Efficient Hg⁰ catalytic removal by direct S-scheme heterostructure of two-dimensional Bi₂MoO₆ (200)/g-C₃N₄ nanosheets under visible light

The gaseous elemental mercury (Hg0) emitted from coal-fired flue gas is extremely harmful to the atmospheric environment and human health. In this study, a 2D/2D Bi2MoO6(2 0 0)/g-C3N4 heterojunction photocatalyst was synthesized and exhibited a high visible-light driven Hg0 removal efficiency up to 99.5% in an atmosphere consisting of N2, O2 (6%), CO2 (12%), NO (100 ppm), SO2 (800 ppm), and H2O (5%). The introduction of surfactant CTAB led to further exposure of the highly active (2 0 0) crystal facet of Bi2MoO6, with a higher reactive oxygen species ratio than the original mainly exposed (1 3 1) crystal facet, and inhibited the agglomeration of Bi2MoO6, thereby greatly reducing the micro-thickness and improving the specific surface area. The smaller thickness effectively promoted the separation of photoinduced carriers and the speed of transfer to the interface. Additionally, through EPR characterization and work function calculation, we observed that the change in the exposed crystal facet regulated the Fermi level of Bi2MoO6 nanosheets, altering the direction of the built-in electric field at the interface with g-C3N4. This formation of an S-scheme 2D/2D Bi2MoO6(2 0 0)/g-C3N4 heterostructure further facilitated the recombination of unintentional carriers and strengthened the separation and catalysis of effective photogenerated carriers. To a certain extent, this work provides a guidance for the research of photocatalysis to achieve efficient and sustainable mercury removal from coal-fired flue gas.