N and O dual-doped porous carbon transformed from graphitic carbon nitride as a peroxymonosulfate activator for tetracycline hydrochloride degradation†

Graphitic carbon nitride (g-C₃N₄) is a promising non-metallic material. However, its low specific surface area and chemical inertness lead to low catalytic efficiency, even in the case of non-metallic heteroatom doping. Herein, we develop a simple strategy using citric acid to convert g-C₃N₄ into a N and O dual-doped porous carbon material (ONPC). Compared with pristine g-C₃N₄, ONPC exhibited significantly enhanced catalytic activity in peroxymonosulfate (PMS) for tetracycline hydrochloride (TC) degradation without light irradiation. In the presence of 0.3 g L⁻¹ ONPC and 2.4 mM PMS at pH 5.7, 90.75% of TC could be removed within 60 min. Singlet oxygen (¹O₂) and superoxide radicals (O₂˙⁻) are the main active species, as verified by quenching experiments and electron paramagnetic resonance (EPR) analysis. Characterization results and DFT calculations confirmed the outstanding contribution of graphite N, pyridine N and carbonyl (CO) to the catalytic performance of ONPC. Three possible pathways for TC degradation were proposed by high-resolution liquid chromatography–mass spectrometry (LC–MS) analysis, and the toxicity of most intermediates was lower than that of TC. Overall, this work will provide a simple approach to the design of efficient carbon catalysts with great potential in catalytic PMS for TC degradation.