extraction-characterization-surfactants-from-atmospheric

Extraction and Characterization of Surfactants from Atmospheric Aerosols

Surface-active compounds, or surfactants, present in atmospheric aerosols are expected to play important roles in the formation of liquid water clouds in ...

IRCELYON, F-69626

In the present study, HPLC/ESI-MS and stopped-flow HPLC/1H NMR methods were developed and applied to separate and characterize the byproducts arising from TiO2-catalyzed photodegradation of the herbicide iodosulfuron methyl ester (IOME) in aqueous solution under UV irradiation. Prior to identification, irradiated solutions of IOME (200 and 1000 mg.L(-1)) were concentrated by solid-phase extraction using two cartridges: Isolute C18 and Isolute ENV+. Analytical separation was achieved on a C18 reversed-phase column with ACN/H2O (HPLC/MS) or ACN/D2O (HPLC/NMR) as mobile phase and a linear gradient with a chromatographic run time of 35 min. The combination of UV and MS data allowed the structural elucidation of more than 20 degradation products, whereas 1H NMR data permitted an unequivocal confirmation of the identities of major products and the differentiation of several positional isomers, in particular, the hydroxylation isomers. The obtained results permitted us to propose a possible degradation scheme and to put in evidence the presence of privileged sites for the attack of OH radicals. This work shows, for the first time, the application of combined HPLC with UV, MS, and NMR detection for complete structural elucidation of photocatalytic degradation products, and it will be of particular value in studies on the elimination of pollutants in aqueous solutions by photocatalysis.

Development of HPLC/ESI-MS and HPLC/1H NMR methods for the identification of photocatalytic degradation products of iodosulfuron.

The effect of positional isomerism on chemical and photochemical degradations of the Imazamethabenz-methyl (IMBM), a pesticide of the imidazolinone family, has been studied. IMBM is proposed in the form of a mixture of the two positional isomers: meta and para. The development of an effective HPLC method (resolution factor R=1.3) allows us to follow either the abiotic disappearance of the meta and para IMBM and the formation of their breakdown products. The abiotic degradation studies include the chemical hydrolysis, as well as the direct and the indirect photodecomposition. We used TiO(2), a well-known initiator of hydroxyl radicals, to highlight the role of *OH in the indirect photodegradation. This work confirms the different behaviours of positional isomers in the environment. Indeed the chemical or direct photochemical degradation is faster for the meta isomer than for the para. Whereas, concerning IMBM, there is not any prevalent influence of this type of isomerism on the indirect photochemical degradation. The degradation products were tentatively identified by LC-MS, NMR and IR and a degradation pathway was proposed.

Effect of positional isomerism on the abiotic degradation of pesticides: Case of m- and p-imazamethabenz-methyl.

The development of photocatalysis processes offers a significant number of perspectives especially in gaseous phase depollution. It is proved that the photo-oxidizing properties of photocatalyst (TiO(2)) activated by UV plays an important role in the degradation of volatile organic compounds (VOC). Heterogeneous photocatalysis is based on the absorption of UV radiations by TiO(2). This phenomenon leads to the degradation and the oxidation of the compounds, according to a mechanism that associates the pollutant's adsorption on the photocatalyst and radical degradation reactions. The main objective of the study is the understanding of the TiO(2)-photocatalysis phenomenon including gaseous and adsorbed phase mechanisms. Results obtained with three different apparatus are compared; gaseous phases are analysed and mechanisms at the gaseous phase/photocatalyst interface are identified. This study leads to improve understanding of various mechanisms during pollutant photodegradation: adsorption of pollutants on TiO(2) first takes place, then desorption and/or photodegradation, and finally, desorption of degradation products on TiO(2). The association of analytical methods and different processes makes the determination of all parameters that affect the photocatalytic process possible. Mastering these parameters is fundamental for the design and construction of industrial size reactors that aim to purify the atmosphere.

Different methods in TiO2 photodegradation mechanism studies: gaseous and TiO2-adsorbed phases.

This paper presents for the first time the investigation of TiO2 photocatalysis for the removal of pesticides in gas phase. Dichlorvos was used as a model pesticide, and experiments were carried out using both static and dynamic reaction systems to explore the different aspects of the process. Thus, adsorption, reaction kinetics, and the influence of several operational parameters such as relative humidity (RH), inlet concentration, flow rate, and association of TiO2 with activated carbon (AC) were all examined in detail. Furthermore, a special attention was devoted to the analysis of reaction products by means of various analytical techniques such as Fourier transform infrared spectroscopy, automated thermal desorption technique coupled to gas chromatography-mass spectrometry instrument, gas chromatography equipped with a pulse discharge helium photoionization detector, and ion chromatography. The results showed an immediate and total removal of dichlorvos at ppbv levels (50-350 ppbv) along with a high mineralization extent (50-85%) into harmless final products (CO2, HCl, PO43-). Moreover, RH was found to significantly affectthe mineralization extent and the formation of reaction intermediates. On the basis of identification data, direct charge transfer and chlorine radical (Cl*) attack were shown to play a key role in the reaction mechanism at low RH, whereas at high RH, HO* radicals were the predominant active species.

Photocatalytic removal of pesticide dichlorvos from indoor air: a study of reaction parameters, intermediates and mineralization.

In this work, the performance of integrated photocatalytic and biological treatment was studied for the degradation of 4-chlorophenol (MCP) present in wastewaters. Photocatalysis was used as a pre-treatment to biological degradation. Pollutant removal efficiency was quantified using MCP removal and total organic carbon (TOC) removal. Both photocatalytic as well as biological treatments were carried out in batch reactors, using TiO(2) as the photocatalyst. The inoculum for biological experiments was obtained from paper mill effluent treatment plant and was developed through a process of selection and acclimatization. Effect of TiO(2) concentration on the photocatalytic degradation of MCP was studied along with the effect of the duration of photochemical oxidation and glucose concentrations (0 g/L, 1 g/L and 2 g/L) on the biodegradation of MCP. Integrated biological and photochemical degradation was found to be more effective in treating MCP, especially at higher concentrations (400 mg/L). An initial MCP concentration of 400 mg/L required 96 h for complete mineralization when treated with the process combination, whereas the treatment went on up to 264 h when biodegradation alone was employed.

The remediation of wastewater containing 4-chlorophenol using integrated photocatalytic and biological treatment.

The extensive utilization of β-blockers worldwide led to frequent detection in natural water. In this study the photolysis behavior of atenolol (ATL) and toxicity of its photodegradation products were investigated in the presence of nitrate ions. The results showed that ATL photodegradation followed pseudo-first-order kinetics upon simulated solar irradiation. The photodegradation was found to be dependent on nitrate concentration and increasing the nitrate from 0.5 mML(-1) to 10 mML(-1) led to the enhancement of rate constant from 0.00101 min(-1) to 0.00716 min(-1). Hydroxyl radical was determined to play a key role in the photolysis process by using isopropanol as molecular probe. Increasing the solution pH from 4.8 to 10.4, the photodegradation rate slightly decreased from 0.00246 min(-1) to 0.00195 min(-1), probably due to pH-dependent effect of nitrate-induced .OH formation. Bicarbonate decreased the photodegradation of ATL in the presence of nitrate ions mainly through pH effect, while humic substance inhibited the photodegradation via both attenuating light and competing radicals. Upon irradiation for 240 min, only 10% reduction of total organic carbon (TOC) can be achieved in spite of 72% transformation rate of ATL, implying a majority of ATL transformed into intermediate products rather than complete mineralization. The main photoproducts of ATL were identified by using solid phase extraction-liquid chromatography-mass spectrometry (SPE-LC-MS) techniques and possible nitrate-induced photodegradation pathways were proposed. The toxicity of the phototransformation products was evaluated using aquatic species Daphnia magna, and the results revealed that photodegradation was an effective mechanism for ATL toxicity reduction in natural waters.

Nitrate-induced photodegradation of atenolol in aqueous solution: kinetics, toxicity and degradation pathways.

The occurrence of sunscreen agents in natural environment is of scientific concern recently due to their potential risk to ecology system and human beings as endocrine disrupting chemicals (EDCs). In this work the photodegradation mechanism and pathways of sunscreen agent 2-phenylbenzimidazole-5-sulfonic acid (PBSA) were investigated under artificial solar irradiation with the goal of assessing the potential of photolysis as a transformation mechanism in aquatic environments. The quantum yield of PBSA direct photolysis in pH 6.8 buffer solution under filtered mercury lamp irradiation was determined as 2.70 × 10(-4). Laser flash photolysis (LFP) experiments confirmed the involvement of PBSA radical cation (PBSA(·+)) during direct photolysis. Acidic or basic condition facilitated PBSA direct photolysis in aqueous solution. Indirect photolysis out-competes direct photolysis as a major process for PBSA attenuation only at higher level of photosensitizers (e.g., NO3(-) > 2 mM). Thus, direct photolysis is likely to be the major loss pathway responsible for the elimination of PBSA in natural sunlit surface waters, while indirect photolysis (e.g., mediated by HO·) appeared to be less important due to a general low level of steady-state concentration of HO· ([HO·]ss) in natural surface waters. Direct photolysis pathways of PBSA includes desulfonation and benzimidazole ring cleavage, which are probably initiated by the excited triplet state ((3)PBSA*) and radical cation (PBSA(·+)). Conversely, hydroxylation products of PBSA and 2-phenyl-1H-benzimidazole as well as their ring opening intermediates were found in nitrate-induced PBSA photolysis, suggesting the indirect photodegradation was primarily mediated by HO and followed a different mechanism.

Photochemical degradation of sunscreen agent 2-phenylbenzimidazole-5-sulfonic acid in different water matrices.

The wide occurrence of antibiotics in groundwater raised great scientific interest as well as public awareness in recent years due to their potential ability to spread antibiotic resistant gene and pose risk to humans. The present study investigated the ferrous ion (Fe(II)) activated decomposition of persulfate (S2O8(2-)), as a potential in situ chemical oxidation (ISCO) approach, for remediation of groundwater contaminated by antibiotics. Fe(II)-persulfate mediated ciprofloxacin (CIP) degradation was found to be more efficient than sulfamethoxazole (SMX) at near neutral pH (pH6.0), probably due to the higher electric density in CIP molecule and its ability to form complex with Fe(II) as a ligand. Hydroxyl (HO) and sulfate radical (SO4(-)) were determined to be responsible for the degradation of CIP and SMX in Fe(II)-persulfate system by molecular probes. No enhancement in the degradation of CIP was observed when citrate (CA), ethylenediaminetetraacetate (EDTA) and (S,S)-ethylenediamine-N,N'-disuccinate (EDDS) were used as Fe(II) chelating agents in Fe(II)-persulfate system. For SMX, CA and EDTA accelerated the degradation by Fe(II)-persulfate. Degradation of antibiotics in river water matrix was nearly the same as that in Milli-Q water, implying the possibility of using Fe(II)-persulfate for antibiotics depletion under environmentally relevant condition. A comparison of the degradation efficiency of SMX with other sulfonamides and sulfanilic acid indicated that the heterocyclic ring has a large impact on the degradation of sulfonamides. Transformation products of CIP and SMX by Fe(II)-persulfate were analyzed by solid phase extraction-liquid chromatography-mass spectrometry (SPE-LC-MS) technique. Based on the intermediate products, Fe(II)-persulfate mediated CIP degradation pathways were tentatively proposed.

Degradation of ciprofloxacin and sulfamethoxazole by ferrous-activated persulfate: implications for remediation of groundwater contaminated by antibiotics.

The photochemical activities of three kinds of carbon nanotubes (CNTs) were investigated in the present study. Efficient procedures of dispersing the three kinds of carbon nanotubes in water were established, and the quantitative analysis methods were also developed by TOC-absorbance method. High pH value or low ionic strength of the colloidal solutions facilitated the dispersion of CNTs. The suspensions of three kinds of CNTs could generate singlet oxygen ((1)O2) and hydroxyl radical (•OH) under irradiation of simulated sunlight, while superoxide radical (O2 (•-)) was not detected. The steady-state concentrations of (1)O2 and •OH generated by these CNTs were also determined. The presence of CNTs in natural waters can affect the photochemical behavior of water constituents, such as nitrate, dissolved organic matter, and Fe(3+). Specifically, in nitrate solution, the presence of CNTs could inhibit the generation of •OH by nitrate through light screening effect, while the quenching effect of hydroxyl radicals by CNTs was not observed. Besides light screening effect, the three kinds of CNTs used in the experiments also have a strong inhibiting effect on the ability of DOM to produce •OH by binding to the active sites. Moreover, the adsorption of Fe(3+) on MWCNT-OH and MWCNT-COOH could lead to its inactivation of formation of •OH in acidic conditions. However, the presence of the three kinds of CNTs did not affect the ligand-to-metal charge transfer (LMCT) reaction of DOM-Fe (III) complex.

Photochemical behavior of carbon nanotubes in natural waters: reactive oxygen species production and effects on •OH generation by Suwannee River fulvic acid, nitrate, and Fe (III).

The widespread occurrence of sulfonamide antibiotics in the environment has raised great concerns about their potential to proliferate antibacterial resistance. Sulfate radical (SO4(•-)) based advanced oxidation processes (SR-AOPs) are promising in-situ chemical oxidation (ISCO) technologies for remediation of soil and groundwater contaminated by antibiotics. The present study reported that thermally activated persulfate oxidation of sulfonamides (SAs) bearing six-membered heterocyclic rings, e.g., sulfamethazine (SMZ), sulfapyridine (SPD), sulfadiazine (SDZ), sulfadimethoxine (SDM), and sulfachloropyridazine (SCP), all produced SO2 extrusion products (SEPs), a phenomenon that is of potential importance, but not systematically studied. As an electrophilic oxidant, SO4(•-) tends to attack the aniline moiety, the reactive site of SAs, via electro-transfer mechanism. The resulting anilinyl radical cations are subjected to further intermolecular Smiles-type rearrangement to produce SEPs. Formation of SEPs is expected to occur in other SR-AOPs as well. The temperature-dependent evolution pattern of SEP of SMZ, 4-(2-imino-4,6-dimethylpyrimidin-1(2H)-yl)aniline, can be well fitted by kinetic modeling concerning sequential formation and transformation of intermediate product. The presence of natural organic matter (NOM) influenced the evolution patterns of 4-(2-imino-4,6-dimethylpyrimidin-1(2H)-yl)aniline significantly. Toxicological effects of SEPs on ecosystem and human health remain largely unknown, thus, further monitoring studies are highly desirable.

Sulfate radical-based oxidation of antibiotics sulfamethazine, sulfapyridine, sulfadiazine, sulfadimethoxine, and sulfachloropyridazine: Formation of SO2 extrusion products and effects of natural organic matter.

Article	Year
Development of HPLC/ESI-MS and HPLC/1H NMR methods for the identification of photocatalytic degradation products of iodosulfuron. Analytical chemistry\| PubMed ID: 16642981	2006
Effect of positional isomerism on the abiotic degradation of pesticides: Case of m- and p-imazamethabenz-methyl. Chemosphere\| PubMed ID: 17320147	2007
Different methods in TiO2 photodegradation mechanism studies: gaseous and TiO2-adsorbed phases. Journal of hazardous materials\| PubMed ID: 17363156	2007
Photocatalytic removal of pesticide dichlorvos from indoor air: a study of reaction parameters, intermediates and mineralization. Environmental science & technology\| PubMed ID: 18497160	2008
The remediation of wastewater containing 4-chlorophenol using integrated photocatalytic and biological treatment. Journal of photochemistry and photobiology. B, Biology\| PubMed ID: 19914843	2010
Nitrate-induced photodegradation of atenolol in aqueous solution: kinetics, toxicity and degradation pathways. Chemosphere\| PubMed ID: 22497785	2012
Photochemical degradation of sunscreen agent 2-phenylbenzimidazole-5-sulfonic acid in different water matrices. Water research\| PubMed ID: 23906777	2013
Degradation of ciprofloxacin and sulfamethoxazole by ferrous-activated persulfate: implications for remediation of groundwater contaminated by antibiotics. The Science of the total environment\| PubMed ID: 24342085	2014
Photochemical behavior of carbon nanotubes in natural waters: reactive oxygen species production and effects on •OH generation by Suwannee River fulvic acid, nitrate, and Fe (III). Environmental science and pollution research international\| PubMed ID: 27388595	2016
Sulfate radical-based oxidation of antibiotics sulfamethazine, sulfapyridine, sulfadiazine, sulfadimethoxine, and sulfachloropyridazine: Formation of SO2 extrusion products and effects of na... The Science of the total environment\| PubMed ID: 28363182	2017

Corinne Ferronato

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