Nitrogen-doped carbonized polyaniline (N-CPANI) for peroxydisulfate (PDS) activation towards efficient degradation of doxycycline (DOX) via the non-radical pathway dominated by electron transfer

• Synthesis of N-doped CPANI for PDS activation towards DOX degradation. • High mineralization of DOX in the N-CPANI-900/PDS with TOC removal efficiency of 83.77%. • High robustness to environmental variations and good recyclability of N-CPANI-900. • The graphitic N and ketonic group(C=O) were the main catalytic reactive sites. • N-CPANI-900/PDS complexes mediated electron transfer accounts for the major DOX degradation. In this study, nitrogen-doped carbonized polyaniline (N-CPANI-T, T is the carbonized temperature) was firstly synthesized to activate peroxydisulfate (PDS) towards the sustainable degradation of doxycycline (DOX). Compared to other carbon-based catalysts reported in the previous studies, N-CPANI-900 had better DOX decomposition rate (91.66%) and higher TOC elimination efficiency (83.77%) within 120 min with the initial DOX concentration as high as 20 mg/L, which could be attributed to the accelerated electron transfer and the large adsorption capacity of N-CPANI-900. The active sites for PDS activation driven by N-CPANI-900 mainly include graphitic N, ketonic group (C=O) and defect sites in the carbon matrix. The results of both quenching experiments and electron paramagnetic resonance (EPR) test illustrated that non-radical pathway was dominated in the N-CPANI-900/PDS/DOX system. Moreover, metastable N-CPANI-900/PDS complexes mediated electron transfer made a remarkable contribution to DOX degradation compared with singlet oxygen. The effects of pH, inorganic anions, NOM and different water matrices on DOX degradation were almost negligible in the N-CPANI-900/PDS system. This research provides a new strategy into the preparation of metal-free PDS activators towards efficient removal of emerging contaminants in real wastewater.