Visible-Light-Induced Photosplitting of Water over γ′-Fe4N and γ′-Fe4N/α-Fe2O3 Nanocatalysts

• Published in: Journal of physical chemistry. C Vol. 116; no. 22; pp. 12156 - 12164
• Main Authors: Dhanasekaran, P, Salunke, Hemant G, Gupta, Narendra M
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 07-06-2012
• Subjects: Catalysis; Catalysts: preparations and properties; Chemistry; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; General and physical chemistry; General, apparatus; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Physics; Surface and interface electron states; Surface physical chemistry; Surface states, band structure, electron density of states; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Stoichiometry; Particle size; Impurity; Active site; Composition effect; Energy level; Energy gap; Optical properties; Size effect; Visible radiation; Defect; Nanocomposite; Charge transfer; Optical absorption; Intermetallic compound; Photocatalysis; Photoinduced effect; Valence band; Quantum yield; Dispersion; Absorption spectrum; Electronic structure; Acceptor center; Catalyst activity; Catalyst; Electron donor; Excited state
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp303255f

The application of γ′-Fe4N, a noble-metal-free, low-cost catalyst, in the photosplitting of neat water into stoichiometric amounts of H2 and O2 under visible-light irradiation is reported for the first time. The catalyst showed optical absorption and photoluminescence emission bands in the entire visible region. The photocatalytic water-splitting activity was wavelength-dependent, the quantum efficiency for H2 evolution being ca. 1.7 and 0.7% at excitation wavelengths of 450 and 500 nm, respectively. Addition of electron donor/acceptor sacrificial reagents considerably affected the yield and stoichiometry of H2 and O2. At the same time, the product yield increased in a composition-dependent manner for (γ′-Fe4N) x + (α-Fe2O3)1–x nanocomposites. This activity augmentation is ascribed to the better dispersion of the active component γ′-Fe4N and also to the availability of more active surface sites at Fe4N/Fe2O3 contacts. Moreover, the proximity of the valence band potential of the component photosystems promotes the preferential transfer/entrapment of photoexcited hole carriers. We envisage that the defect/impurity-induced interband-gap energy states may play a vital role in these charge-transfer processes, leading thereby to more effective e––h+ separation and the enhanced rate of the water-splitting reaction. First-principles electronic structure analysis suggests that the extraordinary photocatalytic and optical properties of intermetallic γ′-Fe4N may arise from the particle-size-dependent changes in electronic structure.