Control Synthesis Of α-Fe₂O₃ Under Moderate Conditions

In this work,the high crystallinityα-Fe₂O₃ materials with adjustable morphology and size have been synthesized in a mild hydrothermal system at100°C for the first time,by introducing propylene oxide（PO）as a proton consumer in the aqueous solution of inorganic iron salt.On the basis of this,the synthesis temperature ofα-Fe₂O₃ is reduced to a lower temperature of 80°C by further introducing a primary amine as an auxiliary agent for the first time.Meanwhile the influence of the synthesis parameters and the preparation conditions on the structure and morphology of the product by using various technologies such as XRD,EDX,SEM,TG and N₂ adsorption have been systematically studied,and the possible formation mechanism has been discussed.The research results of this work provide a novel method for further expanding the applicable range ofα-Fe₂O₃ materials,which is highly efficient,low-cost and scalable.The specific research results are as follows:1.In a simple binary system composed of FeCl₃·6H₂O-H₂O,α-Fe₂O₃spherical particles with high crystallinity and nearly monodisperse have been synthesized by introducing PO under the mild hydrothermal condition of 100°C.It is found that the presence of PO plays a decisive role in the low-temperature synthesis ofα-Fe₂O₃.The proton-consumping hydrolysis process of PO leads to an increase in the pH value of the reaction system and subsequent nucleophilic attack of chloride ions to promote the formation of the target product.The adjustment of the synthesis parameters can achieve an effective adjustment of the material size from 55 nm to 320 nm,and the change of the solvent polarity can achieve the control of the morphology（spherical or ellipsoidal）ofα-Fe₂O₃.2.In the above FeCl₃·6H₂O-PO-H₂O system,the synthesis temperature ofα-Fe₂O₃ is reduced to a milder temperature of 80°C without affecting the crystallinity by further introducing primary amines(C_nH_2n+1NH₂,n=8-18)as an additive for the first time.The introduction of primary amines contributes to further increase the pH value of the system and promotes the conversion of initially formedβ-FeOOH toα-Fe₂O₃ at lower temperatures.The regulation ofα-Fe₂O₃ morphologies among the nanospheres,nanodisks and nanoparticle aggregates can be achieved by adjusting the length of the primary amine chain and the polarity of the solvent.Compared with the existing work,the synthesis method ofα-Fe₂O₃proposed by this work not only makes the process more gentle,concise,efficient and environmentally friendly,but also can effectively control the morphology and size of the material.And further research work on electrochemical properties and adsorption properties of dyes and heavy metal wastewater of the material has been fully carried out.