Phase-controllable synthesis of MOF-templated maghemite–carbonaceous composites for efficient photocatalytic hydrogen production

Abstract

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.