MOF derived hollow CuO/ZnO nanocages for the efficient and rapid degradation of fluoroquinolones under natural sunlight

In this study, we prepared hollow ZnO nanocages by calcining ZIF-8 and then synthesized CuO in situ on the surface of nanocages by wet-chemistry method, culminating in the synthesis of hollow CuO/ZnO nanocages as a novel photocatalyst. This work is the first to realize the position-controllable synthesis of CuO/ZnO heterojunction on the inner and outer surfaces of the hollow nanocages. The structure and composition of photocatalysts have been characterized by XPS, XRD, SEM, FE-TEM, and BET, indicating the successful synthesis of h-CZN. Secondly, comprehensive experimental studies on fluoroquinolones photodegradation were conducted, thereby obtaining the optimal parameters. The experimental results suggested the synergistic action of h-CZN relative to h-ZN and pure CuO, and the synergy index was 1.49. Not only that, we monitored the water quality parameters (chemical oxygen demand, total organic carbon, carbon oxidation state, and average oxidation state). The results demonstrated the significant potential of h-CZN in practical applications. In addition, the band structure of h-CZN was probed using UV–Vis diffuse reflectance spectra and Mott-Schottky analysis. The transient photocurrent response, electrochemical impedance spectroscopy, time-resolved photoluminescence, and photoluminescence proved that the h-CZN favored the separation of photogenerated carriers. And, these results also offered reasonable explanations for the enhancement in photocatalytic property of h-CZN. The free radical trapping experiments and electron paramagnetic resonance investigated that superoxide radicals were the primary active substances. Finally, the suitable photocatalytic degradation mechanism was proposed based on the above results.