Abstract:In this paper, a simple and cheap method to prepare porous ZnO by using zinc nitrate, ethanol and triethanolamine (TEA) is reported. The as-prepared sample consisted of nano and micro pores. The sample was calcined at 300 ℃, 400 ℃ and 500 ℃ with different heating rates. At 500 ℃, the nano pores disappeared but the sample maintained its micro porosity. Field emission scanning electron microscopy (FE-SEM) pictures confirmed that the size and growth of ZnO nanoparticles depended on the heating conditions. The infrared (IR) absorption peak of Zn-O stretching vibration positioned at 457 cm 1 was split into two peaks centered at 518 cm 1 and 682 cm 1 with the change of morphology. These results confirmed that Fourier transform infrared (FT-IR) spectrum was sensitive to variations in particle size, shape and morphology. The photoluminescence (PL) spectrum of porous ZnO contained five emission peaks at 397 nm, 437 nm, 466 nm, 492 nm and 527 nm. Emission intensity enhanced monotonously with increase of temperature and the change was rapid between temperatures of 300 ℃ and 500 ℃. This was due to the elimination of organic species and improvement in the crystallanity of the sample at 500 ℃.
Nanosized Cobalt ferrite (CoFe2O4) particles are prepared through the sol-gel method using polyvinyl alcohol (PVA) as a chelating agent. The powder as prepared is annealed at three different temperatures (400 o C, 500 o C and 1000 o C) for one hour. The X-ray diffraction patterns confirm the spinel structure of the samples. The XRD patterns of the samples indicate broad peaks and the full width at half maximum decreased with increasing annealing temperature. Infrared (IR) spectra of the samples confirm the presence of metal -oxygen complexes within the spinel lattice. The average particle size obtained from TEM micrographs demonstrates ultrafine particles having spherical morphology. The particle size of the annealed samples is in between 4.5-6.8 nm. The saturation magnetization (Ms) and remnant magnetization (Mr) of the samples show dependence on particle size and crystallinity of the samples. The highest saturation magnetization (78.1 emu/g) is achieved for the sample annealed at 1000 0 C having average particle size of 6.8 nm. The high saturation magnetization of the samples suggests the present method is suitable for obtaining nanocrystalline magnetic ferrites which is desirable for practical applications.
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