Palladium Nanoparticles Embedded Nutshell-like Bi2WO6 as an Efficient and Stable Visible-Light-Responsive Photocatalysts for NO Removal

Bi2WO6 is a promising photocatalyst for NOx removal, owing to its wide solar light absorption and specific photoelectric properties. Nevertheless, enhancing its efficiency remains a major concern. Palladium proves to be a good co-catalyst for semiconductor materials, but how the combination of Pd and bismuth tungstate affects the efficiency of NO removal and relevant process is still vague. In this work, nutshell-like bismuth tungstate was synthesized using a hydrothermal method, followed by photo-depositing Pd nanoparticles with different contents. The obtained photocatalysts were characterized by X-ray diffraction, specific surface area analyzer (BET), X-ray photoelectron spectroscopy, and scanning electron microscopy. Among the prepared photocatalysts, Bi2WO6 deposited with 1 wt % Pd shows the best photocatalytic activity with a NO removal efficiency of 58%, which is 2.9 times that of the Bi2WO6 under the same conditions. The enhanced photocatalytic activities were attributed to the comprehensive effects of the high efficiency in separating electrons and holes, improvement in invisible light utilization and BET specific surface areas of Pd–Bi2WO6 nanocomposites. More importantly, it was found that NO2 is the main product over Bi2WO6, whereas the conversion of NO to NO3– (an environmentally friendly product) is dominant over Pd-modified Bi2WO6 due to the enhanced separation of electrons and holes. Active species capture experiments show that photo-generated holes (h+) and •O2– play an important role in NO removal. The present work provides new insights into the role of Pd cocatalysts in NO removal.