Orthorhombic Polar Phase in Sodium Niobate Nanoribbons.

Ferroelectric materials exhibit switchable spontaneous polarization below Curie's temperature, driven by octahedral distortions and rotations, as well as ionic displacements. The ability to manipulate polarization coupled with persistent remanence, drives diverse applications, including piezoelectric devices. In the last two decades, nanoscale exploration has unveiled unique material properties influenced by morphology, including the capability to manipulate polarization, patterns, and domains. This paper focuses on the characterization of nanometric sodium niobate (SN) synthesized from metallic niobium through alkali hydrothermal treatment, utilizing electron microscopy techniques, including high-resolution differential phase contrast (DPC) in scanning transmission electron microscopy (STEM). The material exhibits a nanoribbon structure forming a tree root-like network. The study identifies crystallographic phase, atomic columns displacement directions, and surface features, such as exposed planes and the absence of particular atomic columns. The high sensitivity of integrated DPC images proves crucial in overcoming observational challenges in other STEM modes. These observations are essential for potential applications in electronic, photocatalytic, and chemical reaction contexts.

Photo-generation of mercury cold vapor mediated by graphene quantum dots/TiO2 nanocomposite: On line time-resolved speciation at ultra-trace levels.

Mercury speciation was achieved using a nanocomposite, consisting of graphene quantum dots (GQDs) and TiO2 nanoparticles, to mediate photo-degradation of mercurial species into the Hg cold vapor detected by atomic spectrometry. Sample solution (containing Hg2+, CH3CH2Hg, and CH3Hg at hundreds of ng L-1) was placed in quartz tube containing formic acid solution (2% v/v) and microliter aliquot of GQDs/TiO2 nanocomposite dispersion (0.6 mg of nanocomposite). The tube was placed inside a photochemical reactor then, adapted to the mercury-dedicated spectrometer. Quantitative speciation was achieved taking advantage of the differences in UV photodegradation kinetics: Hg2+ (5 min), CH3CH2Hg (9 min) and CH3Hg (13 min). Gas-chromatography cold vapor atomic fluorescence spectrometry was used to confirm the evolution of the reactions over time during photo-reaction. The limits of detection were 10 ng L-1 for CH3CH2Hg and 7 ng L-1 for Hg2+ and CH3Hg.