Preparation And Properties Of Fe₃O₄ Mesocrystal

In the past decades,magnetic Fe₃O₄ nanoparticles have been widely used in biomedical,catalysis,information storage and energy field due to their unique physical and chemical properties.It has been well-known that the properties of Fe₃O₄ nanoparticles are closely related to its size,morphology and structure.The Fe₃O₄ nanoparticles differ in size and morphology always show extremely different properties.Therefore,it is important to prepare Fe₃O₄ nanoparticles various in size,morphology and structure.Mesocrystal structured nanoparticles have attracted lots of researches due to its unique structure and properties in recent years.So far,the preparation and especially for the growing mechanism of mesocrystals are still under researching.So,in this thesis,Fe₃O₄ mesocrystal were successfully prepared via polyol method,and their growing mechanisms were further comprehensive studied.Finally,the performance of Fe₃O₄ mesocrystals in the field of magnetic resonance imaging was investigated.The main contents and results are focused on the follows:1.A simple Polyol process was used to synthesis Fe₃O₄ mesocrystal,which using FeCl3,NaOH,H₂O,and EG as reactants.The effects of the concentration of ferric ions,NaOH,and H₂O were studied,which showed that the dosage of NaOH will intensively influence the size and morphology of final products.Only when the mole ratio of NaOH and feric ions is near 3/1,the reaction will lead to high quality Fe₃O₄ mesocrystal.By changing the solution pH in a suitable range,the size of Fe₃O₄ mesocrystal can be adjusted within certain ranges.Likewise,H₂O was another necessary reagent in our system.The reaction will not lead to Fe₃O₄ phase if H₂O was excluded from the polyol system.The size of Fe₃O₄ mesocrystal can also be adjusted within certain ranges by changing the dosage of water in a suitable range.In addition,in our polyol system,the size and morphology of final products were strongly changed by changing the reactants mixing process,which will result in the porous-single-crystal Fe₃O₄ mesocrystal and primary-particle-self-assembled Fe₃O₄ mesocrystal.2.The growing mechanism of Fe₃O₄ mesocrystal in EG solvent was systematically studied,which indicates an non-classical nucleation process.At first,when all the reactants were mixed well,the compounds mixed with amorphous iron hydroxide and EG molecules were formed.Then with the temperature rising,the reducing of ferric ions was begun,oval-shaped lamellar iron alkoxide was formed.More and more ferrous ions were generated with the solution temperature reaching higher,the lamellar structured iron alkoxide tend to dehydration.Inside of the lamellar iron alkoxide began to transformed to several small hydrous iron oxide with the adsorbed ferrous ions delivering electron to the ferric ions,which results in the breaking up of the iron alkoxide and leads to the releasing of several primary iron oxide nanoparticles.In order to decreasing the surface energy,the new formed hydrous primary iron oxide nanoparticles tends to self-assembled with each others to form large emulsion.And the primary particles in the emulsion will rotate along with the crystallographic direction.With further dehydration,the solid liquid interface was disappeared,resulting in ordinal mesocrystal.In addition,the adsorption of ferrous ions and aggregation process of iron oxide was mainly influenced by solution pH and organic acid,which have intensive effects on the size and morphology of final products.3.Superparamagnetic porous Fe₃O₄ mesocrystal was synthesized and its surface was decorated with sodium polyphosphate,which can be mono dispersed in aqueous solution.The proton relaxation enhancement properties of as-prepared iron oxide was studied,which shows it has outstanding T2 relaxation enhancement properties?r2 is 435.16 mM-1s-1?.In addition,the cytotoxicity test indicated the superparamagnetic porous Fe₃O₄ mesocrystal was biocompatible.And the experiment in mice showed that the as-prepared sample was rapidly adsorbed by the liver and kidney of mice and caused intensively relaxation enhancement effect,which further indicates the superparamagnetic porous Fe₃O₄ mesocrystal has the potential to be developed as excellent T2 MRI contrast agent.