Elaboration of Cellulose Nanocrystal/Ge-Imogolite Nanotube Multilayered Thin Films

Multilayered thin films combining two oppositely charged nanoparticles (NPs), i.e., cellulose nanocrystals (CNCs) and Ge-imogolites, have been successfully obtained by the layer-by-layer method. CNC/Ge-imogolite (NP/NP) film growth patterns were studied by comparing growth mode of all of the nanoparticles thin films to that of films composed of CNC or Ge-imogolites combined with polyelectrolytes (PEs), i.e., cationic poly­(allylamine hydrochloride) and anionic poly-4-styrene sulfonate (NP/PE films). NP/NP and NP/PE films growth patterns were found to be different. To get a deeper understanding of the growth mode of NP/NP, impact of different parameters, such as imogolites aspect ratio, adsorption time, ionic strength, and repeated immersion/drying, was evaluated and influence of the drying step is emphasized. The aspect ratio of imogolites was identified as an important feature for the film’s architecture. The short Ge-imogolites form denser films because the surface packing was more efficient

Adsorption of Arsenic on Polyaluminum Granulate

The kinetics and efficiencies of arsenite and arsenate removal from water were evaluated using polyaluminum granulates (PAG) with high content of aluminum nanoclusters. PAG was characterized to be meso- and macroporous, with a specific surface area of 35 ± 1 m² g^–1. Adsorption experiments were conducted at pH 7.5 in deionized water and synthetic water with composition of As-contaminated groundwater in the Pannonian Basin. As­(III) and As­(V) sorption was best described by the Freundlich and Langmuir isotherm, respectively, with a maximum As­(V) uptake capacity of ∼200 μmol g^–1 in synthetic water. While As­(III) removal reached equilibrium within 40 h, As­(V) was removed almost entirely within 20 h. Micro X-ray fluorescence and electron microscopy revealed that As­(III) was distributed uniformly within the grain, whereas As­(V) diffused up to 81 μm into PAG. The results imply that As­(V) is adsorbed 3 times faster while being transported 10⁵ times slower than As­(III) in Al hydroxide materials

Physico-chemical Control over the Single- or Double-Wall Structure of Aluminogermanate Imogolite-like Nanotubes

It is known that silicon can be successfully replaced by germanium atoms in the synthesis of imogolite nanotubes, leading to shorter and larger AlGe nanotubes. Beside the change in morphology, two characteristics of the AlGe nanotube synthesis were recently discovered. AlGe imogolite nanotubes can be synthesized at much higher concentrations than AlSi imogolite. AlGe imogolite exists in the form of both single-walled (SW) and double-walled (DW) nanotubes, whereas DW AlSi imogolites have never been observed. In this article, we give details on the physicochemical control over the SW or DW AlGe imogolite structure. For some conditions, an almost 100% yield of SW or DW nanotubes is demonstrated. We propose a model for the formation of SW or DW AlGe imogolite, which also explains why DW AlSi imogolites or higher wall numbers for AlGe imogolite are not likely to be formed

Molecular Insights of Oxidation Process of Iron Nanoparticles: Spectroscopic, Magnetic, and Microscopic Evidence

Oxidation behavior of nano-Fe⁰ particles in an anoxic environment was determined using different state-of-the-art analytical approaches, including high resolution transmission electron microscopy (HR-TEM) combined with energy filtered transmission electron microscopy (EFTEM), X-ray absorption spectroscopy (XAS), and magnetic measurements. Oxidation in controlled experiments was compared in standard double distilled (DD) water, DD water spiked with trichloroethene (TCE), and TCE contaminated site water. Using HR-TEM and EFTEM, we observed a surface oxide layer (∼3 nm) formed immediately after the particles were exposed to water. XAS analysis followed the dynamic change in total metallic iron concentration and iron oxide concentration for the experimental duration of 35 days. The metallic iron concentration in nano-Fe⁰ particles exposed to water, was ∼40% after 35 days; in contrast, the samples containing TCE were reduced to ∼15% and even to nil in the case of TCE contaminated site water, suggesting that the contaminants enhance the oxidation of nano-Fe⁰. Frequency dependence measurements confirmed the formation of superparamagnetic particles in the system. Overall, our results suggest that nano-Fe⁰ oxidized via the Fe⁰ – Fe­(OH)₂ – Fe₃O₄ – (γ-Fe₂O₃) route and the formation of superparamagnetic maghemite nanoparticles due to disruption of the surface oxide layer

Thallium Long-Term Fate from Rock-Deposit to Soil: The Jas Roux Sulfosalt Natural Analogue

Inorganic contaminant release resulting from mining activities can impact surrounding ecosystems. Ores formed by primary sulfide minerals produce sulfuric acid after mineral oxidation, which is the driving force of metal release. Yet secondary metal sulfates may form and play a crucial role in controlling the metal fate. In the case of thallium (Tl), it has been shown that in natural Tl-rich sulfide deposits and those found in mining areas, Tl can be trapped by Tl-jarosite (Tl-rich iron sulfate) and dorallcharite (TlFe3(SO4)2(OH)6). Our Tl speciation characterization results have generated novel insight into the long-term behavior of this metal derived from a unique natural hotspot: the Jas Roux site (France). The biogeochemical cycle of the soil ecosystems of Jas Roux dates back almost 15000 years ago and has now reached a steady state. A chemical gradient was found in soils across the toposequence underlying the Jas Roux outcrop. X-ray absorption spectroscopy revealed that Tl was mainly present in secondary minerals at the top of the studied zone. Oxidative dissolution of Tl-rich sulfide minerals and pyrite accounts for the presence of Tl-jarosite in soils, either by direct formation in soils or by gravity erosion from the outcrop. The Tl-jarosite quantity was found to decrease from the top to the bottom of the toposequence, probably due to sulfate leaching. Released Tl likely adsorbed on phyllosilicates such as Illite or muscovite, and a fraction of Tl was found to have oxidized into Tl(III) along the toposequence

Influence of the Length of Imogolite-Like Nanotubes on Their Cytotoxicity and Genotoxicity toward Human Dermal Cells

Physical–chemical parameters such as purity, structure, chemistry, length, and aspect ratio of nanoparticles (NPs) are linked to their toxicity. Here, synthetic imogolite-like nanotubes with a set chemical composition but various sizes and shapes were used as models to investigate the influence of these physical parameters on the cyto- and genotoxicity and cellular uptake of NPs. The NPs were characterized using X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and atomic force microscopy (AFM). Imogolite precursors (PR, ca. 5 nm curved platelets), as well as short tubes (ST, ca. 6 nm) and long tubes (LT, ca. 50 nm), remained stable in the cell culture medium. Internalization into human fibroblasts was observed only for the small particles PR and ST. None of the tested particles induced a significant cytotoxicity up to a concentration of 10^–1 mg·mL^–1. However, small sized NPs (PR and ST) were found to be genotoxic at very low concentration 10^–6 mg·mL^–1, while LT particles exhibited a weak genotoxicity. Our results indicate that small size NPs (PR, ST) were able to induce primary lesions of DNA at very low concentrations and that this DNA damage was exclusively induced by oxidative stress. The higher aspect ratio LT particles exhibited a weaker genotoxicity, where oxidative stress is a minor factor, and the likely involvement of other mechanisms. Moreover, a relationship among cell uptake, particle aspect ratio, and DNA damage of NPs was observed