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This editorial reports on a thorough analysis of the abundance and scarcity distribution of chemical elements and the minerals they form in the Earth, Sun, and Universe in connection with their number of neutrons and binding energy per nucleon. On one hand, understanding the elements’ formation and their specific properties related to their electronic and nucleonic structure may lead to understanding whether future solutions to replace certain elements or materials for specific technical applications are realistic. On the other hand, finding solutions to the critical availability of some of these elements is an urgent need. Even the analysis of the availability of scarce minerals from European Union sources leads to the suggestion that a wide-ranging approach is essential. These two fundamental assumptions represent also the logical approach that led the European Commission to ask for a multi-disciplinary effort from the scientific community to tackle the challenge of Critical Raw Materials. This editorial is also the story of one of the first fulcrum around which a wide network of material scientists gathered thanks to the support of the funding organization for research and innovation networks, COST (European Cooperation in Science and Technology).

Microwave remote sensing has widely demonstrated its potential in the continuous monitoring of our rapidly changing planet. This review provides an overview of state-of-the-art methodologies for multi-temporal synthetic aperture radar change detection and its applications to biosphere and hydrosphere monitoring, with special focus on topics like forestry, water resources management in semi-arid environments and floods. The analyzed literature is categorized on the base of the approach adopted and the data exploited and discussed in light of the downstream remote sensing market. The purpose is to highlight the main issues and limitations preventing the diffusion of synthetic aperture radar data in both industrial and multidisciplinary research contexts and the possible solutions for boosting their usage among end-users.

Electrically driven acousto-optic light modulators are limited to frequencies of a few hundred megahertz and are typically no smaller than a few micrometres. Here, the authors demonstrate gigahertz acousto-optic conversion of light polarization in a region of a few nanometres using pulsed laser stimulation of a ferroelectric.

The impact of europium doping on the electronic and structural properties of the topological insulator Bi2Te3 is studied in this paper. The crystallographic structure studied by electron diffraction and transmission microscopy confirms that grown by Molecular Beam Epitaxy (MBE) system film with the Eu content of about 3% has a trigonal structure with relatively large monocrystalline grains. The X-ray photoemission spectroscopy indicates that europium in Bi2Te3 matrix remains divalent and substitutes bismuth in a Bi2Te3 matrix. An exceptional ratio of the photoemission 4d multiplet components in Eu doped film was observed. However, some spatial inhomogeneity at the nanometer scale is revealed. Firstly, local conductivity measurements indicate that the surface conductivity is inhomogeneous and is correlated with a topographic image revealing possible coexistence of conducting surface states with insulating regions. Secondly, Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) depth-profiling also shows partial chemical segregation. Such in-depth inhomogeneity has an impact on the lattice dynamics (phonon lifetime) evaluated by femtosecond spectroscopy. This unprecedented set of experimental investigations provides important insights for optimizing the process of growth of high-quality Eu-doped thin films of a Bi2Te3 topological insulator. Understanding such complex behaviors at the nanoscale level is a necessary step before considering topological insulator thin films as a component of innovative devices.

Electrospinning is known to be a facile and effective technique to fabricate fibers of a controlled diameter-distribution. Among a multitude of polymers available for the purpose, the attention should be addressed to the environmentally compatible ones, with a special focus on sustainability. Polylactic acid (PLA) is a widespread, non-toxic polymer, originating from renewable sources and it can degrade into innocuous products. While the production of fibrous membranes is attractive for airborne particles filtration applications, their impact on the removal of gaseous compounds is generally neglected. In this study, electrospun PLA-based nanofibers were functionalized with cyclodextrins, because of their characteristic hydrophobic central cavity and a hydrophilic outer surface, in order to provide adsorptive properties to the composite. The aim of this work is to investigate a hybrid composite, from renewable sources, for the combined filtration of particulate matter (PM) and adsorption of volatile organic compounds (VOCs). Results show how their inclusion into the polymer strongly affects the fiber morphology, while their attachment onto the fiber surface only positively affects the filtration efficiency.

In this paper, we present a new approach to the fusion of Sentinel 1 (S1) and Sentinel 2 (S2) data for land cover mapping. The proposed solution aims at improving methods based on Sentinel 2 data, that are unusable in case of cloud cover. This goal is achieved by using S1 data to generate S2-like segmentation maps to be used to integrate S2 acquisitions forbidden by cloud cover. In particular, we propose for the first time in remote sensing a multi-temporal W-Net approach for the segmentation of Interferometric Wide swath mode (IW) Sentinel-1 data collected along ascending/descending orbit to discriminate rice, water, and bare soil. The quantitative assessment of segmentation accuracy shows an improvement of 0.18 and 0.25 in terms of accuracy and F1-score by applying the proposed multi-temporal procedure with respect to the previous single-date approach. Advantages and disadvantages of the proposed W-Net based solution have been tested in the National Park of Albufera, Valencia, and we show a performance gain in terms of the classical metrics used in segmentation tasks and the computational time.

This paper reports a study on 8 unconventional hydraulic lime-based mortars able to improve indoor air quality by acting as passive systems. Mortars have been prepared with commercial sand or highly adsorbent materials as aggregates with/without TiO2 as photocatalytic agent, to test also the decomposition of airborne pollutants. Mechanical properties, hygrometric behavior, inhibition of growth of molds and depollution properties have been tested. Despite using porous materials (zeolite and activated carbon), in mortars with unconventional aggregates, compressive strength is higher than in sand-based ones, with a more than double higher water vapor permeability. Zeolite-based mortars have the highest moisture buffering capacity followed by silica gel- and activated carbon-based mortars (1.5–2 times higher than reference, respectively, because of the high porosity of unconventional aggregates). Sand-based mortars show optimum inhibitory capacity against fungal growth. Concerning unconventional aggregates, silica gel mortars have good inhibitory capacity, whereas zeolite and activated carbon give to mortars an optimum substrate for molds. Mortars with unconventional aggregates as silica gel remove more than 80% of tracer pollutant after 2 h of test, whereas zeolite-based mortars remove the 65% of it after 120 min. TiO2 enhances depollution properties as photocatalytic oxidation agent when the mortar is close to saturation.

Landfill leachate possesses high concentrations of ammonia, micropollutants, and heavy metals, and are characterised for low biodegradability. For this reason, conventional treatment technologies may result ineffective for complete pollutant removal. Electrochemical oxidation allows most of the of recalcitrant pollutants to be oxidised effectively within an easy operational and acceptable retention time, without the need to provide additional chemicals, and without producing waste materials. The mineralisation efficiency and electrode durability depend on the nature of the electrode material. The conventionally adopted anodes can contain critical raw materials (CRMs), and are subject to extreme corrosion conditions. CRM-free electrodes, such as carbon and graphite-based, exhibit a lower efficiency, and are subject to faster deactivation, or, as for lead-dioxide-based electrodes, can constitute a hazard due to the release into the effluent of the coating corrosion products. In this study, the relationship between electrode type, CRM content, and the removal efficiencies of organic compounds and ammonium-nitrogen (N-NH4) was investigated. Material criticality was estimated by the supply risk with economic importance indexes reported in the 2017 EU CRM List. The COD and N-NH4 removal efficiencies were obtained from a literature analysis of 25 publications. The results show that, while single and multi-oxide-coated electrodes may contain low amounts of CRM, but with limited efficiency, boron-doped diamonds (BDD) may constitute the best compromise in terms of a reduced content of CRM and a high mineralisation efficiency.