Enhanced Visible Activities of α-Fe₂O₃ by Coupling N-Doped Graphene and Mechanism Insight

In this work, we first have prepared graphene doped with different amounts of N through a one-pot ammonia-modified hydrothermal process and then successfully coupled them with nanocrystalline α-Fe 2 O 3 by a common wet-chemical method. On the basis of the atmosphere-controlled surface photovoltage spectra, time-resolved surface photovoltage responses, and photoinduced hydroxyl radical amount measurements, it is confirmed that the photogenerated charge separation of α-Fe 2 O 3 could be enhanced in N 2 or in air atmosphere after coupling with a certain ratio of graphene. It is especially obvious with the graphene doped with a proper amount of nitrogen. This is responsible for the obviously improved visible activities of α-Fe 2 O 3 for photoelectrochemical water oxidation to produce O 2 and photocatalytic degradation of gas-phase acetaldehyde and liquid-phase phenol after coupling graphene doped with a proper amount of N species. It is suggested for the first time, mainly by means of N1s XPS data, electrochemical impedance spectra, O 2 temperature-programmed desorption curves, surface acidity-related pyridine-adsorbed FT-IR spectra, and electrochemical O 2 reduction measurements, that the increased amount of doped quaternary-type N would be quite favorable for photogenerated charge transfer and transportation and for O 2 adsorption. As a result, photogenerated charge separation of the resulting N-doped graphene–Fe 2 O 3 nanocomposite is greatly promoted. In addition, the enhanced O 2 adsorption of α-Fe 2 O 3 results mainly from the increased surface acidity after coupling with graphene, especially with quaternary-type N-doped graphene. This work would help us to better understand the important roles of doped N in graphene in the fabricated nanocomposites and also provide us with a feasible route to improve visible photocatalytic activities of α-Fe 2 O 3 greatly.