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In this study, the influence of the surface oxygen vacancies on the energy storage performance of electrodes based on nickel oxide (NiO) nanoparticles was investigated. NiO samples were synthesized by three facile and low-cost syntheses routes: nitrate calcination, citrate, and combustion methods. The concentration of surface defects in NiO powders was determined using XPS analyses, which showed a higher amount of oxygen vacancies for the sample obtained by nitrate calcination. According to the cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) curves, NiO-based electrodes were classified as battery-like. CV results suggest that redox reactions are diffusion-controlled processes with a faster diffusion rate for the sample obtained by the nitrate calcination method. This is in accordance with the GCD and electrochemical impedance spectroscopy (EIS) results, with higher specific capacity and higher electrical conductivity (lower equivalent series resistance) for the sample obtained by nitrate calcination. The results indicate that oxygen vacancies play an important role in the electrochemical performance of battery-type NiO electrodes

Progressive freeze-concentration is a technology to separate water from solutions by freezing. In the present investigation, ethanol-water solutions were freeze-concentrated by the progressive stirred technique. The freezing stage was carried out in a stirring vessel. Solute recovery by the fractionated thawing of ice was also studied. The effects of stirring speed (500, 1000, and 2000 rpm), initial concentration of the solution (3%, 5%, and 8% ethanol), and temperature of the thawing stage (0, 10, and 20 °C) on the solute yield and average distribution coefficient were determined using response surface analysis. The ethanol concentration was found to have increased by 1.3 and 2.1 times at the end of the freeze concentration process. It was found that the initial concentration had a significant effect on the distribution coefficient. In addition, the average yield was increased by 28% by fractionated thawing. Subsequently, a non-dimensional analysis of the distribution coefficient was developed to yield a model to predict the distribution coefficient as a function of the Reynolds number, the relationship between the average ice growth rate and the stirring speed, the agitator diameter, and the liquid fraction. This technique proved to be valid with respect to the concentration of ethanol-water solutions, with better yields being obtained at low initial concentrations. This model is the first of its kind to describe the ethanol-water interaction in agitated freeze-concentration systems.

We report the synthesis of Ca2Fe2O5 nanoparticles by high-energy ball milling and thermal annealing from α-Fe2O3 and CaCO3. Magnetization measurements, Mossbauer and X-ray spectra reveal that annealing at high temperatures leads to better quality samples. Our results indicate nanoparticles produced by 10 h high-energy ball milling and thermal annealing for 2 h at 1100 °C achieve improved stoichiometry and the full weak ferromagnetic signal of Ca2Fe2O5. Samples annealed at lower temperatures show departure from stoichiometry, with a higher occupancy of Fe3+ in octahedral sites, and a reduced magnetization. Thermal relaxation for temperatures in the 700–1100 °C range is well represented by a Neel model, assuming a random orientation of the weak ferromagnetic moment of the Ca2Fe2O5 nanoparticles.

Core/shell nanoparticles of CoFe2O4=CoFe2 were prepared by reducing nanoparticles of CoFe2O4 under hydrogen atmospheres. The structure, morphology and room temperature magnetization of the core/ shell nanoparticles were analyzed by X-ray diffraction, transmission electron microscopy and magnetometry, respectively. The sample preparation procedure allowed the diameter of the CoFe2O4 core to be varied from 67.7 to 2.8 nm. From the magnetic data it was found that the core couples to the shell through the exchange-spring mechanism while the critical thickness of the soft phase (shell) was estimated using a current theoretical model to be 8.0 nm. This value is very close to the one (7.8 nm) obtained for nanoparticles with same composition but obtained using different synthesis route and having an average particle size (32 nm) less than half of the value estimated (73 nm) for the samples investigated in the present work