Hierarchical MOF-derived cobalt/zirconium-implanted boron and nitrogen co-doped carbon nanotubes for rapid visible-light-driven tetracycline mineralization

The pervasive contamination of aquatic environments by tetracycline (TC) antibiotics poses severe threats to ecosystem integrity and public health, primarily due to its chemical stability, resistance to conventional treatment, and role in propagating antibiotic resistance. Herein, we report the rational design and synthesis of cobalt/zirconium-implanted boron and nitrogen co-doped hierarchical carbon nanotubes (CoZr@BCN) via controlled pyrolysis of a porphyrinic Z-MOF (PCN-222) at 900 °C in the presence of polyethylene glycol, boric acid, and urea as auxiliary sources. This innovative strategy yields hollow carbon nanotubes (approximately 800 nm in length, with an average diameter of 100 nm and an average wall thickness of 15 nm) featuring a hierarchically mesoporous structure. Comprehensive characterization confirms the coexistence of B/N-doped graphitic carbon nitride within a moderately disordered graphitic matrix, as indicated by an ID/IG ratio of 1.41. Notably, under visible light irradiation, CoZr@BCN showed 98.1% degradation of TC (20 mg L−1) within 30 min at pH 6 (catalyst dosage: 0.75 g L−1), accompanied by ∼89% total organic carbon removal, demonstrating near-complete mineralization rather than mere chromophore destruction. The degradation follows pseudo-first-order kinetics (k1 = 0.122–0.068 min−1 for 10–50 mg L−1 TC), with radical scavenging studies establishing the reactive species order: photogenerated holes (h+) > superoxide radicals (O2•⁻) > hydroxyl radicals (•OH). Remarkably, CoZr@BCN retains over 94% of its degradation efficiency after five consecutive cycles with <1% loss in activity, underscoring exceptional structural stability and recyclability. By elucidating the underlying mechanistic pathways, this study provides critical insights for the advancement of next-generation water treatment technologies.