Water and soil pollution by heavy metals and other hazardous compounds is a global problem threatening the entire biosphere and affecting the life of many millions of people around the world. For instance, approximately two million tons of industrial, sewage and agriculture waste are discharged every day into water, causing serious health problems and the death of many thousands of people every day on a worldwide basis. Design and assessment of technologies for immobilization and removal of hazardous elements (HEs) is one of the highest priorities for environmental protection both in the industrialized and the developing countries.

The incorporation of HEs into crystalline and glassy silicate ceramics (the “harder” geomaterials) provides a perfect example to show that modelling the preferential distribution and the efficiency of immobilization of HEs in the crystal lattice and vitreous phase requires a detailed crystallographic knowledge at both the long- (XRD) and the short- (XAS) range.

Concerning the application of “softer” geomaterials, crystallographic knowledge of the zeolite structures proved successful for removal of heavy metals and VOCs from contaminated water and for the clean-up of water polluted with antibiotics. Simultaneous toxic metal uptake and bacteria disinfection from aqueous solution was achieved using well characterized nanocomposites of both the softer (zeolite) and the harder (e.g. Fe₃O₄) geomaterials.

Despite cadmium being a toxic element for environmental and human health, it is widely used in industries for fabrication of nickel-cadmium batteries, as anticorrosive agent, color pigment, etc. The most common and effective techniques for Cd removal from wastewater include filtration, chemical precipitation, bio-remediation and ion exchange [1]. Because of their microporous structure and extremely efficient cation exchange capacity, natural zeolites are good candidates for use as ionic filters. Moreover, heavy-metal exchanged zeolites show improved catalytic properties that can be exploited in post remediation processes [2,3]. Therefore, the chemical reactivity and stability of heavy-metal enriched zeolite is of paramount importance. Additionally, the nature of the metal species and their interaction with the zeolite framework play a fundamental role. Nevertheless, the correct determination of the aforementioned aspects can be compromised by the high disorder of the extraframework species, making difficult an unequivocal interpretation of the coordination chemistry of the metal cations. In this respect, the combination of X-ray diffraction (XRD) based techniques together with X-ray absorption spectroscopy (XAS) represents a valid tool to probe the long and short-range order of the species of interest.

In this contribution, we used a complementary experimental and theoretical approach to investigate in detail the structure of two Cd²⁺ -exchangedzeolites, levyne (LEV) and erionite (ERI). These two minerals are classified as small-pore zeolites (pore size between 0.35 and 40 nm) and, due to their structural similarity, they are often found as intergrown phase in nature [4]. In this study, experimental data from single crystal XRD and XAFS were coupled with Molecular Dynamics (MD) simulations to determine the distribution and coordination chemistry of Cd²⁺ in the two framework types (LEV and ERI). Our results showed that in Cd-LEV, Cd²⁺ ions have a fairly ordered distribution, resembling that characteristic of the pristine material [5]. In contrast, a strong disorder of the extraframework species (Cd²⁺ and H₂O) is detected in Cd-ERI pores, where the occupancy of the EF sites is lower than 20%. Such disorder was attributed to the presence of Cd⁺²(H₂O)₆ complexes, which are only partially coordinated to framework oxygen and, therefore, more mobile. To discriminate between the effect of thermal and structural disorder in the measured and theoretically calculated EXAFS spectra, we propose a theoretical approach based on a set of geometry optimizations performed starting from the uncorrelated atomic configuration of MD simulations [6]. Moreover, based on EXAFS analysis, the formation of metallic Cd within the pores of both zeolites could be ruled out.

Finally, we present the effect of Cd²⁺ incorporation on the thermal stability of Cd-LEV. The structural changes were monitored in situ from 25 to 400°C by single crystal X-ray diffraction. Our results demonstrated that, even if Cd had little influence on the room temperature structure, the dehydration behaviour drastically changes compared to that of the pristine material (natural levyne-Ca). The most relevant differences can be summarized by: i) a stronger volume contraction of the unit-cell volume (8% and 5% for Cd-LEV and levyne-Ca [5], respectively) in the investigated temperature range, and ii) the lack, at high temperatures, of the phase transformation to levyne B’ topology, characteristic of natural levyne-Ca.

[1] Rodriguez-Narvaez, O. M, Peralta-Hernandez, J. M., Goonetilleke, A., Bandala, E. R. (2017). Chem. Eng. J. 323, 361.

[2] Onyestyak, G., Kallo, D. (2003) Microporous and Mesoporous Mater. 61, 199.

[3] Zhang, Y., Qu, Y., Wang, D., Zeng, X. C., Wang, J. (2017) Ind. Eng. Chem. Res. 56, 12508.

[4] Passaglia, E., Galli, E., Rinaldi, R. (1974) Contrib. Mineral. Petrol. 43, 253.

[5] Cametti, G. (2018) Microporous and Mesoporous Mater. 265, 162.

[6] Cametti, G., Scheinost, A. C., Churakov, S. V. (2021) Microporous and Mesoporous Mater. 313, 110835.

In recent years, the occurrence and fate of perfluoroalkyl substances (PFAS) in the aquatic environment was recognized as one of the emerging issues in environmental chemistry. In particular, PFOA (C8HF15O2) and PFOS (C8HF17O3S) have recently become the targets of global concern due to their ubiquitous presence in the environment, persistence, and bioaccumulative properties. Strong carbon-fluorine (C–F) bonds make PFOA and PFOS extremely resistant to chemical, thermal and biological degradation, consequently, their removal from water is a crucial scientific and social challenge [1-2]. This work aims to investigate, for the first time, the structural modifications and the desorption kinetics during the thermal activation of FAU and Ag-exchanged FAU-type zeolites used for removal of PFOA and PFOS from water. The introduction of Ag in the framework confers them unique physical, chemical, and antibacterial properties along with strong absorption property, good stability and catalytic activity [3]. In situ high-temperature synchrotron X-ray powder diffraction and thermal analysis coupled with Elemental Analyzer – Isotope Ratio Mass Spectrometry (EA-IRMS) provided to: i) investigate high temperature structural modifications experienced after during PFOA and PFOS thermal desorption and to check the crystallinity preservation of the porous matrix; ii) monitor and evaluate the organics decomposition process upon heating; iii) estimate the influence of Ag active sites in working zeolites; iv) verify the best regeneration temperature in order to verify whether they can be re-used for PFAS removal from wastewater. This information was crucial for designing and optimizing the regeneration treatment of such zeolites, which are revealed to be highly effective in water-remediation technology. Powder diffraction data of each sample were collected at the synchrotron MCX beamline (Elettra, Trieste, Italy) and were subjected to the same heat treatment profile encompassing the heating ramp with a rate of 5°C/min from room temperature to 800 °C. The powder samples were loaded and packed into a 0.5 mm quartz capillary open at one end and heated in situ using a hot air stream. The analysis of the patterns collected using in situ synchrotron XRPD on zeolites showed no heat-induced symmetry change. Moreover, to carry out a comparison, structural data relating to bare zeolites are also reported in order to check the contribution of the loaded organic molecules. The differential thermal analysis (DTA) curve shows two DTA exothermic events between 300 and 600 ºC due to the PFAs degradation, in very good agreement with the EA-IRMS analyses. The complete thermal regeneration of selected materials was achieved at ~600 and 750 °C for PFOA and PFOS loaded samples, respectively. No relevant variations were observed in Ag-exchanged materials. This information is crucial to examine the efficiency of Ag-exchanged zeolites compared to same samples taken separately for the adsorption of PFOS and PFOA from water. The diffraction peaks were also accurately monitored to study in real-time their evolution (in terms of broadening, shift, changes of intensities) compared with the Y zeolites without any treatment, after silver activation and as well as after PFOS and PFOA adsorption. The XRD analysis demonstrated that the adsorption/desorption process occurred without significant loss of zeolite crystallinity, but with slight deformations in the channel apertures. The regenerated zeolites regain the unit-cell parameters of the bare materials almost perfectly, however. Only a slight memory effect in terms of structural deformations is registered in channel geometry thus demonstrating that the regenerated samples which could be able to re-adsorb similar amounts of PFOS.

[1] Ferreira, L., Fonseca, A.M., Botelho, G, Almeida-Aguiar, C, Neves, I.C. (2012). Antimicrobial activity of faujasite zeolites doped with silver. Microporous and Mesoporous Materials. 160, 126–132.

[2] Kucharzyk, K.H., Darlington, R., Benotti, M., Deeb, R., Hawley, E. (2017). Novel treatment technologies for PFAS compounds: A critical review. Journal of Environmental Management. 204, 757-764.

[3] Ziwen, D., Denga, S., Bei, Y., Huang, Q., Wang, B., Huang, J., Yua, G. (2014). Adsorption behavior and mechanism of perfluorinated compounds on various adsorbents—A review. Journal of Hazardous Materials. 274, 443–454.

Humans have used asbestos for about 5,000 years in various parts of the world [1] because of its outstanding properties. The massive use of asbestos turned out to be a global environmental problem when animal carcinogenicity tests and long-term epidemiological studies proved that inhalation of asbestos fibres may induce fatal lung diseases like asbestosis, carcinoma, malignant mesothelioma (MM) and many more after a latency period of decades [2].

Besides the morphological and chemical characterization conveyed by ESD-supported electron microscopy, X-ray diffraction is considered a reliable tool for the characterization of asbestos fibres. Due to problems of peak overlap in powder data, it is not possible though, to carry out a free refinement of these complex atomic structures in order to detect and measure subtle chemical changes to prove the biopersistence.

Since 2016, ID11 offered a new end station, called “nanoscope” where it is possible to focus the beam to the deep sub-micron scale. This is possible by using the in-line crossed silicon compound refractive lenses [3] and using a crossed pair of vertical and horizontal line foci. Combining the very small beam size with a diffractometer to align and maintain a sample in the beam during rotation is very promising for the crystallographic characterization of natural fibres. Here we report a proof of the in vivo biopersistence of asbestos fibres in human lung tissues (figure1) at the atomic scale using synchrotron micro-diffraction. We show that the atomic structure of an amosite fibre remained stable for about 40 years in the lungs of a subject diagnosed with malignant mesothelioma (MM) and originally exposed to a mixture of chrysotile, amosite and crocidolite [4].

Metal oxide aluminosilicate and aluminogermanate nanotubes, called imogolite nanotubes (INT), are nanotubes with well-controlled diameter and with different morphologies [1,2]. These nanotubes undergo major structural changes at high temperatures, including the transformation from one-dimensional nanochannels into a structure which is supposed to be lamellar [3,4].

Here, we report a complete analysis of the structural transformations of single and double-walled aluminogermanate nanotubes, up to 900°C. We applied an original approach combining (i) in-situ X-ray absorption spectroscopy measurements (LUCIA & DiffAbs beamlines, synchrotron SOLEIL), allowing us to investigate the evolution of both Al and Ge atoms coordination during the transformation process, and (ii) in-situ diffraction. It reveals that the dehydroxylation of nanotubes does not lead to a lamellar phase but to metastable intermediate states that we named “meta-imogolite” states by analogy with meta-kaolinite. A mechanism explaining the major structural reorganizations is proposed based on atomic jump processes. The understanding of these structural modifications represents a benchmark for further studies concerning the properties of transformed INT-based compounds.

[1] Paineau E. & Launois P. (2019) In. Nanomaterials from clay minerals. Amsterdam, Netherlands: Elsevier, pp. 257-284.

[2] Monet G., Amara M.S., Rouzière S., Paineau E., Chai Z., Elliott J.D., Poli E., Liu L.M., Teobaldi, G. & Launois P. (2018) Structural resolution of inorganic nanotubes with complex stoichiometry. Nat. Commun., 9, 2033.

[3] MacKenzie K.J.D., Bowden M.E., Brown I.W.M. & Meinhold R.H. (1989) Structure and thermal transformations of imogolite studied by ²⁹Si and ²⁷Al high resolution solid-state nuclear magnetic resonance. Clays Clay Miner., 37, 317-324.

[4] Zanzottera C., Vicente A., Armandi M., Fernandez C., Garrone E. & Bonelli B. (2012) Thermal collapse of single-walled alumino-silicate nanotubes: Transformation mechanisms and morphology of the resulting lamellar phases. J. Phys. Chem. C, 116, 23577-23584.

Naica's giant crystals caves have astonished scientists since their discovery in 2000. Their gypsum crystals have been the subject of extensive studies and reports, both on scientific aspects and general cultural news. This work reports a detailed investigation of the wall-crystal interface of a blocky type crystal pulled off the "Cueva de los Cristales" wall. At the interface, the zones that probably correspond to the nucleation and growth of the blocky were identified. Representative samples were extracted at different depths of the wall-crystal junction and studied by ICP-OES, light and electron microscopies, XRD, and synchrotron-based m-XRF and m-XANES methods. The interface layer, of an average thickness of about 30 to 60 mm, contains various crystalline and amorphous aggregates with diameters ranging from 1 to 30 mm. Calcite, silica, goethite, as well as several Pb, Mn, Cu, and Zn aggregates, have been identified as main components (Figure 1).

Figure 1.The wall-crystal interface of Cueva de los Cristales, with Fe and Zn μ-XRF and μ-XANES obtained from the sample.

The study of the shape and composition of these mineral aggregates, as well as the morphology of the wall-crystal interface, allowed deducing their transformation and role in crystal nucleation and growth. It has been concluded [1] that the nucleation and growth of the Naica giant crystals have occurred under conditions of a slightly supersaturated solution, almost in equilibrium, and stable over a long time. In addition, considering the non-classical theory of crystal nucleation [2] and the results presented here, we can formulate that the heterogeneous nucleation of the giant Naica crystals was initiated with the adsorption of nanocrystalline monomers. These clusters formed in the solution were successively physi- and chemisorbed on the cave walls and on the crystal surface, assembling the crystalline planes during the crystal growth.

The CONACYT (México), Projects 183706, 257912 and 270738, and Project MINECO(Spain) MAT2017-86168-R are acknowledged.

[1] Otalora, F. & Garcia-Ruiz, J. (2014). Chem. Soc. Rev. 43, 2013-2026.

[2] Van Driessche, A. E. S., Stawski, T. M. & Kellermeier, M. (2019). Chem. Geol. 530, 119274.μ