A novel 3D Fe2O3@ZnBi2O4 n–p heterojunction with high photocatalytic activity under visible light

A novel n–p Fe₂O₃@ZnBi₂O₄ (FZB) heterojunction with a unique 3D structure was fabricated in two simple steps to break down MB under visible light. First, the polymer gel combustion technique was employed to fabricate a 3D Fe₂O₃ framework. Next, a microwave-assisted precipitation approach was used to incorporate 3D ZnBi₂O₄ flakes onto the framework surface. FZB can effectively collect a broad range of UV-Vis light and sunlight. Surprisingly, the core–shell p–n heterojunction structure makes it easier for photogenerated charges to move and separate. This is because the semiconductor parts are better connected and the electric field is inside the two junctions. UV-Vis-DRS, EIS, PL, and XPS analyses confirmed this phenomenon. As a result, n–p FZB, with a Fe₂O₃/ZnBi₂O₄ molar ratio of 2 : 1, showed the highest photocatalytic activity, increasing the reaction rate by 4.2 times compared to Fe₂O₃ and 2.8 times compared to ZnBi₂O₄. Exposure to light for 100 min at a concentration of 0.7 g L⁻¹ the FZB catalyst and pH = 9 led to the breakdown of more than 95% of the 50 ppm MB solution. In addition, the photodegradation of MB by n–p FZB increased the reaction rate by 2.15 times by adding hydrogen peroxide (H₂O₂), which is known as the photo-Fenton reaction. The efficacy showed remarkable photocatalytic activity, which increased the reaction rate by 5.95 times when persulfate was used. Finally, after examination of the energy band structure of the materials and the findings regarding the function of the oxidizing sites in the photocatalytic process, a reaction mechanism was proposed.