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• The N, S dual-doped rGO was obtained via hydrothermal route with ammonium sulphate. • The symmetric NSGO cell delivered an energy density of 65 Wh Kg-1 in KI-HQ/1 M H 2 SO 4. • Enhanced energy density was observed for the dual redox additives. • The NSGO modified GCE used as sensor for the detection of DNP, DNT, HQ and RC. • Simultaneous and selective detection of HQ and RC was achieved via SWV technique. The dual application-based scenario in electrochemistry has gained substantial reliability and benefits across various domains. In this study, N, S dual-doped graphene (NSGO) was synthesized via hydrothermal method and utilized for supercapacitor and electrochemical sensing applications. For electrochemical sensing, the NSGO-modified glassy carbon electrode (NSGO/GCE) was used to detect 2,4-dinitrophenol (DNP), 2,4-dinitrotoluene (DNT), hydroquinone (HQ) and resorcinol (RC). The NSGO/GCE demonstrated enhanced sensing performance with low detection limits of 16 nM (DNP), 12 nM (DNT), 0.1 µM (HQ) and 0.08 µM (RC) in a linear dynamic range from 0.1 µM to 60.0 µM (DNP, DNT) and 1.0 µM to 500.0 µM (HQ, RC). The NSGO/GCE sensor exhibited excellent reproducibility and stability, with its practical utility validated through real water sample testing. In supercapacitor applications, the NSGO electrode achieved an impressive gravimetric capacitance of 373 F g-1 in 1 M H 2 SO 4 solution at 0.5 A g-1. Symmetric supercapacitor analyses demonstrated that the NSGO cell in 0.01 M KI-0.01 HQ/1 M H 2 SO 4 achieved an enhanced energy density of 65 Wh Kg-1 at 4 A g-1, which is three times superior to 0.01 M HQ/1 M H 2 SO 4 (21.7 Wh Kg-1). [Display omitted] [ABSTRACT FROM AUTHOR]

A novel implementation of an electrochemical sensors making use of Screen-Printed Electrodes (SPE) has been discussed. SPE's modified with Carbon-supported Platinum (Pt/C) and Gold (Au/C) were used to detect the three benzenediol isomers, Catechol (CC), Hydroquinone (HQ) and Resorcinol (RS) in acidic media using traditional electrochemical analytical methods such as Cyclic Voltammetry (CV), Chronoamperometry (CA) and Differential Pulse Voltammetry (DPV). Detection of each benzenediol in isolation was possible by CV measurements, and peak oxidation potentials for each isomer were noted. Simultaneous detection of more than one, or all analytes in the same solution was also observed through DPV, once again noting the peak oxidation potentials. Quantification limits were observed using CA's across concentration values ranging from close to saturation down to 1 mM for CC and HQ, and 100 nM for RS, until the recorded current values were nearly indistinguishable to a blank 1 M HCl solution containing no analyte(s), and also evaluating the maximum possible linear range of sensing. The analytes were introduced to the sensor elements in controlled amounts and the electrochemical responses of the sensor elements were recorded and processed. Measurements were repeated across two potentiostats to ensure reproducibility. With these results, successful detection of benzenediols in acidic environment was possible using modified SPE's, proving a potential viable mechanism for quick, simple and inexpensive Volatile Toxic Organic Compounds (VTOC) detection and monitoring. [ABSTRACT FROM AUTHOR]

• Cresyl violet electropolymerized in neutralized ternary deep eutectic solvent (DES). • Ternary DES comprised of choline chloride, ethylene glycol and acetic acid. • Formation of anthraquinone groups during electropolymerization on carbon nanotubes. • Electrochemical, microscopic and impedance evaluation of polymerization conditions. • Sensor applied to determination of hydroquinone in dermatological cream. The phenazine dye cresyl violet (CVio) has been evaluated as precursor for the preparation of a new electrochemical sensor based on poly(cresyl violet) deposited on multiwalled carbon nanotube (CNT) modified glassy carbon electrodes (GCE) in neutralized acid-doped ternary deep eutectic solvents (DES). DES with choline chloride as hydrogen bond acceptor and with different hydrogen bond donors (HBD), namely acetic acid, ethylene glycol and oxalic acid were evaluated for CVio electropolymerization by potential cycling. The best polymer films were obtained in ternary DES with the two HBD acetic acid plus ethylene glycol doped with H 2 SO 4 and followed by NaOH neutralization. Electrochemical characterization (voltammetric and electrochemical impedance) showed the formation of anthraquinone groups during electropolymerization, which is initiated on the CNT by the formation of a cation radical. Anthraquinones in the polymer film led to an increased response at the modified electrode for the determination of hydroquinone (H 2 Q) with low LOD (0.25 µmol L−1) in a broad linear range (1–80 µmol L−1), with good reproducibility, repeatability, and stability. The sensor was successfully applied to the quantification of H 2 Q in dermatological creams with no matrix effect towards hydroquinone response. [Display omitted] [ABSTRACT FROM AUTHOR]

A simple and efficient electrochemical sensing platform for simultaneous detection of hydroquinone (HQ), catechol (CC) and resorcinol (RC) based on in-situ prepared sodium hydroxide (NaOH) nanorods was reported for the first time. Sodium hydroxide (NaOH) nanorods on glassy carbon electrode (GCE) was synthesized via one electrochemical deposition step in NaOH solution using constant current. The affecting factors including content of NaOH solution, deposition current and deposition time were investigated. The obtained electrodes were also examined by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The electrochemical behaviour analysis and dynamic study indicated that the three dihydroxybenzene isomers can be catalytically oxidized and discriminated simultaneously on the proposed electrode. Using square wave voltammetry (SWV), the ultrasensitive and simultaneous detection of HQ, CC and RC was realized with wide linear range from 0.03 to 1500 μM and low detection limit of 0.01, 0.01, 0.09 μM, respectively. The detection of them in real water samples was also successfully performed and good recovery was obtained. Image 102308 • Simultaneous detection of HQ, CC and RC was realized based on NaOH nanorods/GCE. • The nano-NaOH/GCE was synthesized via electrochemical deposition for seconds. • The effect of deposition current, time and content of NaOH solution were investigated. • The LODs of HQ, CC and RC were much lower than previous reports. • The detection in real water samples was successfully performed. [ABSTRACT FROM AUTHOR]

We propose electronic structure modeling, in accordance with the Gerischer conceptualization, to explain the electrochemical response of the benzoquinone/hydroquinone (BQ/HQ) redox couple on gold and glassy carbon (GC) electrodes. Specifically, coupling differed to gold compared to GC; this is of interest because BQ/HQ are representative of a promising class of molecules used in redox flow batteries (RFBs). We calculated the energy difference between the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO), Fermi levels ( E F ), and density of states (DOS) of the electrode materials via density functional theory in periodic systems. The Au (111) surface was considered for gold modeling, whereas graphite and graphene were used for GC. We compared these results with experimental data to explain the differences in the reversible behavior of the BQ/HQ couple in both electrode materials, setting the pH, electrolyte composition, and electrode geometry equal in both electrodes. The loss of reversibility in GC can be attributed to the anodic branch of the cyclic voltammetry response, which is consistent with the larger energetic distance found for the HQ–HOMO from the E F of the electrode compared to BQ–LUMO. In contrast, the energetic distances in gold are similar in both cases and agree with the symmetry of the experimental current–potential response for both the anodic and cathodic branch. To validate the model, we calculated the total DOS and projected DOS for different quinone molecules—such as 2,5-dichloro-1,4-benzoquinone, 2-hydroxy-1,4-naphthoquinone, and 1,2,4-trihydroxynaphtalene—adsorbed on gold and GC. The experimental findings support our hypothesis. Additionally, graphite and graphene models equivalently described GC electrodes; both models showed a similar trend in adsorption energy for quinone molecules [due to van der Waals (VDW) interactions], DOS, and partial charge density. For the gold electrode, we found a similar trend in adsorption energy to the graphite and graphene, also attributable to VDW interactions. Our results indicate that theoretical modeling can explain electrochemical principles which underpin quinone-based energy storage systems and RFBs. [ABSTRACT FROM AUTHOR]

Illustrating the roles of electron withdrawing/donating groups upon the capacitive behaviors of p -hydroquinone (PHQ) can benefit for achieving superior supercapacitors. In present work, sulfonic acid and methoxyl group are adopted as electron withdrawing group (EWG) and electron donating group (EDG), respectively, that is, the substances of 2,5-dihydroxybenzenesulfonate (DHBS) and 2-methoxyhydroquinone (MHQ). It is revealed that PHQ, DHBS and MHQ can serve as effective redox additives in H 2 SO 4 electrolyte, and two-proton/two-electron redox reactions occur at the electrode-electrolyte interface. DHBS exerts higher faradaic effect than that of MHQ, implying the EWG is more active than the EDG when adhered to PHQ. Furthermore, from the point of kinetics, all the relevant redox processes are limited by semi-infinite diffusion. And high energy density of 15.6 Wh kg −1 is obtained towards the DHBS sample with concentration of 2 mmol L −1 when measured in 1 mol L −1  H 2 SO 4 . The present work would favors for understanding other supercapacitor systems possessing electron withdrawing/donating groups. [ABSTRACT FROM AUTHOR]

In this paper, we developed a direct way for the study of hydroquinone oxidation through in situ electrochemistry-combined nuclear magnetic resonance (EC-NMR). Electro-polymerization-induced nano-polyaniline film was utilized as the catalyst in the process of electrochemical oxidation of hydroquinone. In situ EC-NMR provides a powerful tool to probe products distribution and reaction rate, which could be useful to investigate electro-catalytic mechanism and evaluate the electro-catalytic capacity. To study the influence of both protic and aprotic media in the electrocatalytic process, we mixed water and dimethylsulfoxide to mimic possible real-life electrochemical environments. The proposed in situ EC-NMR is capable of quantitatively monitoring the generation of products under varied solvent composition and pH values. A positive effect to electro-catalysis capacity is observed when the concentration of DMSO or water is increased from the volume equivalent point, implying that there should be a competition between protic and aprotic media, which can be characterized by EC-NMR technique. [ABSTRACT FROM AUTHOR]

The electrochemistry, optical properties, wettability and morphology of polydopamine (PDA) thin films were extensively studied on carbon electrodes, in order to evaluate their potential to be used as electrochemical biosensor interfaces. To fulfil this purpose, several PDA films with different thicknesses were allowed to grow spontaneously and their electrochemical stability and coverage of active quinone/hydroquinone groups were assessed by cyclic voltammetry. Ellipsometry was used to evaluate the dielectric properties of PDA, and film thickness increase with the deposition time on glassy carbon electrodes. Atomic Force Microscopy corroborates film thickness and revealed the formation of uniform coatings for all dopamine incubation times. PDA wettability validates the presence of hydrophilic quinone/hydroquinone. Electrochemical and optical characterization of the modified electrodes points to the formation of a poorly conducting polymeric matrix, yet allowing the charge transfer process of electroactive probes, for 3 ± 1 nm thick films, proving their applicability as electrochemical transducers. The catalytic activity of immobilized Glucose Oxidase or Laccase on graphite/PDA electrodes were validated against glucose and 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), respectively. The analytical parameters are particularly promising for Laccase modified electrodes towards ABTS detection, undoubtedly proving the biocompatibility and excellent electrochemical transduction of thin polydopamine films. [ABSTRACT FROM AUTHOR]

• Oxidation of gallic acid (GA) on gold electrode is examined in a broad pH range. • Oxidation mechanism of GA based on bi-cubic scheme is proposed. • pKa value of the final ortho-quinone product is experimentally determined. • Spectroelectrochemical studies identify the different intermediates and the products. • The kinetics of gallic acid redox process involves a disproportionation reaction. A clear understanding of redox mechanism of antioxidants, like gallic acid (GA) is important to decipher their radical scavenging functioning in the biochemical environment of the body. Herein, electrooxidation process of GA is reexamined in an aqueous medium through a combination of cyclic voltammetric and spectroelectrochemical studies on gold electrode in wide pH and concentration ranges. These studies reveal redox process of GA as an irreversible two electrons process, resulting in the formation of ortho-quinone, where the second electron transfer is the rate limiting step. The redox process of GA at different pH is presented in the form of a bicubic scheme and the associated thermodynamic parameters are analyzed using Laviron's theory. It allows for the first time the determination of the acidity constant of the corresponding ortho-quinone (pK a = 5.33). The number of exchanged electrons and protons depends on the pH conditions, such that (2e−, 2H+) are exchanged at pH < 4.24 and pH > 5.33, while (2e−, 1H+) are exchanged at 4.24 ≤ pH ≤ 5.33. A careful analysis using the theoretical treatment proposed by Amatore and Saveant for an ECE-DISP mechanism demonstrates the existence of a DISP2 mechanism leading to the formation of ortho-quinone through disproportionation of the semiquinone radicals, made possible thanks to their stabilization. [Display omitted] [ABSTRACT FROM AUTHOR]

To distribute gold nanoparticles uniformly into porous biochar, a facile pyrolysis approach was developed. Dracaena sanderiana was first soaked in an aqueous solution of HAuCl 4 as a precursor and then pyrolysed under a nitrogen atmosphere at high temperatures. The morphologies, structures, and properties of the gold nanoparticle-decorated biochar (Au-NPs/BC) nanocomposites were characterized by various electron microscopy, spectroscopic, and electrochemical methods. As-synthesized Au-NPs/BC nanocomposites possessed high porosities, large specific surface areas, and excellent electrical conductivities. Moreover, the preparative strategy was facile and cost-effective. Further, the potential applications of these Au-NPs/BC nanocomposites for electrochemical sensing of hydroquinone and catechol were explored. Sensitive and simultaneous determination of hydroquinone and catechol was realized with very low detection limits (in the nanomolar range) and high sensitivities. [ABSTRACT FROM AUTHOR]

The effect of electron donating tendency on the oxidative behavior of hydroquinone (HQ) on glassy carbon electrode (GCE) at room temperature was studied by means of cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV) techniques in aqueous acetonitrile solution. The oxidation potential of HQ shifted to increasingly more negative direction as electron donating tendency increased due to the presence of electron donating substituent's in the benzene ring of hydroquinone moiety. The study was further extended to observe their oxidative behavior with pH. The results showed that an easy oxidation of hydroquinone compounds with the rise in pH. In order to get a proper insight into to an oxidative behavior, the DFT quantum chemical calculation was performed for all hydroquinone molecules at the B3LYP level and by using 6–311++(d, p) basis set. The calculated quantum chemical and molecular reactivity parameters from optimized structures were good agreement with experimental findings. [ABSTRACT FROM AUTHOR]

Hybrid of metal oxide and graphene quantum dots may pave one way to improve their electronic, chemical and electrochemical properties. The paper reports one new strategy for synthesis of Co 3 O 4 -histidine-functionalized graphene quantum dots (Co 3 O 4 -His-GQD). Here, His-GQDs are combined with Co 2+ ions to rapidly produce Co-His-GQD complex. Followed by the thermal annealing at 350 °C in air to form Co 3 O 4 -His-GQD. The resulting nanohybrid offers a well-defined three-dimensional architecture with the rich of porous structures. The regulation of His-GQDs on the release rate of Co 2+ ions during the oxidation process of Co 2+ make the formed Co 3 O 4 crystals have a small particle size of about 22 nm. The in situ synthesis of Co 3 O 4 on the surface of graphene sheets achieves to the intimate chemical and electrical contacts of Co 3 O 4 with His-GQDs. This creates a fast energy and electron transfer between Co 3 O 4 and His-GQDs in the nanohybrid. The sensor based on the Co 3 O 4 -His-GQD exhibits an ultrahigh electrochemical response towards hydroquinone. Its differential pulse voltammetric peak current linearly increases with increasing hydroquinone in the range of 2 × 10 −9 –8.0 × 10 −4 M with the detection limit 8.2 × 10 −10 M (S/N = 3). The sensitivity is better than that of both His-GQDs sensor and Co 3 O 4 sensor. The analytical method provides the advantage of sensitivity, selectivity and stability, it has been successfully applied in the determination of hydroquinone in environmental water samples. The study also provides a promising approach for fabrication of functional graphene quantum dot-based electrode materials with high-performance for sensing, electrocatalysis, supercapacitors and lithium ion batteries. [ABSTRACT FROM AUTHOR]

We report a novel sensing platform for biosensor and pseudocapacitor application based on electron beam (EB) irradiated polypyrrole/cerium-nickel@modified guar gum (EB-PPy/Ce-Ni@MGG) nanobiocomposite. The EB irradiated PPy nanospheres (NSs) and Ce-Ni bimetallic NSs prepared are functionalized into the amine MGG matrix film for the improvisation of energy storage as well as charge transfer mechanism. MGG film also found to be an effective conducting material in composite formation like reduced graphene oxide (r-GO) with excellent electrocatalytic activity. The nanobiocomposite was confirmed by SEM, EDAX, XRD, Raman and FT-IR analysis. Interestingly, the EB-PPy/Ce-Ni@MGG modified glassy carbon electrode exhibited an excellent electrocatalytic activity towards the simultaneous sensing of hydroquinone, catechol, resorcinol and nitrite with lower detection limits as 87 nM, 84 nM, 518 nM and 786 nM. Furthermore, EB-PPy/Ce-Ni@MGG modified Ni foam electrode was evaluated in 1 M NaOH by cyclic voltammetry and galvanostatic charge-discharge methods for pseudocapacitor application. The Ce-Ni bimetal NSs in the EB-PPy@MGG shows a significant improvisation of specific capacitance to 605 Fg −1 at a current density of 1 Ag −1 . The optimized electrolyte concentration, current density, scan rate and cycle stability shows promising results to low cost energy storage with wearable power device fabrication. [ABSTRACT FROM AUTHOR]

A simple and efficient eletrochemical sensing platform for simultaneous detection of hydroquinone (HQ), catechol (CC) and resorcinol (RC) based on the Au-Pd bimetallic and graphene is described in this paper. The Au-Pd reduced graphene oxide (Au-Pd NF/rGO) was prepared by the electrochemical co-reduction deposition via cyclic voltammetry method (CV). The Au-Pd NF/rGO nanocomposite was examined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and electrochemical methods CV and differential pulse voltammety (DPV) study showed that the three dihydroxybenzene isomers can be catalytically oxidized and discriminated simultaneously on the Au-Pd NF/rGO/GCE. The presence of Pd makes the performance of the sensor superior to that of in the absence of it. Owing to the integrated superior conductivity and excellent catalytic property of Au-Pd NF/rGO, the sensitive and simultaneous detection of HQ, CC and RC was realized in the individual or triple-components solution based on the as proposed Au-Pd NF/rGO/GCE, which shows wide linear range and low detection limit. The detection of them in tap water, river water and lake water were also successfully performed and good recovery was obtained. [ABSTRACT FROM AUTHOR]

• MnO 2 /GQDs nanocomposite presents enzyme-like properties suitable for sensing. • Phenolic compounds (PC) were detected by electrochemical and colorimetric methods. • Electrochemical detection presented higher sensitivity for catechol and dopamine. • River water tests prove the material's potential for detecting PCs in the environment. Phenolic compounds (PCs) have been widely employed in industrial activities and have also been found at threatening levels in natural environments, posing risks to human health and the environment. As a consequence, there is an increasing demand for the development of simple and sensitive detection methods of such pollutants. In this work, we report the use of manganese dioxide and graphene quantum dot (MnO 2 /GQD) composites as a dual-functional sensing platform for the electrochemical and colorimetric detection of catechol (CC) and dopamine (DA), two important PCs. Regarding the electrochemical detection, differential pulse voltammetry showed a linear relationship between current signal intensity and concentration of DA and CC over the linear ranges of 0.5–100 μM and 5–150 μM, with limits of detection of 0.05 µM and 0.09 µM for DA and CC, respectively. In addition, the composite was employed for the colorimetric detection of CC and DA through the oxidase mimic activity of the MnO 2 /GQD in the presence of 3,5,3,5-tetramethylbenzidine (TMB). Analysis in real samples showed that the MnO 2 /GQD composite can be used for the sensitive detection of CC and DA in river samples. The high surface area and improved electrochemical properties of the MnO 2 /GQD were demonstrated to be beneficial for dual sensing applications of phenolic compounds. [ABSTRACT FROM AUTHOR]

In this work, a sensitive and reliable electrochemical platform was developed for catechol (CC) and hydroquinone (HQ) individual and sensitive simultaneous detection. Due to the outstanding advantages of low cost, excellent flexibility, large surface area, and good conductivity, an exfoliated graphite paper (EGP) was used as a supported electrode for gold nanoparticles (AuNPs) electrodeposition to fabricate a sensor (AuNPs/EGP). Scanning electron microscope and cyclic voltammetry results revealed that AuNPs/EGP was successfully prepared with multi-layered structure and enhanced electron transfer ability. Under the optimized conditions, the sensor showed wide linear range for CC and HQ detection of 5.0 × 10 −7 - 1.0 × 10 −4 mol/L and 7.0 × 10 −8 - 1.0 × 10 −4 mol/L with limitation of detection (S/N = 3) of 4.13 × 10 −8 mol/L and 2.73 × 10 −8 mol/L, respectively. And the proposed sensing platform was successfully applied to the simultaneous determination of CC and HQ in real samples of three kinds of water with reliable recovery. The low cost, facile preparation, and attractive electrochemical performances made the graphite paper based sensor promise perspectives in the field of electroanalysis. [ABSTRACT FROM AUTHOR]

This work reports the electrochemical determination of bisphenol A (BPA), hydroquinone (HQ) and catechol (CC) using glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNT) and nickel oxide nanoparticles (NiO). MWCNT were functionalized with sulfonitric solution (3H 2 SO 4 :1HNO 3 ) and dispersed in dimethylformamide for the MWCNT/GCE manufacturing. The MWCNT/GCE was modified with NiO using cyclic potential in pH 4 maintained by an acetate buffer solution containing 0.008 mol L −1 of nickel nitrate. The concentration of the nickel solution and the number of cycles in the electrodeposition were studied. Morphological characterization of NiO/MWCNT/GCE was carried out by scanning electron microscopy and the presence of NiO was observed. The electrochemical behavior was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy using BPA solution and the results were compared with those of GCE. The NiO/MWCNT/GCE presented the lowest charge transfer resistance. The electrochemical detection of BPA, HQ and CC was developed using differential pulse voltammetry. The analytical curves showed an excellent linear response and the detection limits for the simultaneous determination of BPA, HQ and CC were 2.8 × 10 −8 mol L −1 , 2.70 × 10 −8 mol L −1 and 5.9 × 10 −8 mol L −1 , respectively. [ABSTRACT FROM AUTHOR]

The long DNA concatemers have been well developed to fabricate various biosensing platforms for the signal amplification. Herein, this signal amplification strategy was firstly used for an ultrasensitive scanning electrochemical microscopy (SECM)-based DNA biosensing platform. This platform was constructed through the hybridization of target DNA (TD) with thiol-tethered DNA capture probes (CP), immobilized on the gold substrate surface, and biotinylated DNA signal probes (SP), which formed then the long DNA concatemers through the continuous self-assembly with alternating DNA auxiliary probes (AP). The streptavidin-horseradish peroxidase (HRP) was linked to the long DNA concatemers through biotin-streptavidin interaction. In the HRP-catalyzed reaction, hydroquinone (H 2 Q) was oxidized to benzoquinone (BQ) with H 2 O 2 at the modified substrate surface where sequence-specific hybridization had occurred, and the BQ generated could be monitored by a SECM tip. This platform exhibited a low detection limit of 0.18 aM estimated by the 3σ rule. Combined with DNA microarrays, four kinds of TDs (100 fM) as the models were detected simultaneously by using this proposed strategy, which also demonstrated sufficient selectivity to distinguish specific DNA sequences and good reproducibility. This method opens a promising direction to improve the SECM sensitivity for high-throughput DNA detection. [ABSTRACT FROM AUTHOR]

An electrostatic self-assembly strategy for the preparation of graphene quantum dots (GQDs) attached to the surface of a glassy carbon electrode (GCE) has been developed. The GQDs were prepared by tuning the carbonization degree of citric acid and characterized by atomic force microscopy, transmission electron microscopy, Raman spectroscopy and UV–vis absorption spectroscopy. In addition, the electrochemical behaviours of hydroquinone (HQ) and catechol (CC) on the resulting modified electrodes were investigated. Under optimum conditions, the as-prepared GQDs modified electrode exhibited high electrochemical activity and good selectivity for the oxidation of HQ and CC, the linear ranges for HQ and CC were 4.0∼600 μM and 6.0∼400 μM respectively, and the detection limit was 0.40 μM and 0.75 μM, respectively. The modified electrode was also applied for the detection of real samples with satisfactory results. [ABSTRACT FROM AUTHOR]

• Poly(neutral red) film was formed on a porous graphene modified electrode. • The modified electrode was applied to determine hydroquinone. • The electrochemical sensor was sensitive, fast, simple and accurate. • Hydroquinone was reliably determined in skin whitening creams. In this work, a glassy carbon electrode was modified with poly(neutral red)/porous graphene (PNR/P-Gr/GCE). The electrode was developed for use in an electrochemical sensor to determine hydroquinone (HQ) in skin whitening creams. The electrode was prepared by drop casting P-Gr on the GCE surface, followed by electro-polymerization of neutral red in deep eutectic solvent (DES) without an acid dopant. The fabrication of the electrode was optimized and then characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The electrochemical properties of the electrode were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The PNR/P-Gr/GCE was used to determine HQ by adsorptive stripping differential pulse voltammetry (AdSDPV). Under optimal detection conditions, the electrode was 2 and 5 times more sensitive toward HQ than a P-Gr/GCE and an unmodified electrode, respectively. The developed electrode determined HQ concentrations from 0.005 to 70 µg mL−1 and exhibited a detection limit of 1.7 ng mL−1. The preparation of the electrode showed good repeatability (RSDs between 2.19 and 3.83%, n = 15), reproducibility (RSD < 1.87%, n = 6), and anti-interference properties. The proposed method successfully quantified HQ in skin whitening creams with recoveries between 89 ± 2 and 105.1 ± 0.2%. There was no significant difference at a 95% confidence level between the results obtained using the proposed method and those from UV-derivative spectrophotometry. This electrode presents a promising approach to HQ determination in skin whitening creams. [Display omitted] [ABSTRACT FROM AUTHOR]

Rocking disc electrode voltammetry (RoDE) is introduced as an experimentally convenient and versatile alternative to rotating disc voltammetry. A 1.6 mm diameter disc electrode is employed with an overall rocking angle of θ = 90 degree applied over a frequency range of 0.83 Hz to 25 Hz. For a set of known aqueous redox systems (the oxidation of Fe(CN) 6 4− in 1 M KCl , the reduction of Ru(NH 3 ) 6 3+ in 0.1 M KCl , the oxidation of hydroquinone in 0.1 M pH 7 phosphate buffer, the oxidation of I − in 0.125 M H 2 SO 4 , and the reduction of H + in 1 M KCl) the mass transport controlled limiting current I lim is demonstrated to follow in good approximation the Levich-type expression I lim = 0.111   n F A c D 2 / 3 v − 1 / 6 Θ f with n , the number of electrons transferred per molecule diffusing to the electrode surface, F , the Faraday constant, A , the geometric area, c , the concentration of the active redox species, D , the diffusion coefficient, v , the kinematic viscosity, θ is the overall rocking angle in degree, and f , the rocking rate in Hz. Quantitative theory is developed based on a two-dimensional (2D) axisymmetric laminar flow model accounting for the conservation of mass, momentum and species along with the kinematic analysis of a “four-bar mechanism” to obtain the rocking motion. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of 1,4-benzoquinone in acetonitrile in the presence of hydroquinone as a hydrogen bonding proton donor was studied. Different association modes and mechanistic regimes were found depending on the hydroquinone concentration. At stoichiometric concentrations, the formation of a dianionic quinhydrone linked by two-equivalent strong hydrogen bonds, was found. At higher concentrations of hydroquinone, the structure of this complex changes to another in which the monoprotonated quinone dianion is stabilized by interaction with hydroquinone and the supporting electrolyte cation. This complex is adsorbed on the glassy carbon electrode during its formation and the amount deposited is influenced by the concentration and size of the electrolyte cations. However, by further increasing of the hydroquinone concentration, the complex adsorption is totally inhibited and the cyclic voltammetry behaviour becomes reversible with the transfer of two-electrons. [ABSTRACT FROM AUTHOR]

Catechol (1,2-dihydroxybenzene) and hydroquinone (1,4-dihydroxybenzene) are two isomers of phenolic compounds which often coexist and interfere with each other during their identification in environmental samples. This study presents simultaneous determination of catechol (CC) and hydroquinone (HQ) using a new electrochemical sensor based on Fe 3 O 4 functionalized graphene oxide-gold nanoparticle composite (AuNPs/Fe 3 O 4 -APTES-GO). CV results show well-defined oxidation peaks with anodic peaks at 0.15 V for CC and 0.05 V for HQ, and the peak-to-peak separation for CC and HQ is about 100 mV. Under the optimized conditions, the current response of AuNPs/Fe 3 O 4 -APTES-GO/GCE is linear for CC and HQ in the range of 2-145 μM and 3-137 μM, respectively. The detection limits for CC and HQ were found to be 0.8 μM and 1.1 μM, respectively. The fabricated sensor was successfully applied for the determination of CC and HQ in tap water sample with satisfactory recovery. [ABSTRACT FROM AUTHOR]

This article reports a composite electrode of Fe 2 O 3 nanoparticles/SWCNTs for hydroquinone electrochemical sensing. The synthesis includes the wet-chemical synthesis of Fe 3 O 4 nanoparticles and the assembly of Fe 3 O 4 nanoparticles onto single walled carbon nanotubes. Fe 3 O 4 /NH 2 -CNTs composite is formed via the electrostatic attraction between positively-charged ammonia-terminated CNTs and negatively-charged Fe 3 O 4 nanoparticles. Subsequent heat treatment oxidizes Fe 3 O 4 to Fe 2 O 3 . The composite can be applied onto FTO glass to form Fe 2 O 3 /CNTs/FTO electrode and the electrode shows good performance in electrochemical sensing of hydroquinone as compared to Fe 2 O 3 /FTO and CNTs/FTO electrodes. SEM and TEM results show the iron oxide NPs were uniformly dispersed onto the surface of SWCNTs. The iron oxide NPs which uniformly anchored on the SWCNTs could accelerate the electron transfer rate which was evidenced by electrochemical impedance spectroscopy. The enhancement of electrochemical response further confirms the synergy between Fe 2 O 3 NPs and SWCNTs. Differential pulse voltammetry was successfully used to quantify hydroquinone within the concentration range of 1.0∼80.0 μM under optimal conditions. The detection limit of Fe 2 O 3 /CNTs/FTO electrode for hydroquinone was 0.50 μM (S/N = 3). The electrode was further applied to test for hydroquinone in tap water and the Fe 2 O 3 /CNTs/FTO electrode also presents good stability and high reproducibility, proofing the potential of Fe 2 O 3 /CNTs electrode as a promising electrochemical sensor. This work presents an electrode using FTO substrate for the first time. It shows that FTO can be a potential alternative to glassy carbon electrode with lower cost, but without compromising too much on the sensitivity. [ABSTRACT FROM AUTHOR]

In this paper, three-dimensional (3D) graphitic carbon nitride nanosheets-carbon nanotube (CNNS-CNT) composite was synthesized via hydrothermal reaction of 2D CNNS and 1D CNT-COOH by π-π stacking and electrostatic interactions. This CNNS-CNT composite was characterized by transmission electron microscope, scanning electron microscope, x-ray diffraction and fourier-transform infrared. In addition, the CNNS-CNT composite displayed excellent conductivity comparing with CNNS and CNT-COOH monomer. This composite was applied for electrochemical simultaneous determination of catechol (CC) and hydroquinone (HQ) with good sensitivity, wide linear range and low detection limit. In addition, this CNNS-CNT composite modified electrode was also applied to detect practical samples with satisfactory results. [ABSTRACT FROM AUTHOR]

The electrochemical activity of functionalized multi-walled carbon nanotubes (MWCNTs) of different sizes (D × L: 100–170 nm × 5–9 μm and 6–9 nm × 5 μm, corresponding to LD- and SD-MWCNTs, respectively) towards the electro-oxidation of hydroquinone (HQ), tert -butylhydroquinone (TBHQ), catechol (CT), and dopamine (DP) was investigated. The electrochemical response for all phenolic compounds at MWCNT-modified glassy-carbon electrodes (GCEs) presented a short decrease in the overpotential of the oxidation reactions (<100 mV); however, the values of ΔE p (peak-to-peak separation) were considerably reduced at the LD-MWCNT surface and even more at the SD-MWCNT-modified GCE in comparison with the unmodified GCE. This result indicates the higher electrocatalytic activity of SD-MWCNTs, which is in agreement with the nanotube diameter and the increased defect density, as revealed by XRD and Raman spectroscopic measurements, respectively. Additionally, a substantial increase (three-fold) in the current for the oxidation of HQ, TBHQ, and DP at the SD-MWCNT-modified GCE was obtained. Amperometric measurements also revealed the improved performance of SD-MWCNT-modified GCE (up to four-fold increase in sensitivity). [ABSTRACT FROM AUTHOR]

This work presents the simultaneous determination of catechol (CC) and hydroquinone (HQ), employing a modified glassy carbon electrode with tetraruthenated oxovanadium (IV) porphyrin. The GCE was modified by electropolymerization of {VOTPyP[RuCl 3 (dppb)] 4 } porphyrin, onto the GCE surface, by cyclic voltammetry. The modified electrode, labeled as VOTPRu-GCE, showed two pairs of well-defined redox peaks for the electrochemical processes of catechol and hydroquinone. In bare GCE, the potential difference (ΔE p ) of CC and HQ were 469 mV and 457 mV, respectively, while with VOTPRu-GCE the potential difference decreased to 29 mV and 30 mV, indicating that the redox processes were reversible onto the VOTPRu-GCE surface. With differential pulse voltammetry, it was possible to simultaneously determine the CC and HQ, with peak-to-peak potential separation of 129 mV, in 0.1 mol L −1 acetate buffer (pH 4.75). Under the optimized conditions, the calibration curves were obtained in the linear concentration ranges of 2–38 μmol L −1 for both isomers using the VOTPRu-GCE, which showed high sensitivity in the determination of CC and HQ, 12.73 and 15.91 μA μmol L −1 cm −2 , respectively. The detection limits were 0.41 and 0.55 μmol L −1 for CC and HQ, respectively. [ABSTRACT FROM AUTHOR]

This study used cyclic voltammetry (CV) and scanning tunneling microscopy (STM) to address the adsorption and oxidative polymerization of aniline on Au(111) electrode in sulfuric acids containing three isomers of benzenediol (BOH) - hydroquinone (HQ), catechol (CA), and resorcinol (RS). Molecular-resolution STM revealed highly ordered aniline adlattices of Au(111) – (√19 × √21) at 0.7 V (versus reversible hydrogen electrode) with all BOHs, compared with the (3 × 2√3) structure found without BOHs. Aniline molecules in the (√19 × √21) structure were adsorbed in the zigzagged chains along the <121> direction of Au(111), which caused an anisotropic oxidative polymerization reaction that produced linear PAN molecules. BOHs slowed down polymerization of aniline on Au(111), and the effect increased in the order of CA < HQ < RS, due to their interactions with aniline molecules and their solubility in sulfuric acid. The corresponding reduction process of oxidized CA molecules at E > 0.8 V was eliminated by reacting with aniline molecules. Although BOHs all interacted with the PAN, they were not incorporated in the PAN films. PAN film supported by Au(111) resulted in 2 and 1.2 times higher currents of HQ and CA than those found with bare Au(111). [ABSTRACT FROM AUTHOR]

Quasi-solid-state supercapacitors were assembled using a pair of activated carbon electrodes and two polyvinyl alcohol (PVA)-H 2 SO 4 gel polymer electrolytes (GPEs) containing respectively redox additives of hydroquinone (HQ) and methylene blue (MB), which were separated by a Nafion 117 membrane in a sandwich-type configuration. PVA-H 2 SO 4 -HQ and PVA-H 2 SO 4 -MB GPEs worked on the sides of the positive and negative electrodes of the supercapacitor, respectively. The electrochemical performances of the supercapacitor with optimized PVA-H 2 SO 4 -HQ and PVA-H 2 SO 4 -MB GPEs were evaluated by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy techniques. After the introduction of HQ and MB, the supercapacitor with PVA-H 2 SO 4 -HQ|PVA-H 2 SO 4 -MB GPEs can exhibit high specific capacitance of 563.7 F g −1 and energy density of 18.7 Wh Kg −1 , increasing by about fourfold in comparison with a supercapacitor with a PVA-H 2 SO 4 GPE. The improved energy storage is ascribed to the reversible Faradaic reactions related to HQ and MB in the corresponding gel polymer electrolytes. Additionally, the supercapacitor shows excellent cyclic durability with 90.0% capacitance retention after 3000 cycles. [ABSTRACT FROM AUTHOR]

Newly developed flow-through coulometric detector with renewable working material of glassy carbon microbeads was fabricated and its basic electrochemical parameters were studied by flow injection analysis using potassium ferrocyanide and hydroquinone as probes. Main advantage of the detector is its simple construction while maintaining good electrochemical parameters and high conversion degree. Practical application of the detector was proved by the development of new HPLC and FIA method of thymol and sulfamethizole determination in pharmaceutical preparations. Optimal determination conditions were found and calibration dependences were measured. A value of quantification limit 0.97 μmol L −1 for thymol and 0.040 μmol L −1 for sulfamethizole were obtained. Newly developed methods were used for determination of the studied compounds in pharmaceutical preparations. HPLC with spectrophotometric detection was used as a comparative method; results from both methods were in good agreement. [ABSTRACT FROM AUTHOR]

• Pristine, binder-free, self-stabilized dispersion polymerised polyaniline-based supercapacitor exhibits high gravimetric specific capacitance of 437.5 F g−1 in H2SO4/hydroquinone redox electrolyte. • High areal capacitance of 875.6 mF cm−2 at 1 mA cm−2. • Exceptional cycling stability of 98.3 % even after 8500 charge-discharge cycles for a pristine conducting polymer-based supercapacitor. Lightweight, high-performance supercapacitors are in great demand in applications including hybrid electric vehicles and wearable electronics. Electrode materials play a very decisive role in determining the electrochemical performance as well as the mass of the supercapacitor. Electronically conducting polymers based pseudocapacitors have commanded much interest in the quest for the realisation of flexible, lightweight devices with high specific capacitance. Reports on the use of pristine polyaniline (PANI) electrodes for supercapacitors are rare due to their low cycling stability. Here, we report the synthesis of pristine crystalline PANI by self-stabilised dispersion polymerisation (SSDP) and its use as electrodes for supercapacitors using a redox-active electrolyte. The SSDP PANI electrode exhibits a gravimetric capacitance of 437.8 F g−1 at a current density of 0.5 A g−1 in the H 2 SO 4 -hydroquinone electrolyte. The pristine PANI supercapacitor exhibits a capacitance retention of 98.3 % even after continuous 8500 charge-discharge cycles performed at a current density of 5 A g−1. The incredibly high areal capacitance of 875.6 mF cm−2 at 1 mA cm−2 and long cycling stability observed in these lightweight pristine polymer supercapacitors can be used to power up wearable integrated devices. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, an excellent electrochemical sensor based on Nafion/multi-walled carbon nanotubes/carbon dots/multi-walled carbon nanotubes (Nafion/MWCNTs/CDs/MWCNTs) for simultaneous determination of hydroquinone (HQ), catechol (CC) and resorcinol (RS) in 0.1 M phosphate buffer solutions (PBS, pH = 7.0) was found. The functioned MWCNTs, which contained amido bond, were combined to CDs via the electrostatic interaction to build the Nafion/MWCNTs/CDs/MWCNTs modified electrode. As we know, MWCNTs have large specific surface area and CDs have electrical conductivity, which were benefited to build the composite modified electrode. The three dihydroxybenzene isomers could well separate from each other at the scan rate of 100 mV s −1 with a potential difference of 119 mV and 419 mV for the oxidation peak potentials of HQ–CC and CC–RS, respectively. Differential pulse voltammetry (DPV) was used for the simultaneous determination of HQ, CC and RS in their ternary mixture. The peak current obtained was linearly dependent on the HQ, CC and RS concentrations in the range of 1.0 to 200.0 μM, 4.0 to 200.0 μM and 3.0 to 400.0 μM and the detection limits for HQ, CC and RS were 0.07 μM, 0.06 μM and 0.15 μM (S/N = 3), respectively. The modified electrode was applied to detect the tap water, well water and river water and the recoveries of tap water, well water and river water samples were 100.3–109.8% for HQ, 96.0–105.8% for CC and 83.4–101.6% for RS, respectively. [ABSTRACT FROM AUTHOR]

The electrochemical behavior of pillar[5]arene (P[5]A) and of its reaction products with Ag + and Cu 2+ ions has been investigated using cyclic voltammetry, optical methods and transmission electron microscopy (TEM). Stepwise oxidation of hydroquinone units of P[5]A molecule is guided by self-assembling and acid-base interactions. From one to three hydroquinone units per P[5]A molecule are oxidized depending on the measurement conditions. The deposition of P[5]A on glassy carbon electrode (GCE) partially blocks the electron transduction. Interfering influence of dissolved oxygen can be partially eliminated by the use of carbon black as immobilization matrix. The reaction of P[5]A with silver ions results in formation of most stable form with three benzoquinone and two hydroquinone units stabilized by quinhydrone-like structure. The Ag nanoparticles formed in the reaction retain electron transduction with the electrode due to involvement of shielding P[5]A molecules. Similar reaction with Cu 2+ ions does not lead to stable products because of the formation of Cu 2 O particles detected by UV spectroscopy and TEM. Possible analytical applications of the materials obtained were proved by electrocatalytic reduction of hydrogen peroxide and mediated oxidation of thiocholine as model systems. In both cases, high sensitivity and wide range of the concentration determined were shown. [ABSTRACT FROM AUTHOR]

Electrochemical syntheses of 2-indolyl-5-arylsulfonyl- p -benzoquinone derivatives were carried out in two successive oxidation steps. The first involves the oxidation of hydroquinone, 4-(piperazin-1-yl) phenol) and 1-(4-(4-hydroxyphenyl) piperazin-1-yl) ethanone in the presence of arylsulfinic acids as nucleophiles. Our voltammetric data indicate that electrochemically generated p -benzoquinone participates in Michael addition reaction with arylsulfinic acids leading to the 2-(arylsulfonyl) benzene-1,4-diols. The second consists of the oxidation of 2-(arylsulfonyl) benzene-1,4-diols in the presence of 1,2-dimethylindole and the formation of 2-indolyl-5-arylsulfonyl- p -benzoquinone derivatives as the final products. A plausible mechanism for the synthesis of 2-indolyl-5-arylsulfonyl- p -benzoquinone derivatives is also presented. [ABSTRACT FROM AUTHOR]

Enzyme amplification is most commonly used to develop electrochemical affinity biosensors. However, single amplification by enzyme labels is not sufficient for detecting an ultra-low analyte concentration. Moreover, some of enzymatic products, such as thiocholine and hydroquinone (HQ), show poor electrochemical signals and/or are unstable in air for long incubation periods. In this work, we reported two “outer-sphere to inner-sphere” electrochemical-chemical-chemical (ECC) redox cycling reactions triggered by thiocholine and HQ. By examining the effect of different redox mediators and reductants, we found that ferrocenecarboxylic acid (FcA) and tris(2-carboxyethyl)phosphine (TCEP) were the optimal redox mediator and reductant, respectively. In the redox cycling, FcA was regenerated by thiocholine or HQ after its electro-oxidization; thiocholine or HQ was also then regenerated by TCEP after its oxidation, thus enhancing the anodic current of FcA. To demonstrate the applications and analytical merits of the two redox cycling reactions in biosensing, thrombin was tested in a “sandwich” format with acetylcholinesterase (AChE) and alkaline phosphatase (ALP) as the enzyme labels. The detection limits were determined to be 5 ng L −1 and 0.5 ng L −1 with the thiocholine- and HQ-triggered redox cycling, respectively. The results will be valuable for developing enzyme-amplified electrochemical affinity biosensors. [ABSTRACT FROM AUTHOR]

A green, fast and facile approach for the preparation of graphene is proposed for constructing an electrochemical sensing platform. The fabricated platform is applied for the simultaneous determination of hydroquinone (HQ) and catechol (CC) based on laser reduced graphene (LRG) which is prepared by a consumer-grade laser pen (< $10). Scanning electron microscopy (SEM), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), Raman spectrum and X-ray diffraction (XRD) confirm that the synthesis of LRG could be achieved through a simple and efficient way without any chemical reducing agents and without time consuming process. The performance of LRG modified electrode shows the excellent electrocatalytic activity of LRG toward the redox reaction of HQ and CC. Under the optimized condition, the calibration curves for HQ and CC were obtained in the range of 1 to 300μM, 2 to 300μM, with detection limits (S/N=3) of 0.5μM and 0.8μM, respectively. Therefore, our study may provide a promising sensing platform for a variety of electroanalysis applications. [ABSTRACT FROM AUTHOR]

In the present work, the electrochemical properties of single-walled carbon nanotube buckypapers (BPs) were examined in terms of carbon nanotubes nature and preparation conditions. The performance of the different free-standing single wall carbon nanotube sheets was evaluated via cyclic voltammetry of several redox probes in aqueous electrolyte. Significant differences are observed in the electron transfer kinetics of the buckypaper-modified electrodes for both the outer- and inner-sphere redox systems. These differences can be ascribed to the nature of the carbon nanotubes (nanotube diameter, chirality and aspect ratio), surface oxidation degree and type of functionalities. In the case of dopamine, ferrocene/ferrocenium, and quinone/hydroquinone redox systems the voltammetric response should be thought as a complex contribution of different tips and sidewall domains which act as mediators for the electron transfer between the adsorbate species and the molecules in solution. In the other redox systems only nanotube ends are active sites for the electron transfer. It is also interesting to point out that a higher electroactive surface area not always lead to an improvement in the electron transfer rate of various redox systems. In addition, the current densities produced by the redox reactions studied here are high enough to ensure a proper electrochemical signal, which enables the use of BPs in sensing devices. [ABSTRACT FROM AUTHOR]

Highlights: [•] Facile and electrodeposition of Pt nanoparticles decorated on the surface of electrochemically reduced graphene oxide -ZrO2 composite modified electrode has been prepared. [•] High sensitive simultaneous determination of hydroquinone and catechol was demonstrated. [•] The proposed method can be used in research assays and environmental diagnosis. [•] Sufficient enough peak separation around 120mV−1 for hydroquinone and catechol in waste water samples. [•] The modified electrode showed good stability, reproducibility, sensitivity and wide linear range. [ABSTRACT FROM AUTHOR]

Abstract: In order to achieve high specific capacitance of polyaniline/SnO2 (PANI/SnO2) supercapacitors, utilizing hydroquinone (HQ) as redox electrolyte for PANI/SnO2 supercapacitors was reported. In this redox electrolyte, the specific capacitance was heightened by 356 F g−1, reaching 857 F g−1 with a specific energy density of 116.6 Wh kg−1 at an applied current of 0.5 A g−1. Long-term cycling experiments performed showed good stability with retention of the initial capacitance values of 81.2% after 2000 galvanostatic cycles. The remarkable results presented here illustrate that the HQ redox electrolyte was a facile and straight forward approach to improve the performances of PANI/SnO2 supercapacitors. [Copyright &y& Elsevier]

We could successfully fabricate a new composite of La 2 O 3 nanoparticles@snowflake-like Cu 2 S nanostructure (La 2 O 3 NP@SF-L Cu 2 S NS composite) for simultaneous detection of hydroquinone (HQ), catechol (CT), and resorcinol (RS). Field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscope (EDX) and X-ray diffraction (XRD) were used to characterize the constructed La 2 O 3 NP@SF-L Cu 2 S NS composites. The presence of HQ, CT and RS was simultaneously detected on the surface of modified La 2 O 3 NP@SF-L Cu 2 S NS composites because of unique properties such as large surface area, high electrical conductivity and potent catalytic activity, with the appearance of three distinctive peaks. Moreover, differential pulse voltammetric (DPV), chronoamperometry (CHA) and cyclic voltammetric (CV) were also employed to determine the electrocatalytic profile of CT, HQ and RS on electrode modified with the nanocomposite (La 2 O 3 NP@SF-L Cu 2 S NS/GCE). There was a significant elevation in the HQ, CT and RS oxidation currents when compared to those on both bare and modified electrodes. The peak of the catalytic current was directly variable based on the concentrations of HQ, CT and RS (0.66 to 266.6 μM), respectively. Further, the limit of detection (LOD) was calculated to be 0.056 μM, 0.058 μM and 0.059 μM for all HQ, CT and RS, respectively. Acceptable outcomes were achieved for the applicability of La 2 O 3 NP@SF-L Cu 2 S NS/GCE in detecting HQ, CT and RS present in real specimens. [ABSTRACT FROM AUTHOR]

Rational design of carbon nanomaterials with high adsorption capability and remarkable catalytic activity is essential to achieve high-performance sensors. In this paper, supramolecular hydrogels cross-linking of Ni2+, chitosan (CS) and multi-walled carbon nanotubes (MWCNT) are prepared and used as the precursors to produce nanocomposites composed of core-shell structures and carbon aerogels (denoted as NCA CNT /Ni) by facile pyrolysis. Due to the anchoring of abundant functional groups on the CS chains and the spatial confinement of MWCNTs, the N-doped carbon shells encapsulating Ni nanoclusters with the small size of ca. 4 nm uniformly distribute in the carbon aerogels. On one hand, the N atoms on the shell accepting electrons from Ni cores can easily adsorb hydroquinone and catechol (HQ and CT) by hydrogen bonding to enhance the local molecular concentration; on the other hand, the highly active NiN x sites can enhance the oxide current response signal. The high adsorption capability and remarkable catalytic activity endow the NCA CNT /Ni with high performance towards qualitative and quantitative determination of HQ and CT with a linear range from 2 to 100 μM and respective limit of detection (LODs) of 0.36 μM (3σ/k) and 0.41 μM (3σ/k). This work paves a new pathway for the rational design and engineering of carbon nanomaterials for electrochemical sensors and environmental analyses. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: By combining introducing functional groups on the surface of carbon nanotubes (CNTs) with adding redox-active molecules—hydroquinone (HQ) into 1M H2SO4 aqueous electrolyte, CNTs’ specific capacitance has been significantly improved. After being treated by alkali and mixed acid, CNTs show higher specific surface area and appropriate pore size distribution, resulting in higher specific capacitance. In H2SO4 electrolyte, a specific capacitance of 85Fg−1 is achieved for those CNTs treated in alkali and mixed acid (CNTs–T), much higher than that of raw CNTs (only 28Fg−1). Furthermore, by introducing redox-active molecules—HQ into H2SO4 electrolytes, CNTs–T electrode presents a specific capacitance as high as 3199Fg−1 at 5mVs−1 in 0.075M HQ+H2SO4 electrolyte, about 38 times as large as that obtained in H2SO4 electrolyte. In addition, HQ's concentration affects the electrochemical performance of CNTs–T electrode. High HQ concentration results in the aggregration of free ions and charges, and therefore a slow diffusion of ions and charges and relative poor electrochemical performance. For CNTs–T electrode, the optimum concentration of HQ is 0.075M. In such electrolyte, CNTs–T displays a stable specific capacitance of about 2250Fg−1 at 5mVs−1 after 350 cycles. [Copyright &y& Elsevier]

Abstract: Phenol was studied as a model pollutant for treatment by adsorption and electrochemical regeneration using a graphite intercalation compound (GIC) adsorbent in an air agitated sequential batch reactor. The mechanism of electrochemical regeneration is important in determining the fate of the adsorbed species. The effect of a range of operating parameters including current density, pH, electrolyte addition, and the initial concentration of phenol on the formation of the intermediate oxidation products was investigated. The main breakdown products detected were benzoquinone and chlorinated organics (chloride was present as an electrolyte in the cathode compartment), with small amounts of hydroquinone, catechol, and carboxylic acids detected under some conditions. The effect of current density on the formation of breakdown products during electrochemical regeneration was found to be similar to effects reported in the literature for the electrochemical oxidation of a phenol solution. In contrast to acidic pH, very low concentrations of benzoquinone were observed during electrochemical regeneration of GIC adsorbent under neutral and alkaline conditions. The results obtained with high initial phenol concentration (100mgL−1) suggested that breakdown products could be formed either by oxidation of adsorbed phenol or indirect oxidation of phenol in solution. Comparison of experiments carried out with different amounts of adsorbed and dissolved phenol suggested that the intermediate oxidation products obtained was formed largely due to indirect electrochemical oxidation of organics in solution. In particular, it was found that the chlorinated organics detected in solution were generated from the indirect oxidation of phenol in solution. [Copyright &y& Elsevier]

Highlights: [•] Ionic liquid was used as a novel carbon source to synthesize mesoporous carbon. [•] A stabilized film of GMC/BMIMPF6 composite can be formed on the electrode surface. [•] Two couples of redox peaks for HQ and CC were observed on GMC/BMIMPF6/GC electrode. [ABSTRACT FROM AUTHOR]

Abstract: A facile and reliable method is applied to prepare the electrolyte based on hydroquinone (HQ)/benzoquinone (BQ) redox couple for dye-sensitized solar cells (DSSCs) in open environment by adding moderate amount of acetic acid (HAc), and the best conversion efficiency (η) of 5.82% is achieved under 100mWcm−2 (AM 1.5G) illumination. Electrochemistry properties of DSSCs using such redox couple are measured and the results show a higher current and better charge transfer in contrast to I −/I 3 −. And a slightly higher efficiency of 5.88% is obtained when HQ and BQ are symmetrically substituted by two methyls. With advantages of high efficiency, compatible with the most common dye N719 and easily tuned by facile structural modification, the redox shuttle employing HQ/BQ via HAc treatment is very promising to be employed in efficient DSSCs. [Copyright &y& Elsevier]