Resumo em Inglês:

Zircon is fundamental to geochronology, yet its crystal lattice accumulates radiation damage from α-decay of U and Th, progressively modifying physical properties. Raman spectroscopy provides a non-destructive probe of this damage through peak shifts and linewidth broadening, but mode-specific sensitivity and the role of thermal annealing remain poorly constrained. Here, we correlate effective uranium (eU), accumulated α-dose, and Raman linewidths in zircons from the Brazilian Carajás Province, Peixe Alkaline Suite, and the Fish Canyon Tuff standard using confocal micro-Raman spectroscopy and LA-ICP-MS. Linewidths increase non-linearly with dose and exhibit strong inter-mode correlations, with the external rotation (ER) mode providing the most robust proxy for structural disorder. Variability in linewidth–eU relationships indicates that Raman broadening primarily records time-integrated α-dose. Inter-band comparisons reveal mode-dependent annealing, while high-resolution mapping highlights micrometer-scale heterogeneity. These results demonstrate that robust quantification of radiation damage requires spatially resolved, multi-parameter calibration.

Resumo em Inglês:

The discharge of synthetic dyes into industrial effluents represents a major environmental challenge due to their high stability and persistence in aquatic systems. Among available treatment strategies, membrane-based separation processes have emerged as promising alternatives for removing organic contaminants from water. However, improving membrane selectivity and efficiency toward different classes of dyes remains an important challenge. In this study, commercial PVDF membranes were modified with polydopamine (PDA) and a graphene oxide/polydopamine (GO/PDA) composite to evaluate their performance in removing methylene blue (MB, a cationic dye) and Congo red (CR, an anionic dye). The modified membranes were prepared through surface deposition of active layers and characterized using UV–Vis spectroscopy, FTIR spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and water contact angle (WCA) measurements. Filtration experiments were carried out to assess dye removal efficiency and selectivity. The results showed that PDA-modified membranes achieved the highest retention efficiency for MB and the mixture, indicating a significant improvement over the unmodified PVDF membrane. However, the pristine membrane exhibited a higher retention of the anionic dye. The incorporation of GO contributed to a more homogeneous surface and enhanced selective filtration behavior. In mixed dye solutions (1:1 MB: CR), the GO/PDA membrane demonstrated a greater ability to preferentially remove CR, with a selectivity factor of 3.50. Overall, the deposition of PDA-based layers proved a promising strategy for enhancing nanofiltration membrane performance in the treatment of dye-containing effluents, while GO/PDA modification improved membrane selectivity.

Resumo em Inglês:

Glass-ceramics based on the Na2O–Al2O3–SiO2 (NAS) system have attracted attention due to their potential in dental, refractory, and electronic applications, particularly associated with the nepheline (NaAlSiO4) phase. This study investigated the non-isothermal crystallization kinetics of a NAS glass containing CaO and TiO2 precursors (19.7 mol%) for the in situ formation of a glass-ceramic composed of nepheline and calcium titanate (CaTiO3). The kinetic parameters were determined using the Ligero method. The activation energy for crystallization (Ea) was equal to 195 ± 1 kJ/mol, remaining constant within the crystallized fraction range (x) of 0.40 to 0.50. The average Avrami index (n ≈ 2), associated with a saturated nucleation mechanism (m = 2), indicates a volumetric crystallization process. In addition, the time ratio (t0.75/t0.25 = 1.48) suggests crystal growth limited by diffusion, leading to the development of polyhedral morphologies. X-ray diffraction (XRD) analysis confirmed the formation of nepheline and CaTiO3 phases after heat treatment, while scanning electron microscopy (SEM) revealed a microstructure composed of polyhedral crystals, supporting the kinetic interpretation.

Resumo em Inglês:

In this work, Density Functional Theory (DFT) calculations were employed to investigate the structural stability and magnetic behavior of c-BN/h-BN heterostructures with different phase proportions (20/80, 40/60, 50/50, 60/40, and 80/20). The results reveal that heterostructures containing thin c-BN regions (20/80 and 40/60) undergo pronounced structural reconstruction toward hexagonal-like configurations during relaxation. In contrast, higher c-BN concentrations (50/50, 60/40, and 80/20) preserve the coexistence of sp2- and sp3-like arrangements, exhibiting enhanced structural stability and reduced interfacial distortions. Additionally, localized magnetic ordering emerges only in the heterostructures that preserve the cubic domains, indicating a strong correlation between the magnetic response and the stability of the sp3 network. These findings demonstrate that the structural and magnetic properties of c-BN/h-BN heterostructures are strongly governed by the cubic phase proportion.