RESUMEN
Biporous microsphere, flower and concaved cuboctahedrans like alpha-Fe2O3 superstructures have been synthesized by using a new synthetic method. Hydrothermal reaction of ferric chloride with potassium thiocyanate at 200 degrees C yields self-assembled microsphere, flower, and concaved cuboctahedrans like intermediates in ethanol, water:ethanol (1:1) mixed solvent and in water, respectively. These intermediates were further converted into corresponding alpha-Fe2O3 in a thermal decomposition process at 600 degrees C under oxygen atmospheric conditions. The influence of solvent, hydrothermal temperature, and concentration of iron precursors on the intermediate morphology was studied, and the growth mechanism has also been proposed. The synthesized intermediates and alpha-Fe2O3 were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM) and nitrogen adsorption analysis. The FE-SEM results indicated formation of biporous flowerlike morphology. The electrochemical properties of the flowerlike alpha-Fe2O3 electrodes in a Li-ion battery have been investigated. Plausible formation mechanisms of these intermediates were proposed.
RESUMEN
Monodispersed highly ordered and homogeneous ZnS microsphere with precisely controlled hierarchical and non-hierarchical surface structure was successfully fabricated in water-ethanol mixed solvent and in water without using any catalysts or templates in a hydrothermal process. The microsphere formation has been facilitated by self-assembly followed by Ostwald ripening process. The products were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectrometry (EDX). The XRD results indicated that the cubic phase ZnS formed in hydrothermal process at various reaction times. Introducing ethanol as a co-solvent with water facilitated hierarchical porous surface structure. The influences of various zinc and sulfur precursors, various alcohols as co-solvent, and solvent ratio on the formation of specific surface structured microsphere was investigated. The water-ethanol (1:1) solvent ratio is the minimum required to facilitate hierarchical porous surface structure. The by-products formed during the hydrothermal process are induced specific surface structure in ZnS microsphere. This is the first report on in situ generated by-products being used as a reagent to facilitate surface structured material fabrication. The formed by-products could be used as recyclable reagents to fabricate hierarchical porous ZnS in three consecutive cycles. A plausible growth mechanism of by-product-induced surface structure in different solvent was discussed. The research results may lay down new vistas for the in situ generated by-product-assisted specific surface structured ZnS fabrication.