Magnetic FeS2 embedded in N doped carbon towards peroxymonosulfate activation for highly efficient methylene blue removal

The unsatisfactory degradation, significant iron leaching and poor recyclability of Fe-based sulfide catalysts for peroxymonosulfate (PMS) activation greatly hinder their wide application. Despite the progress by constructing Fe-based sulfide/carbon composites, the degradation performance is still unsatisfactory and the synergistic mechanism of Fe sites and nitrogen configurations in PMS activation is ambiguous. Herein, using dopamine as C and N source, the magnetic FeS 2 embedded in N doped carbon (FeS 2 @NC) catalyst was prepared by hydrothermal-pyrolytic sulfidation method. The as-synthesized catalyst was systematically characterized by XRD, SEM, TEM, Raman, XPS and BET. The methylene blue (MB) degradation experiment in catalyst/PMS system showed FeS 2 @NC4-500 prepared under 0.4 g sulfur powder and pyrolysis temperature of 500 °C exhibited excellent performance with 94 % MB removal rate within 30 min. The optimal degradation condition was determined to be 0.2 g/L catalyst, 0.3 g/L PMS, 20 mg/L MB and initial pH 7.0. The scavenging experiment of reactive oxygen species (ROS), electron paramagnetic resonance (EPR) and electrochemical measurement confirmed the involvement of sulfate radical (SO 4 · – ), superoxide radical (O 2 · – ) and singlet oxygen ( 1 O 2 ) in MB degradation, but SO 4 · – and 1 O 2 were the major contributors. Combined with the XPS spectra of the fresh and used FeS 2 @NC4-500, the synergistic mechanism with Fe(Ⅱ) and pyrrolic N as active sites for PMS activation was clarified. The degradation intermediates were identified by liquid chromatograph-mass spectrometer (LC-MS) and the possible degradation pathway of MB in FeS 2 @NC4-500/PMS system was proposed. The ecotoxicity of the intermediates was predicted by using the ECOSAR software. This work deciphers the important role of Fe(Ⅱ) and pyrrolic N in PMS activation and can provide a reference for designing highly efficient Fe-based sulfide/N doped carbon hybrid for persistent wastewater remediation.