Preparation: |
2.5 M NaOH was slowly added to 0.5 M Fe(NO3)3 until the pH reached 12. After incubation of the mixture at 60 °C for 100 h, the precipitates were collected by centrifugation, dialyzed with deionized water to remove excess salt, purged with wet N2 for > 2 weeks to remove CO2 on the surface, and then freeze-dried for further use |