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Fluorescence spectroscopy is one of the most useful techniques currently available for the characterisation of organic matter in natural water samples, because it combines easy availability of instrumentation, high sensitivity and limited requirements for sample treatment. The main fluorophores that can be found in natural waters are usually proteins (and/or free amino acids) and humic substances (humic and fulvic acids). The identification of these fluorescent compounds in water samples helps to obtain information about, among others, biological activity in the water body, possible transport of organic matter from soil, and the phenomenon of photobleaching that decreases both the absorbance and (usually) the fluorescence of natural organic matter. Interestingly, all these phenomena can be affected by climate change, which could alter to different extents the ratio between aquagenic and pedogenic fluorophores. Several events induced by warming in natural waters (and especially lake water) could enhance algal growth, thereby also enhancing the production of aquagenic organic matter. Intense precipitation events could increase the export of pedogenic material to surface waters, while photobleaching would be enhanced in the epilimnion of lakes when summer stratification becomes longer and more stable because of higher temperatures. Interestingly, photobleaching affects humic substances to a higher extent compared to protein-like material, thus protein fluorescence signals could be more preserved in stratified waters.

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 (

International audience; The irradiation under simulated sunlight of some phenolic compounds typically emitted in ambient air by biomass burning, namely vanillin and acetosyringone, yielded intermediates with humic-like fluorescence properties that can be assimilated to humic-like substances (HULIS). Evidence was obtained by ultra-high-resolution mass spectrometry of the occurrence of oligomerization processes up to the formation of trimeric species. In contrast, the irradiation of other biomass-burning compounds such as vanillic acid, m-cresol and guaiacol did not yield either HULIS-type fluorescence or oligomers. We suggest that the photolysis of biomass-burning compounds is a potential HULIS source in the atmosphere, if the relevant substrates undergo photoinduced oligomerization reactions.

We present here a photoactive system for water decontamination consisting of ZnO nanocrystals supported on a flexible mat of electrospun semiconducting nanofibers. The nanofibers have a core–sheath structure with a polyacrylonitrile (PAN) core and a sheath made of polypyrrole (PPY), a low band gap p-type semiconductor. Under UVA irradiation, the heterojunction formed between PPY and ZnO, an n-type semiconductor, promotes the separation of the charge carriers photogenerated at the interface. This decreases the charge recombination rate and increases the photocatalytic efficiency compared to a system where the same ZnO particles are supported on insulating bare PAN nanofibers. Based on photocatalytic tests and photoelectrochemical characterization, we find that the photoexcited electrons are preferentially collected on the PPY sheath and react with the dissolved oxygen while the holes in excess on the ZnO surface generate highly oxidizing radicals and degrade the persistent pollutants. The nanofiber production is scalable and sustainable, as the synthesis of the PPY sheath is carried out in water under ambient conditions. While previous studies immobilized photoactive metal oxide nanoparticles on insulating mats to help their collection after use, this is the first report showing that a flexible semiconducting supporting material can play an active role in the photocatalytic process and significantly enhance its efficiency. This approach paves the way for the design of new supported hybrid materials for photocatalytic applications.

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.

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.

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.

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.

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.

We report the electrosynthesis of a water oxidation catalyst based on Ag oxides (AgCat). The deposited AgCat is composed of mixed valence crystalline Ag oxides with the presence of particle aggregates whose size is ∼1 μm. This catalyst, coupled with TiO2 and hematite, and under photoelectrochemical conditions, substantially increases photocurrents in a wide range of applied potentials compared with bare and Co-Pi-modified photocatalysts. AgCat can sustain current densities comparable with other water oxidation catalysts. Dark bulk electrolysis demonstrated that AgCat is stable and can sustain high turnover number in operative conditions. Oxygen evolution from water occurs in mild conditions: pH = 2–13, room temperature and pressure, and moderate overpotentials (600 mV) compatible with the coupling with semiconducting oxides as sensitizers. Using hematite in sustained electrolysis O2 production is significant, both in the dark and under irradiation, after an initial slow induction time in which modificatio...

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.

The electrochemical behavior of fac-[Mn(pdbpy)(CO)3 Br] (pdbpy=4-phenyl-6-(phenyl-2,6-diol)-2,2'-bipyridine) (1) in acetonitrile under Ar, and its catalytic performances for CO2 reduction with added water, 2,2,2-trifluoroethanol (TFE), and phenol are discussed in detail. Preparative-scale electrolysis experiments, carried out at -1.5 V versus the standard calomel electrode (SCE) in CO2 -saturated acetonitrile, reveal that the process selectivity is extremely sensitive to the acid strength, producing CO and formate in different faradaic yields. A detailed spectroelectrochemical (IR and UV/Vis) study under Ar and CO2 atmospheres shows that 1 undergoes fast solvolysis; however, dimer formation in acetonitrile is suppressed, resulting in an atypical reduction mechanism in comparison with other reported MnI catalysts. Spectroscopic evidence of Mn hydride formation supports the existence of different electrocatalytic CO2 reduction pathways. Furthermore, a comparative investigation performed on the new fac-[Mn(ptbpy)(CO)3 Br] (ptbpy=4-phenyl-6-(phenyl-3,4,5-triol)-2,2'-bipyridine) catalyst (2), bearing a bipyridyl derivative with OH groups in different positions to those in 1, provides complementary information about the role that the local proton source plays during the electrochemical reduction of CO2 .

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.

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.

The photo-induced reactivity of compounds at the surface of photocatalytic materials is used to maintain the cleanliness of the surface of glass, concretes and paints. A standard method to quantify the photocatalytic self-cleaning (SC) properties of non-transparent materials was recently published. It is based on the covering of the sample surface with a defined amount of dye and on the evaluation of the reflectance spectra of the coloured surface under irradiation. The calibration of the spectral changes allowed the quantification of the surface residual dye and the evaluation of the self-cleaning kinetics. The method was tested on seven white and coloured photocatalytic materials using methylene blue (MB), rhodamine B (RhB) and metanil yellow (MY). The main by-products of the MB photocatalytic degradation at the solid/solid interface were identified, showing that MB degradation in solution follows a path quite different from that at the solid/solid interface. Also MY showed a different order of photoreactivity. Furthermore, experiments at the solid/solid interface are more trustworthy than tests in solution for evaluating the self-cleaning ability. The differences of the photocatalytic phenomena at the solid/solid interface in comparison with the most studied photoactivated processes at the solid/liquid interface are outlined. Furthermore, photocatalytic materials showed selectivity toward some specific dyes. This encourages the use of more than one dye for the evaluation of the self-cleaning ability of a photocatalytic material.

The release in the environment of antibiotics develop microbial resistance. In this work we investigated the feasibility of the electrochemical degradation in synthetic urine of cefazolin (CFZ), an antibiotic used for the treatment of antibiotic-resistant infections, which could be carried out in hospital wards on source-separated urine. CFZ is primarily excreted in urine without modifications. The removal of CFZ from human wastes would contribute to slow down the diffusion of CFZ-resistant bacterial strains more efficiently, compared to the treatment of much larger volumes of wastewater. CFZ can be electrochemically degraded using relatively low current density (≥0.5 mA cm−2) and without important generation of toxic by-products such as chlorate (

The addition of graphene nanoplatelets (GNP) to TiO2 nanoparticles (NPs) has been recently considered as a method to improve the photocatalytic efficiency of TiO2 by favoring charge carrier separation. Here, we show that it is possible to improve the efficiency of GNP-TiO2 composites by controlling the shape, stability, and facets of TiO2 NPs grown on GNP functionalized with either COOH or NH2 groups, while adding ethylendiamine (EDA) and oleic acid (OA) during a hydrothermal synthesis. We studied the photocatalytic activity of all synthesized materials under UV-A light using phenol as a target molecule. GNP-TiO2 composites synthesized on COOH-functionalized GNP, exposing {101} facets, were more efficient at abating phenol than those synthesized on NH2-functionalized GNP, exposing {101} and {100} facets. However, neither of these composites was stable under irradiation. The addition of both OA and EDA stabilized the materials under irradiation; however, only the composite prepared on COOH-functionalized GNP in the presence of EDA showed a significant increase in phenol degradation rate, leading to results that were better than those obtained with TiO2 alone. This result can be attributed to Ti-OH complexation by EDA, which protects GNP from oxidation. The orientation of the most reducing {101} facets toward GNP and the most oxidizing {100} facets toward the solution induces faster phenol degradation owing to a better separation of the charge carriers.

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.

Nitrite photochemical transformation is an important sink for nitrite and a source of nitric oxide, which affects the air–water partitioning of NO. It is shown here that aliphatic and aromatic OH scavengers alter the photochemical fate of nitrogen, in addition to enhancing nitrite photodegradation. In aerated solution, the addition of phenol as scavenger induced a significant formation of gas-phase nitrogen species from irradiated nitrite, differently from nitrite alone or in the presence of 2-propanol. Moreover, phenol strongly favoured the photochemical production of gas-phase nitric oxide in aerated solution: an upper limit of about 20% could be established for the nitrite fraction that may be transformed into gas-phase NO under these conditions. The photochemical production of NO was considerably higher in the absence of oxygen, most likely because the scavenging of nitric oxide by superoxide is an important NO sink in aerated systems. These results suggest that the concentration of dissolved oxygen and the nature of the OH scavenger(s) may considerably affect the phototransformation of nitrite into gas-phase nitrogen compounds, and particularly into nitric oxide, in aqueous solution and at water-air interfaces.

The photoreactivity of graphene oxide (GO) suspensions was investigated with a double aim: (i) to give insights into the previously reported photo-reduction process, which allows a partial elimination of the oxygen-containing groups from the 2D graphitic structure; (ii) to explore the possible use of GO as photo-activator able to promote the photo-transformation/abatement of organic molecules. To reach these goals and clarify some peculiar aspects of the photochemistry of GO till now obscure or confuse, we synthesized and characterized stable GO suspensions which were then subjected to UV–Vis irradiation for prolonged times. GO underwent partial photo-reduction with the release of gaseous molecules and soluble organic species (e.g., carboxylic acid). The mechanisms of photo-reduction occurring under air or N2 are different, as assessed by the release in solution of diverse soluble molecules. In the presence of oxygen, at long irradiation time, a complete solubilization of the graphenic structures was observed. No difference in the nature and amount of released gases (principally CO2 and CO) was observed in the oxic or anoxic conditions. The possible use of GO as photo-activator was evaluated using phenol as probe molecule. GO revealed a double role of photo-activator and reagent in phenol degradation, as competition was assessed between GO self-transformation/reduction and phenol degradation. At prolonged irradiation time, a marked reactivity of the photoformed species was observed and the complete degradation was achieved for both organic small molecules formed from GO and the phenol added as probe molecule.

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.

According to numerous previous reports, a Z-scheme with two photon absorbers is the most promising strategy to achieve artificial photosynthesis, but in addition to two efficient catalysts — one for oxygen evolution, the other for CO2 reduction — two different and complementary semiconducting sensitizers are required. Here we present the synthesis of two bipyridine-functionalized terthiophenes, which can be electropolymerized to give photoactive p-type semiconductors the capability to perform as photocathode in photoelectrochemical cells for water photosplitting or artificial photosynthesis. Indeed the bipyridine moiety in their structure allows the binding of transition metal carbonyl complexes employed in CO2 reduction, and their band-gap is suitable for the coupling with wide band-gap semiconductors, which have already found application as photoanodes. Finally, they are characterized by photogenerated charge carrier density between 1.1 and 1.4 × 1019 cm−3, with first-order recombination constant of 0.7–1.8 × 10−2 s−1. These figures are of the same order of magnitude of their inorganic counterparts and would therefore guarantee photoconductivity of the device and the activation of the organometallic catalysts with which they should be coupled to function as photocathodes for CO2 reduction.

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).

Gemfibrozil (GFZ) is a relatively persistent pollutant in surface-water environments and it is rather recalcitrant to biological degradation. The GFZ photochemical lifetimes are relatively short in shallow waters with low levels of dissolved organic carbon (DOC), but they can reach the month-year range in deep and high-DOC waters. The main reason is that GFZ undergoes negligible reaction with singlet oxygen or degradation sensitised by the triplet states of chromophoric dissolved organic matter, which are the usually prevalent photochemical pathways in deep and high-DOC sunlit waters. Nitrate and nitrite scarcely affect the overall GFZ lifetimes, but they can shift photodegradation from direct photolysis to the OH process. These two pathways are the main GFZ phototransformation routes, with the direct photolysis prevailing in shallow environments during summer. Under these conditions the GFZ photochemical lifetimes are also shorter and the environmental significance of photodegradation correspondingly higher. The direct photolysis of GFZ under UVB irradiation yielded several transformation intermediates deriving from oxidation or cleavage of the aliphatic lateral chain. A quinone derivative (2,5-dimethyl-1,4-benzoquinone), a likely oxidation product of the transformation intermediate 2,5-dimethylphenol, is expected to be the most acutely and chronically toxic compound arising from GFZ direct photolysis. Interestingly, literature evidence suggests that the same toxic intermediate would be formed upon OH reaction.

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.