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  • 1.
    Arbid, Yara
    et al.
    Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, France.
    Usman, Muhammad
    Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, France.
    Luong, N. Tan
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Mathon, Baptiste
    Treewater, Lyon, France.
    Cedat, Bruno
    Treewater, Lyon, France.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hanna, Khalil
    Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, France; Department of Chemistry, Durham University, Durham, United Kingdom.
    Use of iron-bearing waste materials in laundry wastewater treatment2024In: Journal of Water Process Engineering, E-ISSN 2214-7144, Vol. 57, article id 104717Article in journal (Refereed)
    Abstract [en]

    This study evaluates the efficiency of a steel waste-derived magnetite (WM) for the treatment of laundry wastewater under various irradiation conditions (ultraviolet-A and C: UVA and UVC), both in the presence and absence of H2O2. Because WM can contain magnetite and elemental iron phases, its ability to remove ciprofloxacin and phenol, here used as model pollutants, and total organic carbon (TOC) from laundry wastewater was compared with that of synthetic magnetite (SM) and zero-valent iron (ZVI). We show that the mixed ZVI/H2O2 system under UVC degraded up to 80 % of the pollutant and 70 % of the TOC. WM had, on the other hand, a lower reactivity for pollutants due to the presence of inorganic impurities, yet removed up to 60 % of TOC. In all cases considered in this work, a higher degradation rate was observed under UVC irradiation than under UVA. Moreover, iron-based materials can adsorb heavy metals co-existing in the laundry wastewater. Recyclability tests showed no significant loss in the activity of WM or SM for up to 5 cycles in laundry wastewater. This study can have strong implications for the development of new remediation technologies relying on industrial solid wastes, especially in the context of a circular economy.

  • 2. Cheng, Wei
    et al.
    Lindholm, Jerry
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Holmboe, Michael
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Luong, N. Tan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ilton, Eugene S.
    Hanna, Khalil
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nanoscale hydration in layered manganese oxides2021In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 37, no 2, p. 666-674Article in journal (Refereed)
    Abstract [en]

    Birnessite is a layered MnO2 mineral capable of intercalating nanometric water films in its bulk. With its variable distributions of Mn oxidation states (MnIV, MnIII, and MnII), cationic vacancies, and interlayer cationic populations, birnessite plays key roles in catalysis, energy storage solutions, and environmental (geo)chemistry. We here report the molecular controls driving the nanoscale intercalation of water in potassium-exchanged birnessite nanoparticles. From microgravimetry, vibrational spectroscopy, and X-ray diffraction, we find that birnessite intercalates no more than one monolayer of water per interlayer when exposed to water vapor at 25 °C, even near the dew point. Molecular dynamics showed that a single monolayer is an energetically favorable hydration state that consists of 1.33 water molecules per unit cell. This monolayer is stabilized by concerted potassium–water and direct water–birnessite interactions, and involves negligible water–water interactions. Using our composite adsorption–condensation–intercalation model, we predicted humidity-dependent water loadings in terms of water intercalated in the internal and adsorbed at external basal faces, the proportions of which vary with particle size. The model also accounts for additional populations condensed on and between particles. By describing the nanoscale hydration of birnessite, our work secures a path for understanding the water-driven catalytic chemistry that this important layered manganese oxide mineral can host in natural and technological settings.

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  • 3.
    Luo, Tao
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Université de Rennes, École Nationale Supérieure de Chimie de Rennes, CNRS, ISCR-UMR 6226, Rennes, France.
    Le Crom, Sébastien
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Luong, N. Tan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hanna, Khalil
    Université de Rennes, École Nationale Supérieure de Chimie de Rennes, CNRS, ISCR-UMR 6226, Rennes, France.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Goethite-bound copper controls the fate of antibiotics in aquatic environments2024In: ACS - ES & T Water, E-ISSN 2690-0637, Vol. 4, no 2, p. 638-647Article in journal (Refereed)
    Abstract [en]

    Ciprofloxacin (CIP), a commonly used antibiotic, is today found in natural waterways and terrestrial environments alongside trace heavy metal contaminants. CIP however has a weak affinity for iron (oxy)hydroxide minerals, which often control contaminant transport in nature. This weak affinity is caused by the electrostatic repulsion between positively charged mineral surfaces and the CIP piperazine ring. Using goethite (α-FeOOH), a representative iron (oxy)hydroxide nanomineral, we show that the presence of Cu(II) greatly enhances CIP adsorption while at the same time catalyzes CIP oxidation to byproducts, which are new to nature. The CIP uptake was greatest at circumneutral pH and in saline conditions, where Cu(II), CIP, and mineral surface charges were the least repulsive. Vibrational spectroscopy and molecular simulations revealed that the enhanced uptake of CIP was caused by the the coordination of metal-bonded Cu(II)-CIP surface complexes on goethite. The inner-sphere Cu(II)-CIP complex also facilitated CIP oxidation into a series of new products, which we identified by mass spectrometry. Finally, to predict Cu(II) and quinolone loadings prior to redox-driven reactions, we propose a multisite surface complexation model using Cu(II)-CIP ternary surface complexes, alongside an ion pair to account for the ionic strength dependence on loadings. The information developed in this work will help tracking the fate of CIP in contaminated aquatic environments.

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  • 4.
    Luong, N. Tan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Water film-mediated mineralogical transformations and photocatalytic reactions2023Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Mineral particles capture water vapor in the atmosphere in the form of water films that are only few monolayers thick. Water films form nanoscale hydration environments that mediate a wide range of important reactions in nature and technology. This thesis explored two important phenomena that commonly occur within the confines of water films: mineralogical transformations (Topic 1) and photocatalytic decomposition of organics (Topic 2). These transformations were chiefly identified by vibrational spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and (Transmission and Scanning) electron microscopy. Interpretations of reaction mechanisms were partially supported by chemometrics, kinetic and thermodynamic modeling, as well as molecular simulations.

    Mineralogical transformations (Topic 1) resolved in this thesis involved the hydroxylation (Papers I, II) and carbonation (Paper III) of periclase (MgO), and the oxidation of rhodochrosite (MnCO3) (Paper IV). Two types of MgO nanocubes with contrasting physical properties were used to resolve nucleation- and diffusion-limited hydroxylation reactions to brucite and carbonation reactions to amorphous magnesium carbonate (AMC). While nucleation-limited reactions completely transformed (8 nm) small and aggregated MgO nanocubes to brucite, the reactions became diffusion-limited in larger (32 nm) monodispersed MgO nanocubes because of brucite surface nanocoatings (Paper I). Additionally, brucite nanosheets grew under (GPa-level) crystallization pressures because of the important volumetric expansion of the reaction, which took place in a complex network of microporosity between the small and within the larger MgO nanocubes. Brucite stacking mechanisms, explored in Paper II, focused on the early stages of MgO-water interaction in water films of different thicknesses. These were suggested to involve the stacking and (epitaxial-like) growth of precursor Mg(OH)2 nanosheets in water films. Carbonation reactions explored in Paper III completely hampered hydroxylation reactions studied in Papers I and II, and produced AMC nanocoatings grown over an unreacted MgO core. Finally, oxidation-driven reactions involving rhodochrosite in Paper IV produced MnO2, Mn3O4, and MnOOH nanocoatings with growth rates being scaled with water loadings.

    Photocatalytic decomposition reactions of organics (Topic 2) were focused on the case of oxalate bound to TiO2 nanoparticles (Paper V). Photodecomposition rates scaled with humidity in oxygenated water films, and were explained by the combination of hole transfer (HT), ligand-to-metal charge transfer (LMCT), and the formation of hydroxyl radicals and reactive oxygen species. Decreasing rates in oxygen-free water films were, on the other hand, explained by water-driven charge localization, which eventually limited radical production and charge transfers via HT and LMCT. The reactions involved limited HT and LMCT processes which also competed with a charge recombination process across all humidity ranges.

    This thesis provides new insight into two key types of transformations mediated by water films on minerals. This knowledge can be used to understand the reactivity of mineral (nano)particles exposed to variations in atmospheric humidity and oxygen content, which are both highly relevant to a wide range of settings in nature and technology. It can also advance new ideas in the study of mineral growth, especially within the confines of nanometer-thick water films.

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  • 5.
    Luong, N. Tan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Water film-driven brucite nanosheet growth and stacking2023In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 39, no 31, p. 11090-11098Article in journal (Refereed)
    Abstract [en]

    Thin water films that form by the adhesion and condensation of air moisture on minerals can initiate phase transformation reactions with broad implications in nature and technology. We here show important effects of water film coverages on reaction rates and products during the transformation of periclase (MgO) nanocubes to brucite [Mg(OH)2] nanosheets. Using vibrational spectroscopy, we found that the first minutes to hours of Mg(OH)2 growth followed first-order kinetics, with rates scaling with water loadings. Growth was tightly linked to periclase surface hydration and to the formation of a brucite precursor solid, akin to poorly stacked/dislocated nanosheets. These nanosheets were the predominant forms of Mg(OH)2 growth in the 2D-like hydration environments of sub-monolayer water films, which formed below ∼50% relative humidity (RH). From molecular simulations, we infer that reactions may have been facilitated near surface defects where sub-monolayer films preferentially accumulated. In contrast, the 3D-like hydration environment of multilayered water films promoted brucite nanoparticle formation by enhancing Mg(OH)2 nanosheet growth and stacking rates and yields. From the structural similarity of periclase and brucite to other metal (hydr)oxide minerals, this concept of contrasting nanosheet growth should even be applicable for explaining water film-driven mineralogical transformations on other related nanominerals.

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  • 6.
    Luong, N. Tan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hanna, Khalil
    Université de Rennes, École Nationale Supérieure de Chimie de Rennes, CNRS, ISCR-UMR 6226, F-35000, Rennes, France.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Water film-mediated photocatalytic oxidation of oxalate on TiO22024In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 432, article id 115425Article in journal (Refereed)
    Abstract [en]

    Water films on minerals under humid environment can be photocatalytic hotspots when exposed to sunlight or artificial sources of ultraviolet (and visible) radiation. In this study, we resolved the water film-mediated photocatalysis of oxalate adsorbed on TiO2 using in situ infrared spectroscopy. We found that 0.5 to 4 monolayer- (ML) thick water films enhanced the photodecomposition rates of oxalate under 21 kPa O2. We explained this through the combined actions of direct hole transfer, ligand-to-metal-charge transfer, as well as the production of hydroxyl radicals and reactive oxygen species. Rates were, however, substantially slower in the absence of O2 because charge recombination, together with water film-mediated charge localization, disrupted hole transfer and hydroxyl radical production. Our work adds insight into the impact of humidity on controlling important photocatalytic processes in nature (drying soils, atmospheric aerosols), and technology (water and air treatment).

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  • 7.
    Luong, N. Tan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Holmboe, Michael
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    MgO nanocube hydroxylation by nanometric water films2023In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 15, no 24, p. 10286-10294Article in journal (Refereed)
    Abstract [en]

    Hydrophilic nanosized minerals exposed to air moisture host thin water films that are key drivers of reactions of interest in nature and technology. Water films can trigger irreversible mineralogical transformations, and control chemical fluxes across networks of aggregated nanomaterials. Using X-ray diffraction, vibrational spectroscopy, electron microscopy, and (micro)gravimetry, we tracked water film-driven transformations of periclase (MgO) nanocubes to brucite (Mg(OH)2) nanosheets. We show that three monolayer-thick water films first triggered the nucleation-limited growth of brucite, and that water film loadings continuously increased as newly-formed brucite nanosheets captured air moisture. Small (8 nm-wide) nanocubes were completely converted to brucite under this regime while growth on larger (32 nm-wide) nanocubes transitioned to a diffusion-limited regime when (∼0.9 nm-thick) brucite nanocoatings began hampering the flux of reactive species. We also show that intra- and inter-particle microporosity hosted a hydration network that sustained GPa-level crystallization pressures, compressing interlayer brucite spacing during growth. This was prevalent in aggregated 8 nm wide nanocubes, which formed a maze-like network of slit-shaped pores. By resolving the impact of nanocube size and microporosity on reaction yields and crystallization pressures, this work provides new insight into the study of mineralogical transformations induced by nanometric water films. Our findings can be applied to structurally related minerals important to nature and technology, as well as to advance ideas on crystal growth under nanoconfinement.

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  • 8.
    Luong, N. Tan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ilton, Eugene S.
    Pacific Northwest National Laboratory, WA, Richland, United States.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Water film-driven Mn (oxy)(hydr)oxide nanocoating growth on rhodochrosite2022In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 329, p. 87-105Article in journal (Refereed)
    Abstract [en]

    Minerals exposed to moist air stabilize thin water films that drive a score of chemical reactions of great importance to water-unsaturated terrestrial environments. In this study, we identified Mn (oxy)(hydr)oxide nanocoatings formed by the dissolution, oxidation and precipitation of Mn in oxygenated water films grown on rhodochrosite (MnCO3) microparticles. Nanocoatings that could be identified by vibrational spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and (scanning and transmission) electron microscopy formed in water films containing the equivalent of at least 7 monolayers (∼84 H2O/nm2). These films were formed by exposing microparticles to moist air with at least 50% relative humidity (RH). Films of neutral pH reacted up to 14% of the MnII located in the topmost ∼5 nm region of the microparticles in atmospheres of up to 90% RH for 7 d. These reactions produced MnOOH, birnessite (MnO2) and hausmannite (Mn3O4) nanoparticles of low crystallinity, while exposure to atmospheric air for 1 yr. converted only 2% of MnII in this region to MnOOH. In contrast, reactions in alkaline water films converted up to ∼75% of the MnII but only after 16 d of reaction. These films produced MnOOH and MnO2 of low crystallinity, as well as crystalline hausmannite. Kinetic modeling of the time-resolved growth of the Mn[sbnd]O stretching vibrational bands of these nanocoatings revealed two concurrent reaction processes. A 1rst-order process was assigned to nucleation events terminating only after a few hours, and a 0-order process was assigned to the sustained growth of nanocoatings from these nuclei over longer reaction time. By identifying nanocoatings formed by water film-driven reactions on rhodochrosite, our study adds new insight into mineralogical transformations relevant to anoxic–oxic boundaries in water-unsaturated environments.

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  • 9.
    Luong, N. Tan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Oderstad, Hanna
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Holmboe, Michael
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Temperature-resolved nanoscale hydration of a layered manganese oxide2023In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 25, no 26, p. 17352-17359Article in journal (Refereed)
    Abstract [en]

    Water films captured in the interlayer region of birnessite (MnO2) nanosheets can play important roles in biogeochemical cycling, catalysis, energy storage, and even atmospheric water harvesting. Understanding the temperature-dependent loadings and properties of these interlayer films is crucial to comprehend birnessite reactivity when exposed to moist air and temperature gradients. Using vibrational spectroscopy we show that birnessite intercalates one water (1W) monolayer at up to ∼40 °C, but that loadings decrease by half at up to 85 °C. Our results also show that the vibrational properties of intercalated water are unaffected by temperature, implying that the hydrogen bonding network of water remains intact. Using molecular simulations, we found that the lowered water storage capacity at high temperatures cannot be explained by variations in hydrogen bond numbers or in the solvation environments of interlayer K+ ions initially present in the interlayer region. It can instead be explained by the compounded effects of larger evolved heat, as inferred from immersion energies, and by the larger temperature-driven mobility of water over that of K+ ions, which are electrostatically bound to birnessite basal oxygens. By shedding new light on the temperature-driven intercalation of water in a nanolayered mineral, this study can guide future efforts to understand the (geo)chemical reactivity of related materials in natural and technological settings.

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  • 10.
    Luong, N. Tan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Veyret, Noémie
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    CO2 mineralization by MgO nanocubes in nanometric water films2023In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 15, no 38, p. 45055-45063Article in journal (Other academic)
    Abstract [en]

    Water films formed by the adhesion and condensation of air moisture on minerals can trigger the formation of secondary minerals of great importance to nature and technology. Magnesium carbonate growth on Mg-bearing minerals is not only of great interest for CO2 capture under enhanced weathering scenarios but is also a prime system for advancing key ideas on mineral formation under nanoconfinement. To help advance ideas on water film-mediated CO2 capture, we tracked the growth of amorphous magnesium carbonate (AMC) on MgO nanocubes exposed to moist CO2 gas. AMC was identified by its characteristic vibrational spectral signature and by its lack of long-range structure by X-ray diffraction. We find that AMC (MgCO3·2.3-2.5H2O) grew in sub-monolayer to 4 monolayer-thick water films, with formation rates and yields scaling with humidity. AMC growth was however slowed down as AMC nanocoatings blocked water films access to the reactive MgO core. Films could however be partially dissolved by exposure to thicker water films, driving AMC reaction for several more hours until nanocoatings blocked the reactions again. These findings shed new light on a potentially important bottleneck for the efficient mineralization of CO2 using MgO-bearing products. Notably, this study shows how variations in air humidity affect CO2 capture by controlling water film coverages on reactive minerals. This process is also of great interest in the study of mineral growth in nanometrically thick water films.

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  • 11.
    Yu, Changxun
    et al.
    Department of Biology and Environmental Science, Linnaeus University, Kalmar, Sweden.
    Luong, Nguyen Tan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hefni, Mohammed E.
    Department of Chemistry and Biomedical Sciences, Linnaeus University, Kalmar, Sweden.
    Song, Zhaoliang
    Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin, China.
    Högfors-Rönnholm, Eva
    Research and Development, Novia University of Applied Sciences, Vaasa, Finland.
    Engblom, Sten
    Research and Development, Novia University of Applied Sciences, Vaasa, Finland.
    Xie, Shurong
    School of Earth Sciences, East China University of Technology, Nanchang, China.
    Chernikov, Roman
    Canadian Light Source, 44 Innovation Boulevard, SK, Saskatoon, Canada.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Boily, Jean-François
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Åström, Mats E.
    Department of Biology and Environmental Science, Linnaeus University, Kalmar, Sweden.
    Storage and distribution of organic carbon and nutrients in acidic soils developed on sulfidic sediments: the roles of reactive iron and macropores2024In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 58, no 21, p. 9200-9212Article in journal (Refereed)
    Abstract [en]

    In a boreal acidic sulfate-rich subsoil (pH 3-4) developing on sulfidic and organic-rich sediments over the past 70 years, extensive brownish-to-yellowish layers have formed on macropores. Our data reveal that these layers ("macropore surfaces") are strongly enriched in 1 M HCl-extractable reactive iron (2-7% dry weight), largely bound to schwertmannite and 2-line ferrihydrite. These reactive iron phases trap large pools of labile organic matter (OM) and HCl-extractable phosphorus, possibly derived from the cultivated layer. Within soil aggregates, the OM is of a different nature from that on the macropore surfaces but similar to that in the underlying sulfidic sediments (C-horizon). This provides evidence that the sedimentary OM in the bulk subsoil has been largely preserved without significant decomposition and/or fractionation, likely due to physiochemical stabilization by the reactive iron phases that also existed abundantly within the aggregates. These findings not only highlight the important yet underappreciated roles of iron oxyhydroxysulfates in OM/nutrient storage and distribution in acidic sulfate-rich and other similar environments but also suggest that boreal acidic sulfate-rich subsoils and other similar soil systems (existing widely on coastal plains worldwide and being increasingly formed in thawing permafrost) may act as global sinks for OM and nutrients in the short run.

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  • 12.
    Zhou, Lian
    et al.
    Ecole Nationale Supérieure de Chimie de Rennes, UMR CNRS 6226, Université Rennes, Rennes, France.
    Lassabatere, Laurent
    Univ Lyon, Université Claude Bernard Lyon 1, CNRS, ENTPE, Vaulx-en- Velin, France.
    Luong, N. Tan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hanna, Khalil
    Ecole Nationale Supérieure de Chimie de Rennes, UMR CNRS 6226, Université Rennes, Rennes, France.
    Mineral nanoparticle aggregation alters contaminant transport under flow2023In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 57, no 6, p. 2415-2422Article in journal (Refereed)
    Abstract [en]

    Iron oxyhydroxide nanoparticle reactivity has been widely investigated, yet little is still known on how particle aggregation controls the mobility and transport of environmental compounds. Here, we examine how aggregates of goethite (α-FeOOH) nanoparticle deposited on 100-300 μm quartz particles (GagCS) alter the transport of two emerging contaminants and two naturally occurring inorganic ligands-silicates and phosphates. Bromide tracer experiments showed no water fractionation into mobile and immobile water zones in an individual goethite-coated sand (GCS) column, whereas around 10% of the total water was immobile in a GagCS column. Reactive compounds were, in contrast, considerably more mobile and affected by diffusion-limited processes. A new simulation approach coupling the mobile-immobile equation with surface complexation reactions to surface reactive sites suggests that ∼90% of the binding sites were likely within the intra-aggregate zones, and that the mass transfer between mobile and immobile fractions was the rate-limited step. The diffusion-controlled processes also affected synergetic and competitive binding, which have otherwise been observed for organic and inorganic compounds at goethite surfaces. These results thereby call for more attention on transport studies, where tracer or conservative tests are often used to describe the reactive transport of environmentally relevant molecules.

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