Self-doping of biological secretions for waste catalyst reuse

The tremendous costs of disposal and potential environmental problems caused by waste catalysts bring about an urgent need for catalyst regeneration without loss of catalytic activity and stability. Here, we report on a simple and reproducible method to regenerate waste ozonation catalysts by carbonization of self-doped biological secretions to synthesize highly active and stable carbon-based nano-single-atom-site catalysts (NSASCs), Cu@graphitic carbon (GC)-Al₂O₃, converting waste catalysts into a sustainable resource. Specifically, Cu metal atoms are dispersed on the GC-Al₂O₃ composite support in the form of Cu₁-C₃ and Cu_n-Cu_n, primarily because the adsorption of biological secretions enhances the dispersibility of the metal nanoparticles. The pilot-scale demonstration reduces the average chemical oxygen demand (COD) of effluent in the Cu@GC-Al₂O₃/O₃ system from 79.56 to 30.01 mg L^-1, demonstrating enhanced catalytic activity and stability relative to the pristine fresh catalyst. The combined experimental and theoretical investigations reveal that the Cu₁-C₃ sites promote the formation of *O_ad, while the Cu_n-Cu_n sites induce the generation of O₂^•- and ¹O₂ from *O_ad, contributing to catalytic synergism in both radical and non-radical pathways. Additionally, the life cycle assessment confirms the economic feasibility and sustainability of the regeneration strategy. Our findings propose a general approach to reactivating waste catalysts, which can also inspire biological secretions in atom dispersal modulation and modification of other materials.