Surface oxygen vacancy defect-promoted electron-hole separation for porous defective ZnO hexagonal plates and enhanced solar-driven photocatalytic performance

Porous defective ZnO cellular hexagonal plates with surface oxygen vacancies (OVZCHPs) are fabricated by hydrothermal and high-temperature NaBH4 reduction methods. The prepared OVZCHPs with a hexagonal structure have a relatively large specific surface area compared to that of pristine ZnO (ZCHPs), and the pore diameter is ~53.5 nm. After reduction, the defective OVZCHPs with a narrow band gap of ~2.95 eV extends the photoresponse to visible light region. Additionally, the surface oxygen vacancy defects are formed during the NaBH4 reduction procedure, which is confirmed by X-ray photoelectron spectroscopy, and favor the electron-hole separation. The solar-driven photocatalytic degradation rate of tetracycline for the OVZCHPs is up to ~99.9%, which is approximately three-times higher than that of the ZCHPs. This enhancement can be attributed to the hexagonal porous structure offering more surface active sites and the surface oxygen vacancy defects favoring the electron-hole separation and visible-light absorption. The novel OVZCHPs are promising photocatalysts for wastewater purification, and the fabrication strategy may provide new insights for designing other high-performance porous photocatalytic materials.