A one-step synthesis of nanostructured bismuth ferrite (BiFeO3) via mechanochemical processing of a α-Fe2O3/Bi2O3 mixture at room temperature is reported. The mechanically induced phase evolution of the mixture is followed by XRD and 57Fe Mössbauer spectroscopy. It is shown that the mechanosynthesis of the rhombohedrally distorted perovskite BiFeO3 phase is completed after 12 h. Compared to the traditional synthesis route, the mechanochemical process used here represents a one-step, high-yield, low-temperature, and low-cost procedure for the synthesis of BiFeO3. High-resolution TEM and XRD studies reveal a nonuniform structure of mechanosynthesized BiFeO3 nanoparticles consisting of a crystalline core surrounded by an amorphous surface shell. The latter is found to exhibit an extraordinarily high metastability causing a rapid crystallization of nanoparticles under irradiation with electrons. In situ high-resolution TEM observations of the crystallization clearly show that the heterogeneous processes of nucleation and growth of bismuth iron oxide crystallites are spatially confined to the amorphous surface regions. This fact provides access to the elucidation of the mechanism of mechanosynthesis. It is demonstrated that the mechanosynthesized ferrite nanoparticles exhibit a partial superparamagnetism at room temperature. Quantitative information on the short-range structure and hyperfine interactions, provided by the nuclear spectroscopic technique, is complemented by an investigation of the magnetic behavior of nanostructured BiFeO3 on a macroscopic scale by means of SQUID technique. As a consequence of canted spins in the surface shell of nanoparticles, the mechanosynthesized BiFeO3 exhibits an enhanced magnetization, an enhanced coercivity, and a shifted hysteresis loop.
In the present paper, the adsorption of amino acids (Ala, Met, Gln, Cys, Asp, Lys, His) on clays (bentonite, kaolinite) was studied at different pH (3.00, 6.00, 8.00). The amino acids were dissolved in seawater, which contains the major elements. There were two main findings in this study. First, amino acids with a charged R group (Asp, Lys, His) and Cys were adsorbed on clays more than Ala, Met and Gln (uncharged R groups). However, 74% of the amino acids in the proteins of modern organisms have uncharged R groups. These results raise some questions about the role of minerals in providing a prebiotic concentration mechanism for amino acids. Several mechanisms are also discussed that could produce peptide with a greater proportion of amino acids with uncharged R groups. Second, Cys could play an important role in prebiotic chemistry besides participating in the structure of peptides/proteins. The FT-IR spectra showed that the adsorption of amino acids on the clays occurs through the amine group. However, the Cys/clay interaction occurs through the sulfhydryl and amine groups. X-ray diffractometry showed that pH affects the bentonite interlayer, and at pH 3.00 the expansion of Cys/bentonite was greater than that of the samples of ethylene glycol/bentonite saturated with Mg. The Mössbauer spectrum for the sample with absorbed Cys showed a large increase ( approximately 20%) in ferrous ions. This means that Cys was able to partially reduce iron present in bentonite. This result is similar to that which occurs with aconitase where the ferric ions are reduced to Fe 2.5.
Far-from-equilibrium nanostructured ZnAl2O4 is prepared via simple and straightforward mechanochemical synthesis. Upon heating above 1100 K, mechanosynthesized ZnAl2O4 relaxes towards a structural state that is similar to the bulk one.
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