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 alpha-Fe2O3 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 alpha-Fe2O3 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 alpha-Fe2O3 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-Fe2O3 nanocomposite is greatly promoted. In addition, the enhanced O-2 adsorption of alpha-Fe2O3 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 alpha-Fe2O3 greatly.