Fe₂O₃/C–C₃N₄-Based Tight Heterojunction for Boosting Visible-Light-Driven Photocatalytic Water Oxidation

Abstract

Recently, photocatalytic water splitting for clean hydrogen (H2) energy through the use of solar energy has been considered to be a promising means of renewable energy conversion. Because of the high activation barriers of oxygen (O2) generation, the half reaction, i.e., water oxidation, is the rate-limiting steps of the overall water splitting efficiency. Photocatalysts with high activity and nonmetal usage are needed. Herein, we report one new thin-layered heterojunction sample of Fe2O3/C–C3N4, containing layered α-Fe2O3 and carbon-coated g-C3N4, obtained through one simple repeatable solid-state synthesis strategy. The layered FeOOH and g-C3N4 are first synthesized working as the precursors. Under N2 atmosphere and 580 °C, the dehydration of FeOOH happens, and it transfers into layered α-Fe2O3; the water vapor destroys the van der Waals force of g-C3N4 and induces the parts of edge carbonization. Under the synergistic effect of vapor and heating, the thin-layered Fe2O3/C–C3N4 heterojunction is obtained. Without cocatalyst addition, the obtained sample shows efficient visible-light-driven photocatalytic water oxidation performance, i.e., a 22.3 μmol/h oxygen evolution rate under the LED lamp of λ = 420 nm illumination, 3, 16, and 30 times higher than reference Fe2O3/C3N4, bare α-Fe2O3, and g-C3N4, respectively. The key parameters for the enhanced photocatalytic activity can be attributable to the carbon layer and the tight contact structure, which can work as the carrier (electrons from g-C3N4 and holes from α-Fe2O3) collection center and provide the small migration resistance. Moreover, the carbon shows a different migration rate for electrons and holes and then facilitates the separation of carriers to some extent. To our knowledge, no other papers on Fe2O3/C–C3N4-based photocatalytic water oxidation have been reported. This work can provide a new insight for synthesis of g-C3N4-based photocatalysts, and also help us understand the water oxidation reaction.