surface texture, and the lack of reactivity toward OH free and bound) suggest that the effective photocatalytic mechanism is based on an outer sphere direct hole transfer to the melamine. Its formal potential lies in the range 1.9–2.3 V vs NHE. Then, the photodegradation of melamine is an efficient tool to evaluate the direct hole transfer ability of a photocatalyst.

In the present study reduced graphene oxide—TiO2 composites were synthesized at two different ratios (1:10 and 1:5) through a hydrothermal method using graphene oxide and commercial P25 as start ing materials. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), BET surface area and ultraviolet–visible (UV–vis) absorption spectroscopy were employed to investigate the morphology and properties of the produced composites. The photocatalytic performance of TiO2–rGO catalysts was evaluated under artifi cial solar light and visible light in distilled water, as well as, different surface waters (at natural pH) with respect to risperidone (antipsychotic drug) degradation. Irrespectively of the irradiated aqueous matrix, the photocatalytic efficiency of the tested composite materials under simulated solar light and visible light irradiation was higher compared to bare TiO2–P25 (reference catalyst). The identification of intermediate compounds, the assessment of mineralization and the evaluation of toxicity were performed as well. LC/HRMS was brought to bear in assessing the temporal course of the photocatalyzed process.Along with risperidone decomposition,the formation oftwenty intermediate compounds (TPs) occurred in the presence of TiO2. Irradiation of risperidone in the presence ofthe hybrid material resulted in the identification of thirty-four TPs. The transformation of risperidone progressed through the formation of compounds more harmful than the drug itself, as assessed by the measurement of acute toxicity, evaluated using the Vibrio fischeri bacteria test. When employing TiO2–rGO, all the identified transformation products were quicker degraded compared to TiO2–P25. At the same time both the reduction of toxicity and mineralization were faster achieved than with bare TiO2–P25. Applied Catalysis B: Environmental

Red cubic and spherical hematite red cool pigments of different particle size were synthesized following two different methods. Cubic and spherical particles with larger particle sizes were obtained through a gel–sol method using chloride and nitrilotriacetate ions as shape controllers, and changing the starting temperature to control the final particles size. Smaller spherical particles were synthesized more rapidly following a catalytic phase transformation method in which the size control is obtained by varying the reagent concentration. Cool properties for the obtained particles were evaluated by calculating the solar reflectance for all hematite samples. The cool properties differ depending on the particle size and shape. By controlling the final size and morphology of pigment particles it is possible to obtain pigments with the desired cool properties. Pigment color properties were also evaluated using CIE XYZ and CIE xyY color spaces.

TiO2 inverse opals present increased photocatalytic production of H2. TiO2 inverse opals with different pore size and TiO2 macroporous structures with disordered arrangement of the pores have been tested in the photocatalytic production of hydrogen in aqueous solution with a formate buffer as hole scavenger. TiO2 inverse opals belong to the family of metamaterials and exhibit unique catalytic properties arising from their peculiar interaction with light. To discriminate the effects of slow photons the hydrogen photoproduction experiments were carried out at two different wavelengths, at 365 nm where the effect of slow photons is maximized, and at 254 nm where it is negligible. The resulting hydrogen production rates suggest a strong effect of the slow light and of the polymer template used in the synthesis of the TiO2 powders. The chemical properties of the polymeric sacrificial template determine the crystalline phase of the sample and as a consequence affect the catalytic performances of the resulting TiO2 structures.

Chromophoric dissolved organic matter (CDOM) in surface waters is a photochemical source of several transient species such as CDOM triplet states (3CDOM*), singlet oxygen (1O2) and the hydroxyl radical ( OH). By irradiation of lake water samples, it is shown here that the quantum yields for the formation of these transients by CDOM vary depending on the irradiation wavelength range, in the order UVB > UVA > blue. A possible explanation is that radiation at longer wavelengths is preferentially absorbed by the larger CDOM fractions, which show lesser photoactivity compared to smaller CDOM moieties. The quantum yield variations in different spectral ranges were definitely more marked for 3CDOM* and OH compared to 1O2. The decrease of the quantum yields with increasing wavelength has important implications for the photochemistry of surface waters, because long-wavelength radiation penetrates deeper in water columns compared to short-wavelength radiation. The average steady-state concentrations of the transients (3CDOM*, 1O2 and OH) were modelled in water columns of different depths, based on the experimentally determined wavelength trends of the formation quantum yields. Important differences were found between such modelling results and those obtained in a wavelength-independent quantum yield scenario.

The effects of the highly fluorescent 4-piperidinyl-1,8-naphthalimide (PNI) chromophore on the CO2 reduction catalytic properties of rhenium-based catalysts are investigated herein. In particular, the electro- and photocatalytic CO2 reduction features of [Re(CO)3(bpy)Cl] (bpy = 2,2′-bipyridine) are compared with the activity of [Re(CO)3(phen–PNI)Cl] (phen = 1,10-phenanthroline), which is known for its long excited-state lifetime. Moreover, another Re complex, namely [Re(CO)3(bpy–Ph–PNI)Cl], has been synthesized and tested as an electro- and photocatalyst. The catalytic properties of the selected compounds were studied by means of electrochemical (cyclic voltammetry and controlled-potential electrolysis) and photophysical measurements together with DFT calculations. [Re(CO)3(bpy–Ph–PNI)Cl] showed good electrocatalytic efficiency toward selective CO2 reduction to CO, as well as reduced electrocatalytic overpotential.

The singlet and triplet excited states of 4-hydroxybenzophenone (4BPOH) undergo deprotonation in the presence of water to produce the anionic ground-state, causing fluorescence quenching and photoactivity inhibition. The same process does not take place in an aprotic solvent such as acetonitrile. In acetonitrile, 4BPOH is fluorescent (interestingly, one of its fluorescence peaks overlaps with peak C of humic substances), it yields singlet oxygen upon irradiation and induces the triplet-sensitised transformation of phenol (with a rate constant of (6.6 ± 0.3) × 107 M−1 s−1 (μ ± σ) between phenol itself and a triplet 4BPOH). The 4BPOH shows an intermediate behaviour in a partially protic solvent such as 2-propanol, where some deprotonation of the excited states is observed. In acetonitrile/2-propanol mixtures (at least up to 50% of 2-propanol) there is also some evidence of alcohol oxidation by the 4BPOH triplet state, while the experimental data are silent concerning such a possibility in pure 2-propanol. Considering that benzophenones are important components of chromophoric dissolved organic matter (CDOM) in surface waters, the present findings could have significance for the photoactivity of the hydrophilic surface layers vs. the hydrophobic cores of CDOM.

International audience; Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) is a widely used antimicrobial agent that undergoes fairly slow biodegradation. It is often found in surface waters in both the acidic (HTric) and basic (Tric−) forms (pKa ∼8), and it can undergo direct photodegradation to produce several intermediates including a dioxin congener (2,8-dichlorodibenzodioxin, hereafter 28DCDD). The latter is formed from Tric− and causes non-negligible environmental concern. Differently from current literature reports, in this paper we show that the direct photolysis would not be the only important transformation pathway of triclosan in surface waters. This is particularly true for HTric, which could undergo very significant reactions with •OH and, if the laser-derived quenching rate constants of this work are comparable to the actual reaction rate constants, with the triplet states of chromophoric dissolved organic matter (3CDOM*). Model calculations suggest that reaction with 3CDOM* could be the main HTric phototransformation pathway in deep waters with high dissolved organic carbon (DOC), while reaction with •OH could prevail in low-DOC waters. In the case of Tric− the direct photolysis is much more important than for HTric, but triplet-sensitised transformation could produce 28DCDD + 27DCDD with higher yield compared to the direct photolysis, and it could play some role as dioxin source in deep waters with elevated DOC.

Tetracarbonyl complexes of low-valent Group VI transition metals (Mo and W), containing diimine bidentate ligands, namely W(CO)4(4,6-diphenyl-2,2′-bipyridine) (1), W(CO)4(6-(2,6-dimethoxyphenyl)-4-phenyl-2,2′-bipyridine) (2), Mo(CO)4(2,2′-dipyridylamine) (3), and W(CO)4(2,2′-dipyridylamine) (4), were synthesized and tested as homogeneous catalysts for the electrochemical reduction of CO2 in nonaqueous media. Cyclic voltammetry performed under a CO2 atmosphere, revealed that these complexes have significant catalytic activity in acetonitrile, and gas chromatographic measurements together with exhaustive electrolysis showed that CO is the major reduction product. Mechanistic insights were obtained by IR-spectroelectrochemical measurements. The substantially different electrocatalytic performances obtained for the two classes of catalysts are compared and discussed.

We show that phenol can be effectively degraded by magnetite in the presence of persulfate (S2O8(2–)) under UVA irradiation. The process involves the radical SO4(–•), formed from S2O8(2–) in the presence of Fe(II). Although magnetite naturally contains Fe(II), the air-exposed oxide surface is fully oxidized to Fe(III) and irradiation is required to produce Fe(II). The magnetite + S2O8(2–) system was superior to the corresponding magnetite + H2O2 one in the presence of radical scavengers and in a natural water matrix, but it induced phenol mineralization in ultrapure water to a lesser extent. The leaching of Fe from the oxide surface was very limited, and much below the wastewater discharge limits. The reasonable performance of the magnetite/persulfate system in a natural water matrix and the low levels of dissolved Fe are potentially important for the removal of organic contaminants in wastewater.

The direct and indirect photodegradation of six cephalosporins was predicted using a photochemical model, on the basis of literature values of photochemical reactivity. Environmental photodegradation would be important in surface water bodies with depth ⩽2–3 m, and/or in deeper waters with low values of the dissolved organic carbon (DOC ⩽ 1 mg C L−1). The half-life times would range from a few days to a couple of weeks in summertime. In deeper and higher-DOC waters and/or in different seasons, hydrolysis could prevail over photodegradation. The direct photolysis of cephalosporins is environmentally concerning because it is known to produce toxic intermediates. It would be a major pathway for cefazolin, an important one for amoxicillin and cefotaxime and, at pH

Hematite particles with controlled size and shape (cubic, spherical and ovoidal, with size range from hundreds nm to μm) were produced by modulating the conditions of synthesis and were characterized by different techniques (XRD spectroscopy, scanning electron microscopy, BET analysis, dynamic light scattering, UV–vis spectroscopy). The photoactivity of the synthesized hematite particles was tested towards the degradation of phenol under photo–Fenton conditions, obtaining optimal results in the pH range 3–4. Although the smaller particles have a larger contact interface between the solid and the solution, no obvious relationship was found between size and photoactivity. A possible explanation is that the smallest particles tested showed an important radiation scattering, which would interfere with radiation absorption and, therefore, with photoactivity. In contrast, the most photoactive samples were those showing the highest concentrations of leached iron. This issue would imply that photoactivity may be related to partial dissolution of hematite with formation of Fe(II) and of photo-active Fe(III) species, which activate the classic photo–Fenton process. Anyway, leached Fe was limited to the μg L −1 range that is safely far from the mg L −1 limits for wastewater.

The irradiation of L-tryptophan, L-tyrosine and 4-phenoxyphenol in aqueous solution produced compounds with similar fluorescence properties as humic substances, and with absorption spectra that were significantly extended into the UVA and visible regions compared to the starting compounds. The irradiated systems had photosensitizing properties, as proven by the photodegradation of 2,4,6-trimethylphenol and furfuryl alcohol (probes of excited triplet states and (1)O2, respectively). The described photochemical processes could constitute an additional pathway for the formation of humic substances in clear and shallow water bodies, which would be added to the complex network of reactions involving dissolved organic matter.

International audience; In this work, magnetite-catalyzed Fenton reaction was investigated under UVA irradiation for the degradation of phenol as model compound. Four kinds of magnetite were used having different particle size, surface area and FeII content. Different kinetic behaviors were observed, thereby underscoring the strong implications of surface and chemical properties of magnetite. The size and surface area of the particles seemed to be less important, while the FeII/FeIII ratio played some role. Despite the link between magnetite reactivity and its structural FeII content, light-induced reduction of FeIII to FeII was found necessary to promote the Fenton-based reactions. As surface FeII may be oxidized or otherwise unavailable, initial photoactivation may be needed to trigger the Fenton reactivity. Two major driving forces were highlighted that account for the photoactivity of magnetite at pH 3: (i) the formation of intermediates such as hydroquinone that are able to reduce FeIII to FeII, and (ii) the accumulation of dissolved Fe due to magnetite dissolution, both in dark and under irradiation. Very interestingly, the photo-Fenton degradation of phenol was also observed under neutral conditions. In this case, for two out of four samples, the degradation rates were quite near those found at pH 3, which is usually reported as the optimum pH value of the process. The magnetite ability to promote photo-Fenton reactions even under circumneutral pH conditions, the limited iron leaching and its easy magnetic separation makes magnetite a promising catalyst in wastewater treatment applications.

This paper gives an overview of the main reactive transient species that are produced in surface waters by sunlight illumination of photoactive molecules (photosensitizers), such as nitrate, nitrite, and chromophoric dissolved organic matter (CDOM). The main transients (˙OH, CO3(-˙) , (1)O2, and CDOM triplet states) are involved in the indirect phototransformation of a very wide range of persistent organic pollutants in surface waters.

Humic substances (HS) are known to act as photosensitizers toward the transformation of pollutants in the surface layer of natural waters. This study focused on the role played by HS toward the transformation of xenobiotics in seawater, with the purpose of assessing the prevailing degradation routes. Phenol was chosen as model xenobiotic and its transformation was investigated under simulated sunlight in the presence of terrestrial or marine humic and fulvic acids, in pure water at pH 8, artificial seawater (ASW) or natural seawater (NSW). The following parameters were determined: (1) the phenol degradation rate; (2) the variation in HS concentration with irradiation time; (3) the production of transformation products; (4) the influence of iron species on the transformation process. Faster transformation of phenol was observed with humic acids (HA) compared to fulvic acids (SRFA), and transformation induced by both HA and SRFA was faster in ASW than that in pure water. These observations can be explained by assuming an interplay between different competing and sometimes opposite processes, including the competition between chloride, bromide and dissolved oxygen for reaction with HS triplet states. The analysis of intermediates formed in the different matrices under study showed the formation of several hydroxylated (hydroquinone, 1,4-benzoquinone, resorcinol) and condensed compounds (2,2′-bisphenol, 4,4′-bisphenol, 4-phenoxyphenol). Although 1,4-benzoquinone was the main transformation product, formation of condensed molecules was significant with both HA and SRFA. Experiments on natural seawater spiked with HS confirmed the favored formation of condensed products, suggesting a key role of humic matter in dimerization reactions occurring in saline water.

Photosensitised reactions can produce compounds that closely resemble the humic-like substances (HULIS) occurring in atmospheric aerosols. The relevant processes have been observed in the laboratory, in both gas-solid systems and the aqueous phase. They involve triplet sensitisers (such as benzophenones, anthraquinones and nitroaromatic compounds, which yield reactive triplet states after sunlight absorption) or photogenerated oxidants like (•)OH, in the presence of substrates that undergo oligomerisation reactions upon oxidation. Formation of higher molecular weight compounds, modification of the wettability properties of organic films and photoproduction of substances with humic-like fluorescence properties have been observed as a consequence of the photosensitised reactions. Ozone plays an important but still not completely clear role in gas-solid systems.

Water samples from shallow lakes located in Terra Nova Bay, Antarctica, were taken in the austral summer season and characterized for chemical composition, optical features, fluorescence excitation-emission matrix (EEM) and photoactivity toward the generation of (•)OH, (1)O2, and (3)CDOM* (triplet states of chromophoric dissolved organic matter). The optical properties suggested that CDOM would be largely of aquagenic origin and possibly characterized by limited photochemical processing before sampling. Moreover, the studied samples were highly photoactive and the quantum yields for the generation of (3)CDOM* and partially of (1)O2 and (•)OH were considerably higher compared to water samples from temperate environments. This finding suggests that water in the studied lakes would have considerable ability to photosensitize the degradation of dissolved compounds during the austral summer, possibly including organic pollutants, also considering that the irradiance conditions of the experiments were not far from those observed on the Antarctic coast during the austral summer.