MHC synthesis
MHC was synthesized by combining co-precipitation and slow alkalinity titration method into one step. First, 150 mL deionized water was added to a three-necked flask and deoxygenated by bubbling N2 gas for 5 min. Under a nitrogen atmosphere, 32.5 g FeCl3·6H2O and 4.8 g FeCl2·4H2O were added, and the mixture was stirred at room temperature for 5 min until dissolved. Then the mixture was gradually heated to 80 ℃, and TPODAC was added at the Si/Fe molar ratio of 1/6. The mixture was titrated by 1 mol/L NaOH (270 mL) for 3 h under rapid stirring. After cooling to room temperature, the product aged for 12 h to obtain MHC.