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.
As vital biological mediators, the accurate detection of nitrite (NO2−) and hydrogen peroxide (H2O2) is desirable for clinical monitoring and diagnosis. Herein, cationic 2,9,16,23-tetra[4-(N-methyl)pyridinyloxy]phthalocyanine cobalt(II) ([TMPyPcCo]4+) and acid-treated multiwalled carbon nanotubes (aCNTs) were alternately self-assembled on the glassy carbon electrode (GCE) by means of the electrostatic interaction, leading to a 3D loose and interconnected assembly of [TMPyPcCo/aCNTs]n multilayer films. In the [TMPyPcCo/aCNTs]n films, [TMPyPcCo]4+ is anchored onto the surface of aCNTs without any inert polymer binders, which is beneficial to expose more active sites for electrocatalysis. The effective combination of [TMPyPcCo]4+ and aCNTs brings many advantages in electrochemical detection, involving the fast oriented transmission of charges, permeable channels for ion adsorption and transport, and more sensing sites, thus the [TMPyPcCo/aCNTs]n films display excellent electrochemical sensitivity towards both NO2− and H2O2. The responses of NO2− and H2O2 vary linearly with respect to the concentration from 5 µM to 30 mM and 10 µM to 9 mM. Furthermore, the superior cycling stability, reproducibility, and selectivity make [TMPyPcCo/aCNTs]n films suitable for the real samples.
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