A novel dual Z-scheme heterojunction: tungsten trioxide nanorods modified with potassium ions loaded with titanium dioxide and bismuth oxybromide for enhanced photocatalytic toluene degradation

In photocatalysis, the construction of a double Z-type heterojunction can effectively improve the photogenerated carrier separation efficiency, enhance the light absorption capacity and improve the photocatalytic reaction rate. Herein, a series of TiO₂/KWO/BiOBr photocatalysts are successfully synthesized via hydrothermal and electrostatic self-assembly methods. All the samples are investigated and characterized by X-ray diffraction, scanning electron microscopy, ultraviolet-visible spectroscopy and X-ray photoelectron spectroscopy to get insight into the microstructures and optical properties. During the photocatalytic degradation of toluene experiments, the optimized TiO₂/KWO/BiOBr sample exhibits excellent photocatalytic performance. Under the irradiation of a xenon lamp for 120 min, the degradation rate of toluene reaches 95%, which is 10.75, 7.59 and 8.40 times higher than that of TiO₂, KWO and BiOBr, respectively. The UV-vis diffuse reflectance, electrochemical impedance spectroscopy and transient photocurrent response of the TiO₂/KWO/BiOBr photocatalyst verify that the enhanced photocatalytic activity is ascribed to its expanded light absorption range and the efficient separation efficiency of photogenerated carriers. In addition, the degradation experiments of toluene are also carried out in different atmospheres which could control the formation of different free radicals. It shows that superoxide anions and hydroxyl radicals play critical roles in toluene degradation. The corresponding photocatalytic degradation mechanism suggests that the excellent photocatalytic activity is attributed to providing more active sites and strong oxidation capacity for toluene.