In this article, we report a novel but simple method for the phase transformation of ZnO 2 to flower-like ZnO microstructures hydrothermally at 90• C with and without the assistance of hexadecylamine as surfactant. The generation of zincate ion ZnO 2− 2 as a growth unit from the reaction between ZnO 2 and peroxide ion O 2− 2 in situ plays a key role in the phase transformation of ZnO 2 to ZnO. The morphology, structure, and composition of the products have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Powder X-ray diffraction (PXRD) and energy dispersive X-ray analysis (EDX). It has been demonstrated that the as-fabricated ZnO flowers are composed of self-assembled brooms and rods in the presence and absence of hexadecylamine respectively. On the basis of experimental results, a possible reaction mechanism and the growth processes involved in the formation of flower-like ZnO microstructures are discussed.
a b s t r a c tDespite considerable efforts undertaken in a rapidly developing area of materials research, controlled synthesis of nanostructured ZnO is still a matter of intensive research. Herein, we report a facile base free approach for the fabrication of nanostructured ZnO hollow spheres. In the synthesis, ethylene glycol has been introduced as solvent and crystal-growth modifier and zinc acetate has been used as zinc precursor and also a source of soft template. ZnO nanoparticles of diameter $ 25 nm are assembled into highly regular hollow spheres. The powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDS), photoluminescence (PL) and UV-visible spectroscopy have been used to characterize the crystal structure, morphology, composition and optical properties. Powder XRD pattern of ZnO confirms the formation of the wurtzite structure. Presence of oxygen deficiency in the prepared ZnO product is revealed by Raman and EDS studies. Strong emission at 422 nm with three weak emissions at 400, 484 and 529 nm were observed by PL spectrum. The growth mechanism for the formation of ZnO hollow spheres has been discussed on the basis of the growth model for the polar ZnO crystals.
Synthesis of molybdenum oxide/hexadecylamine (MoO 2 /HDA) microspheres in aqueous solution has been investigated systematically by varying the concentration of the precursor, surfactant and reducing agent, as well as the reaction temperature and duration. To understand this, the nature of the solid has been probed by PXRD, FTIR, UV-visible and SEM equipped with an EDS. The PXRD patterns of as-prepared products reveal that MoO 2 microspheres are of monoclinic structure. The bands at 985 and 952 cm À1 reflect the n(Mo-O) stretch vibration of terminal -Mo VI O t and -Mo IV O t groups. UV-vis spectrum of calcined sample exhibits maximum absorption at 358 nm. SEM images reveal that the average diameters of the MoO 2 microspheres are in the range 1-3 mm. The reduction of the precursor yields a metastable poorly crystalline oxide of lower valence molybdenum, which is crystallized to a-MoO 3 on calcination to 400 8C. #
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