Electron Transfer Trade-offs in MOF-Derived Cobalt-Embedded Nitrogen-Doped Carbon Nanotubes Boost Catalytic Ozonation for Gaseous Sulfur-Containing VOC Elimination

Abstract

High-performance and robust catalysts act as core drivers for catalytic ozonation to eliminate gaseous sulfur-containing volatile organic compounds (VOCs). Herein, nitrogen-doped carbon nanotubes embedded with Co species (Co@NCNT) are synthesized by thermolysis of a ZIF-67/melamine mixture. The carbon-confinement effects in Co@NCNT not only improve the stability of Co species but also regulate the electronic structure of Co─C bonds, consequently synergistically improving the catalytic ozonation performance. The experimental results indicate that the Co@NCNT catalyst could still remove ∼86% of odorous methyl mercaptan (CH3SH) after running for 60 h at 25 °C under an initial concentration of 50 ppm CH3SH and 40 ppm ozone, relative humidity of 60%, and space velocity of 600,000 mL h–1 g–1, outdistancing reported values under comparable reaction conditions. Detailed characterization and theoretical simulations reveal that the electronic metal–support interaction of Co─C bonds in Co@NCNT significantly adjusts the electronic structure of Co species, thereby promoting ozone-specific adsorption/activation to convert the surface atomic oxygen (*Oad) and ·OH/1O2/·O2–. Also, the electrons obtained from CH3SH in the electron-poor center transferred through the C─Co bond bridge to maintain the redox cycle of ≡Co0/2+ → ≡Co3+ → ≡Co0/2+ and realize the efficient and stable removal of CH3SH into CO2/SO42–/H2O. This work demonstrates that MOF-derived materials with tunable electronic structures achieve the stable removal efficiency for gaseous sulfur-containing VOCs via electron transfer trade-offs and provide potential candidate catalysts for the application of air purification.