Anchoring defective metal-free catalysts on montmorillonite nanosheets for tetracycline removal: synergetic adsorption-catalysis and mechanism insights†

Abstract

A one-step thermal polymerization approach was adopted to combine C₃N₅ with montmorillonite nanosheets (MMT Ns) to form xCN-MMT for the degradation of pollutants in water. Benefitting from the abundant hydroxyl groups on the MMT surfaces, double defects (–CN and N defects) were introduced in xCN-MMT catalysts to promote the adsorption of tetracycline (TC), peroxymonosulfate (PMS), and oxygen. 10CN-MMT exhibited superior adsorption performance toward TC, with the adsorption capacity being 5.65-fold that of MMT Ns and 2.64-fold that of C₃N₅. Further, 10CN-MMT exhibited better PMS activation performance than MMT Ns and C₃N₅, which could degrade 95% of TC within 120 min. Moreover, the total organic carbon (TOC) removal efficiency of the present system reached 81.1%, and the chemical oxygen demand (COD) decreased from 50.7 to 12.2 mg L⁻¹. The degradation process of TC was characterized using liquid chromatography-tandem mass spectrometry (LC-MS), and a reasonable degradation pathway and catalytic mechanism were given by combining with active species analysis. The toxicological analysis of the degradation products also showed a significant decrease in toxicity. The degradation experiments in different water environments were also simulated, and it was found that 10CN-MMT showed good adsorption effects. This study provides a green metal-free clay-based catalyst and shows good applicability in removing antibiotics.