Probing the photo- and electro-catalytic degradation mechanism of methylene blue dye over ZIF-derived ZnO

Due to the severe water pollution from effluent dyes, the need of the hour is to find a suitable dye degradation technology, and appropriate catalyst materials. Semiconducting ZnO was produced by pyrolysis of ZIF-8 template. The materials were well characterized with in situ and ex situ XRD and TGA, FE-SEM, HRTEM, UV-DRS, PL, and FRET. The results showed that upon calcination the body centered cubic ZIF-8 produces hexagonal primitive ZnO while retaining the truncated cubic shaped particles. The materials were screened for photo- and electro-catalytic oxidation of methylene blue. In both the different degradation technologies, ZnO synthesized from ZIF-8 outperformed the ZIF-8. The FRET dynamics showed significant spectral overlap of ZnO emission and the methylene blue absorption. It was found to be responsible for the better photocatalytic efficacy of ZnO samples than ZIF-8. The proposed reaction mechanism showed that the surface-bound reactive oxygen species produced either by light exposure or due to applied bias is key to dye degradation. The cytotoxicity of the untreated and ZnO and ZIF-8 treated dye over melanoma cells was evaluated, and it was found that the cytotoxicity of the degraded dye from ZIF-derived ZnO was less compared to that of ZIF-8 treated one.