Performance of mesoporous α-Fe2O3/g-C3N4 heterojunction for photoreduction of Hg(II) under visible light illumination

In this study, mesoporous alpha-Fe2O3/g-C3N4 nanocomposites were constructed with diverse alpha-Fe2O3 contents for photocatalytic Hg(II) reduction under visible light by employing formic acid as a sacrificial donor and compared with either pure mesoporous alpha-Fe2O3/g-C3N4. The alpha-Fe2O3 nanoparticles (NPs) were uniformly dispersed onto a layered g-C3N4 nanosheet with a particle size of 5-15 nm. The photocatalytic Hg(II) reduction efficiency of the alpha-Fe2O3/g-C3N4 nanocomposites was increased from 41.1% to 90% within 60 min with increasing alpha-Fe2O3 contents (1-6%). Interestingly, the photocatalytic Hg(II) reduction rate of the mesoporous 6%alpha-Fe2O3/g-C3N4 nanocomposite was 4.6 times and 6.8 times greater than that of both pure alpha-Fe2O3/g-C3N4 nanosheets, respectively. The key benefits of photocatalytic Hg(II) reduction over the use of mesoporous alpha-Fe2O3/g-C3N4 nanocomposites include the high crystallinity, narrow bandgap, large surface area, mesoporous structure, highly dispersed particles and small particle sizes of alpha-Fe2O3, and the use of a construction Z-scheme photocatalyst. The alpha-Fe2O3/g-C3N4 photocatalyst exhibited nearly stable photocatalytic Hg(II) reduction activity (for up to five respective recycles) without a significant reduction in photocatalytic efficiency. The obtained results may provide methods for the fabrication and design of new categories of Z-scheme photocatalysts for photocatalytic reduction and oxidation of toxic organic and inorganic pollutants under visible light.