Salt-assisted Synthesis of Hollow Bi₂WO₆ Microspheres with Superior Photocatalytic Activity for NO Removal

Hollow Bi₂WO₆ microspheres are successfully synthesized by a facile ultrasonic spray pyrolysis (USP) method using NaCl as a salt template. The as-prepared hollow microspheres assembled as nanoplates with dimensions of approximately 41-148 nm and are dispersed with non-uniform pores on the template surface. By swapping the salt template with KCl or Na₂SO₄, different morphologies of Bi₂WO₆ are obtained. The experimental results demonstrate that NaCl plays a key role on the formation of Bi₂WO₆ with hollow structures. The specific growth mechanism of hollow microspheres was studied in detail. The Bi₂WO₆ hollow microspheres exhibit an excellent photocatalytic efficiency for NO removal under solar light irradiation, which is 1.73 times higher than for the Bi₂WO₆ obtained in the absence of any salt template. This enhancement can be ascribed to the simultaneous improvement on the surface area and visible light-harvesting ability from the hollow structures. Electron spin resonance (ESR) results suggest that both radicals of •OH and •O₂^- are involved in the photocatalytic process over the BWO-NaCl sample. The production of •O₂^- radicals offers better durability for NO removal.