Photocatalytic Mercury Removal from Coal-Fired Flue Gas over γ-Fe₂O₃/Bi₂WO₆ with Heterojunction Structure

The elemental mercury (Hg0) present in coal-fired flue gas poses a significant challenge for removal due to its gaseous form, high stability, and low reactivity, making it one of the key obstacles in environmental pollution control. Traditional catalytic methods struggle to remove Hg0 efficiently, thus underscoring the urgent need to develop novel, high-efficiency photocatalytic materials. In this work, a γ-Fe2O3/Bi2WO6 composite photocatalyst was synthesized using a two-step solvothermal method to enhance the photocatalytic removal efficiency of Hg0. By adjusting the γ-Fe2O3 content, it was found that the composite photocatalyst with 5 wt % γ-Fe2O3 achieved the highest Hg0 removal efficiency of 85.88%. Characterization analyses, including scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), photoluminescence spectroscopy (PL), and density-functional theory (DFT) calculations, indicated that the formation of Z-scheme heterojunction structure between γ-Fe2O3 and Bi2WO6 effectively promoted the separation and migration of photogenerated carriers. The construction of an internal electric field (IEF) significantly enhanced the light absorption capability and charged the separation efficiency of the photocatalyst, thereby accelerating the photocatalytic reaction rate. Additionally, the composite photocatalyst demonstrated excellent stability in multiple cycling experiments, with no significant performance degradation observed. This study elucidates the photocatalytic reaction mechanism driven by the synergistic effects of the heterojunction structure and internal electric field, providing new material selection and design strategies for the application of photocatalytic technology in environmental pollution control and clean energy production.