Phase-controllable synthesis of MOF-templated maghemite–carbonaceous composites for efficient photocatalytic hydrogen production†
Solar water splitting to produce H2 represents a solution with high potential for the current severe energy and environmental issues. Iron oxides are earth-abundant and nontoxic, with narrow bandgaps and suitable valence band positions for the visible-light-driven water oxidation reaction; however, an energy limitation for hydrogen generation is encountered due to the improper conduction band level. Herein, we demonstrated that this limitation could be overcome by the incorporation of small amounts of GO in the metal–organic framework (MOF)-templated synthesis of iron oxide, affording a uniform and highly ordered ferrite octahedral nanostructure embedded on graphene nanosheets. Such structural superiorities would result in a highly synergistic effect between Fe2O3 and reduced graphene oxide (rGO), affording an elevated flat band potential and a promoted photogenerated charge carrier separation and transportation. As a consequence, the resulting maghemite–carbonaceous composite exhibited a high photocatalytic H2 evolution rate of 318.0 μmol h−1 g−1 in the absence of noble metal cocatalysts and external bias. This work provides for the first time an ideal pathway for the utilization of Fe2O3 as the dominant component of a nanocomposite in efficient photocatalytic H2 production, as well as the prospect of developing highly active photocatalysts for overall water splitting. In addition, different phases of iron oxide, including maghemite (γ-Fe2O3), hematite (α-Fe2O3) and magnetite (Fe3O4), and their carbonaceous composites can be obtained through the cautiously selected thermolysis of Fe-MOF and MOF/GO composites. The maghemite phase could be maintained with high saturation magnetization values under a large temperature gradient, implying a great potential for applications in magnetism and biomedicine-related research fields.