Enhanced degradation of aqueous tetracycline hydrochloride by integrating eggshell-derived CaCO₃/CuS nanocomposite with advanced oxidation process

Persulfate (PS)-based advanced oxidation process (AOP) has attracted wide attention in recent years, in which it is crucial to develop a cost-effective and environmentally friendly catalyst. Herein, a waste eggshell derived eggshell/CuS (ES-CuS) composite catalyst was successfully prepared in a simple way, and used in combination with PS to degrade tetracycline hydrochloride (TCH). Our results showed that the coated CuS had a sheet-like structure and was evenly distributed on the surface of the eggshell, which could effectively prevent agglomeration and enhance catalytic performance. Electron spin resonance (ESR) and free radical capturing experiments confirmed that a series of active species such as sulfate radicals (SO₄⁻), hydroxyl radicals (OH), as well as carbonate radicals (CO₃-) were produced during the catalysis process, which is the main reason for enhanced catalytic effect compared with that of the pure CuS. A possible degradation pathway was proposed. It can be expected that discarded eggshells can be used as a low-cost carrier for the synthesis of various composites to achieve its valorization, which have very broad development prospects in the field of environmental remediation or catalysis.