Strategy for colorimetric and reversible recognition of strong acid in solution, solid, and dyed fabric conditions: Substitution of aminophenoxy groups to phthalocyanine

A series of novel peripherally tetra- and octa-substituted copper phthalocyanines (CuPcs) bearing various aminophenoxy groups was designed and synthesized for detecting strong Brønsted acids. Octa-(diethyl-aminophenoxy)-substituted CuPc 5 exhibited excellent HCl detection capability with high sensitivity (limit of detection: 240 ppb), rapid (<2s), and selectivity for strong acids in versatile conditions including solution, solid, and dyed fabric. Furthermore, CuPc 5 noted reusability in recyclable tests with HCl and NH₃, demonstrating its great potential for practical detection of HCl and ammonia gas leak under various environments. Based on systemic characterizations based on UV-Vis absorption spectra and NMR, we suggest that the proton of HCl associated with the N atom of CuPc 5, and the proton sensing abilities are directly related to the dissociation constants of the amine groups. The steric hindrance of alkyl chains and molar absorption coefficient of the CuPc species in THF solvent, as well as the H₂O content of the solvent system, also affected the sensing performance. Due to less bulky nature of diethyl-amino groups having higher pK_a and stronger basicity, CuPc 5 featured effective recognition of strong acids with pK_a value less than -2.0 (K_a > 100). To the best of our knowledge, this is the first demonstration of pKa-sensitive colorimetric chemosensor using CuPc backbone, in particular for distinguishing strong Brønsted acids such as HCl.

Platinized agarose microspheres as a new modifier in graphite paste electrodes for the electrochemical determination of 4-aminophenol

In the environment, 4-aminophenol (4-AP) is present as a highly toxic compound and water pollutant. In this study, platinized agarose microspheres (PtAM) were used for the first time, for the preparation of a novel, modified graphite paste electrode (GPE/PtAM) for the electrochemical determination of 4-AP. PtAM was characterized using transmission electron microscopy, field emission scanning electron microscopy and energy dispersive X-ray analysis. The electrochemical response characteristics of GPE/PtAM towards 4-AP were investigated via electrochemical impedance spectroscopy, cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The value of the charge transfer resistance obtained for GPE/PtAM was 27.3 Ω. Microscopic surface areas and the surface concentration of the electroactive species for GPE/PtAM were calculated to be 0.077 cm² and 1.13 × 10⁻³ mol cm⁻², respectively. The electron transfer coefficient, diffusion coefficient and standard heterogeneous rate constants of 4-AP were calculated as 0.274, 4.56 × 10⁻⁴ cm² s⁻¹, and 3.32 × 10⁻¹ cm s⁻¹, respectively. The influence of pH on the oxidation of 4-AP was investigated and a pH value of 2.0 (using a phosphate buffer solution) was selected as the optimum pH. Under optimum conditions, the calibration was linear between 0.8 and 87 μM with a detection limit of 45 nM. Moreover, GPE/PtAM was applied to determine the concentrations of 4-AP in water samples with satisfactory results.

In the environment, 4-aminophenol (4-AP) is present as a highly toxic compound and water pollutant.

Reduced Graphene Oxide-Conjugated Urchin-Like NiCo2O4 Nanostructures for Individual Detection of o-Nitro and p-Amino Phenol

This work introduced a facile synthesis method of reduced graphene oxide-conjugated urchin-like NiCo2O4 nanostructures via a simple, cost-effective, and environmental-friendly one-pot hydrothermal method. The as-prepared rGO-NiCo2O4 nanocomposites were used to fabricate 3-aminopropyltriethoxysilane-modified glassy carbon electrode (GCE/APTES/rGO-NiCo2O4) for ultrasensitive electrochemical detection of o-nitro (o-NP) and p-amino (p-AP) phenols. The structure and morphology of the nanocomposite were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical experiments revealed that the nanocomposite exhibited remarkable electrochemical performances. A linear relationship is observed with the differential pulse voltammetry experiment between the peak currents and the concentrations in the ranges of 5.0 × 10-9 to 5.0 × 10-7 M (R 2 = 0.996) and 1.0 × 10-6 to 2.5 × 10-5 M (R 2 = 0.992) for o-NP and of 1.0 × 10-8 to 5.0 × 10-7 M (R 2 = 0.996) and 1.0 × 10-6 to 1.0 × 10-4 M (R 2 = 0.987) for p-AP. The calculated detection limits (S/N = 3) are 5.0 × 10-9 M and 1.0 ×10-8 M for o-NP and p-AP, respectively. Furthermore, a very high recovery percentage is obtained with the proposed sensor after successful application in the determination of target analytes in tap water samples.

An electrochemical bifunctional sensor for the detection of nitrite and hydrogen peroxide based on layer-by-layer multilayer films of cationic phthalocyanine cobalt(ii) and carbon nanotubes

Binder-free multilayer films composed of phthalocyanine and carbon nanotubes were constructed by the layer-by-layer electrostatic assembly and applied for the electrochemical detection of NO₂⁻ and H₂O₂.