Photocatalytic production of superoxide ion in the aqueous suspensions of two kinds of ZnO under simulated solar light

Photocatalytic production of superoxide ion in the suspensions of tetrapod-like ZnO whisker (t-ZnO) or nano-sized ZnO particles (n-ZnO) under simulated solar light was quantitatively studied. The yield of superoxide ion in suspension of t-ZnO with smaller specific surface area is much higher than that of n-ZnO. This indicates that the specific surface area, generally regarded as a key factor affecting photocatalytic activity, does not play a critical role in generating superoxide ion. The difference in the production of superoxide ion from t-ZnO and n-ZnO is mainly attributed to the smaller microstrain, less defects and special surface properties of t-ZnO.

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► T-ZnO with smaller surface area produces more superoxide ion than n-ZnO.
► T-ZnO with smaller surface area exhibits higher photocatalytic activity than n-ZnO.
► Crystalline defect and morphology have distinct effects on superoxide ion production.