Investigation Of Preparation Of Spinel Ferrite From Hydrotalcite-Like Precursors

In this thesis, methods for preparation of spinel ferrite from hydrotalcite-like precursors is presented, which bases that high-temperature calcination of LDHs leads to MIIMIII2O4 spinal, and the conventional method of preparation of MIIMIII2O4 spinal have some disadvantages. According to the fact that high-temperature calcination of LDHs leads to a mixture of MIIMIII2O4 spinal and MIIO, we synthesize LDHs containing Zn2+ ions in the layer. The calcination of the LDHs affords a mixture of MIIMIII2O4 spinal and ZnO by control of content of metal ions in the layer. Treatment of the calcined products with aqueous NaOH leads to dissolution of the ZnO and the formation of a porous MIIMIII2O4 ferrite phase with high surface area and pore volume. According to the fact that the metal ions in the layer can be controlled and the anions in the gallery space of LDHs can be exchanged, we synthesize LDHs containing Fe2+ ions in the layer, and LDHs intercalated by [Fe(CN)6]3- anions. The calcination of the LDHs leads to the formation of MIIMIII2O4 ferrite with excellent magnetic properities.1. The investigation of highly porous ferrite prepared from layered double hydroxide precursor1.1 The synthesis of ZnFeIII-SO4-LDHs and NiZnFeIII-SO4-LDHs precursorZnFeIII-SO4-LDHs have been prepared from zinc and iron(II) precursors by coprecipitation method. The effect of pH, aging temperature, aging time and Zn/FeII molar ratio for the structure of the LDHs has been investigated. And NiZnFeIII-SO4-LDHs have been synthesized and their structure and thermal stability have been investigated. 1.2 The investigation of properties of porous ferrite ZnFe2O4 and NixZn1-xFe2O41.2.1 The investigation of porosity of materials produced by calcination of ZnFeIII-SO4-LDHs and NiZnFeIII-SO4-LDHsTreatment of the calcined products of ZnFeIII-SO4-LDHs with aqueous NaOH leads to dissolution of the ZnO and the formation of a pure zinc ferrite phase with high surface area and pore volume, and uniform pore size distributions in micropore and mesopore regions. The pore volume and BET surface area of the materials producted by calcination of NiZnFeIII-SO4-LDHs with different Ni/Zn/FeIII molar ratios at 500 oC after treatment with apueous NaOH obviously increase and the materials have uniform pore distributions in micropore and mesopore regions. The pore volume in micropore region is increased slightly by increasing Zn content in the layer precursor. In the case of Ni/Zn/FeIII molar ratio of 1/15/4, the pore volume in micropore region is decreased. Nevertheless, compared with the micropore, change of pore volume in mesopore is opposite. The pore volume is decreased slightly by increasing Zn content in the layer precursor. In the case of Ni/Zn/FeIII molar ratio of 1/15/4, the pore volume in is increased. When the temperature of calcination of NiZnFeIII-SO4-LDHs with Ni/Zn/FeIII molar ratio of 1/15/4 increases from 500 oC to 600 oC, the pore volume and BET surface area of the calcined products after treatment with apueous NaOH markedly decrease. When the calcination temperature is up to 700 oC, the BET surface area decrease but the pore volume increase clearly because of existence of large pore of 31 nm.1.2.2 The investigation of magnetic properties of materials produced by calcination of ZnFeIII-SO4-LDHs and NiZnFeIII-SO4-LDHsZnFe2O4 ferrite prepared by calcination of ZnFeIII-SO4-LDHs is a normal spinel. The ferrite present paramagnetism at 300 K whereas its magnetic properties are affected by changing calcination temperature of the ZnFeIII-SO4-LDHs precursor and the saturation magnetization of the calcined product of the LDH at 500 ℃ is higher than that at upwards 500 ℃. The saturation magnetizations of NixZn1-xFe2O4 ferrite produced by calcination of NiZnFeIII-SO4-LDHs were reduced by increasing Zn content in the LDHs precursor. When the calcination temperature is 500 ℃, the NixZn1-xFe2O4 ferrite present paramagnetism. When the calcination temperature is up to 600 ℃, the NixZn1-xFe2O4 ferrite present ferromagnetism and its sat...