The Study On The Preparation Of Transition Metal Oxides By Improved Molten Salt Method With Liquid Phase And Its Control

In recent years,transition metal oxides have gradually become one of the current research hotspots because of their unique physical and chemical properties and broad application prospects.Based on the unique advantages of the molten salt method,three kinds of transition metal oxides,TiO₂,ZnO and Co₃O₄,were prepared using the liquid phase initiated modified molten salt method to explore the orientation and growth mechanism of the anisotropic growth of the target product in the molten salt environment.The effects of calcining temperature,molten salt content,molten salt species and other factors on the preparation of the target product are mainly discussed,and the distribution of the morphology,size and size of the material can be controlled.During the preparation of TiO₂,the presence of molten salt was found to inhibit the transition of the anatase phase to the rutile phase to some extent,increase the phase transition temperature,and provide the liquid phase environment required for the anisotropic growth of TiO₂.Acidic conditions can inhibit the hydrolysis of ntetrabutyl titanate to a certain extent,which promotes the growth of Ti O₂ into nanorods but promotes the conversion of anatase to rutile.The results show that the pure rutile TiO₂ nanorods can be prepared in NaCl-KCl composite molten salt using n-tetrabutyl titanate as raw material.If NaCl-KCl-NaNO₃ molten salt is used,the volume ratio of ntetrabutyl titanate to distilled water is 1:10,the molar ratio of salt to water is 1:1,and the temperature regime is 600°C-3h,it can produce anatase Ti O₂nanoplates with a thickness of about 50 nm,with regular appearance and uniform distribution,but the lack of impurity peaks.In contrast,pure anatase TiO₂ nanorods and nanoparticles are more easily produced.In addition,TiO₂ reacts with nitrates in molten salts to form titanates,and industrially produced Degussa p25 does not exhibit anisotropic growth orientation in molten salt environments.During the preparation of ZnO,the presence of molten salt was found to increase the decomposition temperature of the zinc source to some extent,therefore,the higher decomposition temperature of zinc sulfate heptahydrate is not suitable as a raw material for the preparation of ZnO,of course,in the same molten salt conditions the same calcination temperature,ZnO prepared from different sources of zinc in the morphology characteristics of the difference;The study shows that:With the zinc nitrate hexahydrate as the zinc source,using NaCl-KCl compound molten salt,a large number of well-distributed,high-purity flaky ZnO are prepared under the calcination conditions with mass ratio of material salt of 1:1,500°C-3h.If three zinc salts with different decomposition temperatures are used as the zinc source,KCl is a molten salt with a mass ratio of 1 to 2,and the porous nanosheet ZnO was prepared under a segmented temperature regime of 300°C/0.5h to 450°C/0.5h to950°C/2h.Based on this,use NaCl-KCl as molten salt,the mass ratio of salt to water is 1:3.300°C/0.5h to 450°C/0.5h to 950°C/2h hexagonal nanosheet structure with good regularity and good dispersity was prepared in this segmented temperature regime.In the preparation of Co₃O₄ system,the research shows that cobalt cobalt acetate dihydrate is used as the cobalt source and NaCl-KCl composite molten salt is used to prepare better nano-tetra-cobalt sulphate particles under calcination conditions with mass ratio of material salt of 1:3,600°C-3h,and the average particle size is about 200 nm;Cobalt nitrate hexahydrate was used as the cobalt source,and octahedron tetroxide was prepared with NaCl-KCl composite molten salt and calcined at the mass ratio of 1:2,600°C-3h,however,some nanosheet structures appeared in NaCl-NaNO₃ composite molten salt.In the preparation of tricobalcium tetroxide by the molten salt method,the choice of molten salt must be carefully considered to introduce a high temperature decomposable molten salt,otherwise it may react to form a cobalt salt.