Fabrication of WO3 photocatalyst by plasma assisted ball milling under different discharge atmospheres

Abstract

A convenient method for producing single oxide WO3-x at room temperature through plasma milling was reported, resulting in a highly efficient visible-light photocatalyst. By altering the discharge atmosphere during plasma milling from ammonia and nitrogen to argon, the color of the milled monoclinic WO3 powders deepens from blue to dark blue, indicating an increased concentration of oxygen vacancies. The morphological and structural properties of the monoclinic WO3 powders, prepared using different ball milling techniques, are characterized using XRD, SEM, TEM, Raman, XPS, EPR, and UV–vis. These results reveal that plasma milling leads to a higher surface area, increased presence of oxygen vacancies, and more defects compared with conventional milling, resulting in a greater number of more reactive sites and a larger contact area between monoclinic WO3 nanoparticles and RhB solution. Consequently, monoclinic WO3 samples fabricated through Ar-P-milling exhibit the highest photocatalytic activity. This is attributed to the reduction of the WO3−x band gap to 2.28 eV by Ar-P-milling with high oxygen vacancies. This lower bandgap markedly improves the light utilization rate, thereby enhancing the overall photocatalytic efficiency. The Ar-P-milled WO3 shows the highest degradation rate constant of 0.037 min−1, which is 4 times higher than that of pure monoclinic WO3.