FeN4-doped carbon nanotubes derived from metal organic frameworks for effective degradation of organic dyes by peroxymonosulfate: Impacts of FeN4 spin states.

[Display omitted] • FeN 4 -doped carbon nanotubes by ball milling and pyrolysis of ZIF-8 and MIL-101. • D 2 -FeN 4 the main active site in PMS activation. • 1O 2 the major active species in the degradation of organic pollutants. • Minor contributions from •OH and SO 4 ∙ - radicals to pollutant degradation. Development of low-cost, high-performance catalysts for the effective degradation of organic dyes is of both fundamental and technological significance for environmental remediation. Herein, FeN 4 -doped carbon nanotubes exhibit a remarkable catalytic activity towards the degradation of acid orange 7 (AO7) in the presence of peroxymonosulfate (PMS). This is accounted for by the abundant well-dispersed FeN 4 sites and appropriate adsorption energy. Radical quenching experiments and electron paramagnetic resonance measurements suggest that singlet oxygen is the main reactive oxygen species. 57Fe Mossbauer spectroscopy measurements show that the FeN 4 moieties contain multiple spin states, and in conjunction with density functional theory calculations, confirm that FeN 4 with a low/medium spin state serves as the key sites for PMS activation and hence AO7 degradation. Results from this study highlight the critical role of spin states in FeN 4 in the generation of singlet oxygen for effective degradation of organic pollutants. [ABSTRACT FROM AUTHOR]