Promotion effects of thermal oxidation on zeolitic imidazolate framework-8 (ZIF-8) for efficient broad-spectrum photocatalysis

The development of photocatalysts with broad-spectrum response and efficient electron transfer yet remains a great challenge. Herein, we report a systematic research on the thermal oxidation mechanism of ZIF-8 and its promotion effects on photocatalytic performance. The activation energy E of organic ligands decomposition during ZIF-8 thermal oxidation was calculated to be 103.7 kJ/mol by Kissinger-Akahira-Sunose (KAS) model. The wurtzite ZnO crystal and oxidizing functional groups (H-N-C=O, C-O, etc.) formed in oxidized ZIF-8 were crucial to the superior photocatalytic performance. In particular, O350/ZIF-8 had the broadest optical absorption band (similar to 750 nm) and largest photocurrent density, which exhibited the highest photocatalytic activity of methylene blue (MB) with rate constant k of 0.0374 min(-1). The photogenerated O-center dot(2)- and (OH)-O-center dot radicals were found to react as main oxygen species in photocatalytic reaction. Taken together, this study not only offered a simple method to prepare ZIF-8 based photocatalyst with high activity and stability, but also provided guidance for the efficient photocatalytic degradation of organic compounds in wastewater.