Morphology effect on piezocatalytic performance of zinc oxide: Overlooked role of surface hydroxyl groups

As an environmentally friendly and non-toxic piezocatalyst, zinc oxide (ZnO) has been extensively utilized in treating organic wastewater, but the effect of surface hydroxyl (–OH) groups on the piezocatalytic activity of ZnO has not been sufficiently investigated. In this study, four ZnO catalysts with different microstructures (columnar-like, flake-like, rod-like, and flower-like) and surface –OH numbers have been fabricated for the catalytic degradation of rhodamine B. Rod-like ZnO possessed the highest number of surface –OH groups. Abundant surface –OH groups assist in suppressing electron–hole pair recombination and promoting charge migration, and thus, rod-like ZnO exhibited better piezocatalytic activity. Under ultrasonic vibration, rod-like ZnO catalyst degraded 95.2 % rhodamine B in 80 min. Holes and hydroxyl radicals were found to be the main reactive species during the piezocatalytic degradation process. The present study provides a novel idea for constructing ideal piezoelectric catalysts.