Suppressing γ- to α-Fe2O3 transformation by reduced graphene oxide hydrogel

Abstract

Maghemite (γ-Fe2O3) is an important magnetic material for wide utilization, however, it tends to transform into hematite (α-Fe2O3) under high temperature and humidity (HT & H). Here, we report that this phase transition can be completely suppressed by reduced graphene oxide (rGO) hydrogel. Experiments demonstrate that γ-Fe2O3 will be dissolved firstly by water and then recrystallize into α-Fe2O3 in hydrothermal autoclave at 180 oC (an HT & H environment). In contrast, after integrating γ-Fe2O3 into graphene oxide (GO) solution, its transformation to α-Fe2O3 is completely prevented during hydrothermal treatment up to 240 oC. The possible mechanism for this phase transition suppression is that rGO hydrogel formed through hydrothermal reduction of GO fully encapsulates γ-Fe2O3 to prevent their contact with water and subsequent dissolution. This work highlights the stabilizing role of rGO hydrogel for improving the stability of metastable metal oxides under HT & H.