The role of ozone and influence of band structure in WO3 photocatalysis and ozone integrated process for pharmaceutical wastewater treatment.

Graphical abstract Highlights • O 3 shows a dual role in photocatalytic ozonation process. • The introduction of O 3 overcomes the drawback of the photocatalysts. • Higher CB position benefit the activity of photocatalysts in the Vis-O 3 system. • Acid solution is beneficial for the photocatalytic ozonation. • WO 3 is also found to be active in catalytic ozonation process. Abstract Photocatalytic ozonation has great potential in wastewater treatment. However, the role of ozone and the contribution of photogenerated hole in this process have not been fully understood. Here three WO 3 materials are synthesized and used as model catalysts in visible-light photocatalytic ozonation for the mineralization of pharmaceutical pollutants. A dual role of ozone in this process has been confirmed: (i) direct oxidation of the pollutant till formation of refractory intermediates, (ii) efficient trapping of photoelectron that cannot be captured by O 2. The latter is crucial because it not only induces the O 3 −-mediated pathway for hydroxyl radical (OH) formation but also separates the hole which has proven to be capable of oxidizing water into OH. Evidenced by photoluminescence results, the intrinsic charge separation ability of WO 3 in photocatalytic ozonation is no more as important as that in photocatalysis with O 2. Finally, this process is more applicable under acidic condition. This work contributes to a better understanding of the significance of ozone in WO 3 photocatalytic ozonation and provides us an insight into the mechanism of photocatalytic ozonation. [ABSTRACT FROM AUTHOR]