Gas chromatography-mass spectroscopy optimization by computer simulation, application to the analysis of 93 volatile organic compounds in workplace ambient air.

International audienceGC-MS optimization method including both advantages from chromatographic separation and mass spectrometric detection was designed for a set of 93 volatile organic compounds. Only a few experiments were necessary to determine the thermodynamic retention parameters for all compounds on a RTX-VMS column. From these data, computer simulation was used in order to predict the retention times of the compounds in temperature programmed gas chromatography. Then, an automatic selection of ions from the NIST database was performed and compared to the optimum conditions (full separation of VOC). This simulation-selection procedure was used to screen a numerous set of GC and MS conditions in order to quickly design a GC-MS method whatever the set of compounds considered

Surface nano-aggregation and photocatalytic activity of TiO2 on H-type activated carbons

International audienceThe main objective of this work is to detect any associative or synergistic effects between TiO2 and activated carbon in 4-chlorophenol photodegradation. Different activated carbons (AC) were prepared from Tabebuia pentaphyla wood by means of physical activation with CO2 or by extensive carbonization under N2 flow at temperatures from 450 8C up to 1000 8C during 1 h. Results indicate a clear correlation between photocatalytic activities of titania with texture and surface chemistry of AC. Kinetic results of 4-chlorophenol photodegradation indicate that for most of mixed TiO2 and AC solids a synergistic effect between both solids is observed. Surface nano-aggregation of TiO2 on AC was observed by scanning electronic microscopy and dispersion of TiO2 nanoparticles was improved as a function of more basic surface pH of AC. In conclusion, an increase of electronic density in carbon support clearly introduces an enhancement in titania's photoactivity for 4CP photodegradation. This beneficial effect indicates that it is possible to obtain clean water in a much shorter period of time by employing some selected AC in conjunction with TiO2

Iodosulfuron degradation by TiO2 photocatalysis: Kinetic and reactional pathway investigations.

International audienceThe photocatalytic degradation of a sulfonylurea herbicide, iodosulfuron methyl ester (IOME), has been studied in TiO2 aqueous suspensions under UV irradiation. The influence of various parameters such as initial concentration, TiO2 concentration and light intensity on the kinetic process was investigated. Disappearance rate of iodosulfuron followed pseudo-first order kinetics. A special attention was devoted to the identification of intermediates, using a new analytical approach which consists of coupling HPLC–DAD (UV), HPLC–ESI-MS and HPLC–1H NMR techniques after a SPE pre-concentration step. By combining UV, MS and NMR data, up to 20 degradation products were unambiguously identified. Furthermore, 1H NMR data allowed the differentiation of several positional isomers, in particular those of hydroxylation resulting from the attack of OH radicals on the benzene ring of IOME. Kinetic evolution profiles of main intermediates, end products (NO3-, NH4 +, SO4 2-) and total organic carbon (TOC) were also examined in detail. From obtained kinetic and analytical results, the presence of privileged sites for the attack of OH radicals was shown and a detailed degradation pathway was proposed

Photocatalytic oxidation of 2-propanol/toluene binary mixtures at indoor air concentration levels

Photocatalytic oxidation (PCO) technology has a great potential for indoor air purification. However, the presence of humidity and different concentrations of a variety of pollutants are critical parameters that must be addressed for indoor air cleaning applications. In this work, the photodegradation over a commercial air cleaning TiO2 filter of a mixture of two common volatile organic compounds (VOCs), 2-propanol and toluene, at indoor air concentration levels was tested and the role played by water vapour on the PCO performance was discussed. Transient and steady state experiments were performed using different inlet VOCs concentrations (80–400 ppbv) and relative humidity values (RH, 0% and 60% at 25 °C) in a gas flow rate of 300 mL min−1. The adsorption, conversion and mineralization efficiencies were studied. The reaction products at ppbv levels were analysed by automated thermal desorption coupled to gas chromatography–mass spectrometry (ATD–GC–MS) and gas chromatography equipped with a pulsed discharge helium photoionization detector (GC–PDHID). Almost total conversion and mineralization of the less concentrated mixtures was achieved at 0% RH. A significant negative effect of water vapour was observed. This effect can be attributed to the weak adsorption and low solubility of toluene and to the fast desorption of 2-propanol reaction intermediates. The presence of different surface species, in the photocatalytic degradation tests performed in dry and humid conditions, suggests the occurrence of different reaction pathways depending on RH.Peer reviewe

Reactivity of sulfate radicals with natural organic matters

International audienceAdvanced oxidation processes based on sulfate radicals (SO4·−) are capable of efficiently degrade organic pollutants from ground, surface and wastewaters. However, this degradation may be limited by aqueous natural organic matter (NOM). Here we measured the absolute rate constants of reaction of SO4·− with four types of organic matter: two fulvic acids and two lake organic matter. We used laser flash photolysis technique to monitor the SO4·− decay and the formation of the transients from organic matters. Reaction rate constants comprised between 1530 and 3500 s−1 mgC−1 L were obtained by numerical analysis of differential equations and the weighted average of the extinction coefficient of the generated organic matters radicals between 400 and 800 M−1 cm−1

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

International audienceThe 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

Investigations of diatrizoate degradation by photo-activated persulfate

SSCI-VIDE+ATARI+LZO:CFE:JMC:MSLInternational audienceThe widespread occurrence of iodinated X-ray contrast media (ICMs) in aquatic systems poses potential risks to ecologic system and human health. The present study investigated the degradation kinetics and mechanisms of a typical ICMs, diatrizoate (DTZ), by using simulated sunlight (from a solar simulator Suntest CPS+) activated persulfate (PS) oxidation process. The influence of key kinetic factors, such as PS concentrations, pH, dissolved organic matter (DOM), bicarbonate and chloride ions was evaluated. The reaction pathways and mechanisms were proposed based on photoproducts identification using HPLC-MS. UV/PS was found to be more efficient than UV/H2O2. Sulfate radicals (SO4 center dot-) was the dominant reactive species in the oxidation process, and the second-order rate constant of sulfate radical with DTZ was calculated as 1.90 x 10(9) M-1 s(-1) based on laser flash photolysis (LFP) experiments. The results indicated that increasing initial PS concentration favored the decomposition of DTZ; whereas, degradation of DTZ was not affected by pH change ranging from 4.5 to 8.5. DOM inhibited DTZ removal rate, while, bicarbonate enhanced it, and chloride ions induced a negative effect above 500 mM. Major oxidation pathways including deiodination-hydroxylation, decarboxylation-hydroxylation and side chain cleavage were proposed, and detailed underlying mechanisms were also discussed. We suggest a direct photodegradation of primary intermediates generated by SO4 center dot- attack. These findings demonstrate that halogenated pollutants can readily react with SO4 center dot- to form light-absorbing intermediates (ranging from 350 to 500 nm). Thus, this activation method could be a promising approach in the removal of ICMs