Roberto Hübler

This study addresses the need for controllable physicochemical activation routes for titanium surfaces by developing a hybrid treatment that combines hydrofluoric acid (HF) microtexturing with reactive glow discharge plasma (GDP) generated in a DC magnetron sputtering (DC-MS) system, applied to commercially pure grade 1 titanium. Sequential acid etching induced controlled microstructural roughening, followed by a 1 min plasma exposure in air at 6 × 10–1 Pa to modify the near-surface oxide chemistry while preserving the etched morphology. Acid treatment preferentially dissolved the α-Ti matrix along grain boundaries, producing band-like corrosion grooves and hierarchical microtexturing, whereas plasma activation induced localized oxidation and produced a superhydrophilic response. Eight activation cycles over 150 days of ambient storage repeatedly restored the hydrophilic state, which persisted approximately 16 h per cycle. Raw X-ray diffraction (XRD) and grazing-incidence XRD patterns remained dominated by α-Ti, with no resolved reflections attributable to crystalline TiO2. X-ray photoelectron spectroscopy indicated the formation of a TiO2-rich surface after plasma activation, accounting for 100% of the fitted Ti 2p area, with no detectable F 1s signal. Adsorbed oxygen-containing species accounted for 4.7%, compared with 4.3% for the etched and 17.4% for the cleaned control. Because biological responses were not evaluated, these physicochemical changes should not be interpreted as direct evidence of improved protein adsorption, cellular behavior, bacterial resistance, or in vivo performance. This approach establishes DC-MS-generated GDP activation as a rapid route for titanium surface activation and advanced surface-engineering applications.

Niobium compounds show considerable structural diversity and can be classified as binary compounds, alkali niobates, or complexes. Although niobium oxides have shown promising results as battery anodes, the perovskite structures are rarely utilized for electrochemical energy storage applications due to their low electrical conductivity. Therefore, this study reports the synthesis of a novel mixed perovskite, Nax(Nb0.5W0.5)O3, through a green, collagen-assisted route. FTIR analysis indicated that the synthesis is facilitated by the possible complexation of the niobium precursor within the protein structures. Furthermore, Rietveld refinement confirmed the formation of a mixed compound consisting of 97% Nax(Nb0.5W0.5)O3 and 3% (Na0.75Nb0.25)WO4. FEG-SEM characterization revealed nanoparticles with an average minimum Feret diameter of 95.03 nm. Postactivation XPS analysis of the electrodes revealed that the charge storage occurs via intercalation-type pseudocapacitance. Another significant aspect is the stabilization of tungsten in the +6 oxidation state, leading to an enhanced theoretical maximum capacity of 270.9 mAh g–1. Finally, galvanostatic charge and discharge confirmed the energy storage process, demonstrating a capacity of 243 mAh g–1 at 200 mA g–1 in an aqueous sodium-ion electrolyte. This enhanced performance is likely attributed to improved material conductivity resulting from the reduction of the bandgap from 3.4 eV (NaNbO3) to 3.04 eV and an Rct of 0.48 Ω by electrochemical impedance spectroscopy.

Zirconium silicon nitride thin films containing 8 at. % Si (Zr₃₉Si₈N₅₃) were codeposited via reactive magnetron sputtering at room temperature and at high substrate temperatures to produce amorphous and crystalline coatings. The main purpose was to investigate the dominant factor that determines the mechanical and thermal properties for these thin films: the crystallinity or the silicon content. Samples were characterized by RBS, SEM-FEG, GIXRD, nanohardness, and high-temperature oxidation. Crystalline Zr₃₉Si₈N₅₃ samples exhibited changes in preference grown orientation and reduction in crystallite size when compared to Zr₄₆Si₂N₅₂ samples (used for comparative purposes). These structural modifications caused a hardness value increase superior to 35% when compared to amorphous Zr₃₉Si₈N₅₃ samples, confirming the direct influence of crystallization on this mechanical property. All crystalline samples failed under high temperature tests, whereas only amorphous Zr₃₉Si₈N₅₃ samples demonstrated resistance to oxidation at 600 °C, indicating that a high silicon content combined with an amorphous structure plays a primary role for improving the oxidation resistance in Zr–Si–N thin films.

The production of green hydrogen via water electrolysis faces challenges due to the sluggish oxygen evolution reaction at the anode. In this study, we developed a self-supported bifunctional Pt/SnO₂/Nb₂O₅/Nb electrocatalyst capable of coupling the hydrogen evolution reaction to the selective ethanol oxidation reaction (EOR) in an acidic medium. The catalyst demonstrated efficacy for the EOR, with an E _onset of +130 mV versus SHE results in a peak current density of 8.97 mA cm^–2. The bifunctional electrocatalyst exhibited a spontaneous and rapid increase in current for the HER, achieving an overpotential of −48 mV for a current density of 5 mA cm^–2 and a Faradaic efficiency of 99.7%. This efficient coupling of the EOR with the HER reduces energy consumption for green hydrogen generation compared to traditional water splitting. With hydrogen being the sole gaseous product, the HER–EOR electrolysis system can operate effectively without a membrane, promising a more cost-effective, sustainable, and efficient green hydrogen production.

Niobium-based oxides are being increasingly evaluated as materials for energy storage applications. Additionally, the use of these oxides as cathodes in aqueous electrolytes has shown promise. Based on this, the pseudocapacitive behavior of protonic niobate nanowires in an aqueous acidic electrolyte (1 M H₂SO₄) was evaluated for the first time. The material was obtained in two simple sequential steps. First, hydrothermal synthesis resulted in sodium niobate; second was ionic exchange (in two concentrations of 2 M and 0.1 M HNO₃), where the protonic niobate was obtained. The resulting protonic niobate was characterized by FEG-SEM, the results demonstrated that the morphology of the oxide was concentration-dependent in the ionic exchange step, and EDS analysis was used to validate the procedure. Using DRX, Raman spectroscopy, and FTIR analysis, the transformation of sodium niobate to protonic niobate was evidenced. The electrochemical tests demonstrated that the protonic niobate presented pseudocapacitive behavior when employed as the cathode in 1 M H₂SO₄, and the ionic exchange in 2 M HNO₃ promoted a better specific capacitance, reaching 119.8 mF·cm⁻² at a 1 mA·cm⁻² current density.

Niobium oxides are promising materials for applications within various research fields, especially as electrocatalysts for various chemical reactions. The tuning of the synthetic parameters can achieve a successful compromise between morphology and structure, aiming to obtain certain properties. Hence, this study aimed to investigate the influence of hydrothermal synthesis parameters on the morphology and structure of niobium oxide growth on a niobium metallic plate. The effect of annealing on the material performance was also evaluated. Afterward, the most crystalline sample was tested for the electrochemical determination of dissolved oxygen, a fundamental reaction in corrosion, biomedicine, and environmental monitoring. This is the first work using this material configuration as an electrochemical sensor. The hydrothermal synthesis produced nanorods formed by poorly crystalline, acidic, hydrated Nb₂O₅. Increasing the mineralizer concentration could increase the crystallinity and the nanorod growth rate, but it could also promote a lack of structural and morphological uniformity throughout the surface. Heat treatment allowed the increase in crystallinity and favored orthorhombic Nb₂O₅. Raman spectroscopy revealed that, at the first moment, acidic, hydrated niobium oxide structures were formed as precursors of crystalline niobium oxide that would be developed with longer reaction times and a higher mineralizer concentration. The obtained niobium oxide showed electrocatalytic activity toward the oxygen reduction reaction, with comparable performance between the samples with and without heat treatment. At all analyzed pH values, the amperometric response was linearly correlated with the dissolved oxygen concentration. pH influenced the sensitivity of the material; a maximum sensitivity of 0.0417 mA/cm²·mg/L O₂ was achieved at pH = 6. The participation of the acidic functionalities of the surface in the ORR reaction was confirmed by Raman spectroscopy.

Hydrophilic and nanotextured surfaces for dental implants have been reported as relevant properties for early osseointegration. However, these surface characteristics are quite sensitive to oral interactions. Therefore, this pilot study aimed to investigate the superficial alterations caused on hydrophilic nanotubular surfaces after early human saliva interaction. Titanium disks were treated using an anodization protocol followed by reactive plasma application in order to achieve nanotopography and hydrophilicity, additionally; surfaces were stored in normal atmospheric oxygen or wet conditioning. Following, samples were interacted with saliva for 10 min and analyzed regarding physical–chemical properties and cellular viability. Saliva interaction did not show any significant influence on morphological characteristics, roughness measurements and chemical composition; however, hydrophilicity was statistically altered compromising this feature when the samples were stored in common air. Cellular viability tested with pre-osteoblasts cell line (MC3T3-E1) reduced significantly at 48 h on the samples without wet storage after saliva contamination. The applied wet-storage methodology appears to be effective in maintaining properties such as hydrophilicity during saliva interaction. In conclusion, saliva contamination might impair important properties of hydrophilic nanotubular surfaces when not stored in wet conditions, suggesting the need of saliva-controlled sites for oral application of hydrophilic surfaces and/or the use of modified-package methods associated with their wet storage.