Co₃O₄@CdS Hollow Spheres Derived from ZIF-67 with a High Phenol and Dye Photodegradation Activity

The Co₃O₄@CdS double-layered hollow spheres were first prepared by the template-removal method with the assistance of the ZIF-67 material; the structure has been proved by transmission electron microscopy (TEM). The Co₃O₄@CdS hollow spheres calcinated at 400 °C exhibited the highest photodegradation activity. Nearly 90% phenol was degraded after 2 h of visible-light irradiation. More than 80% rhodamine-B (RhB) was degraded within the first 30 min and nearly eliminated after 1 h of irradiation. The mechanism of the photodegradation reaction was investigated. Based on the analysis of electron spin resonance (ESR) spectra and radical trapping test, it was found that superoxide radicals are the major oxidative species for dye degradation and holes and hydroxyl radicals are the major oxidative species for phenol degradation. These results may be used in industrial wastewater treatment. The reaction obeys first-order reaction kinetics, and the rate constant of the Co₃O₄@CdS hollow sphere in dye degradation is 0.05 min^-1 and that in phenol degradation is 0.02 min^-1, which is three times higher than that of CdS nanoparticles. These results indicated the high oxidizing ability of the samples.