Metalloporphyrin sensitized polymer-SWCNT composites: Modulating central metal for room temperature NO2 sensor

Abstract

Detection of harmful gases is crucial for environmental monitoring and protecting human health against safety hazards. Developing room-temperature gas sensors is essential for the real-time and on-site monitoring of toxic gases with high sensitivity. In this work, we propose chemiresistive gas sensors comprising poly(4-vinylpyridine) (P4VP) wrapped single-walled carbon nanotubes (P4VP-SWCNT) composites for NO2 at room temperature. To improve sensitivity and selectivity, metalloporphyrins (M-TPyP, M = Zn, Cu, Fe, and Mn) were functionalized on the P4VP-SWCNT composites through a combination of coordination, pi-pi interaction, and van der Waals interaction. The result revealed that Zn-TPyP functionalized P4VP-SWCNT (Zn-TPyP-P4VP-SWCNT) exhibited a 5.93-fold higher NO2 response [(Rair-Rgas)/Rairx 100 (%)] of 25.62 % compared to the response (4.32 %) of pristine P4VP-SWCNT toward 5 ppm of NO2 at room temperature. In addition, selective NO2 sensing property was achieved with Zn-TPyP-P4VP-SWCNT against other interfering gases. The NO2 sensing mechanism was elucidated by X-ray photoelectron spectroscopy (XPS) in conjunction with density functional theory (DFT) calculations, wherein pre-adsorbed oxygen species such as O- at the metal center promote surface chemical reaction with NO2 converting into NO3-. This work demonstrates the catalytic sensitization effect of M-TPyP on the P4VPSWCNT for applications in room-temperature NO2 sensors with on-site detection capability.