A glassy carbon electrode modified with cerium phosphate nanotubes for the simultaneous determination of hydroquinone, catechol and resorcinol

Hydrothermally Grown MoS2 as an Efficient Electrode Material for the Fabrication of a Resorcinol Sensor

Recently, the active surface modification of glassy carbon electrodes (GCE) has received much attention for the development of electrochemical sensors. Nanomaterials are widely explored as surface-modifying materials. Herein, we have reported the hydrothermal synthesis of molybdenum disulfide (MoS₂) and its electro-catalytic properties for the fabrication of a resorcinol sensor. Structural properties such as surface morphology of the prepared MoS₂ was investigated by scanning electron microscopy and phase purity was examined by employing the powder X-ray diffraction technique. The presence of Mo and S elements in the obtained MoS₂ was confirmed by energy-dispersive X-ray spectroscopy. Finally, the active surface of the glassy carbon electrode was modified with MoS₂. This MoS₂-modified glassy carbon electrode (MGC) was explored as a potential candidate for the determination of resorcinol. The fabricated MGC showed a good sensitivity of 0.79 µA/µMcm² and a detection limit of 1.13 µM for the determination of resorcinol. This fabricated MGC also demonstrated good selectivity, and stability towards the detection of resorcinol.

Facile synthesis of flower-like CePO4 with a hierarchical structure for the simultaneous electrochemical detection of dopamine, uric acid and acetaminophen

A flower-like CePO4 with a hierarchical structure was hydrothermally prepared for electrochemical sensing of dopamine, uric acid and acetaminophen.

Specific sensing of resorcin based on the hierarchical porous nanoprobes constructed by cuttlefish-derived biomaterials through differential pulse voltammetry

The specific detection of resorcin from its isomers is a current research hotspot. Thus in our work, a ternary hierarchical porous nanoprobe has been constructed based on the combination of cuttlefish ink and bimetallic Au@Ag nanoclusters for the specific sensing of resorcin. Briefly, through electrostatic interaction, Au@Ag core-shell nanoclusters are immobilized on the surface of polydopamine extracted from cuttlefish, which is turned into nitrogen-doped porous carbon functionalized by bimetallic Au@Ag by topological transformation subsequently. Afterward, an electrochemical sensor is fabricated based on the nanoprobes for specifically determining resorcin in solution by differential pulse voltammetry, and the linear detection ranges of the sensor are 1-100 μM and 1.2-4 mM while the detection limit reaches 0.06 μM. Meanwhile, the sensing mechanism of resorcin by the pre-fabricated sensor is detailedly studied by density functional theory to obtain a clear electrochemical process. Besides, the selectivity, stability, plus reproducibility of the pre-fabricated sensor have been also tested, and the determinations for resorcin in real environmental water samples have also been performed with good recoveries, revealing the auspicious application potential in the environmental monitoring.

Direct synthesis of highly porous interconnected carbon nanosheets from sodium d-isoascorbic acid for the simultaneous determination of catechol and hydroquinone

Interconnected porous carbon was prepared by pyrolyzing sodium d-isoascorbic acid. An electrochemical sensor for simultaneous detection of hydroquinone and catechol was fabricated by modification with porous carbon on the glassy carbon electrode surface.

Electrochemical oxidation of resorcinol: mechanistic insights from experimental and computational studies

This work investigates the mechanisms of resorcinol oxidation by density functional theory (DFT) calculation and cyclic voltammetry measurements. Complementary data from experimental and computational studies provide new insights into the reaction mechanisms. At both macro- and micro-electrodes, cyclic voltammetry of resorcinol is chemically and electrochemically irreversible over the whole pH range (1–14). Resorcinol molecules undergo a 1H⁺ 1e⁻ oxidation at pH < pK_a1 and a 1e⁻ oxidation at pH > pK_a2 to form radicals. The radicals then readily react to form dimers/polymers deposited on the electrode surface. All of the experimental findings are consistent with the proposed mechanisms, including the apparent transfer coefficient (β) of 0.6 ± 0.1, the slope of the peak potential (E_p) against pH of −54 mV pH⁻¹, the peak-shaped responses at micro-electrodes, and the fouling of the electrodes upon the oxidation of resorcinol. DFT calculation of the reaction energy of elementary steps and the eigenvalues of the highest occupied molecular orbital (HOMO) of the radical intermediates confirms that the (1H⁺) 1e⁻ oxidation is the energetically favorable pathway. In addition to mechanistic insights, an electrochemical sensor is developed for resorcinol detection at microelectrodes in low ionic strength samples with the sensitivity of 123 ± 4 nA μM⁻¹ and the limit of detection (3 s_B m⁻¹) of 0.03 μM.

Resorcinol oxidation mechanism was investigated by DFT calculation and cyclic voltammetry experiments at macro- and micro-electrodes (1 ≤ pH ≤ 14).

Synthesis of self-assembled spindle-like CePO4 with electrochemical sensing performance

Three different morphologies of CePO₄ nanocrystals (rods, columns, and spindle-like assembled nanosheets), spindle-like LaPO₄, spindle-like PrPO₄, and TbPO₄ microspheres were successfully synthesized using a hydrothermal method.

A glassy carbon electrode modified with a monolayer of zirconium(IV) phosphonate for sensing of methyl-parathion by square wave voltammetry

A glassy carbon electrode (GCE) was consecutively modified with amino groups and phosphate groups, and then loaded with Zr(IV) ions. Fourier transform infrared spectrophotometry, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy and cyclic voltammetry were used to characterize the morphologies and electrochemical properties. The sensor was used to detect p-nitrophenyl-substituted organophosphorus pesticides, with methyl-parathion (MP) as the model analyte. Under optimized conditions, the oxidation current of square wave voltammetry (typically measured at around -0.28 V vs. saturated calomel electrode) increases linearly in the 1.0 to 100 ng mL^-1 MP concentration range, and the detection limit is 0.25 ng mL^-1 (at a signal to noise ratio of 3). Average recoveries from (spiked) real water samples are 99.9-102.2%, with relative standard deviations of 0.3-2.6% (n = 3) at three levels. The reliability and accuracy of the method was validated by HPLC. Graphical abstract Zr(IV) modified GCE is prepared via three steps. The electrode shows high specificity and selectivity towards methyl-parathion. And the linear range is 1.0 - 100.0 ng mL-¹ with the detection limit as low as 0.25 ng mL-¹ with SWV.

Synergistic effect of a cobalt fluoroporphyrin and graphene oxide on the simultaneous voltammetric determination of catechol and hydroquinone

Graphene oxide (GO) was modified with the cobalt(II) and zinc(II) complexes (CoTFPP and ZnTFPP) of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin in order to improve the electrocatalytic activity of GO towards catechol (CC) and hydroquinone (HQ). It is found that the CoTFPP-modified GO on a glassy carbon electrode (GCE) displays the highest electrocatalytic activity. The response to CC (at 0.14 V vs. SCE) is linear in the 1-220 μM concentration range. The response to HQ (at 0.04 V vs. SCE) extends from 1 μM to 200 μM. The sensitivity and detection limits are 10.40 μA∙μM^-1∙cm^-2 and 0.17 μM for CC, and 8.40 μA∙μM^-1∙cm^-2 and 0.21 μM for HQ. Experimental results indicate that the Co(II) and Zn(II) ions in the porphyrins positively affect the electron transfer rate in the hybrid materials. The GCE modified with CoTFPP/GO was successfully applied to the simultaneous determination of CC and HQ in spiked samples of tap and lake water. Graphical abstract Schematic presentation of a voltammetric method for simultaneous determination of catechol (CC) and hydroquinone (HQ). It is based on the use of a cobalt (II) fluoroporphyrin (CoTFPP) functionalized graphene oxide (GO) hybrid.

Synthesis of hollow Mo2C/carbon spheres, and their application to simultaneous electrochemical detection of hydroquinone, catechol, and resorcinol

Hollow molybdenum-dopamine spheres were synthesized and thermally annealed to form hollow Mo₂C/C spheres. The morphology, composition and electrochemical behavior of spheres were characterized. A glassy carbon electrode (GCE) was modified with the spheres and then used for simultaneous detection of hydroquinone (HQ), catechol (CC), and resorcinol (RS). Distinct oxidation peaks can be observed for HQ, CC and RS at potentials of -0.004 V, 0.10 V and 0.44 V (vs. SCE). The responses to HQ, CC and RS are linear in the concentration ranges of 0.3~1000 μM, 2~2000 μM and 3~600 μM, respectively. The corresponding detection limits are 0.12, 0.19 and 1.1 μM (at S/N = 3). The sensor was then applied to quantify HQ, CC, and RS in tap water, river water and vegetable juice. Recoveries ranged from 93.5% to 106.5%. The modified GCE is repeatable, reproducible, stable and selective for HQ, CC and RS. Graphical abstract Schematic presentation of a novel electrochemical sensor based on a glassy carbon electrode modified with  hollow Mo₂C/ carbon spheres for determination of hydroquinone, catechol, and resorcinol.

Mesoporous Carbon and Ceria Nanoparticles Composite Modified Electrode for the Simultaneous Determination of Hydroquinone and Catechol

In this work, a novel material that was based on mesoporous carbon and ceria nanoparticles composite (MC–CeNPs) was synthesized, and a modified electrode was fabricated. When compared with a bare glass electrode, the modified electrode exhibited enhanced electrocatalytic activity towards the simultaneous determination of hydroquinone (HQ) and catechol (CC), which is attributed to the large specific area and fast electron transfer ability of MC–CeNPs. Additionally, it exhibited linear response ranges in the concentrations of 0.5–500 µM and 0.4–320 µM for HQ and CC, with detection limits (S/N = 3) of 0.24 µM and 0.13 µM, respectively. This method also displayed good stability and reproducibility. Furthermore, the modified electrode was applied to the simultaneous determination of HQ and CC in tap and lake water samples, and it exhibited satisfactory recovery levels of 98.5–103.2% and 98–103.4% for HQ and CC, respectively. All of these results indicate that a MC–CeNPs modified electrode could be a candidate for the determination of HQ and CC.

A carbon paste electrode modified with a nickel titanate nanoceramic for simultaneous voltammetric determination of ortho- and para-hydroxybenzoic acids

An electrochemical sensor is described for the simultaneous determination of ortho-hydroxybenzoic acid (OHB) and para-hydroxybenzoic acid (PHB). The sensor consists of a carbon paste electrode modified with nickel titanate nanoceramics (NiTiO₃/CPE). The NiTiO₃ nanoceramics and the nanostructured modified CPE were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. Differential pulse voltammetry indicates that the response to OHB (best measured at 0.90 V vs. Ag/AgCl) and PHB (measured at 0.80 V vs. Ag/AgCl) is significantly improved at the modified CPE compared to a bare CPE. The limits of detection (at S/N = 3) are 0.38 and 0.10 μM for OHB and PHB, respectively. The method was applied to the determination of the two isomers in peeling skin lotion and during the Kolbe-Schmitt reaction. Graphical abstract Nickel titanate nanoceramics (NiTiO₃) were synthesized by a sol-gel method. Then, a carbon paste electrode modified with NiTiO₃ (NiTiO₃/CPE) was constructed. The modified electrode was applied to the interference-free and simultaneous determination of ortho-hydroxybenzoic acid (OHB) and para-hydroxybenzoic acid (PHB).