B18-Core EXAFS
I18-Microfocus Spectroscopy
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[31873, 31884, 38007]
Open Access
Abstract: Some of the largest Mexican uranium (U) deposits are located in Chihuahua. The most important is in Sierra Peña Blanca, northwest of the capital, which was explored and partially exploited in the 1980s. After the closure of activities, the mining projects were left exposed to weathering. To characterize the spread of U minerals towards the neighboring Laguna del Cuervo, sediment samples were collected in the main streams of the drainage pattern of the largest deposits. The U mineral fragments from the fine sand portion were extracted using fluorescence light at 365 nm. The morphology and elemental composition of these particles were analyzed by focused ion beam microscopy (FIB) and scanning transmission electron microscopy (STEM). The particle density in samples close to the U sources was quantified using gamma spectrometry. The highest density was 2500 part./g, and the lowest was 124 part./g. X-ray absorption spectroscopy (XAS) allowed us to establish via XANES the speciation of U in the U particles, confirming the U(VI) oxidation state, while the exploitation of the EXAFS spectrum put in evidence of the presence of uranophane. Finally, the Fe, Sr, and U distributions in the particle and its matrix were obtained via X-ray fluorescence microtomography (XRF-µCT). It was concluded that the particle is composed of uranophane, imbricated with quartz and other oxides.
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Mar 2025
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I22-Small angle scattering & Diffraction
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Open Access
Abstract: Atmospheric aerosol hygroscopicity and reactivity play key roles in determining the aerosol’s fate and are strongly affected by its composition and physical properties. Fatty acids are surfactants commonly found in organic aerosol emissions. They form a wide range of different nanostructures dependent on water content and mixture composition. We follow nano-structural changes in mixtures frequently found in urban organic aerosol emissions, i.e. linoleic acid (LOA), oleic acid (OA), sodium oleate and fructose, during humidity change and exposure to the atmospheric oxidant ozone. Small-Angle X-ray Scattering (SAXS) was employed (Milsom et al., 2024) to derive the hygroscopicity of each nanostructure by measuring time- and humidity-resolved changes in nano-structural parameters. We found that hygroscopicity is directly linked to the specific nanostructure. Reaction with ozone revealed a clear nanostructure-reactivity trend, with notable differences between the individual nanostructures investigated. Simultaneous Raman microscopy complementing the SAXS studies revealed the persistence of oleic acid even after extensive oxidation. Our findings demonstrate that self-assembly of fatty acid nanostructures can significantly impact water uptake and chemical reactivity, thus directly affecting the atmospheric lifetime of these materials.
Another focus of our studies are one-molecule thin layers of LOA and their behaviours when exposed to ozone in multi-component films at the air–water interface (Woden et al., 2024). LOA’s two double bonds allow for ozone-initiated autoxidation, a radical self-oxidation process, as well as traditional ozonolysis. Neutron reflectometry was employed to follow the kinetics of these films in real time in a temperature-controlled environment. We oxidised deuterated LOA (d-LOA) as a monolayer, and in mixed two-component films with either oleic acid (h-OA) or its methyl ester, methyl oleate (h-MO), at room temperature and atmospherically more realistic temperatures of 3 ± 1 °C. We found that the temperature change did not notably affect the reaction rate which was similar to that of pure OA. Kinetic multi-layer modelling using our Multilayer-Py package showed that neither temperature change nor introduction of co-deposited film components alongside d-LOA consistently affected oxidation rates, but the deviation from a single process decay behaviour (indicative of autoxidation) at 98 ppb is clearest for pure d-LOA, weaker for h-MO mixtures and weakest for h-OA mixtures. As atmospheric surfactants will be present in complex, multi-component mixtures, it is important to understand the reasons for these different behaviours even in two-component mixtures of closely related species. Our work demonstrates that it is essential to employ atmospherically realistic ozone levels as well as multi-component mixtures to understand LOA behaviour at low O3 in the atmosphere. Residue formation may be affected by the temperature change, potentially impacting on the persistence of the organic character at the surface of aqueous droplets. Our findings could have impacts on both urban air quality (e.g. protecting harmful urban emissions from atmospheric degradation and therefore enabling their long-range transport), and climate (e.g. affecting cloud formation), with implications for human health and wellbeing.
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Mar 2025
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[29808]
Open Access
Abstract: Historical disposal of coal mine wastes in the coastal zone has left a significant environmental pollution legacy. Climate change is increasing the likelihood that erosion of these wastes will lead to release of metal(loid)s to coastal environments. Whilst previous research has focussed on the generation of acidic, metal-rich waters from coal mine wastes in freshwater environments, a comprehensive investigation of metal(loid) leaching from such wastes in the coastal zone has not been undertaken. This study investigated the leaching behaviour of coal mine wastes under freshwater and saline conditions and determined the impacts of spatial heterogeneity of waste composition on such behaviour. The degree of leaching varied considerably within and between sites due to the heterogenous nature of the waste. Leachate pH varied from 1.80 to 6.99 with acidic leachates particularly enriched in Fe (≤17,000 mg/kg dry waste) and sulfate (≤48,000 mg/kg dry waste) due to dissolution of acid sulfate phases. Dissolution of Fe and Mn oxides, hydroxides and oxyhydroxides also led to release of surface adsorbed metal(loid)s such as As (≤21 mg/kg dry waste), Zn (≤86 mg/kg dry waste) and Cu (≤14 mg/kg dry waste). Adsorption of As to high surface area minerals was confirmed by X-ray Absorption Near Edge Spectroscopy (XANES) analysis. Metal(loid) release was typically lower in the presence of seawater than deionised water due to the greater pH buffering capacity of seawater. This research provides an insight into the considerable challenges faced by coastal managers globally as they seek to mitigate the risks from such legacy pollution.
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Mar 2025
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[13493]
Open Access
Abstract: Water-insoluble organic material extracted from atmospheric aerosol samples collected in urban (Royal Holloway, University of London, UK) and remote (Halley Research Station, Antarctica) locations were shown to form stable thin surfactant films at an air–water interface. These organic films reacted quickly with gas-phase OH radicals and may impact planetary albedo. The X-ray reflectivity measurements additionally indicate that the film may be consistent with having a structure with increased electron density of film molecules towards the water, suggesting amphiphilic behaviour. Assuming the material extracted from atmospheric aerosol produces thin films on aqueous particles and cloud droplets, modelling the oxidation kinetics with a kinetic model of aerosol surface and bulk chemistry (KM-SUB) suggests half-lives of minutes to an hour and values of ksurf of and cm2 s−1 for urban and remote aerosol film extracts, respectively. The superfluous half-lives calculated at typical OH atmospheric ambient mixing ratios are smaller than the typical residence time of atmospheric aerosols; thus, oxidation of organic material should be considered in atmospheric modelling. Thin organic films at the air–water interface of atmospheric aerosol or cloud droplets may alter the light-scattering properties of the aerosol. X-ray reflectivity measurements of atmospheric aerosol film material at the air–water interface resulted in calculated film thickness values to be either ∼10 or ∼17 Å for remote or urban aerosol extracts, respectively, and oxidation did not remove the films completely. One-dimensional radiative transfer modelling suggests the oxidation of thin organic films on atmospheric particles by OH radicals may reduce the planetary albedo by a small, but potentially significant, amount.
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Feb 2025
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B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[24074, 21441]
Open Access
Abstract: Operations at uranium (U)-mining and nuclear facilities have left a global legacy of significant radionuclide contamination in groundwaters which must be managed to minimize environmental harm. Uranium groundwater contamination is present at several sites globally, including Oak Ridge National Laboratory and Hanford, USA and Sellafield nuclear site, UK. In situ phosphate biomineralisation offers a promising method for radionuclide (including 90Sr and U) remediation at these sites. Typically, phosphate-generating amendments are injected into the subsurface to sequester select radionuclides in groundwaters by precipitation of poorly soluble Ca-phosphate phases and subsequent adsorption and/or incorporation of radionuclides to these poorly soluble phases, a remediation route being explored for both U and 90Sr. In this study, we investigate the mechanisms of U-phosphate precipitation in two phosphate-generating amendments (Ca-citrate/Na-phosphate and glycerol phosphate) under conditions relevant to Sellafield, UK. Using aerobic batch sediment experiments, we show both Ca-citrate/Na-phosphate and glycerol phosphate amendments are effective at enhancing removal of U(VI) from representative groundwaters (from 94% to >97%). Aqueous geochemical data coupled to speciation modelling highlighted that precipitation of U(VI) phosphate phases was the likely mechanism of U(VI) removal from groundwaters. Further X-ray absorption spectroscopy (XAS) analysis of solids confirmed U was present as a highly insoluble uranyl orthophosphate-like phase after treatment with both Ca-citrate/Na-phosphate and glycerol phosphate amendments. These data provide underpinning information on U-phosphate remediation in Sellafield relevant conditions thus expanding the range of treatment options for radionuclide contaminated groundwaters and defining the transport and fate of U during phosphate biomineralisation.
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Feb 2025
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Abstract: Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous persistent organic pollutants that accumulate in soils because of their high affinity for soil organic matter (SOM). As these pollutants are toxic to humans and the environment, a better understanding of their fate in the environment is required. This study aimed to assess the PAH distribution within soils according to different soil fractions: the free particulate organic matter (fPOM), the occluded particulate organic matter (oPOM) and the mineral-associated organic matter (MaOM). PAH contents were measured in bulk soils and SOM fractions of alpine soils along an elevation gradient in the French Alps (Lautaret) from 1920 m to 2840 m a.s.l. A specific PAH distribution was identified, with highest PAH contents in the oPOM, followed by the fPOM, then the MaOM. Organic matter (OM) contents of each fraction can partly explain this distribution, but results of nuclear magnetic resonance (NMR) spectroscopy on fPOM and oPOM also highlighted a correlation between the PAH contents and the degree of decomposition of SOM. This indicates that the PAH distribution may be linked to the formation and transformation of fractions: (i) PAHs in the fPOM correspond to relatively recent deposits and mainly reflect the background contamination, (ii) in the oPOM are the PAHs that resist biodegradation during the transformation of fPOM into oPOM and accumulate in the oPOM; this accumulation may be further enhanced by the formation of aggregates. Finally, (iii) in the MaOM, the lower PAH contents can be explained by the different formation pathway of this fraction and its high degree of decomposition. As the PAH distribution may have an impact on their dynamics in soils, it should be taken into consideration in future research.
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Jan 2025
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B18-Core EXAFS
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Victoria
Pérez-Reyes
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Rocio M.
Cabral-Lares
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Jesús G.
Canche-Tello
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Marusia
Rentería-Villalobos
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Guillermo
González-Sánchez
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Blanca P.
Carmona-Lara
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Cristina
Hernández-Herrera
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Fabián
Faudoa-Gómez
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Yair
Rodríguez-Guerra
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Gregorio
Vázquez-Olvera
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Jorge
Carrillo-Flores
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Ignacio A.
Reyes-Cortés
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Daniel
Hernández-Cruz
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René
Loredo-Portales
,
Maria E.
Montero-Cabrera
Diamond Proposal Number(s):
[31873]
Open Access
Abstract: The Sierra Peña Blanca (SPB) region in Chihuahua, Mexico contains a significant uranium deposit representing about 40% of the country’s reserves. Common uranium minerals in this area include uranophane, schoepite, and weeksite/boltwoodite, with several superficial occurrences. Mining activities in the 1980s left unprocessed uranium ore exposed to weathering, with potential transport towards Laguna del Cuervo. This study presents an experimental simulation of uranium transport in SPB sediments using three approaches: (i) a batch experiment to evaluate the ideal adsorption of (UO2)2+ by fine sediment; (ii) a column system fed with 569 mgU L−1 UO2(NO3)2 to simulate adsorption by different sediment particle sizes; (iii) a column system with an upper horizon of uranophane from the area, fed with deionized water, to simulate uranium weathering and transport in particulate material, determined by liquid scintillation counting, revealed that the clay fraction had the highest adsorption capacity for U. X-ray Absorption Fine Structure (XAFS) analysis at the U L3 edge confirmed the U(IV) oxidation state and the fittings of the extended XAFS spectra confirmed the presence of the uranophane group of minerals. X-ray tomography further corroborated the distribution of particulate minerals along the column. The results suggest that the primary transport mechanism in SPB involves the fragmentation of uranium minerals, accompanied by eventual dissolution and subsequent adsorption of U onto sediments.
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Jan 2025
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[31541]
Open Access
Abstract: Hydrophobic molecules lost in water systems can have significant impacts on local ecology. Notably, the discharge of unmetabolized medications, specifically hormones, and hygiene products into effluent wastewater is a pressing environmental challenge. While selective capture of these molecules has been demonstrated by metal-organic cages (MOCs), these studies typically employ an organic solvent system that does not reflect aqueous environmental conditions. In this study, we report a rare, water-soluble, tetrahedral MOC bearing hydrosolvating sulfonate moieties alongside an aromatic naphthyl spacer. The MOC encloses a large (657 Å3) cavity that can bind a range of polycyclic structures in aqueous media. Isothermal titration calorimetry measurements support guest binding being an enthalpically driven hydrophobic binding process. The synthetic strategy employed to prepare the MOC is extensible and thus serves as a promising route to a range of large, water-soluble MOCs containing hydrophobic binding cavities with exciting prospects.
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Jan 2025
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I22-Small angle scattering & Diffraction
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Abstract: The magnesium phosphate mineral struvite (MgNH4PO4·6H2O) has gained scientific significance in the field of phosphorous and nitrogen recovery from wastewater. The recovery of these elements has become critical due to the limited availability of natural P resources like phosphorites and as a tool to reduce the environmental harm linked to mining such deposits. Furthermore, recovered struvite is employed as a slow-release fertiliser for agriculture. Fertilisers from wastewater-derived struvite are produced through intentional precipitation in wastewater treatment plants. However, it is fundamental to gain an in-depth understanding of the conditions necessary for the formation of struvite to maximise the efficiency of this process. This includes the formation conditions of struvite and the kinetics involved in its nucleation and growth. While the formation conditions of struvite-forming wastewater have been widely examined, a significant scientific knowledge gap still exists regarding the formation of struvite from pure salt solutions and the kinetic parameters of nucleation and growth. Aspects such as the nucleation and growth mechanisms of struvite and the role of temperature in the formation of struvite remain poorly understood. Better understanding these parameters is paramount to predicting struvite nucleation in complex solutions like the ones found in residual wastewater. As a result, my first aim for this study was to investigate the nucleation and growth kinetics of struvite from pure salt solutions at different temperatures.
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Jan 2025
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B23-Circular Dichroism
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Abstract: The accumulation of plastic waste in the environment is an ecological disaster and will require multiple solutions to tackle the problem. Despite recent initiatives to close the plastics loop, only 9% of plastic was recycled in 2019, with the remaining waste either incinerated or accumulating in landfills or natural environments, posing hazards to both living and non-living systems. Bioplastics, derived from renewable sources, have been investigated as green alternatives to conventional fossil-based plastics. However, costly synthetic routes and low recyclability continue to challenge the growth of bioplastics. Poly(lactic acid) (PLA) is the most popular polymer for commercial bioplastics, but its recycling is limited by challenging mechanical recycling and slow biodegradation. A team of researchers from King’s College London has developed a generalisable biocatalysis engineering strategy to enhance the use of enzymes to depolymerise a broad class of plastics, in a publication recently published in Cell Reports Physical Science. This novel approach is 84 times faster than the 12-week-long industrial composting process currently used for recycling bioplastic materials.
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Jan 2025
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