Delphine Vantelon

The Cation Exchange Capacity (CEC) of clay minerals has been extensively studied in wide applications / purposes, using various imaging techniques to highlight changes of the clay sheet chargeability. Among the clay minerals, swelling clays such as smectite or vermiculite are particularly interesting regarding their adsorption-desorption properties strongly related to their high CEC (80-150 to 100-150 meq/100g respectively). To better monitor and predict cation exchange processes, the CEC has been investigated by different methodological approaches, including X-ray absorption spectroscopy (XAS) and geoelectrical methods. The Spectral Induced Polarization (SIP) is particularly well designed to quantify CEC because its complex conductivity measurements (in phase and quadrature) characterizes the electrical conduction of charge carriers (liquid) and the polarization phenomenon resulting from the local accumulation of electrical charge carriers in the porous medium (mineral interface).The aim of this work is to investigate in situ how K cations are incorporated within the interlayer of a Ca-montmorillonite by coupling XAS and SIP experimental methods. This novel approach brings multi-scale information at the atomic and clay-sheet levels, providing new insights on enhancing the understanding of CEC mechanisms in terms of time and space and our ability to monitor it with SIP. The experiment was carried out on LUCIA (Soleil synchrotron), at the low energy of potassium K-edge with a microbeam size (2.5 x 2.5 µm²).We used a 1.7 mm3 cell filled with 0.1 g of Ca-Montmorillonite isolated in a 0.8 µm sieve to avoid flushing of the clay sample during the experiment. The cell was subjected to a solution flux of a few cc per minute with 4 different KCl salinities (0.01, 0.05, 0.1, 1 M of KCl). In situ SIP spectra are compared with XAS to conjointly monitor the CEC exchange at different scales. Preliminary results are shown to test-proof the methods as a new in situ / in operando cross-scale methods for CEC spatio-temporal characterization. Overall,this work is the first step of a technological development project, merging the approaches of geophysicists, mineralogists and physicists to monitor in real time the cation exchange processes of a Ca-montmorillonite by K in swelling clay minerals.

The solid-phase speciation of Pb in legacy plastics controls its leaching behaviour upon ingestion. Risk assessments of plastic pollution should move beyond bulk geochemical approaches and account for metal speciation.

Isolating adsorption under controlled laminar flow shows that Pb( ii ) adsorption by carboxylated nanoparticles is transport-limited: surface reactions are instantaneous, and adsorption completes within milliseconds in the droplet stage.

Some bacteria genetically control the biomineralization of intracellular amorphous calcium carbonates (iACC) with potential implications for microbial physiology, evolution, bioremediation and biogeochemical cycling. Until now, this capacity has been documented in Cyanobacteria , the giant gammaproteobacterium Achromatium and a few magnetotactic Pseudomonadota and Nitrospirota . Here, we report the discovery of iACC biomineralization in members of the Methylococcaceae , a family of aerobic methanotrophic Gammaproteobacteria . A homolog of the ccyA gene, previously considered a diagnostic marker for iACC formation in Cyanobacteria , was identified in several Methylococcaceae genomes, based on a search of the conserved C-terminal (GlyZip)3 domain of the encoded calcyanin protein, with a sequence coverage higher than 60% and an E-value lower than 1e ^-20 . Moreover, two cultivated strains, Methylococcus geothermalis and Methylococcus mesophilus , whose genomes contained the ccyA gene, were consistently shown to form iACC granules. The ccyA genes of Methylococcaceae and Microcystis share higher sequence similarity (47%) than with other Cyanobacteria (around 30%) within their common (GlyZip) ₃ domain, suggesting horizontal gene transfer (HGT) from an ancestral Microcystis -like cyanobacterium to Methylococcaceae . This finding extends the known taxonomic distribution of ccyA and suggests that the capability to biomineralize iACC was acquired by HGT, possibly in environments such as those close to the oxyclines of lakes, where Cyanobacteria and Methylococcaceae commonly co-exist. The discovery of iACC in methane-oxidizing Methylococcaceae highlights a previously unrecognized coupling between calcium carbonate biomineralization and methane cycling in aquatic environments, suggesting that iACC formation may play an overlooked role in microbial carbon storage and local geochemical regulation.

Immobilisation of Zn, Pb, Cd, and As was achieved in smelting-affected soil showing changes over time. The oxidation of Fe⁰ was not directly proportional with time.

While our awareness of the toxicity of rare earth elements to aquatic organisms increases, our understanding of their direct interaction and accumulation remains limited. This study describes the acute toxicity of lanthanum (La) and gadolinium (Gd) in Daphnia magna neonates and discusses potential modes of action on the basis of the respective patterns of biodistribution. Ecotoxicological bioassays for acute toxicity were conducted and dissolved metal concentrations at the end of the tests were determined. The results showed a significant difference in nominal EC50 (immobility) between La (> 30 mg L^-1) and Gd (13.93 (10.92 to 17.38) mg L^-1). Daphnids that were then exposed to a concentration close to the determined EC50 of Gd (15 mg L^-1, nominal concentration) for 48 h and 72 h were studied by synchrotron micro and nano-X-ray fluorescence to evaluate the biodistribution of potentially accumulated metals. X-ray fluorescence analyses showed that La was mainly found in the intestinal track and appeared to accumulate in the hindgut. This accumulation might be explained by the ingestion of solid La precipitates formed in the media. In contrast, Gd could only be detected in a small amount, if at all, in the intestinal tract, but was present at a much higher concentration in the tissues and became more pronounced with longer exposure time. The solubility of Gd is higher in the media used, leading to higher dissolved concentrations and uptake into tissue in ionic form via common metal transporting proteins. By studying La and Gd biodistribution in D. magna after an acute exposure, the present study has demonstrated that different uptake pathways of solid and dissolved metal species may lead to different accumulation patterns and toxicity.

Imogolite nanotubes present a unique spatial separation of conduction and valence bands but the large bandgap inhibits potential application as a photocatalyst. The first step toward using these well-defined nanotubes in photocatalysis and exploiting their natural polarization-promoting charge separation across the nanotubes wall, is to tune their bandgap energy. Here, titanium modified double walled aluminogermanate imogolite nanotubes are prepared to overcome this limitation. Structural and optical properties are determined at different scales and the photocatalytic performance is evaluated for H2 production under UV-visible light irradiation. Although the incorporation of Ti atoms into the structure remains limited, the resulting nanotubes reveal a remarkable hydrogen evolution rate of ~1500 µmol g-1 h-1, corresponding to a 65-fold increase relative to a reference TiO2P25 photocatalyst. These results confirm the theoretical predictions regarding the untapped potential of modified imogolite nanotubes as promising 1D photoactive polarized nanoreactors.