Defect-rich ZnO nanosheets of high surface area as an efficient visible-light photocatalyst

A facile ultra-rapid solution method was developed to fabricate ZnO nanosheets with tunable BET surface area and rich oxygen-vacancy defects. The addition of 1 mol L^-1 Na₂SO₄ led to an increase of BET surface area of ZnO nanosheets from 6.7 to 34.5 m²/g, through an electrostatic-controlled growth and self-assembly mechanism. Detailed analysis based on Raman scattering, room-temperature photoluminescence, X-ray photoelectron spectroscopy and electron spin resonance revealed that the as-prepared ZnO nanosheets were rich in oxygen-vacancies. Increased BET surface area led to a further increase of surface oxygen-vacancy concentration. The rich oxygen-vacancies promoted the visible-light absorption of the ZnO nanosheets, leading to high photocurrent responses and photocatalytic activities towards the degradation of rhodamine B (apparent rate constants, k = 0.0179 min^-1) under visible-light illumination (λ > 420 nm), about 13 and 11 times higher, respectively than that of ZnO nanoparticles with few oxygen defects. In addition, the high-surface-area ZnO nanosheets could be effectively hybridized with Ag₃PO₄ nanoparticles, resulting in a further enhancement of the visible-light photocatalytic performance (k = 0.0421 min^-1). This increase in performance was attributed to the increased visible-light absorption as well as the energy level matching, the latter leading to efficient charge transfer between oxygen-vacancy-rich ZnO nanosheet and Ag₃PO₄, suggesting a synergistic effect of surface oxygen vacancies and Ag₃PO₄ coupling.