Construction of coated Z-scheme Pd-BaZrO3@WO3 composite with enhanced sonocatalytic activity for diazinon degradation in aqueous solution

Highlights: • Pd nanorods in coated Z-scheme sonocatalysts can migrate electrons from internal to external. • Z-scheme system promotes separation efficiency of the photo-generated electrons and holes. • Pd nanorods as conductive passageway are used to accelerate the electron transfer. • Pd nanorods as co-catalyst are used to promote superoxide radical (O₂⁻) formation. • Coated Z-scheme Pd-BaZrO₃@WO₃ provides largest WO₃ oxidation surface for degradation. -- Abstract: The coated Z-scheme Pd-BaZrO₃@WO₃ composite as a new-type sonocatalyst with highly sonocatalytic performance is first constructed through sol-gel and hydro-thermal synthesis methods. The chemical configuration, structure and component are characterized by a series of characterization methods. The sonocatalytic degradation of diazinon as a model pollutant is studied to estimate the sonocatalytic performance of coated Z-scheme Pd-BaZrO₃@WO₃ composite. Some affecting factors such as Pd-BaZrO₃ and WO₃ mass proportions, ultrasonic (US) irradiation time, reusability and catalyst dosage are researched in detail through UV–vis spectra and gas chromatography (GC). The produced intermediates are detected in the degradation process of diazinon by using gas chromatography-mass spectrometer (GC–MS). The possible reaction mechanism of coated Z-scheme Pd-BaZrO₃@WO₃ sonocatalyst in sonocatalytic degradation process is also explored. Subsequently, the hydroxyl radicals (OH) and holes (h⁺) are discriminated to further elaborate the possible sonocatalytic mechanism. The experimental results manifest that the coated Z-scheme Pd-BaZrO₃@WO₃ sonocatalyst displays a preeminent sonocatalytic performance under ultrasonic irradiation because it can efficaciously suppress recombination of electrons (e⁻) and holes (h⁺), extend light response scope and provide almost 100% oxidization surface. In addition, the introduced palladium (Pd) nanorods connecting BaZrO₃ and WO₃ can expedite e⁻ transfer. Under optimal conditions, the most of diazinon molecules can be disintegrated in the existence of the coated Z-scheme Pd-BaZrO₃@WO₃ under ultrasonic irradiation for 150 min. This study provides a feasible method for the treatment of environmental pollutions.