Mechanistic Insights into the Phase Formation of an Atypical Iron Oxynitride (Fe x O y N z ) System and Its Multifunctional Photocatalytic Applications

Apart from metal oxides, materials with different anionic setups such as metal chalcogenides and metal oxyhalides have been largely explored for photocatalytic applications. In this direction, metal oxynitrides also exhibit interesting properties, and the development of the oxynitride phase of the conventional metal oxides has gained significant interest in photocatalysis research. In this context, an iron oxynitride (Fe x O y N z ) system is developed from iron nitride (Fe x N) via solid-state annealing at relatively low temperatures. The formation of the oxynitride phase is driven by the partial replacement of lattice nitrogen with oxygen, which is confirmed via the new peaks appearing in the XRD patterns followed by the Rietveld refinement analysis. The XPS analysis of the samples indicated that the oxynitride phase is stabilized via the N3–-Fe3+/2+-O2– network in the system. The structure–property relationship of the formed iron oxynitride phase is analyzed by using various optical (UV–vis, PL, and TRPL), photoelectrochemical (CV, LSV, EIS, photocurrent, Mott–Schottky), surface (BET), and magnetic property (SQUID) analysis techniques. These obtained results suggest that the iron nitride counterpart synergistically contributed to the overall enhancements in the properties of the resulting oxynitride phase. Consequently, the photocatalytic properties of the developed iron nitride, oxide, and oxynitride systems are studied for dye degradation and H2 generation under solar irradiation. A maximum of ∼97% dye degradation in 180 min and an evolution of H2 at a rate of 897.6 μmol g–1 h–1 are observed over the developed iron oxynitride system, and the rate of evolution of H2 is greater than those in the bare iron oxide (790.8 μmol g–1 h–1) and nitride (664.8 μmol g–1 h–1) systems. The observed improved magnetic properties and photostabilities of the synthesized Fe x O y N z system enabled its easy recovery and reusability, which are confirmed through postcharacterizations. The insights gained from various characterizations and experimental studies suggest that the iron oxynitride could be considered an atypical pristine system rather than a modified system.