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Interface segregation plays a governing role in nanocrystalline ceramics properties due to the relative increase in the interfacial volume fraction. However, due to the complexity of the detection and quantification of interfacial excesses at the nanoscale, the role of ionic dopants or additives on microstructural evolution and thermodynamics can be easily underestimated. In this work, we address the spatial distribution of Li+ as a dopant in magnesium aluminate spinel nanoparticles. This is achieved through a novel method for the detection and quantification of Li+ across the surface, grain boundary, and bulk (crystal lattice). Based on selective lixiviation combined with chemical analysis, we were able to quantify the amount of Li+ forming surface excess, whereas the quantitative solid‐state nuclear magnetic resonance technique enabled the quantification of Li+ segregated in the grain boundaries and dissolved in the lattice. This comprehensive understanding of the Li+ distribution across the nanoparticles makes possible an unprecedented interpretation of coarsening and sintering, with a clear correlation between the microstructure and the Li+ distribution. Although the work focuses on MgAl2O4, the proposed combination of techniques is expected to have a positive impact on the understanding of other multicomponent nanoscale systems. [ABSTRACT FROM AUTHOR]

The reduction of graphene oxide (GO) by means of thermal and/or chemical treatments leads to the production of reduced graphene oxide (rGO)—a material with improved electrical conductivity and considered a viable and low-cost alternative to pure graphene in several applications, including the production of supercapacitor electrodes. In the present work, GO was prepared by the oxidation of graphite recycled from spent Li-ion batteries using mixtures of sulfuric and phosphoric acids (with different H2SO4/H3PO4 ratios), leading to the production of materials with significant S and P contents. These materials were then thermally reduced, resulting in rGO papers that were investigated by solid-state 13C and 31P nuclear magnetic resonance, along with other methods. The electrochemical properties of the produced rGO papers were evaluated, including the recording of cyclic voltammetry and galvanostatic charge–discharge curves, besides electrochemical impedance spectroscopy analyses. The samples obtained by thermal reduction at 150 °C exhibited good rate capability at high current density and high capacitance retention after a large number of charge–discharge cycles. The results evidenced a strong relationship between the electrochemical properties of the produced materials and their chemical and structural features, especially for the samples containing both S and P elements. The methods described in this work represent, then, a facile and low-cost alternative for the production of rGO papers using graphite recycled from spent batteries, with promising applications as supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

Design of metal oxide nanoparticles is a key study for obtaining high-functional materials with tunable properties. For that purpose, great progress on chemical methods for controlling the growth of nanoparticles during the synthesis has been made. However, an important challenge faced by this field of study is to completely understand the crystallization process and the chemical pathways during the syntheses that use growth-controlling agents. In this study, the synthesis of ZrO2 was conducted by a solvothermal methodology using three different organic solvents (oleic acid, benzyl alcohol and octyl alcohol) and adjusting the Zr precursor concentration, aiming to control the ZrO2 nanocrystal growth and obtain single-phase nanocrystalline particles. X-ray diffraction and Raman spectroscopy experiments indicated the formation of pure monoclinic, cubic and tetragonal ZrO2 nanocrystals for the syntheses using oleic acid, benzyl alcohol and octyl alcohol as solvents with precursor concentrations of 0.25, 0.50 and 0.50 mol L−1, respectively. Transmission electron microscopy was used to analyze the nanocrystal structure and to assess the crystal size distribution. Infrared and solid-state 13C nuclear magnetic resonance spectroscopy confirmed the presence of the organic ligands chemically bonded to the surface of the nanocrystals. Thermogravimetric analysis indicated an increasing ratio of ligand molecules/surface area as the acidity of the solvent increased. With the observations from this study, the solvent pKa value, the chemical structure and the type of coordination of the capping agents are ascribed as responsible for promoting different growth pathways, allowing pure crystalline phase zirconium oxide nanocrystals to be obtained. [ABSTRACT FROM AUTHOR]

The difficulties and pitfalls with the interpretation of solid-state 13C nuclear magnetic resonance (NMR) spectra in graphitic materials are discussed in detail here, with special emphasis on the case of 13C-enriched samples, which have been used in several recent NMR studies. The issues with the spectral simulation and the interpretation of the spectral parameters obtained by some arbitrary models reported in the recent literature are examined and alternative methods to obtain informative experimental data and to analyze them in a more appropriate way are presented. [ABSTRACT FROM AUTHOR]

Scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction were successfully used to observe the location and morphology of the silica phytoliths in biomass-derived carbons and their transformation into SiC and SiO2 particles at high heat treatment temperatures (HTT). The analyses were conducted in chars derived from the endocarp of babassu coconut (EBC), which naturally contains 1.6 wt% of silica in its mineral matter. It was observed that EBC chars with 500-1200 °C HTT present globular echinate SiO2 phytoliths with sizes of 12-16 μm; these phytoliths are mostly concentrated around the surface of the submillimeter char fibers and also in the carbonaceous char matrix. No phytoliths are found in the interior of the char fibers. At 1200 °C HTT, the phytoliths begin to be rounded, and above 1300 °C HTT, most phytoliths decompose and silicon reacts with carbon-forming nanocrystalline β-SiC particles (~ 35 nm crystallite size). Numerous (tens to hundreds) micro- and sub-micro-amorphous or nanostructured SiO2 particles (with sizes predominantly below 2 µm) are then observed at the sites previously occupied by the phytoliths. Few rounded phytoliths survive at 1400 °C HTT, but disappear at higher HTTs (1600-2000 °C). It is likely that the ensembles of micro- and sub-micro-SiO2 particles observed in many sites correspond to the inner remaining part of the original phytoliths, whose most external SiO2 structures (at and near the surface) decompose and take part in the carbothermal reaction for the formation of SiC. [ABSTRACT FROM AUTHOR]