Size-dependent spectroscopic insight into the steady-state and time-resolved optical properties of ZnO photocatalysts

In this paper, we present a spectroscopic insight into the structural and optical properties of ZnO nanoparticles (NPs) applied for water depollution using the photocatalytic process. Samples of various sizes and shapes were synthesized using simple, cost-effective chemical methods. The steady-state optical properties were analyzed using absorption and fluorescence emission spectroscopy and the band-gap and emission energies revealed an inverse dependence on the ZnO particles size. The time-resolved fluorescence properties were studied using time correlated single photon counting (TCSPC) technique. Three emissive states were identified for all ZnO samples, with lifetimes that showed an overall decrease with increasing the particles diameter. The insights into the photocatalytic process toward understanding the ZnO nanoparticles mediated photocatalysis for degradation of Rhodamine (RhB) and oxytetracycline (OTC) was elucidated. The increase of photocatalytic activity was due to charge carrier partition and mobility.