Tetracycline removal via adsorption and metal-free catalysis with 3D macroscopic N-doped porous carbon nanosheets: Non-radical mechanism and degradation pathway

Recently,metal-based carbon materials have been verified to be an effective persulfate acti-vator,but secondary pollution caused by metal leaching is inevitable.Hence,a green metal-free 3D macroscopic N-doped porous carbon nanosheets (NPCN) was synthesized success-fully.The obtained NPCN showed high adsorption capacity of tetracycline (TC) and excellent persulfate (PS) activation ability,especially when calcined at 700 ℃ (NPCN-700).The maxi-mum adsorption capacity of NPCN-700 was 121.51 mg/g by H-bonds interactions.Moreover,the adsorption process followed pseudo-second-order kinetics model and Langmuir adsorp-tion isotherm.The large specific surface area (365.27 mg/g) and hierarchical porous structure of NPCN-700 reduced the mass transfer resistance and increased the adsorption capacity.About 96.39％ of TC was removed after adding PS.The effective adsorption of the catalyst greatly shortened the time for the target organic molecules to migrate to the catalyst.More-over,the NPCN-700 demonstrated high reusability with the TC removal rate of 80.23％ after 4 cycles.Quenching experiment and electron paramagnetic resonance (EPR) test confirmed the non-radical mechanism dominated by 102.More importantly,the C =O groups,defects and Graphitic N acted as active sites to generate 102.Correspondingly,electrochemical mea-surement revealed the direct electron transfer pathway of TC degradation.Finally,multiple degradation intermediates were recognized by the LC-MS measurement and three possible degradation pathways were proposed.Overall,the prepared NPCN had excellent application prospects for removal of antibiotics due to its remarkable adsorption and catalytic degrada-tion capabilities.