Efficient degradation of ciprofloxacin by waste eggshells derived ES/CuS heterostructure under visible light

The transformation of discarded eggshells (ES) into high value-added materials through technological means and the realization of turning waste ES “stone into gold” are of great significance to the environment and sustainable economic development. CuS is a typical semiconductor with broad and powerful light absorption properties, which is widely used in photocatalytic wastewater remediation. However, the high recombination rate of CuS photogenerated electron-hole pairs limits its application. In this study, a novel waste eggshell-derived ES/CuS heterojunction photocatalyst is innovatively constructed using an adsorption-precipitation method to realize the efficient degradation of ciprofloxacin (CIP) under visible light. The results showed that the ES/CuS heterojunction photocatalyst, under visible light irradiation, could degrade CIP (20 mg/L) with a degradation efficiency of 93.7% at 5 h (including 1 h of dark reaction), which compared to the degradation efficiency of CuS (52.3%) its CIP removal was significantly increased by a factor of 1.78, and showed good stability and reusability. The superior CIP degradation performance is mainly attributed to the introduction of ES to improve the separation efficiency of CuS photogenerated carriers and can participate in redox reactions through the formation of e${}^{-}$ and h${}^{+}$ on the surface of heterojunctions under visible light irradiation, which generation of oxidizing powerful .O₂${}^{-}$ radicals which can also directly oxidize CIP. This work provides a new perspective on the reuse of waste ES and the design of CuS catalysts.