This study assessed the photoactivity of amorphous and crystalline TiO₂ nanotube arrays (TNA) films in gas phase CO₂ reduction. The TNA photocatalysts were fabricated by titanium anodization and submitted to an annealing treatment for crystallization and/or cathodic reduction to introduce Ti³⁺ and oxygen vacancies into the TiO₂ structure. The cathodic reduction demonstrated a significant effect on the generated photocurrent. The photoactivity of the four TNA catalysts in CO₂ reduction with water vapor was evaluated under UV irradiation for 3 h, where CH₄ and H₂ were detected as products. The annealed sample exhibited the best performance towards methane with a production rate of 78 μmol g_cat⁻¹ h⁻¹, followed by the amorphous film, which also exhibited an impressive formation rate of 64 μmol g_cat⁻¹ h⁻¹. The amorphous and reduced-amorphous films exhibited outstanding photoactivity regarding H₂ production (142 and 144 μmol g_cat⁻¹ h⁻¹, respectively). The annealed catalyst also revealed a good performance for H₂ production (132 μmol g_cat⁻¹ h⁻¹) and high stability up to five reaction cycles. Molecular dynamic simulations demonstrated the changes in the band structure by introducing oxygen vacancies. The topics covered in this study contribute to the Sustainable Development Goals (SDG), involving affordable and clean energy (SDG#7) and industry, innovation, and infrastructure (SDG#9).

This study presents environmentally friendly and low-cost synthetic routes to produce antimicrobial coatings over 5052 Al alloy based on plasma electrolytic oxidation (PEO) technology. Two methodologies were explored: the decoration with copper and anodic doping with copper ions. The porous oxide layers produced in silicate media presented two porous layers consisting of γ-Al₂O₃ crystalline phase and amorphous phases of aluminosilicate, silica, and Al(OH)₃. Small amounts of copper (<0.3 at.%) were detected in the PEO films. In the Cu-decorated film, copper clusters composed of Cu⁰ and Cu²⁺ species were observed visually as small black dots on the surface. In the Cu-doped film, the Cu²⁺ and Cu⁺ species were homogeneously distributed on the surface. The copper content affected the corrosion performance in aggressive corrosive media. The PEO coatings showed a remarkable antimicrobial activity after 24 h in standard tests. The antimicrobial effectiveness of the Cu-decorated sample was higher against S. aureus, while the Cu-doped sample was more effective against E. coli. The results demonstrated that differences in the PEO coating architecture can affect the material composition and, consequently, the bacterial inactivation mechanism. These findings can serve as a guide to tailor aluminum alloys for specific antimicrobial surfaces.

High-entropy alloys (HEAs) have rapidly become one of the hottest research topics in several fields, including materials science, corrosion technology, and catalysis because of their multiple advantages and their potential applications. In this study, using a novel straightforward electroless deposition method, multi-elemental alloys (FeCoNiCuZn) supported on graphite were prepared with controlled metal loading (HEA/g-X; X = 40, 80, 100) without any high temperature post-treatments. These materials were characterized using scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction, and showed a composition ranging from 11 at.% to 31 at.% for each metallic element, a total metal loading varying from 1.3 to 5.2 at.% (5.9 to 21.5 wt.%), homogeneous distribution, and an amorphous structure. Electrochemical impedance spectroscopy, cyclic voltammetry, linear sweep voltammetry, and chronoamperometry were used to evaluate the surface dynamics and the effect of the solution pH during the electrochemical hydrogenation of nitrobenzene using the HEA/g-40 material. The nitrobenzene conversion (>9 mmol_NB g_cat-¹ h⁻¹) and aniline production (≈ 4 mmol_AN g_cat-¹ h⁻¹) rates in Na₂SO₄ solution (at −1.0 V vs. Ag/AgCl) demonstrated a strong dependence on the applied potential. After comparing the results in alkaline medium (KOH), a competitive adsorption of species (nitrobenzene and H₂O) was observed, showing a synergistic effect that greatly improved the selectivity of the nitrobenzene hydrogenation to aniline, from 23% in Na₂SO₄ to an outstanding 94% in KOH at the same applied potential, surpassing the results of a platinum electrode (34% in KOH). These results provide insightful information regarding the nature of the active sites involved in each step of the reaction mechanism, and gives useful means to develop new, tailored multifunctional HEA electrocatalyst materials.