[Show abstract][Hide abstract] ABSTRACT: 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 ((3)CDOM*). Model calculations suggest that reaction with (3)CDOM* 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.
[Show abstract][Hide abstract] ABSTRACT: The present work compares the efficiency of homogenous Fenton and photo-Fenton processes in the presence of Fe(III)-EDDS complex under different experimental conditions. 4-tert-Butylphenol (4-t-BP), which is one of the endocrine disrupting chemicals, was used as a model pollutant to investigate the Fenton and photo-Fenton application. The efficiency of homogenous photo-Fenton process was significantly much higher than homogenous Fenton process, which is due to the rapid formation of Fe(2+) under UV irradiation of the iron complex and the photochemical formation of HO(•) from the photolysis of the complex Fe(III)-EDDS. Through the degradation of 4-t-BP, the effect of Fe(III)-EDDS concentration, H2O2 concentration, pH, and oxygen was investigated in both processes. Such trend was also correlated with pH calculating the polychromatic Fe(2+) quantum yield formation at pH 4.0, 6.0, and 8.6. The results showed that at high Fe(III)-EDDS and H2O2 concentrations, a negative effect was found. By the way, the Fenton process was found to be enhanced at basic pH. These results can be very useful for the use and optimization of such iron complex in water treatment process as function of different physico-chemical conditions.
Environmental Science and Pollution Research 05/2014; · 2.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background
The objective of this work is to prepare various TiO2/SiO2 composites, determine their photocatalytic activity and suggest the most promising materials for further application.ResultsTiO2/SiO2composite materials were prepared starting from aqueous suspensions of each component. Colloidal suspension of TiO2was prepared by hydrolysis of TiCl4. As a source of SiO2the commercial product (Ludox AS30) was used. The TiO2/SiO2 composites were successfully prepared as a powder, obtained from the heterocoagulation of mixed TiO2 and SiO2 aqueous colloidal suspensions. The heterocoagulation of prepared amorphous TiO2 in presence of SiO2 led to the crystallization of TiO2 with anatase structure. Photocatalytic activity was tested in liquid phase by the dye degradation and in gas phase by the hexane degradation. In aqueous phase the presence of SiO2 increase the rate of degradation of Methylene Blue in comparison with pure TiO2 in acidic conditions whereas Acid Orange 7 photodegradation was faster in basic solution in presence of TiO2/SiO2 1:1 composite. In gaseous phase composites prepared by heterocoagulation showed improved photoactivity (conversion around 35%).Conclusion
Composites prepared by heterocoagulation with ratio TiO2/SiO2 1:10 can be used as photocatalyst in self-cleaning paints, SiO2 partly cover the TiO2 surface and acts as a barrier which separates an active surface of TiO2 from the contact with binder or polymeric substrate.
Journal of Chemical Technology & Biotechnology 05/2014; · 2.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This work investigated the fate of nicotine (Nico) in aqueous solution upon reaction with singlet oxygen ((1)O2) and hydroxyl radical (HO). The second-order rate constants of Nico with (1)O2 ( [Formula: see text] = (3.38 ± 0.14) × 10(6) M(-1) s(-1)) and HO (kNico,OH = (1.08 ± 0.10) × 10(9) M(-1) s(-1)) were determined using competition kinetics. Photochemical modelling showed that the reaction of Nico with HO would prevail over that with (1)O2 in surface waters transformation pathway. The Nico photochemical half-life time could be accounted for by the two reactions. This value would vary in the month-year range depending on the environmental conditions: phototransformation would be favoured in shallow water poor in organic matter and rich in nitrate and nitrite. Irradiation experiments of Nico with nitrite suggested that transformation could not be accounted for by HO reaction alone. Indeed, a variable fraction of Nico transformation (30-80% depending on the conditions) would take place upon reaction with additional transients, photogenerated NOx being possible candidates. The chemical structures of the transformation intermediates were derived by means of HPLC-MS. The detection of nitroderivatives upon irradiation of Nico with nitrite suggests the involvement of nitrogen dioxide in the relevant photoprocesses.
Water Research 02/2014; 55C:106-114. · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Long-term monitoring of the chemical composition of clouds (73 cloud events representing 199 individual samples) sampled at the puy de Dôme (pdD) station (France) was performed between 2001 and 2011. Physicochemical parameters, as well as the concentrations of the major organic and inorganic constituents, were measured and analyzed by multicomponent statistical analysis. Along with the corresponding back-trajectory plots, this allowed for distinguishing four different categories of air masses reaching the summit of the pdD: polluted, continental, marine and highly marine. The statistical analysis led to the determination of criteria (concentrations of inorganic compounds, pH) that differentiate each category of air masses. Highly marine clouds exhibited high concentrations of Na+ and Cl−; the marine category presented lower concentration of ions but more elevated pH. Finally, the two remaining clusters were classified as "continental" and "polluted"; these clusters had the second-highest and highest levels of NH4+, NO3−, and SO24−, respectively. This unique data set of cloud chemical composition is then discussed as a function of this classification. Total organic carbon (TOC) is significantly higher in polluted air masses than in the other categories, which suggests additional anthropogenic sources. Concentrations of carboxylic acids and carbonyls represent around 10% of the organic matter in all categories of air masses and are studied for their relative importance. Iron concentrations are significantly higher for polluted air masses and iron is mainly present in its oxidation state (+II) in all categories of air masses. Finally, H2O2 concentrations are much more varied in marine and highly marine clouds than in polluted clouds, which are characterized by the lowest average concentration of H2O2. This data set provides concentration ranges of main inorganic and organic compounds for modeling purposes on multiphase cloud chemistry.
ATMOSPHERIC CHEMISTRY AND PHYSICS 02/2014; 14:1485-1506. · 5.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The occurrence of Cl2(-·) in natural waters would depend on the budget between triplet-sensitised photogeneration (which might have second-order rate constant of 10(7)-10(9) M(-1) s(-1)) and scavenging by dissolved organic matter (DOM, with possible rate constant of 10-10(3) L (mg C)(-1) s(-1)). The steady-state [Cl2(-·)] in brackish to saline waters might be in the range of 10(-14)-10(-12) M in mid-latitude summertime, coherently with data of phenol photochlorination in seawater. Steady-state [Cl2(-·)] would be enhanced by chloride (up to a plateau above 0.1 M Cl(-)) and inhibited by DOM. The radical Cl2(-·) would also be a major oxidant of nitrite to the nitrating agent (·)NO2 in brackish- and salt-water. This issue may explain the sustained formation of nitrophenols in phenol-spiked seawater and in natural brackish waters impacted by phenolic pollutants (Rhône delta, Southern France).
[Show abstract][Hide abstract] ABSTRACT: The present work describes in details the chemical structure of the complex Fe(III)-EDDS and the predominance of different species with respect to pH. These results were obtained with Ab initio calculations. From the photoredox process, the formation of hydroxyl radical was confirmed and HO● is the main species responsible for the degradation of the organic compound present in aqueous solution. The degradation of 4-tert-butylphenol (4-t-BP), used as a model pollutant, was investigated in different conditions. For the first time the second-order rate constant of the reaction between HO● and 4-t-BP and the formation rate of HO● (Rf•OH) from the photochemical process were evaluated. Through the degradation of 4-t-BP, the effect of Fe(III)-EDDS concentration, oxygen and pH was also investigated. The pH, which play a role on the iron cycle and on the Fe(III)-EDDS speciation, was noticed as an important parameter for the efficiency of 4-t-BP degradation. Such result could be explained taking into account the complex speciation and presence of a predominant form (FeL-) up to pH 8. These results are very useful for the use optimization of such iron complex in water treatment process.
The Journal of Physical Chemistry A 12/2013; · 2.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In addition to direct photolysis, degradation of organic compounds by
solar light can also occur by indirect photolysis or photo-sensitised
processes. These reactions are important because they are involved in,
among others, direct and indirect climate changes, adverse health
effects from inhaled particles, effects on cloud chemistry and ozone
production. In this work, the importance of atmospheric
photo-sensitisation is evaluated in bulk aqueous solution and on the
surface of aerosol deliquescent particles. Irradiation experiments in
aqueous solution indicate that 4-carboxybenzophenone (CBP) is able to
photosensitise the degradation of 4-phenoxyphenol (4 PP). The
process takes place via the CBP triplet state (3CBP*), which
has an oxidising nature. 4 PP is fluorescent, unlike the
photosensitiser CBP, with two emission bands at ˜320 and
˜380 nm. However, addition of CBP to a 4 PP solution
considerably decreases the intensity of 4 PP fluorescence bands and
causes a very intense new band to appear at ˜420 nm. This
behaviour suggests a possible interaction between CBP and 4 PP in
solution, which could favour further light-induced processes. Moreover,
the new band overlaps with the fluorescence spectrum of atmospheric
HULIS (HUmic-LIke Substances), suggesting that supramolecular
photosensitiser-substrate interactions may have a role in HULIS
fluorescence properties. The interaction between CBP and 4 PP
coated on silica particles (gas-solid system) was also
investigated under simulated sunlight, and in the presence of variable
relative humidity. The water molecules inhibit the degradation of
4 PP, induced by 3CBP* on the surface of aerosol
particles, indicating that the process could be even faster on particles
than in solution. We demonstrate that phenol substances adsorbed on
aerosol surfaces and in bulk solution are substantially altered upon