Partial and almost complete barium exchange on clinoptilolite is performed and structurally studied for different durations (2 h, 24 h, 72 h, 168 h, 12 d, 22 d) at room temperature and 90 °C of the ion exchange process. Continuing ion exchange up to the 22nd day is proved by EDS analyses data and powder XRD (intensity changes of 020 and 200 peaks). Rietveld structure refinement was first performed on the maximum Ba exchanged clinoptilolite at 90 °C for 22 days (3.04 atoms per unit cell). Four barium positions and 9 H₂O sites were refined. The split positions Ba2 and BaK (around M3 site in channel C) were found mostly occupied by 2.23 atoms per unit cell. The rest of refined samples showed different occupations of the positions of incoming Ba²⁺ and outgoing cations (Na⁺, Ca²⁺, K⁺, Mg²⁺) during ion exchange, describing extra-framework cationic movements, which are released easily without preferable directions. The exchanges at 90 °C and room temperature were found proceeding similarly up to the 2nd hour, but then at room temperature the process is slowed and at 22nd day 1.64 barium atoms per unit cell are structurally refined.

Nd–Fe–B permanent magnets are vital for numerous key technologies in strategic sectors such as renewable energy production, e-mobility, defense, and aerospace. Accordingly, the demand for rare earth elements (REEs) enormously increases in parallel to a significant uncertainty in their supply. Thus, research and innovative studies are focus on the investigation of sustainable solutions to the problem and a closed-loop value chain. The present study is based on two benign-by-design approaches aimed at decreasing the recycling loop span by preparing standardized batches of EoL Nd–Fe–B materials to be treated separately depending on their properties, as well as using mechanochemical method for waste processing. The previously reported benefits of both direct recycling and mechanochemistry include significant improvements in processing metrics, such as energy use, ecological impact, technology simplification, and cost reduction. Waste-sintered Nd–Fe–B magnets from motorbikes were collected, precisely sorted, selected, and pre-treated. The study presents a protocol of resource-efficient recycling through mechanochemical processing of non-oxidized sintered EoL magnets, involving the extraction of Nd₂Fe₁₄B magnetic grains and refining the material’s microstructure and particle size after 120 min of high-energy ball milling in a zirconia reactor. The recycled material preserves the main Nd₂Fe₁₄B magnetic phase, while an anisotropic particle shape and formation of a thin Nd/REE-rich layer on the grain surface were achieved.

This work investigated the optical characteristics of BaWO₄ nanoparticles that were produced through direct mechanochemical synthesis at varying speeds and times. This research expands upon our previous study. We demonstrated that the mechanochemical activation of the precursor of BaCO₃ and WO₃, at elevated milling speeds (850 rpm), facilitates the formation of tetragonal BaWO₄ in a reduced reaction time. The final products were characterized by scanning electron microscopy (SEM), as well as Raman, infrared (IR), UV-Vis diffuse reflectance, and photoluminescence spectroscopies. The crystallite sizes and particles shapes were determined by X-ray diffraction and SEM analysis. Round particles with a size below 50 nm formed under different milling conditions. The Raman spectra of the synthesized samples confirmed the presence of a scheelite-type structure with the typical six distinct vibrational peaks. The symmetry of the structural WO₄ groups was determined by IR spectroscopy. The absorption spectra of both samples exhibited intensive peaks at 210 nm, and the calculated optical band gaps of BaWO₄ were 5.10 eV (3 h/500 rpm) and 5.24 eV (1 h/850 rpm). A strong (400 nm) and weak (465 nm) emission were observed for the BaWO₄ that was obtained at a higher milling speed, while wider emission at 410 nm was visible for the BaWO₄ that was prepared at a lower milling speed. The CIE coordinates of the mechanochemically synthesized BaWO₄ were located within the blue area, exhibiting various positions.

This article presents the results of preliminary mineralogical characterization of scapolite from a new for Bulgaria locality – Mishevsko, Central Rhodopes. The examined samples exhibit a characteristic yellow luminescence under long-wave ultraviolet light. There are compositional variations, primarily affecting the extra-framework cation and anion species in the structure of the studied mineral and thus also the meionite component (62 < Me <74). At the end, considerations on the factors controlling the scapolitization process, as well as speculations on possible causes of scapolite fluorescence are presented.

The present study investigates the effect of synthetic diamond nanoparticles as functional modifiers of NiCoP coatings, simultaneously addressing their corrosion resistance and bifunctional HER/OER electrocatalytic performance on Fe-steel substrates. A direct comparison between electroless and electrodeposition routes is presented. The corrosion behaviour of the coatings was evaluated ex situ in 1 M and 6 M KOH electrolytes to assess their stability under both operating and accelerated degradation conditions. The as-prepared and alkali-treated coatings were characterized by potentiodynamic polarization measurements, X-ray diffraction (XRD), field-emission scanning electron microscopy coupled with energy-dispersive spectroscopy (FE-SEM/EDS), and X-ray fluorescence (XRF) analysis. In addition, their bifunctional electrocatalytic performance toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) was evaluated. The results demonstrate that synthetic diamond incorporation influences the corrosion behaviour of NiCoP coatings; however, the magnitude and direction of this effect depend strongly on both the deposition route and the electrolyte concentration. Furthermore, co-electrodeposition combined with synthetic diamond nanoparticles emerges as a promising approach for developing PGM-free, diamond-modified NiCoP composite coatings on commercially available Fe-steel substrates, providing an effective balance between coating microstructure, corrosion resistance, and bifunctional electrocatalytic performance.

This study focuses on the synthesis of Co_0.5Cu_0.5Fe₂O₄ mixed ferrites supported on nanoporous carbon materials. The carbon supports were derived from two mixtures: a mixture of spent motor oil and pine wood chips (designated as AC-A), and a mixture of spent motor oil and crushed coal obtained from the Chukurovo mine (designated as AC-B). Additionally, two types of carbon components—nanodiamond and graphene oxide—were used for the synthesis of nanosized ceria-based hybrid nanocomposites. The results revealed that the active phase deposited on the carbon supports consists of a complex mixture of finely dispersed ferrite nanoparticles as well as small CeO₂ crystallites in the case of hybrid nanocomposites. The dispersion and phase composition of the deposited copper–cobalt ferrites depends on the textural properties of the carbon supports. Among the investigated materials, the graphene oxide-modified composites exhibited the highest catalytic activity at 670 K, achieving a methanol conversion of 90%.