Stably dispersed carbon nanotubes covalently bonded to phthalocyanine cobalt(ii) for ppb-level H2S sensing at room temperature

Abstract

Cost-efficient, highly sensitive and stable sensing materials play a key role in developing H₂S sensors. Herein, tetra-β-carboxyphenyloxyphthalocyanine cobalt(II) (cPcCo) has been successfully bonded on the surface of acidified multiwalled carbon nanotubes (aCNTs) by a facile two-step condensation reaction in the presence of N,N′-dicyclohexylcarbodiimide (DCC), using hydroquinone (HQ), p-aminophenol (PAP), and p-phenylenediamine (PPD) as linking molecules, respectively. The obtained cPcCo–B–aCNT (B= HQ, PAP, and PPD) hybrids display good dispersibility in ethanol, which is beneficial to construct uniform sensing devices. The cPcCo–B–aCNT sensors, with a loose network-like structure, present abundant exposed sensing sites, oriented transmission of charges, and unimpeded pathways for H₂S diffusion, which endow the cPcCo–B–aCNT hybrids with excellent sensing performance, in terms of sensitivity, reliability, reproducibility, and detection limit. The detection limit of the sensors composed of cPcCo–B–aCNT hybrids towards H₂S reaches the ppb-level at room temperature, which is about the same as the odor threshold level for humans. For the cPcCo–HQ–aCNT sensor, the response to H₂S varies linearly with respect to its concentration from 20 to 160 ppb and from 320 to 2560 ppb, with the highest gas response of 2.5% to 80 ppb H₂S and a low detection limit of 5 ppb. Furthermore, the linking molecules play a critical role in the sensitivity of H₂S, as evidenced from the current–voltage characteristics. The systematic study developed here provides a valid way to fabricate other high-efficient H₂S sensors.