Co single-atom-anchored carbon nitride quantum dots activate peroxymonosulfate for efficient tetracycline degradation

Abstract

Tetracycline (TC) persists in aqueous environments and is difficult to remove. Peroxymonosulfate (PMS) activation has high selectivity for removal of TC. However, the existing PMS catalysts still suffer from low efficiency, low stability, and metal ion leaching. To address these issues, a cobalt single-atom catalyst on carbon nitride quantum dots (Co@CNQDs) was synthesized via a hydrothermal method and used to degrade TC. In this catalyst, atomically dispersed Co–N sites anchored on g-C₃N₄ strongly coupled with CNQDs formed a dense and highly accessible catalytic interface. This structure provided abundant catalytic active sites and erosion resistance stability. With PMS, only 20 mg L⁻¹ of Co@CNQDs was required to remove almost all TC in 1 min across a wide pH and temperature range, while dissolved Co leaching remained very low. The characterization results revealed that PMS is activated at Co–N sites via O–O bond scission to generate ¹O₂ as the dominant oxidant, whereas ·OH/SO₄˙⁻ mainly sustain the Co(II)/Co(III) cycle. TC mainly undergoes demethylation, hydrolysis, and ring-opening, ultimately yielding small-molecule organic products CO₂ and H₂O. Toxicity analysis showed that acute aquatic and developmental toxicity, bioaccumulation potential, and mutagenicity all decreased during TC degradation, indicating stepwise detoxification. This work develops a new stable Co@CNQDs PMS catalyst that enables efficient and environmentally friendly degradation of TC in aqueous environments.