Emerging investigator series: enhancing the degradation of ciprofloxacin in water using Oxone activated by urchin-like cubic and hollow-structured cobalt@N-doped carbon prepared by etching-engineering: a comparative study with mechanistic and eco-toxic assessments

Abstract

Ciprofloxacin (CIP) represents the most typical fluoroquinolone antibiotic and is increasingly detected in water environments. For eliminating CIP from water, a hollow-engineered nanostructured cobalt-embedded nitrogen-doped carbon (H-Co@NC) is developed through an etching-engineering technique. H-Co@NC exhibits a cubiform morphology with a hollow configuration covered by thin urchin-like layers, whereas cobalt (Co) nanoparticles are embedded throughout the entire surface. Thus, H-Co@NC shows remarkable catalytic activities for Oxone activation to eliminate CIP from water and outperforms the non-hollow analogue, S-Co@NC, and the commercial Co₃O₄. The activation energy (E_a) was measured as 48.2 kJ mol⁻¹, which is lower than that reported for most of the catalysts for CIP degradation. The degradation pathway of CIP by H-Co@NC + Oxone is also proposed based on theoretical calculations and detected intermediates. SO₄˙⁻, OH˙, and ¹O₂ are simultaneously generated from H-Co@NC + Oxone, in which SO₄˙⁻ shows a dominant role in the CIP degradation. Besides, H-Co@NC preserves its structure over multi-cycle CIP degradation and remains highly effective in various water matrices. CIP degradation by H-Co@NC + Oxone does not lead to the formation of toxic and very toxic by-products during its decomposition process by the eco-toxicity assessment. These features validate that H-Co@NC is an advantageous and promising heterogeneous catalyst for activating Oxone to eliminate CIP from aqueous systems.