Preparation Of Iron Oxides Nanomaterials With The Isolation Of Salts

Nano-iron oxides have a wide range of applications in many fields such as photocatalysis,inorganic pigments,biomedicine,magnetic materials,and gas sensing because their excellent electrical,magnetic and optical properties.The existing preparation methods of nano-iron oxides have the problems of easy agglomeration,poor crystallinity,large size,high preparation cost,complicated operation and high toxicity of raw materials.So the simple and efficient preparation of nano-iron oxides has been one of the goal that researchers in this field to pursuit.In this paper,water-soluble salt isolation method is used to prepare iron oxide nanoparticles innovatively.By introducing a high-melting point and water-soluble salt isolation phase,agglomeration and growth of nanoparticles in the process of high temperature are effectively inhibited.Three kinds of iron oxide nanoparticles,?-Fe₂O₃,?-Fe₂O₃ and Fe₃O₄ with small size,good crystallization and good dispersion,are successfully prepared,and the preparation process is simple,efficient and environmentally friendly.The basic idea of this preparation method is to prepare a Fe(OH)₃ hydrosol containing water-soluble salt(potassium sulfate),add an anti-solvent to precipitate the Fe(OH)₃ precursor and potassium sulfate at the same time,and then calcinate or reduce at high temperature after drying,finally highly crystalline and highly dispersed iron oxide nanoparticles can be obtained after washing.In this method,the precursor particles are dispersed and isolated by potassium sulfate,which effectively inhibits the contact and sintering growth of nanoparticles in the process of high temperature.After calcining the mixture of potassium sulfate salt and precursor in air at 350?,?-Fe₂O₃ nanoparticles with a particle size of only 5 nm,uniform size,good dispersibility and superparamagnetism were obtained.It has been found that?-Fe₂O₃ with particle size from 5nm to 17nm can be obtained by adjusting the type of surfactant and calcination time,and the saturation magnetization and coercivity of nanoparticles increase with the increase of the size.When the calcination temperature rises above 400?,?-Fe₂O₃ begins to transform into?-Fe₂O₃ phase,and pure phase?-Fe₂O₃ nanoparticles are obtained at 600?.The minimum average particle size is 22 nm,which has high crystallinity and dispersity.Studies have shown that the particle size of?-Fe₂O₃ increases with the increase of calcination temperature,and an appropriate salt ratio can also effectively control the size of nanoparticles.The?-Fe₂O₃ nanoparticles prepared by the method has good photocatalytic performance that after 70 minutes of visible light irradiation,the degradation rate of the organic pollutant Rh B reaches 96%.The mixture of salt and precursor was calcined in a reducing atmosphere to prepare well-dispersed and crystalline Fe₃O₄ nanoparticles.Studies have shown that proper calcination conditions contribute to the formation of Fe₃O₄.The increase of reduction temperature and time will promote the diffusion of atoms,which will improve the crystallinity of the nanoparticles and make the particle size continue to increase from the minimum 12nm to 500nm.Fe₃O₄ with an average particle size of 12 nm and 14 nm exhibits superparamagnetism.As the size increases,the superparamagnetism disappears and the saturation magnetization increases.