Publications by authors named "Grégory Lefèvre"

35 Publications

Emerging investigator series: municipal wastewater as a year-round point source of neonicotinoid insecticides that persist in an effluent-dominated stream.

Environ Sci Process Impacts 2021 Apr 23. Epub 2021 Apr 23.

Department of Civil & Environmental Engineering, University of Iowa, 4105 Seamans Center, Iowa City, IA 52242, USA. and IIHR-Hydroscience & Engineering, 100 C. Maxwell Stanley Hydraulics Laboratory, Iowa City, IA 52242, USA.

Neonicotinoids in aquatic systems have been predominantly associated with agriculture, but some are increasingly being linked to municipal wastewater. Thus, the aim of this work was to understand the municipal wastewater contribution to neonicotinoids in a representative, characterized effluent-dominated temperate-region stream. Our approach was to quantify the spatiotemporal concentrations of imidacloprid, clothianidin, thiamethoxam, and transformation product imidacloprid urea: 0.1 km upstream, the municipal wastewater effluent, and 0.1 and 5.1 km downstream from the wastewater outfall (collected twice-monthly for one year under baseflow conditions). Quantified results demonstrated that wastewater effluent was a point-source of imidacloprid (consistently) and clothianidin (episodically), where chronic invertebrate exposure benchmarks were exceeded for imidacloprid (36/52 samples; 3/52 > acute exposure benchmark) and clothianidin (8/52 samples). Neonicotinoids persisted downstream where mass loads were not significantly different than those in the effluent. The combined analysis of neonicotinoid effluent concentrations, instream seasonality, and registered uses in Iowa all indicate imidacloprid, and seasonally clothianidin, were driven by wastewater effluent, whereas thiamethoxam and imidacloprid urea were primarily from upstream non-point sources (or potential in-stream transformation for imidacloprid urea). This is the first study to quantify neonicotinoid persistence in an effluent-dominated stream throughout the year-implicating wastewater effluent as a point-source for imidacloprid (year-round) and clothianidin (seasonal). These findings suggest possible overlooked neonicotinoid indoor human exposure routes with subsequent implications for instream ecotoxicological exposure.
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http://dx.doi.org/10.1039/d1em00065aDOI Listing
April 2021

Improving the spatial and temporal monitoring of cyanotoxins in Iowa lakes using a multiscale and multi-modal monitoring approach.

Sci Total Environ 2021 Mar 13;760:143327. Epub 2020 Nov 13.

Department of Civil & Environmental Engineering, University of Iowa, 4105 Seamans Center, Iowa City, IA 52242, United States; IIHR-Hydroscience & Engineering, 100 C. Maxwell Stanley Hydraulics Laboratory, Iowa City, IA 52242, United States. Electronic address:

Cyanobacterial harmful algal blooms (CyanoHABs) are pervasive and negatively impact lake water quality, resulting in economic losses and public health risks through exposure to cyanotoxins. Therefore, it is critical to better monitor and understand the complexity of CyanoHABs, but current methods do not fully describe the spatial and temporal variability of bloom events. In this work, we developed a framework for a multiscale and multi-modal monitoring approach for CyanoHABs combining drone-based near-range remote sensing with analytical measurements of microcystin cyanotoxins and chlorophyll-a. We analyzed weekly beach monitoring samples from 37 lakes geographically distributed across the state of Iowa (USA) over a 15-week period in the summer of 2019 to quantify ELISA (bioassay), 12 microcystin congeners (LC-MS/MS), and chlorophyll-a. We developed a novel microcystin congener-normalized equivalent toxin metric to compare CyanoHAB impacted waters; this microcystin-LR normalized sum-of-congeners approach yields lower predicted toxicity than parallel ELISA results suggesting ELISA is conservative for assessment. A significant linear relationship existed between chlorophyll-a and microcystin for lakes throughout Iowa (R = 0.39, p < 0.001); lakes with low watershed:lake area ratio and long residence times exhibited a stronger correlation. We then developed a novel geometry-based image processing approach to allow for stitching over-water drone images, a previous barrier in photogrammetry. We applied our mutli-modal framework to a case study on Green Valley Lake to assess initial viability and predicted microcystin concentrations within 33%. We concluded that multispectral imaging is possible but may presently be insufficient for predicting microcystin concentrations due to limitations in the spectral capabilities of the multispectral camera, but technologies are quickly advancing, and lightweight hyperspectral imaging could soon become feasible for investigating spatial bloom variability on lakes.
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http://dx.doi.org/10.1016/j.scitotenv.2020.143327DOI Listing
March 2021

Differences in Neonicotinoid and Metabolite Sorption to Activated Carbon Are Driven by Alterations to the Insecticidal Pharmacophore.

Environ Sci Technol 2020 11 29;54(22):14694-14705. Epub 2020 Oct 29.

Department of Civil & Environmental Engineering, University of Iowa, 4105 Seamans Center, Iowa City, Iowa 52242, United States.

Widespread application of neonicotinoids has led to their proliferation in waters. Despite low neonicotinoid hydrophobicity, our prior studies implicated granular activated carbon (GAC) in neonicotinoid removal. Based on known receptor binding characteristics, we hypothesized that the insecticidal pharmacophore influences neonicotinoid sorption. Our objectives were to illuminate drivers of neonicotinoid sorption for parent neonicotinoids (imidacloprid, clothianidin, thiamethoxam, and thiacloprid) and pharmacophore-altered metabolites (desnitro-imidacloprid and imidacloprid urea) to GAC, powdered activated carbon, and carbon nanotubes (CNTs). Neonicotinoid sorption to GAC was extensive and largely irreversible, with significantly greater sorption of imidacloprid than desnitro-imidacloprid. Imidacloprid and imidacloprid urea (electronegative pharmacophores) sorbed most extensively to nonfunctionalized CNTs, whereas desnitro-imidacloprid (positive pharmacophore) sorbed most to COOH-CNTs, indicating the importance of charge interactions and/or hydrogen bonding between the pharmacophore and carbon surface. Water chemistry parameters (temperature, alkalinity, ionic strength, and humic acid) inhibited overall neonicotinoid sorption, suggesting that pharmacophore-driven sorption in real waters may be diminished. Analysis of a full-scale drinking water treatment plant GAC filter influent, effluent, and spent GAC attributes neonicotinoid/metabolite removal to GAC under real-world conditions for the first time. Our results demonstrate that the neonicotinoid pharmacophore not only confers insecticide selectivity but also impacts sorption behavior, leading to less effective removal of metabolites by GAC filters in water treatment.
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http://dx.doi.org/10.1021/acs.est.0c04187DOI Listing
November 2020

Occurrence and Spatiotemporal Dynamics of Pharmaceuticals in a Temperate-Region Wastewater Effluent-Dominated Stream: Variable Inputs and Differential Attenuation Yield Evolving Complex Exposure Mixtures.

Environ Sci Technol 2020 10 6;54(20):12967-12978. Epub 2020 Oct 6.

Department of Civil & Environmental Engineering, University of Iowa, 4105 Seamans Center, Iowa City, Iowa 52242, United States.

Effluent-dominated streams are becoming increasingly common in temperate regions and generate complex pharmaceutical mixture exposure conditions that may impact aquatic organisms via drug-drug interactions. Here, we quantified spatiotemporal pharmaceutical exposure concentrations and composition mixture dynamics during baseflow conditions at four sites in a temperate-region effluent-dominated stream (upstream, at, and progressively downstream from effluent discharge). Samples were analyzed monthly for 1 year for 109 pharmaceuticals/degradates using a comprehensive U.S. Geological Survey analytical method and biweekly for 2 years focused on 14 most common pharmaceuticals/degradates. We observed a strong chemical gradient with pharmaceuticals only sporadically detected upstream from the effluent. Seventy-four individual pharmaceuticals/degradates were detected, spanning 5 orders of magnitude from 0.28 to 13 500 ng/L, with 38 compounds detected in >50% of samples. "Biweekly" compounds represented 77 ± 8% of the overall pharmaceutical concentration. The antidiabetic drug metformin consistently had the highest concentration with limited in-stream attenuation. The antihistamine drug fexofenadine inputs were greater during warm- than cool-season conditions but also attenuated faster. Differential attenuation of individual pharmaceuticals (i.e., high = citalopram; low = metformin) contributed to complex mixture evolution along the stream reach. This research demonstrates that variable inputs over multiple years and differential in-stream attenuation of individual compounds generate evolving complex mixture exposure conditions for biota, with implications for interactive effects.
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http://dx.doi.org/10.1021/acs.est.0c02328DOI Listing
October 2020

Polymeric Nanofiber-Carbon Nanotube Composite Mats as Fast-Equilibrium Passive Samplers for Polar Organic Contaminants.

Environ Sci Technol 2020 06 12;54(11):6703-6712. Epub 2020 May 12.

Department of Chemical & Biochemical Engineering, University of Iowa, Iowa City, Iowa 52242, United States.

To improve the performance of polymeric electrospun nanofiber mats (ENMs) for equilibrium passive sampling applications in water, we integrated two types of multiwalled carbon nanotubes (CNTs; with and without surface carboxyl groups) into polyacrylonitrile (PAN) and polystyrene (PS) ENMs. For 11 polar and moderately hydrophobic compounds (-0.07 ≤ log ≤ 3.13), 90% of equilibrium uptake was achieved in under 0.8 days ( values) in nonmixed ENM-CNT systems. Sorption capacity of ENM-CNTs was between 2- and 50-fold greater than pure polymer ENMs, with equilibrium partition coefficients ( values) ranging from 1.4 to 3.1 log units (L/kg) depending on polymer type (hydrophilic PAN or hydrophobic PS), CNT loading (i.e., values increased with weight percent (wt %) of CNTs), and CNT type (i.e., greater uptake with carboxylated CNTs composites). During field deployment at Muddy Creek in North Liberty, Iowa, optimal ENM-CNTs (PAN with 20 wt % carboxylated CNTs) yielded atrazine concentrations in surface water with a 40% difference relative to analysis of a same-day grab sample. We also observed a mean percent difference of 30 (±20)% when comparing ENM-CNT sampler results to grab sample data collected within 1 week of deployment. With their rapid, high capacity uptake and small material footprint, ENM-CNT equilibrium passive samplers represent a promising alternative to complement traditional integrative passive samplers while offering convenience over large volume grab sampling.
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http://dx.doi.org/10.1021/acs.est.0c00609DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7665838PMC
June 2020

A critical review on the potential impacts of neonicotinoid insecticide use: current knowledge of environmental fate, toxicity, and implications for human health.

Environ Sci Process Impacts 2020 Jun;22(6):1315-1346

University of Iowa, College of Public Health, Iowa City, IA, USA.

Neonicotinoid insecticides are widely used in both urban and agricultural settings around the world. Historically, neonicotinoid insecticides have been viewed as ideal replacements for more toxic compounds, like organophosphates, due in part to their perceived limited potential to affect the environment and human health. This critical review investigates the environmental fate and toxicity of neonicotinoids and their metabolites and the potential risks associated with exposure. Neonicotinoids are found to be ubiquitous in the environment, drinking water, and food, with low-level exposure commonly documented below acceptable daily intake standards. Available toxicological data from animal studies indicate possible genotoxicity, cytotoxicity, impaired immune function, and reduced growth and reproductive success at low concentrations, while limited data from ecological or cross-sectional epidemiological studies have identified acute and chronic health effects ranging from acute respiratory, cardiovascular, and neurological symptoms to oxidative genetic damage and birth defects. Due to the heavy use of neonicotinoids and potential for cumulative chronic exposure, these insecticides represent novel risks and necessitate further study to fully understand their risks to humans.
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http://dx.doi.org/10.1039/c9em00586bDOI Listing
June 2020

MUSIC Speciation of γ-AlO at the Solid Liquid Interface: How DFT Calculations Can Help with Amorphous and Poorly Crystalline Materials.

Langmuir 2019 Oct 24;35(40):12986-12992. Epub 2019 Sep 24.

Chimie ParisTech, PSL Research University, CNRS, Institut de Recherche de Chimie Paris (IRCP) , F-75005 Paris , France.

Transition aluminum oxides, such as γ-AlO or alumina, are widely used in many different technical applications that rely on the surface reactivity of this material at the solid liquid interface. The speciation of surface sites of this material confronts several obstacles. On the one hand, alumina is a poorly crystalline oxide, thus allowing for a limited amount of empirical structural information for an important number of surface sites with different trends in reactivity and, on the other hand, it is a metastable material. In this work, we show several ways in which the multisite complexation model, combined with atomistic information from density functional theory and ab initio molecular dynamics (AIMD), can manage to perform speciation calculations of γ-AlO surface sites at the solid liquid interface. Although the results are in good qualitative agreement with experimental titration curves, and they can serve as a guide for the interpretation of the reactivity of this material at the initial stages of an impregnation experiment and chemical weathering phenomena, this work highlights the need of more complex AIMD simulations to accurately model these phenomena in γ-AlO surface/liquid interfaces.
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http://dx.doi.org/10.1021/acs.langmuir.9b02788DOI Listing
October 2019

Electrokinetic mobility, pH and conductance/conductivity data for aqueous silica and PTFE suspension of controlled composition for selected temperature ranges.

Data Brief 2019 Aug 5;25:104354. Epub 2019 Aug 5.

Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102A, HR-10000, Zagreb, Croatia.

The Data in Brief contains data on the electrokinetic mobility of PTFE and silica particles in aqueous suspensions as a function of pH and temperature. Furthermore, the concomitant conductivities and pH values are reported both for systems in the absence and presence of PTFE particles as a function of temperature and are compatible with the associated research paper "The influence of temperature on the charging of Polytetrafluoroethylene surfaces in electrolyte solutions" (Barisic et al.). The trend of the electrokinetic charging with temperature can be inferred from this for both kinds of particles. The data on the evolution of the pH and the measured conductivities are valuable input for future models that simulate the charge of inert surfaces at variable temperature.
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http://dx.doi.org/10.1016/j.dib.2019.104354DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6706758PMC
August 2019

Interdisciplinary Round-Robin Test on Molecular Spectroscopy of the U(VI) Acetate System.

ACS Omega 2019 May 3;4(5):8167-8177. Epub 2019 May 3.

Department of Environmental Engineering and Earth Sciences, Department of Chemistry, Clemson University, 342 Computer Court, Anderson, 29625 South Carolina, United States.

A comprehensive molecular analysis of a simple aqueous complexing system-U(VI) acetate-selected to be independently investigated by various spectroscopic (vibrational, luminescence, X-ray absorption, and nuclear magnetic resonance spectroscopy) and quantum chemical methods was achieved by an international round-robin test (RRT). Twenty laboratories from six different countries with a focus on actinide or geochemical research participated and contributed to this scientific endeavor. The outcomes of this RRT were considered on two levels of complexity: first, within each technical discipline, conformities as well as discrepancies of the results and their sources were evaluated. The raw data from the different experimental approaches were found to be generally consistent. In particular, for complex setups such as accelerator-based X-ray absorption spectroscopy, the agreement between the raw data was high. By contrast, luminescence spectroscopic data turned out to be strongly related to the chosen acquisition parameters. Second, the potentials and limitations of coupling various spectroscopic and theoretical approaches for the comprehensive study of actinide molecular complexes were assessed. Previous spectroscopic data from the literature were revised and the benchmark data on the U(VI) acetate system provided an unambiguous molecular interpretation based on the correlation of spectroscopic and theoretical results. The multimethodologic approach and the conclusions drawn address not only important aspects of actinide spectroscopy but particularly general aspects of modern molecular analytical chemistry.
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http://dx.doi.org/10.1021/acsomega.9b00164DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6648335PMC
May 2019

Photochemical Transformations of Dichloroacetamide Safeners.

Environ Sci Technol 2019 06 31;53(12):6738-6746. Epub 2019 May 31.

Department of Civil & Environmental Engineering , University of Iowa , 4105 Seamans Center for the Engineering Arts and Sciences, Iowa City , Iowa 52242 , United States.

Dichloroacetamide safeners are commonly added to commercial chloroacetamide herbicide formulations and widely used worldwide, but their environmental fate has garnered little scrutiny as a result of their classification as "inert" ingredients. Here, we investigated the photolysis of dichloroacetamide safeners to better understand their persistence and the nature of their transformation products in surface waters. High-resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR) spectroscopy were used to characterize photoproducts. Of the four commonly used dichloroacetamide safeners, only benoxacor undergoes direct photolysis under simulated natural sunlight ( t ∼ 10 min). Via a photoinitiated ring closure, benoxacor initially yields a monochlorinated intermediate that degrades over longer irradiation time scales to produce two fully dechlorinated diastereomers and a tautomer, which further photodegrade over several days to a structurally related aldehyde confirmed via NMR. Dichlormid, AD-67, and furilazole were more slowly degraded by indirect photolysis in the presence of the photosensitizers nitrate, nitrite, and humic acid. Reactive entities involved in these reactions are likely hydroxyl radical and singlet oxygen based on the use of selective quenchers. These safeners also directly photolyzed under higher energy ultraviolet (UV) light, suggesting their potential transformation in engineered systems using UV for disinfection. The finding that dichloroacetamide safeners can undergo photolysis in environmental systems over relevant time scales demonstrates the importance of evaluating the fate of this class of "inert" agrochemicals.
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http://dx.doi.org/10.1021/acs.est.9b00861DOI Listing
June 2019

Evaluation of pilot-scale biochar-amended woodchip bioreactors to remove nitrate, metals, and trace organic contaminants from urban stormwater runoff.

Water Res 2019 05 2;154:1-11. Epub 2019 Feb 2.

Re-inventing the Nation's Urban Water Infrastructure (ReNUWIt), National Science Foundation Engineering Research Center, USA; Department of Civil & Environmental Engineering, Stanford University, Stanford, CA, USA. Electronic address:

Stormwater is increasingly being valued as a freshwater resource in arid regions and can provide opportunities for beneficial reuse via aquifer recharge if adequate pollutant removal can be achieved. We envision a multi-unit operation approach to capture, treat, and recharge (CTR) stormwater using low energy, cost-effective technologies appropriate for larger magnitude, less frequent events. Herein, we tested nutrient, metal, and trace organic contaminant removal of a pilot-scale CTR system in the laboratory using biochar-amended woodchip bioreactors following eight months of aging under field conditions with exposure to real stormwater. Replicate columns with woodchips and biochar (33% by weight), woodchips and straw, or woodchips only were operated with continuous, saturated flow for eight months using water from a watershed that drained an urban area consisting of residential housing and parks in Sonoma, California. After aging, columns were challenged for five months by continuous exposure to synthetic stormwater amended with 50 μg L of six trace organic contaminants (i.e., fipronil, diuron, 1H-benzotriazole, atrazine, 2,4-D, and TCEP) and five metals (Cd, Cu, Ni, Pb, Zn) frequently detected in stormwater in order to replicate the treatment unit operation of a CTR system. Throughout the eight-month aging and five-month challenge experiment, nitrate concentrations were below the detection limit after treatment (i.e., <0.05 mg N L). The removal efficiencies for metals in all treatments were >80% for Ni, Cu, Cd, and Pb. For Zn, about 50% removal occurred in the woodchip-biochar systems while the other systems achieved about 20% removal. No breakthrough of the trace organic compounds was observed in any biochar-containing columns. Woodchip columns without biochar removed approximately 99% of influent atrazine and 90% of influent fipronil, but exhibited relatively rapid breakthrough of TCEP, 2,4-D, 1H-benzotriazole, and diuron. The addition of straw to the woodchip columns provided no significant benefit compared to woodchips alone. Due to the lack of breakthrough of trace organics in the biochar-woodchip columns, we estimated column breakthrough with a diffusion-limited sorption model. Results of the model indicate breakthrough for the trace organics would occur between 10,000 and 32,000 pore volumes. Under ideal conditions this could be equivalent to decades of service, assuming failure by other processes (e.g., clogging, biofouling) does not occur. These results indicate that multiple contaminants can be removed in woodchip-biochar reactors employed in stormwater treatment systems with suitable flow control and that the removal of trace organic contaminants is enhanced significantly by addition of biochar.
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http://dx.doi.org/10.1016/j.watres.2019.01.040DOI Listing
May 2019

Influence of phosphate on tungstate sorption on hematite: A macroscopic and spectroscopic evaluation of the mechanism.

Chemosphere 2018 Dec 28;213:596-601. Epub 2018 Sep 28.

Institut de Recherche de Chimie Paris, CNRS-Chimie ParisTech, 11 rue Pierre et Marie Curie, 75005, Paris, France.

The environmental fate of the tungstate (VI) oxyanion [ e.g. mono tungstate and several polytungstate, generally expressed by W (VI)] is largely controlled by sorption on soil minerals, especially on iron oxide minerals. Molecular scale evaluation of W (VI) retention on iron oxides in the presence of competing oxyanions is scarce in literature. Here we report surface interaction mechanisms of W (VI) on hematite in the presence of phosphate (P) using macroscopic and in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic experiments. Batch sorption experiments were conducted using 2 g L hematite and 100 μM W (VI) and P, in single ion system and in binary mixtures as a function of pH (4-11). In situ ATR-FTIR spectroscopic evaluation of P and W (VI) sorption on hematite was also carried out. The results from macroscopic experiments indicated that W (VI) sorption on hematite was not affected by P when W (VI) was added first. The influence of P on W (VI) sorption was noticed when W (VI) & P were added simultaneously or P was added first. The in situ ATR-FTIR spectroscopic data corroborated these findings. In addition, the spectroscopic data revealed that in the presence of P, the surface complexation mode of W (VI) differed as noted from either the absence of WO antisymmetric infrared (IR) band or the WOW stretching band. This study provides useful information on molecular level understanding of W (VI) surface complexation on hematite in the presence of competing ions such as P.
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http://dx.doi.org/10.1016/j.chemosphere.2018.09.157DOI Listing
December 2018

Prediction of Isoelectric Point of Manganese and Cobalt Lamellar Oxides: Application to Controlled Synthesis of Mixed Oxides.

Langmuir 2018 06 30;34(23):6670-6677. Epub 2018 May 30.

Chimie-ParisTech, PSL Research University, CNRS Institut de Recherche de Chimie-Paris (IRCP) , 75005 Paris , France.

To design novel layered materials, bottom-up strategy is very promising. It consists of (1) synthesizing various layered oxides, (2) exfoliating them, then (3) restacking them in a controlled way. The last step is based on electrostatic interactions between different layered oxides and is difficult to control. The aim of this study is to facilitate this step by predicting the isoelectric point (IEP) of exfoliated materials. The Multisite Complexation model (MUSIC) was used for this objective and was shown to be able to predict IEP from the mean oxidation state of the metal in the (hydr)oxides, as the main parameter. Moreover, the effect of exfoliation on IEP has also been calculated. Starting from platelets with a high basal surface area over total surface area, we show that the exfoliation process has no impact on calculated IEP value, as verified with experiments. Moreover, the restacked materials containing different monometallic (hydr)oxide layers also have an IEP consistent with values calculated with the model. This study proves that MUSIC model is a useful tool to predict IEP of various complex metal oxides and hydroxides.
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http://dx.doi.org/10.1021/acs.langmuir.8b00190DOI Listing
June 2018

Adsorption of Uranium over NH-Functionalized Ordered Silica in Aqueous Solutions.

ACS Appl Mater Interfaces 2017 May 27;9(18):15672-15684. Epub 2017 Apr 27.

Université de Poitiers/CNRS, UMR 7285 IC2MP, Institut de Chimie des Milieux et Matériaux de Poitiers , 5 rue Albert Turpain, 86073 Poitiers, France.

The aim of this work was to obtain an in-depth understanding of the U(VI) adsorption mechanism over amino-functionalized mesoporous silica SBA-15 and highlights its high efficiency in aqueous media for U(VI) removal and preconcentration. The samples were synthesized and functionalized by both grafting and co-condensation methods, using different alkyl-substituted amine groups and were characterized using X-ray diffraction, N physisorption, Fourier transform infrared spectroscopy, and elemental C-H-N-S analyses. The properties for U(VI) adsorption were evaluated under discontinuous conditions, with the determination of the effect of several parameters (initial pH, contact time, initial U(VI) concentration, functionalization method, and organic moiety composition). U(VI) adsorption over grafted materials reached equilibrium at around 30 min, with a maximum adsorption capacity of 573 mg·g for the most efficient material at its optimal adsorption pH (equal to 6) at 20 °C. Functionalized materials by grafting exhibit better adsorption capacities than co-condensed samples because of higher function surface density and function availability. U(VI) adsorption mechanisms were also studied by measuring the electrophoretic mobilities of the particles, aqueous U(VI) speciation, in situ attenuated total reflection infrared and Raman spectroscopies, and transmission electron microscopy analysis. U(VI) adsorption occurred through the formation of an inner sphere complex. The localization of adsorbed U(VI) has also been determined inside of the mesopores, with the formation of several particles on the nanometer scale, in the size of U-hydroxy phases. Besides, the study of the reusability of amino-functionalized SBA-15 by applying adsorption-desorption cycles was also conducted. The adsorption capacity of the material remains stable for at least four adsorption-desorption cycles without any noticeable capacity decrease.
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http://dx.doi.org/10.1021/acsami.6b16158DOI Listing
May 2017

Evaluation of Mechanistic Models for Nitrate Removal in Woodchip Bioreactors.

Environ Sci Technol 2017 May 13;51(9):5156-5164. Epub 2017 Apr 13.

Re-inventing the Nation's Urban Water Infrastructure (ReNUWIt), National Science Foundation Engineering Research Center, Stanford, California 94305-4020, United States.

Woodchip bioreactors (WBRs) are increasingly being applied to remove nitrate from runoff. In this study, replicate columns with aged woodchips were subjected to a range of measured flow rates and influent nitrate concentrations with an artificial stormwater matrix. Dissolved oxygen (DO), nitrate, and dissolved organic carbon (DOC) were measured along the length of the columns. A multispecies reactive transport model with Michaelis-Menten kinetics was developed to explain the concentration profiles of DO, nitrate, and DOC. Four additional models were developed based on simplifying assumptions, and all five models were tested for their ability to predict nitrate concentrations in the experimental columns. Global sensitivity analysis and constrained optimization determined the set of parameters that minimized the root-mean-squared error (RMSE) between the model and the experimental data. A k-fold validation test revealed no statistical difference in RMSE for predicting nitrate concentrations between a zero-order model and the other multispecies reactive transport models tested. Additionally, the multispecies reactive transport models demonstrated no significant differences in predicting DO and DOC concentrations. These results suggest that denitrification in an aged woodchip bioreactor at constant temperature can effectively be modeled using zero-order kinetics when nitrate concentrations are >2 mg-N L. A multispecies model may be used if predicting DOC or DO concentrations is desired.
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http://dx.doi.org/10.1021/acs.est.7b01025DOI Listing
May 2017

Tungstate (VI) sorption on hematite: An in situ ATR-FTIR probe on the mechanism.

Chemosphere 2017 Feb 9;168:685-691. Epub 2016 Nov 9.

PSL Research University, Chimie Paris Tech-CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France.

Owing to the suspected toxicity and carcinogenicity of tungstate (VI) oxyanions [i.e. mono tungstate and several polytungstate, generally represented by W (VI)], the environmental fate of W (VI) has been widely studied. Sorption is regarded as a major mechanism by which W (VI) species are retained in the solid/water interface. Iron (hydr)oxides have been considered important environmental sinks for W (VI) species. Here we report sorption mechanisms of W (VI) on a common iron oxide mineral-hematite under environmentally relevant solution properties using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic probes. Initial W (VI) loadings varied from 10 to 200 μM at fixed pH values ranged from 4.6 to 8.1. For pH envelop (pHs = 4.6, 5.0, 5.5, 6.0, 6.5, 7.5, and 8.1) experiments, fixed W (VI) concentrations (i.e. 10 & 200 μM) were used to understand the effects of pH. The results indicated that at acidic pH values (pH < 6.0) the sorbed polytungstate surface species are prominent at 200 μM initial W (VI) conc. The pH envelop experiments revealed that sorbed polytungstates can be present even at lower initial W (VI) conc. (i.e. 10 μM) at pH values <5.5. Overall, our in situ ATR-FTIR experiments indicated that W (VI) forms inner-sphere type bonds on hematite surface and the strength of the interaction increases with decreasing pH. In addition, initial W (VI) concentration affected the sorption mechanisms of W (VI) on hematite. Our study will aid the molecular level understanding of W (VI) retention on iron oxide surfaces.
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http://dx.doi.org/10.1016/j.chemosphere.2016.11.007DOI Listing
February 2017

Metabolization and degradation kinetics of the urban-use pesticide fipronil by white rot fungus Trametes versicolor.

Environ Sci Process Impacts 2016 Oct;18(10):1256-1265

ReNUWIt Engineering Research Center, Stanford University, Stanford, CA, USA and Department of Civil & Environmental Engineering, Stanford University, 473 Via Ortega, Stanford, CA 94305, USA.

Fipronil is a recalcitrant phenylpyrazole-based pesticide used for flea/tick treatment and termite control that is distributed in urban aquatic environments via stormwater and contributes to stream toxicity. We discovered that fipronil is rapidly metabolized (t = 4.2 d) by the white rot fungus Trametes versicolor to fipronil sulfone and multiple previously unknown fipronil transformation products, lowering fipronil concentration by 96.5%. Using an LC-QTOF-MS untargeted metabolomics approach, we identified four novel fipronil fungal transformation products: hydroxylated fipronil sulfone, glycosylated fipronil sulfone, and two compounds with unresolved structures. These results are consistent with identified enzymatic detoxification pathways wherein conjugation with sugar moieties follows initial ring functionalization (hydroxylation). The proposed pathway is supported by kinetic evidence of transformation product formation. Fipronil loss by sorption, hydrolysis, and photolysis was negligible. When T. versicolor was exposed to the cytochrome P450 enzyme inhibitor 1-aminobenzotriazole, oxidation of fipronil and production of hydroxylated and glycosylated transformation products significantly decreased (p = 0.038, 0.0037, 0.0023, respectively), indicating that fipronil is metabolized intracellularly by cytochrome P450 enzymes. Elucidating fipronil transformation products is critical because pesticide target specificity can be lost via structural alteration, broadening classes of impacted organisms. Integration of fungi in engineered natural treatment systems could be a viable strategy for pesticide removal from stormwater runoff.
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http://dx.doi.org/10.1039/c6em00344cDOI Listing
October 2016

Plant Assimilation Kinetics and Metabolism of 2-Mercaptobenzothiazole Tire Rubber Vulcanizers by Arabidopsis.

Environ Sci Technol 2016 07 8;50(13):6762-71. Epub 2016 Jan 8.

Institute of Environmental Engineering, ETH Zürich , Zürich, Zürich 8093, Switzerland.

2-Mercaptobenzothiazole (MBT) is a tire rubber vulcanizer found in potential sources of reclaimed water where it may come in contact with vegetation. In this work, we quantified the plant assimilation kinetics of MBT using Arabidopsis under hydroponic conditions. MBT depletion kinetics in the hydroponic medium with plants were second order (t1/2 = 0.52 to 2.4 h) and significantly greater than any abiotic losses (>18 times faster; p = 0.0056). MBT depletion rate was related to the initial exposure concentration with higher rates at greater concentrations from 1.6 μg/L to 147 μg/L until a potentially inhibitory level (1973 μg/L) lowered the assimilation rate. 9.8% of the initial MBT mass spike was present in the plants after 3 h and decreased through time. In-source LC-MS/MS fragmentation revealed that MBT was converted by Arabidopsis seedlings to multiple conjugated-MBT metabolites of differential polarity that accumulate in both the plant tissue and hydroponic medium; metabolite representation evolved temporally. Multiple novel MBT-derived plant metabolites were detected via LC-QTOF-MS analysis; proposed transformation products include glucose and amino acid conjugated MBT metabolites. Elucidating plant transformation products of trace organic contaminants has broad implications for water reuse because plant assimilation could be employed advantageously in engineered natural treatment systems, and plant metabolites in food crops could present an unintended exposure route to consumers.
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http://dx.doi.org/10.1021/acs.est.5b04716DOI Listing
July 2016

Competing mechanisms for perfluoroalkyl acid accumulation in plants revealed using an Arabidopsis model system.

Environ Toxicol Chem 2016 May 4;35(5):1138-47. Epub 2016 Mar 4.

Re-Inventing the Nation's Urban Water Infrastructure Engineering Research Center (ReNUWIt), Stanford University, Stanford, California, USA.

Perfluoroalkyl acids (PFAAs) bioaccumulate in plants, presenting a human exposure route if present in irrigation water. Curiously, accumulation of PFAAs in plant tissues is greatest for both the short-chain and long-chain PFAAs, generating a U-shaped relationship with chain length. In the present study, the authors decouple competing mechanisms of PFAA accumulation using a hydroponic model plant system (Arabidopsis thaliana) exposed to a suite of 10 PFAAs to determine uptake, depuration, and translocation kinetics. Rapid saturation of root concentrations occurred for all PFAAs except perfluorobutanoate, the least-sorptive (shortest-chain) PFAA. Shoot concentrations increased continuously, indicating that PFAAs are efficiently transported and accumulate in shoots. Tissue concentrations of PFAAs during depuration rapidly declined in roots but remained constant in shoots, demonstrating irreversibility of the translocation process. Root and shoot concentration factors followed the U-shaped trend with perfluoroalkyl chain length; however, when normalized to dead-tissue sorption, this relationship linearized. The authors therefore introduce a novel term, the "sorption normalized concentration factor," to describe PFAA accumulation in plants; because of their hydrophobicity, sorption is the determining factor for long-chain PFAAs, whereas the shortest-chain PFAAs are most effectively transported in the plant. The present study provides a mechanistic explanation for previously unexplained PFAA accumulation trends in plants and suggests that shorter-chained PFAAs may bioaccumulate more readily in edible portions.
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http://dx.doi.org/10.1002/etc.3251DOI Listing
May 2016

Rapid Phytotransformation of Benzotriazole Generates Synthetic Tryptophan and Auxin Analogs in Arabidopsis.

Environ Sci Technol 2015 Sep 4;49(18):10959-68. Epub 2015 Sep 4.

ReNUWIt Engineering Research Center, ‡Department of Civil & Environmental Engineering, §Department of Chemistry, ∥Department of Chemical Engineering, Stanford University , Stanford, California 94305, United States.

Benzotriazoles (BTs) are xenobiotic contaminants widely distributed in aquatic environments and of emerging concern due to their polarity, recalcitrance, and common use. During some water reclamation activities, such as stormwater bioretention or crop irrigation with recycled water, BTs come in contact with vegetation, presenting a potential exposure route to consumers. We discovered that BT in hydroponic systems was rapidly (approximately 1-log per day) assimilated by Arabidopsis plants and metabolized to novel BT metabolites structurally resembling tryptophan and auxin plant hormones; <1% remained as parent compound. Using LC-QTOF-MS untargeted metabolomics, we identified two major types of BT transformation products: glycosylation and incorporation into the tryptophan biosynthetic pathway. BT amino acid metabolites are structurally analogous to tryptophan and the storage forms of auxin plant hormones. Critical intermediates were synthesized (authenticated by (1)H/(13)C NMR) for product verification. In a multiple-exposure temporal mass balance, three major metabolites accounted for >60% of BT. Glycosylated BT was excreted by the plants into the hydroponic medium, a phenomenon not observed previously. The observed amino acid metabolites are likely formed when tryptophan biosynthetic enzymes substitute synthetic BT for native indolic molecules, generating potential phytohormone mimics. These results suggest that BT metabolism by plants could mask the presence of BT contamination in the environment. Furthermore, BT-derived metabolites are structurally related to plant auxin hormones and should be evaluated for undesirable biological effects.
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http://dx.doi.org/10.1021/acs.est.5b02749DOI Listing
September 2015

A new stochastic approach for the simulation of agglomeration between colloidal particles.

Langmuir 2013 Nov 30;29(45):13694-707. Epub 2013 Oct 30.

Institute of Fluid-Flow Machinery, Polish Academy of Sciences ul. Fiszera 14, 80-231 Gdańsk, Poland.

This paper presents a stochastic approach for the simulation of particle agglomeration, which is addressed as a two-step process: first, particles are transported by the flow toward each other (collision step) and, second, short-ranged particle-particle interactions lead either to the formation of an agglomerate or prevent it (adhesion step). Particle collisions are treated in the framework of Lagrangian approaches where the motions of a large number of particles are explicitly tracked. The key idea to detect collisions is to account for the whole continuous relative trajectory of particle pairs within each time step and not only the initial and final relative distances between two possible colliding partners at the beginning and at the end of the time steps. The present paper is thus the continuation of a previous work (Mohaupt M., Minier, J.-P., Tanière, A. A new approach for the detection of particle interactions for large-inertia and colloidal particles in a turbulent flow, Int. J. Multiphase Flow, 2011, 37, 746-755) and is devoted to an extension of the approach to the treatment of particle agglomeration. For that purpose, the attachment step is modeled using the DLVO theory (Derjaguin and Landau, Verwey and Overbeek) which describes particle-particle interactions as the sum of van der Waals and electrostatic forces. The attachment step is coupled with the collision step using a common energy balance approach, where particles are assumed to agglomerate only if their relative kinetic energy is high enough to overcome the maximum repulsive interaction energy between particles. Numerical results obtained with this model are shown to compare well with available experimental data on agglomeration. These promising results assert the applicability of the present modeling approach over a whole range of particle sizes (even nanoscopic) and solution conditions (both attractive and repulsive cases).
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http://dx.doi.org/10.1021/la403615wDOI Listing
November 2013

Root exudate enhanced contaminant desorption: an abiotic contribution to the rhizosphere effect.

Environ Sci Technol 2013 Oct 4;47(20):11545-53. Epub 2013 Oct 4.

Department of Civil Engineering, University of Minnesota , 500 Pillsbury Drive S.E., Minneapolis, Minnesota 55455, United States.

Despite reports in the literature of superior contaminant degradation in the root-zone of plants, this phenomenon, known as the rhizosphere effect, is poorly understood. We investigated whether root exudates could enhance desorption of residual pollutants, thus improving bioavailability and subsequent biodegradation potential. Root exudates were harvested from three species of hydroponically grown plants, and artificial root exudates (AREs) were created using a literature recipe. Aliquots of the exudates were metabolized by soil bacteria to investigate whether biotransformed exudates exhibited different chemical characteristics or had different effects on contaminant bioavailability than 'raw exudates.' Slurries of naphthalene-aged soil containing raw exudates had a significantly lower soil-water distribution coefficient (Kd) than slurries with metabolized exudates or no-exudate controls, exhibiting median reductions of 50% and 55%, respectively. Raw exudates had a significantly lower surface tension while not increasing overall solubility, indicating the presence of surface-active compounds below the critical micelle concentration; this is a newly observed mechanism of the rhizosphere effect. Exudate samples were characterized by specific UV absorbance, spectral slope, fluorescence index, and excitation-emission matrices. Substantial changes in organic carbon character pre- and postmetabolism, and between harvested exudates and AREs, suggest that AREs are not chemically representative of plant root exudates. Overall, we present evidence that enhanced contaminant desorption in the presence of exudates provides an abiotic contribution to the rhizosphere effect.
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http://dx.doi.org/10.1021/es402446vDOI Listing
October 2013

Water evaporation in silica colloidal deposits.

J Colloid Interface Sci 2013 Oct 23;408:206-11. Epub 2013 Jul 23.

Chimie-ParisTech & CNRS UMR 7575, 11 rue Pierre et Marie Curie, 75005 Paris, France.

The results of an experimental study on the evaporation and boiling of water confined in the pores of deposits made of mono-dispersed silica colloidal micro-spheres are reported. The deposits are studied using scanning electron microscopy, adsorption of nitrogen, and adsorption of water through attenuated total reflection-infrared spectroscopy. The evaporation is characterized using differential scanning calorimetry and thermal gravimetric analysis. Optical microscopy is used to observe the patterns on the deposits after evaporation. When heating at a constant rate and above boiling temperature, the release of water out of the deposits is a two step process. The first step is due to the evaporation and boiling of the surrounding and bulk water and the second is due to the desorption of water from the pores. Additional experiments on the evaporation of water from membranes having cylindrical pores and of heptane from silica deposits suggest that the second step is due to the morphology of the deposits.
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http://dx.doi.org/10.1016/j.jcis.2013.07.013DOI Listing
October 2013

Towards a description of particulate fouling: from single particle deposition to clogging.

Adv Colloid Interface Sci 2012 Dec 18;185-186:34-76. Epub 2012 Oct 18.

Fluid Dynamics, Power Generation and Environment, EDF R&D, 6 quai Watier, Chatou 78401, France.

Particulate fouling generally arises from the continuous deposition of colloidal particles on initially clean surfaces, a process which can even lead to a complete blockage of the fluid cross-section. In the present paper, the initial stages of the fouling process (which include single-particle deposition and reentrainment) are first addressed and current modelling state-of-the-art for particle-turbulence and particle-wall interactions is presented. Then, attention is specifically focused on the later stages (which include multilayer formation, clogging and blockage). A detailed review of experimental works brings out the essential mechanisms occurring during these later stages: as for the initial stages, it is found that clogging results from the competition between particle-fluid, particle-surface and particle-particle interactions. Numerical models that have been proposed to reproduce the later stages of fouling are then assessed and a new Lagrangian stochastic approach to clogging in industrial cases is detailed. These models further confirm that, depending on hydrodynamical conditions (the flow velocity), fluid characteristics (such as the ionic strength) as well as particle and substrate properties (such as zeta potentials), particle deposition can lead to the formation of either a single monolayer or multilayers. The present paper outlines also future numerical developments and experimental works that are needed to complete our understanding of the later stages of the fouling process.
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http://dx.doi.org/10.1016/j.cis.2012.10.001DOI Listing
December 2012

The role of biodegradation in limiting the accumulation of petroleum hydrocarbons in raingarden soils.

Water Res 2012 Dec 4;46(20):6753-62. Epub 2012 Jan 4.

Environmental Engineering Program, Department of Civil Engineering, University of Minnesota, 500 Pillsbury Drive S.E. Minneapolis, MI 55455-0116, USA.

Previous studies have indicated that raingardens are effective at removing petroleum hydrocarbons from stormwater. There are concerns, however, that petroleum hydrocarbons could accumulate in raingarden soil, potentially resulting in liability for the site owner. In this work, 75 soil samples were collected from 58 raingardens and 4 upland (i.e., control) sites in the Minneapolis, Minnesota area, representing a range of raingarden ages and catchment land uses. Total petroleum hydrocarbon (TPH) concentrations in the samples were quantified, as were 16S rRNA genes for Bacteria and two functional genes that encode for enzymes used in the degradation of petroleum hydrocarbons. TPH levels in all of the raingarden soil samples were low (<3 μg/kg) and not significantly different from one another. The TPH concentration in raingarden soil samples was, however, significantly greater (p ≤ 0.002) than TPH levels in upland sites. In addition, the number of copies of Bacteria 16S rRNA genes and functional genes were greater in the raingardens planted with deeply-rooted natives and cultivars than in raingardens containing simply turf grass or mulch (p < 0.036), suggesting that planted raingardens may be better able to assimilate TPH inputs. The ability of microorganisms present in the soil samples to degrade a representative petroleum hydrocarbon (naphthalene) was also investigated in batch experiments. A sub-set of the field sites was selected for re-sampling, and all soil samples tested (n = 8) were able to mineralize naphthalene. In these experiments the initial mineralization rate correlated with the number of copies of Bacteria 16S rRNA genes present.
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http://dx.doi.org/10.1016/j.watres.2011.12.040DOI Listing
December 2012

Fate of naphthalene in laboratory-scale bioretention cells: implications for sustainable stormwater management.

Environ Sci Technol 2012 Jan 23;46(2):995-1002. Epub 2011 Dec 23.

Department of Civil Engineering, University of Minnesota, 500 Pillsbury Drive SE, Minneapolis, Minnesota 55455, United States.

Bioretention cells are increasingly popular in low-impact development as a means to sustainably mitigate the environmental problems associated with stormwater runoff. Yet, much remains to be known regarding the removal and ultimate fate of pollutants such as petroleum hydrocarbons in bioretention cells. In this work, laboratory-scale bioretention cells were constructed inside sealed glass columns. The columns were periodically spiked with (14)C-naphthalene over a 5-month period and the fate of this representative hydrocarbon and the influence of vegetation on naphthalene fate was studied. Three column setups were used: one planted with a legume (Purple Prairie Clover, Dalea purpureum), one planted with grass (Blue-Joint Grass, Calamagrostis canadensis), and one unplanted (i.e., control). Overall naphthalene removal efficiency was 93% for the planted columns and 78% for the control column. Adsorption to soil was the dominant naphthalene removal mechanism (56-73% of added naphthalene), although mineralization (12-18%) and plant uptake (2-23%) were also important. Volatilization was negligible (<0.04%). Significant enrichment of naphthalene-degrading bacteria occurred due to contaminant exposure and plant growth as evidenced by increased biodegradation activity and increased naphthalene dioxygenase gene concentrations in the bioretention media. This research suggests that bioretention is a viable solution for sustainable petroleum hydrocarbon removal from stormwater, and that vegetation can enhance overall performance and stimulate biodegradation.
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http://dx.doi.org/10.1021/es202266zDOI Listing
January 2012

Numerical study on the adhesion and reentrainment of nondeformable particles on surfaces: the role of surface roughness and electrostatic forces.

Langmuir 2012 Jan 9;28(1):438-52. Epub 2011 Dec 9.

Fluid Dynamics, Power Generation and Environment, EDF R&D, 6 quai Watier, Chatou 78401, France.

In this paper, the reentrainment of nanosized and microsized particles from rough walls under various electrostatic conditions and various hydrodynamic conditions (either in air or aqueous media) is numerically investigated. This issue arises in the general context of particulate fouling in industrial applications, which involves (among other phenomena) particle deposition and particle reentrainment. The deposition phenomenon has been studied previously and, in the present work, we focus our attention on resuspension. Once particles are deposited on a surface, the balance between hydrodynamic forces (which tend to move particles away from the surface) and adhesion forces (which maintain particles on the surface) can lead to particle removal. Adhesion forces are generally described using van der Waals attractive forces, but the limit of these models is that any dependence of adhesion forces on electrostatic forces (due to variations in pH or ionic strength) cannot be reproduced numerically. For this purpose, we develop a model of adhesion forces that is based on the DLVO (Derjaguin and Landau, Verwey and Overbeek) theory and which includes also the effect of surface roughness through the use of hemispherical asperities on the surface. We first highlight the effect of the curvature radius on adhesion forces. Then some numerical predictions of adhesion forces or adhesion energies are compared to experimental data. Finally, the overall effects of surface roughness and electrostatic forces are demonstrated with some applications of the complete reentrainment model in some simple test cases.
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http://dx.doi.org/10.1021/la203659qDOI Listing
January 2012

Vibrational characteristics of outer-sphere surface complexes: example of sulfate ions adsorbed onto metal (hydr)oxides.

Langmuir 2011 Jun 6;27(11):6830-5. Epub 2011 May 6.

LECIME-UMR7575, CNRS-ENSCP, 11 Rue Pierre et Marie Curie, 75231 Paris, Cedex 05, France.

The vibrational characteristics of outer-sphere complexes of sulfate at several mineral oxide-water interfaces were investigated by in situ attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy. In the IR spectra obtained from surface outer-sphere complexes, only one peak of the asymmetric stretching vibrational mode υ(3) similar to that of free sulfate ion SO(4)(2-) in aqueous solution is observed. However, on the investigated (hydr)oxide surfaces of Al(3+), Ti(4+), Fe(2+/3+), Cr(3+), Ce(4+), Cu(2+), Y(3+), Zn(2+), and Nd(3+), a shift of up to 14 cm(-1) was found, which was correlated to the polarizing power of the metal cations. A high polarizing power was found to result in a stronger shift of υ(3) compared to that of the aqueous SO(4)(2-) ion. Furthermore, the impact of the metal oxide structure on the characteristics of the formed outer-sphere complex was negligible because different Al and Fe (hydr)oxides did not show any changes in the respective IR spectra. Finally, the ionic strength (1-10(-4) M) and pH (6.8-3.1) have been modified to change the surface potential, showing no direct influence on the spectra (i.e., on the geometry of the outer-sphere complex).
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http://dx.doi.org/10.1021/la200514zDOI Listing
June 2011

Numerical study on the deposition rate of hematite particle on polypropylene walls: role of surface roughness.

Langmuir 2011 Apr 15;27(8):4603-12. Epub 2011 Mar 15.

Fluid Dynamics, Power Generation and Environment, EDF R&D, 6 quai Watier, Chatou 78401, France.

In this paper, we investigate the deposition of nanosized and microsized particles on rough surfaces under electrostatic repulsive conditions in an aqueous suspension. This issue arises in the general context of modeling particle deposition which, in the present work, is addressed as a two-step process: first particles are transported by the motions of the flow toward surfaces and, second, in the immediate vicinity of the walls, the forces between the incoming particles and the walls are determined using the classical DLVO theory. The interest of this approach is to take into account both hydrodynamical and physicochemical effects within a single model. Satisfactory results have been obtained in attractive conditions but some discrepancies have been revealed in the case of repulsive conditions, in line with other studies which have noted differences between predictions based on the DLVO theory and experimental measurements for similar repulsive conditions. Consequently, the aim of the present work is to focus on this particular range and, more specifically, to assess the influence of surface roughness on the DLVO potential energy. For this purpose, we introduce a new simplified model of surface roughness where spherical protruding asperities are placed randomly on a smooth plate. On the basis of this geometrical description, approximate DLVO expressions are used and numerical calculations are performed. We first highlight the existence of a critical asperity size which brings about the highest reduction of the DLVO interaction energy. Then, the influence of the surface covered by the asperities is investigated as well as retardation effects which can play a role in the reduction of the interaction energy. Finally, by considering the random distribution of the energy barrier of the DLVO potential due to the random geometrical configurations, the overall effect of surface roughness is demonstrated with one application of the complete deposition model in an industrial test case. These new numerical results show that nonzero deposition rates are now obtained even in repulsive conditions, which confirms that surface roughness is a relevant aspect to introduce in general approaches to deposition.
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http://dx.doi.org/10.1021/la104488aDOI Listing
April 2011

Acetylacetone, an interesting anchoring group for ZnO-based organic-inorganic hybrid materials: a combined experimental and theoretical study.

Langmuir 2011 Apr 22;27(7):3442-50. Epub 2011 Feb 22.

Laboratoire d'Electrochimie, Chimie des Interfaces et Modélisation pour l'Energie, CNRS UMR-7575, Ecole Nationale Supérieure de Chimie de Paris, Chimie ParisTech, 11 rue P. et M. Curie, 75231 Paris Cedex 05, France.

Acetylacetone (acacH) adsorption on ZnO (10-10) surface has been studied by a theoretical periodic approach using density functional theory. Two dissociative adsorption modes were investigated and compared to the most stable adsorption mode of formic acid. Acetylacetone appears as a suitable anchoring group for hybrid materials, with adsorption energies of the same order of magnitude as formic acid. IR spectra of the acac/ZnO systems were computed in order to determine the spectral signature of adsorption and, possibly, of each adsorption mode to follow the coordination of acac on ZnO at the experimental level. The results have been compared to Fourier transform infrared (attenuated total reflection-IR) experimental spectra. The present investigation points out the interest of acetylacetone as an anchoring group for the development of new ZnO-based functionalized hybrid layers for corrosion protection, light emitting diodes, photocatalytic systems, and dye-sensitized solar cells.
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http://dx.doi.org/10.1021/la103634vDOI Listing
April 2011