Research On Preparation Of α-Fe₂O₃ Nanoparticles By Coupling Hydrolysis And Extraction

Precursorα-FeOOH was achieved by Fe(III) hydrolyzing coupling extract acid. Then the productα-Fe₂O₃ was acquired by annealing at high temperature. Conditions and reaction mechanism of preparingα-Fe₂O₃ by extraction coupling hydrolysis process has been studied.In aqueous-solution system, optimal conditions of preparingα-FeOOH were reaction temperature 17 oC, starting pH 2.78, reaction time 24 h, the concentration of extractant 33%, phase rate (O/W) 3:1, the initial Fe (II) concentration of 0.10 mol/L, and drying temperature of 45 oC. Under these conditions, the iron conversion rate was 99.55 %, the pictures of SEM and TEM show that the morphology of powder was needle-like, and the particle size was about 15 nm. Orthogonal experimental results show that phase rate affected both crystal and extracting acid reactions most, and the effect of reaction temperature on extracting acid reactions and Fe (II) conversion rate was relatively significant. The optimal condition for the precursor annealling to beα-Fe₂O₃ was roasting at 600 oC for 2 h, the morphology of the calcined powder was rod-like, and the particle size was about 20 nm.In nonaqueous-solution system, optimal conditions of preparingα-FeOOH were reaction temperature 15 oC, the concentration of extractant 33 %, phase rate (O/W) 4:1, Fe (III) concentration 0.20 mol/L, drying temperature 50 oC. Under these conditions, the iron conversion rate was 98.85 %, the pictures of SEM and TEM show that the morphology of powder was ellipsoidal, and the particle size was about 10 nm. Orthogonal experimental results show that reaction temperature affected Fe (III) conversion rate significantly, and the effect of initial Fe (III) concentration on crystal was relatively significant. The optimal condition for the precursor annealling to beα-Fe₂O₃ was roasting at 600 oC for 0.5 h, the morphology of the calcined powder was spherical, and the particle size was about 25 nm.The electrochemical performance of the rodlike nanoα-Fe₂O₃ was tested. It was found that when the ratio ofα-Fe₂O₃ to acetylene black (AB) to binder was 7:2:1, the cell has a first-time discharge capacity of 1343 mAh/g, and the capacity remains about 220 mAh/g after 30 loops of charge and discharge.The process of reaction is explored using a constant interfacial area stirred cell. When the phase ratio (O/W) was kept 2:1 and the extractant concentration was kept 33 %, it is found that both lifting initial concentration of Fe2+ and lifting reaction tempreture affects the extracted acid reaction. Using initial rate method, the activation energy of the system, which is 72.69 kJ/mol, is achieved when the initial concentration of Fe2+ was 0.10 mol/L. The reaction rate equation at 20 oC is r = 9.32×10 ^-2 [ Fe^{2 +}]^0.79. This reaction is interface chemical reaction control.