One-dimensional confinement effect in hematite quantum rod arrays

Synchrotron-based spectroscopic investigations of 1-D nanomaterials consisting of designed oriented nanorod-arrays of hematite grown by aqueous chemical growth reveal significant differences in the electronic structure and bandgap compared to bulk samples. Resonant inelastic x-ray scattering (RIXS) study of α-Fe₂O₃ crystalline nanorod bundle arrays at the Fe L-edge is reported. The low energy excitations, namely d-d and charge-transfer excitations, are identified in the region from 1 to 5 eV. The 1-eV and 1.6-eV energy-loss features are weak transitions from multiple excitations. The 2.5-eV excitation which corresponds to the bandgap transition appears significantly larger than the typical 1.9-2.2-eV-bandgap of single-crystal or polycrystalline hematite samples, revealing a one-dimensional (1-D) quantum confinement effect in the bundled ultrafine nanorod-arrays. Such conclusion strongly suggest that bandgap and band edge position criteria for direct photo-oxidation of water by solar irradiation without an applied bias are therefore satisfied for such purpose-built nanomaterials. The outcome of such a result is of great importance for the solar production of hydrogen, an environmental friendly energy source carrier for the future. Indeed, the generation of hydrogen by visible light irradiation with an environmental friendly and economical photoactive material would thus advance a step closer to reality.