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 H 2 S sensors.Herein, tetra-b-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 0 -dicyclohexylcarbodiimide (DCC), using hydroquinone (HQ), p-aminophenol (PAP), and p-phenylenediamine (PPD) as linking molecules, respectively. The obtained cPcCo-B-aCNT (B¼ 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 H 2 S 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 H 2 S 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 H 2 S 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 H 2 S and a low detection limit of 5 ppb. Furthermore, the linking molecules play a critical role in the sensitivity of H 2 S, as evidenced from the current-voltage characteristics. The systematic study developed here provides a valid way to fabricate other high-efficient H 2 S sensors.Scheme 1 A schematic illustration of the synthesis procedure for cPcCo-B-aCNT hybrids. J. Mater. Chem. A This journal is Fig. 5 Cross-sensitivities to various gases for the aCNT sensor (A) and cPcCo-HQ-aCNT sensor (B) at room temperature; MeOH ¼ methanol, EtOH ¼ ethanol, DMK ¼ acetone, DCM ¼ dichloromethane, TCM ¼ trichloromethane, CTC ¼ carbon tetrachloride, PhH ¼ benzene, Tol ¼ toluene, THF ¼ tetrahydrofuran, MA ¼ methyl aldehyde, AA ¼ acetic acid, DEE ¼ diethyl ether, and EA ¼ ethyl acetate. J. Mater. Chem. A This journal is

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