The Specific Role Of Propylene Oxide In The Synthesis Of α-Fe₂O₃

It is one of the eternal topics in the field of material chemistry to realize the efficient controlled synthesis of target materials under milder and more environmentally friendly conditions.In this work,ferric chloride was used as iron source,and the controlled synthesis of high-quality single crystalα-Fe₂O₃with different morphologies at 80℃was realized by ring-opening of propylene oxide（PO）in the aqueous systems of organic amine,urea and inorganic alkali respectively.On the basis of systematic characterization of its synthesis rules and control parameters by means of XRD,SEM,TEM,N₂adsorption and TG,the synthesis temperature ofα-Fe₂O₃was further lowered to 60℃.At the same time,its adsorption performance in simulated dye wastewater was preliminarily evaluated.The main research results are as follows:1.In FeCl₃·6H₂O-H₂O-PO system,by introducing small organic amines,including ethylamine,butylamine,hexylamine,diethylamine,triethylamine,ethylenediamine,butanediamine and hexamethylenediamine,the synthesis ofα-Fe₂O₃was reduced from 100℃without amine to 80℃.It shows that PO promotes the ring-opening action of ferric salt hydrolysis and the initial transformation ofβ-Fe OOH intoα-Fe₂O₃is accelerated by the presence of organic amine.However,it is impossible to realize the controlled synthesis ofα-Fe₂O₃at 80℃with only organic amine without PO or only PO without organic amine,and the reactions involved in this synthesis system seem to be rarely affected by the nature of solvents.The controlled synthesis ofα-Fe₂O₃with different morphologies can be realized by adjusting the concentration of polar,nonpolar and even organic amines in a wide range.2.In FeCl₃·6H₂O-Urea-PO system,the controlled synthesis of high-quality single crystalα-Fe₂O₃can also be realized at 80℃by using the ring-opening effect of PO and the alkalinity produced by urea hydrolysis.3.The above ideas are extended to inorganic alkali sources such as ammonia water,sodium hydroxide or tetramethylammonium hydroxide system,and the controlled synthesis of high-qualityα-Fe₂O₃is also realized at 80℃.Further research results show that the synthesis temperature ofα-Fe₂O₃can be reduced to 60℃ under the condition of properly increasing alkalinity,which indicates that there is a certain restriction relationship between the hydrolysis of ferric salt induced by PO ring opening and the subsequent phase transformation fromβ-Fe OOH toα-Fe₂O₃and the alkalinity of the system.4.The adsorption results in simulated dye wastewater show thatα-Fe₂O₃synthesized by this work has the same adsorption performance as other materials synthesized by more severe methods,and the adsorption capacity of Congo red can reach 146 mg/g.Compared with the existing synthesis methods of α-Fe₂O₃,the synthesis method of α-Fe₂O₃proposed in this work is not only milder,more concise,more efficient and more environmentally friendly,but also can effectively control the morphology and size of the material,which provides a new idea for further expanding the application range and scale production ofα-Fe₂O₃.