The Fabrication And Properties Of Fe₃O₄ And Its Structural Particles

The goal of this dissertation is to explore and study novel synthetic methods to fabricate magnetic materials.On the basis of review of previous work and large amount of references,a mild route to synthesize corresponding Fe₃O₄ and their structural composite particles has been developed.In this work,hydrothermal method was firstly invited to synthesize Fe₃O₄ particles.Then,the synthesis of Fe₃O₄ core/shell-like particles by one-step method was investigated.At last,polymer was introduced into the synthetic system to assist the fabrication of Fe₃O₄ core/shell-like particles with different morphologies and chemical properties.The details are summarized as follows:1.The synthesis of Fe₃O₄ particles in the FeCl₃-Na₂CO₃-Ascorbic acid(AA) system.Through the investigation of the relationships between the reaction conditions and the products,various morphologies of FeCO₃ micro-particles(peanut,ellipsoidal, rod-like,sphere-like)were controlled synthesized in the ascorbie acid assistant hydrothermal system;The dynamic formation process of the FeCO₃ precursor and influence of reaction conditions on the FeCO₃ morphology are discussed in detail.It is believed that AA may be act as a suffactant to kinetically control the growth rates of various crystallographic facets of hexagonal FeCO₃ through selectively absorbing on these facets;Micro-sized magnetic particle Fe₃O₄ with peanut-like morphology is successfully prepared from FeCO₃ with the same morphology via direct sealed thermal decomposition;Furthermore,water-soluble Fe₃O₄ nanocrystals have been prepared through hydrothermal approach.These nanocrystals capped with C₆H₆O₆ (the oxidation state of ascorbic acid)could be readily dispersed in hydrated aqueous. From XRD patterns,we confirm the product to be Fe₃O₄.Magnetic hysteresis loop measurements exhibited that the Fe₃O₄ nanocrystals display superparamagnetism.A possible formation mechanism of the Fe₃O₄ nanocrystals was suggested.These nanocrystals with 5.2 nanometers were well dispersed in the water solution,and they can form stable magnetic fluid.2.A hydrothermal method is reported to fabricate Fe₃O₄@C composite particles. At first,core/shell-like Fe₃O₄@C particles were successfully synthesized in the one-step glucose carbonization system;The Fe₃O₄ cores were formed via the reduction of Fe³⁺by glucose under alkaline conditions obtained by the decomposition of urea,and the amorphous carbon shells were carbonized from glucose;Secondly, well-dispersed Fe₃O₄/Fe@C porous core shell particles were fabricated by hydrogen reduction of the Fe₃O_a/Fe₂O₃@C precursors,which originated from the glucose carbonization system by change the reaction conditions;At last,superparamagnetic Fe₃O₄@C composites were also obtained in this in-situ hydrothermal method,and this products can be used as the noble catalyst carrier.The obtained Fe₃O₄/C/Pd catalyst shows well catalysis in the Suzuki reaction,they can keep 95%catalysis ability after 5 cycled reaction.3.Novel Fe₃O₄@C core/shell-like particles with spindle-like morphology were fabricated by combined the in-situ polymerization and hydrogen reduction method together.The synthetic route can be divided into two parts:first,by using a surface-modified templating method,Fe₂O₃@PPy core/shell spindles have been successfully prepared.The Fe₂O₃ particles with spindle morphology were initially fabricated as core materials.After the PVP modification,the Fe₂O₃ spindles were subsequently coated with a tunable thickness layer of PPy by in-situ deposition of the conducting polymer from aqueous solution.Hollow PPy spindles were produced by dissolution of the Fe₂O₃ core from the core/shell particles.High-temperature treatment under vacuum condition covert the hollow PPy spindles into carbon capsules by carbonization of the PPy shell;then,nitrogen-doped magnetic carbon particles with rice-like structure have been fabricated by using Fe₂O₃@ PPy core/shell spindles as precursor.Both Fe₃O₄@C and Fe@C products with spindle-like morphology could be successfully obtained by altering experiment conditions in this hydrogen reduction progress.These spindle-like products show ferromagnetic behavior at room temperature.4.Magnetically separable Fe₃O₄/TiO₂ photocatalyst with hollow sphere like structure was firstly reported by templating method.Monodisperse PSA latex with 270 nm size used as colloidal templates because they are readily available in a wide range of sizes;These PSA latex can be magnetic funetionalized by deposit a layer of magnetic Fe₃O₄ nanoparticles on the surface of latex via the cooperate between Fe³⁺ and -COOH;Ti(OH)_x can be further coating on the PSA Fe₃O₄@spheres to form PSA@Fe₃O₄/Ti(OH)_x based on the wet chemical deposition technology because there are large quality of functional groups and cavities in the PSA latex;then, Fe₃O_a/Ti(OH)_x composite hollow spheres which obtained by dissolve the PSA cores were convert to Fe₃O₄/TiO₂ hollow spheres by the solvethermal method;these Fe₃O₄/TiO₂ hollow spheres showed well photo-catalysis due to the small size of the TiO₂ nanocrystals in the hollow spheres;These products show superparamagnetic behavior at room temperature,and they can well dispersed in solution for a long time. In addition,this templating method can be used as a general method to fabricate other magnetic composite catalyst with hollow natural.