| Because of the widely application of nanosized iron oxides in many aspects, such as catalysis, antisepsis, pigments and magnetic recording materials, the preparation of the nanosized iron oxides attracts much attention. The preparation methods can be divided into two sorts according to their raw materials: one is based on Fe(Ⅱ)ion as its raw material;the other is Fe(Ⅲ)ion. The novelty of the article lies in the new style raft-like lepidocrocite prepared by O3 oxidant, moreover, we firstly take into account of the light in the research and give primary discuss on its influential mechanism.In this article, we used FeSO4 and NaOH as the raw material, and investigated the oxidation mechanisms of Fe(OH)2 suspension at different conditions. The present work is aimed to find the rule, in order that we can supply necessary basis for the preparation of iron oxides in later use.The author used O3 as the oxidant to investigate the oxidation process of Fe(OH)2 suspension, and did respective researches on its main influential factors: initial pH and the concentration of EDTA. The results indicated that the initial pH has more effect on the product at higher pH. At pH 8.6 or 8.5, pure lepidocrocite was obtained;when pH >8.7, the main product is pure goethite. TEM images showed that lepidocrocite was raft-like, while goethite was amorphous. At room temperature, the species of the transformation products for Fe(OH)2 depend on both pH and oxidation speed. The result in the current system may be explained by the following mechanism. According to literature data O3 in aqueous solution pH>8.7 is decomposed to newly-formed[O], which is a very strong oxidant, and[·OH]. Fe(Ⅱ) can be oxidized speedly to form amorphous α-FeOOH. When pH<8.7, O3 is predominately decomposed to O2 and O2 is transformed to [O2-·] by the interaction between O2 and FeⅡ-EDTA. Thus Fe(OH)2 can be transformed speedly to y-FeOOH. The results also suggested that trace of EDTA could accelerate the reaction rate noticeably, as well as enhance the purity of the product. While more EDTA in the system seemed no more effect. It's may be attributed to the protective function between EDTA and Fe(Ⅱ)ion.Initial pH and the concentration of EDTA were also the two main influential factors in the air oxidation. The results revealed that when pH 8.6 we can obtain pure lepidocrocite, as therising of pH, more goethite was prepared. When pH 9.0, we can obtain pure goethite, the higher pH was suitable to the preparation of magnetite. We can conclude that the cooperation of trace of EDTA reduced the reaction time. It was considered that EDTA can form the charge-transfer complexes with the dissolved oxygen and superoxide anions(OY) were produced via a outer-sphere electron transformation. As a result, the oxidation rate of Fe( II )ion was accelerated. The slow down of the reaction with the increasing of EDTA may be attributed to the protective function between EDTA and Fe( II )ion.Fe(III)ion was usually used as light catalyst in the disposal of sewage, the iron-catalyzed photochemical decomposed oxalic acid and generation of hydrogen peroxide in atmospheric liquid phases. In our experiment system, according to the results, we found that light played some role in the reaction. Moreover the results revealed that increasing of light intensity, the reaction was sped up, and more lepidocrocite was obtained. We also compared with different lamps, and found that ultraviolet-light was in favor of the formation of magnetite.In the research, transmission electron microscopy(TEM), X-ray diffraction(XRD), and infrared(IR) spectrum were applied as our token method, and we gave some explanations on the reaction mechanism of Fe( II )ion oxidation by air under the light effect.
|
PDF Full Text Request