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A composite film of nickel hexacyanoferrate (NiHCF) and bentonite (Bt) clay (abbreviated as NiHCF−Bt) is synthesized by an in situ electrochemical method. For this synthesis, nickel ions are immobilized on Bt clay by an ion‐exchange process, equilibrating Bt clay with nickel nitrate. On a glassy carbon electrode (GCE), the nickel ion‐exchanged Bt clay (Ni2+−Bt) is coated to get the modified electrode which is represented as GCE/Ni2+−Bt. The NiHCF−Bt composite film is prepared on the GCE surface using the GCE/Ni2+−Bt and scanning the electrode potentials between −0.10 to 1.00 V continuously in an aqueous solution containing potassium hexacyanoferrate and potassium chloride. This NiHCF−Bt modified GCE (GCE/NiHCF−Bt) exhibits redox peaks due to the oxidation and reduction of the central metal ion, Fe2+. The electro‐generated Fe3+ present in the GCE/NiHCF−Bt, electrocatalytically oxidizes a range of drugs like acetaminophen (AC), dopamine (DA), and tyrosine (TY) at decreased overpotentials with high current. This property is advantageously used for the precise quantification of AC, DA, and TY. Sensitivity, limit of detection, and linear calibration range for the determination of AC are found to be 0.20 μA μM−1 cm−2, 1.5 μM, and 25.0–1000.0 μM, respectively. Further, the amount of AC present in pharmaceutical products is satisfactorily quantified which demonstrated the use of the NiHCF−Bt composite film in electroanalysis. [ABSTRACT FROM AUTHOR]

Single‐walled carbon nanotubes (SWCNTs) were immobilized on glassy carbon (GC) electrode by drop casting The resulting modified electrode (represented as GC/SWCNTs) efficiently oxidizes acetaminophen (AC), dopamine (DA) and pyridoxine (PY) by decreasing the respective oxidation potentials and increasing peak currents in comparison to bare GC electrode. The extent of lowering of overpotentials is in the order of AC>PY>DA, in agreement with the order of decrease in the HOMO‐LUMO energy gap (ΔE) of these analytes, as determined from Density Functional Theory (DFT) calculations. DFT calculations further reveal that due to the interaction of the analytes on the SWCNT(10,10) there is a negative charge density transfer (higher probability of electron transfer, lower ΔE value) to the frontier molecular orbitals of the analytes, which eases their oxidation. Since AC, DA and PY oxidize distinctly at distinct potential values, the present SWCNTs modified electrodes could be used to simultaneously determine them. Cyclic voltammetry, differential pulse voltammetry and amperometry techniques are utilized to understand the electrochemical characteristics of the analytes (AC, DA and PY) and subsequent sensing of them at the GC/SWCNTs electrode. The electrode is then applied to the determination of AC as a case study. Sensitivity, detection limit and linear calibration range for the AC are found to be 7.9 μA μM−1 cm−2, 1.1 μM and 2.0–100.0 μM, respectively. The increased electroactive surface area of the GC/SWCNTs increases the oxidation peak currents and hence increases the sensitivity of the determination. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phenosafranine immobilized –SO 3 − functionalized mesoporous silica microspheres, PSF+-MS-SO 3 − is prepared and characterized. • PSF+-MS-SO 3 − shows stable redox behavior. • PSF+-MS-SO 3 − electrocatalytically reduces Cr(VI) to Cr(III). • Highly selective and sensitive determination of Cr(VI) is achieved. • Real sample analysis was demonstrated with different water samples. This work presents an easy, highly specific, and sensitive route for the electrochemical reduction of Cr(VI) by phenosafranine (PSF+) integrated sulfonic acid functionalized mesoporous silica microspheres (MS-SO 3 −), denoted as PSF+-MS-SO 3 −. The synthesized material is characterized using various spectroscopic and microscopic methods. The glassy carbon electrode (GCE) is modified with this material (represented as GCE/PSF+-MS-SO 3 −) and employed for electroanalytical applications. The electrochemical characteristics of PSF+-MS-SO 3 − are established by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Further, it is exploited for the electrocatalytic reduction of, Cr(VI). Superior electron transfer kinetics and stable electrochemical response for Cr(VI) are observed at the GCE/PSF+-MS-SO 3 − electrode. Moreover, the quantitative estimation of Cr(VI) at the GCE/PSF+-MS-SO 3 − done using linear sweep voltammetry (LSV). Dual linear calibration ranges (1 to 20 µM and 20 to 100 µM) is obtained from the LSV response. A low limit of detection (0.5 µM) and superior sensitivity (1.1 µA µM−1 cm−2) are recognized at this electrode. In addition, significant selectivity in the existence of other interfering ions is also shown by fabricated sensing scaffold. The precise measurement of Cr(VI) in spiked water samples with simple matrix is also demonstrated successfully with sufficient durability and reproducibility. [ABSTRACT FROM AUTHOR]

Layered double hydroxides (LDHs) have recently attracted intense research attention because of their applications in the development of highly active and cost-effective electrocatalysts for the oxygen evolution reaction and in the fields of drug delivery, energy storage, for example. In this work, we report a cheap and simple route for the synthesis of nickel-iron LDH (Ni−Fe LDH) using an iron-based metal−organic framework, Fe-MIL-88 as a template. The prepared Ni−Fe LDH is characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and X-ray diffraction techniques. Ni−Fe LDH is found to be highly active and stable for water oxidation in alkaline solution as compared to commercial Pt/C. The concept of using a metal−organic framework as a structure-directing agent to synthesize Ni−Fe LDH and the use of the material for the oxygen evolution reaction is explored for the first time. [ABSTRACT FROM AUTHOR]

This work reports the individual as well as simultaneous determination of ascorbic acid (AA) and uric acid (UA) by glassy carbon electrode (GCE) modified with a nanocomposite film of gold nanoparticles (Au NPs) inclusively adhered to MCM-41 type mesoporous silica spheres (Au-MSS). The impregnation of Au NPs into mesoporous silica spheres (MSS) is well established by surface characterization and electrochemical techniques. The Au-MSS modified GCE (GCE/Au-MSS) exhibits stable redox peaks, characteristics of Au NPs. Further, GCE/Au-MSS shows effective electrocatalytic oxidation of both AA and UA diminishing the overpotentials by 580 and 405 mV, respectively, than at bare GCE. Similarly, GCE/Au-MSS diminishes the oxidation overpotentials of AA and UA by 200 and 210 mV, respectively, relative to GCE/MSS. Differential pulse voltammetry technique is employed for the simultaneous determination of AA and UA in the presence of one another. The limit of detection is found to be 1.65 μM and 2.14 μM for AA and UA, respectively. The kinetic parameters like diffusion coefficient and the catalytic rate constant for the AA and UA electro-oxidations have been computed using chronoamperometric techniques. High sensitivity is displayed by the modified electrode and has been successfully employed for the analysis of UA in human blood serum. [ABSTRACT FROM AUTHOR]

Abstract This study demonstrates the hydrothermal synthesis of cobalt oxide (Co 3 O 4) nanocrystals on reduced graphene oxide (rGO) which is further utilized to construct an electrochemical sensing scaffold for precise determination of chloramphenicol (CP). CP is an antibiotic used for the treatment of typhoid fever and infections including salmonellosis. Due to its antibacterial property, low cost and availability it was extensively used in the fields of agriculture, but its presence in animal derived food products create detrimental effects on consumers. Therefore it is important to monitor the level of CP in different food products. The formation of Co 3 O 4 on rGO (Co 3 O 4 @rGO) is characterized with FT-IR, XRD, TEM and SEM techniques. The working electrode is fabricated by drop coating the catalyst (0.1% Co 3 O 4 @rGO in DMF) on glassy carbon (GC) electrode (symbolized as GC/Co 3 O 4 @rGO) and further used for electrochemical sensing of CP with cyclic voltammetry (CV), amperometry and differential pulse voltammetry (DPV) techniques. The calibration curve for the determination of CP through CV shows a linear range from 1 to 2000 μM with two different slopes. Sensitivity of the CP determination and limit of detection (LOD) are calculated to be 1.32 μA μM cm−2 and 0.55 μM, respectively. Further the sensing scaffold, GC/Co 3 O 4 @rGO is successfully applied for the CP determination present in real samples like milk products. Graphical abstract Unlabelled Image Highlights • Cobalt oxide decorated reduced grapheme oxide sheets (Co 3 O 4 @rGO) are synthesized. • Co 3 O 4 @rGO electrocatalytically reduces chloramphenicol (CP). • Sensitive determination of CP is achieved (Sensitivity: 1.32 μA μM cm−2 and limit of detection: 0.55 μM) using the Co 3 O 4 @rGO. • CP present in real samples are satisfactorily determined using Co 3 O 4 @rGO. [ABSTRACT FROM AUTHOR]

Abstract Efficient, durable and low cost electrocatalysts for O 2 and CO 2 reductions are required as alternate to expensive metal based catalysts in fuel cells and in the CO 2 reduction process. Herein, we describe the synthesis of reduced graphene oxide (rGO)-nickel phthalocyanine (NiPc) composite (rGO-NiPc) as a bifunctional electrocatalyst for O 2 and CO 2 reductions. The composite material, rGO-NiPc is coated on glassy carbon (GC) electrode (GC/rGO-NiPc) and used as a low cost efficient electrocatalyst for O 2 and CO 2 reductions. The results show that the addition of rGO to NiPc increases the catalytic efficiency and electrochemical charge transfer rate of NiPc. GC/rGO-NiPc provides the low potentials, +0.25 and −0.11 V (vs RHE) for O 2 and CO 2 reductions, respectively in 0.1 M HClO 4. Kinetic interpretation based on rotating disc electrode studies provides the support for the two electron pathway for CO 2 reduction to CO in 0.1 M HClO 4. Product analysis by 13C NMR confirms CO as the CO 2 reduction product. GC/rGO-NiPc shows a facile four electron pathway for O 2 reduction which can be exploited in fuel cells, metal-air batteries, chlor-alkali electrolyzers and oxygen sensing. In addition, GC/rGO-NiPc has efficient methanol tolerance capability for O 2 reduction process which is suitable to use in fuel cells. Moreover, GC/rGO-NiPc shows the high operational stability more than an hour for both O 2 and CO 2 reductions in 0.1 M HClO 4. Graphical abstract Unlabelled Image Highlights • Reduced graphene oxide (rGO)-nickel phthalocyanine (NiPc) composite (rGO-NiPc) is prepared. • Synergistic electrocatalysis is observed between rGO and NiPc. • rGO-NiPc enhances O 2 and CO 2 reductions at low overpotential. • rGO-NiPc exhibits 4 and 2 electron pathway for O 2 and CO 2 reductions, respectively. • CO 2 is selectively reduced to CO which is confirmed by 13C NMR. [ABSTRACT FROM AUTHOR]

Highlights: [•] An electrochemical sensing platform based on new anion exchange polymer is constructed. [•] Ion exchange voltammetry and electrocatalysis are used for ascorbic acid (AA) determination. [•] Kinetic parameters of electrocatalytic oxidation of AA are evaluated. [•] Low detection limit with moderate sensitivity is achieved for AA determination. [Copyright &y& Elsevier]

A nanocomposite of Mn(salen)Cl (where salen is N , N ′-bis(salicylidene)ethylenediamine) and multiwalled carbon nanotubes (MWCNTs) is prepared. The advantageous properties of MWCNTs and catalytic properties of Mn(salen)Cl (represented as Mn III salen) are combined in this new nanocomposite (represented as MWCNTs-Mn III salen). Several techniques including electrochemical ones are used for the characterization of the MWCNTs-Mn III salen nanostructure. After complete characterization it is utilized for simultaneous determination of vitamin B 2 (riboflavin) and B 6 (pyridoxine) using differential pulse voltammetry (DPV). MWCNTs-Mn III salen coated on glassy carbon electrode (GC), represented as GC/MWCNTs-Mn III salen exhibits high sensitivity and low detection limit. This electrode demonstrates high reproducibility (R.S.D. = 3.7% and 3.4% for vitamin B 2 and B 6, respectively) and long storage stability (more than 10 days under normal room temperature condition). Methodologies for the analysis of vitamins B 2 and B 6 using GC/MWCNTs-Mn III salen in pharmaceutical formulations using simple electrochemical techniques are elucidated. [ABSTRACT FROM AUTHOR]

Classical Metal-Organic Frameworks (MOFs), although able to accumulate chemicals from solution, are usually electrochemically “inactive”. Here, it is demonstrated for the zinc-containing MOF-5(Zn) (and MOF-5W(Zn)) system, that silver incorporation (Ag@MOF-5(Zn), prepared via a solvothermal process) can be used to assist/promote release and electrochemical oxidation of accumulated nitrophenols (2-methyl-4-nitrophenol, 4-nitrophenol, and 2-nitrophenol). Nitrophenols belong to a group of compounds that are present in diesel exhaust and considered harmful pollutants. The enhanced electrochemical detection of nitrophenols at a glassy carbon electrode modified with Ag@MOF-5(Zn) is suggested to be due to analyte accumulation with estimated Langmuirian binding constants of 40 × 10 3 M −1 (for 2-methyl-4-nitrophenol and 4-nitrophenol) and 15 × 10 3 M −1 (for 2-nitrophenol) and electrochemical detection/conversion with a current enhancement of more than one order of magnitude due to potential driven release from Ag@MOF-5(Zn). Surface characterization and electrochemical techniques suggest that silver is present in Ag@MOF-5(Zn) in metallic form and probably also embedded into the framework. This silver incorporation changes the electrochemical oxidation behavior towards nitrophenols in MOF-5(Zn) from “inactive” to “active”. The new class of metal@MOF materials is highlighted as practical nano-composites. [ABSTRACT FROM AUTHOR]

An electrochemical sensing platform which comprises gold nanoparticles (Au NPs) incorporated zinc based metal-organic framework (MOF-5) is developed for the sensitive determination of nitrite and nitrobenzene. MOF-5 and Au NPs incorporated MOF-5 (Au-MOF-5) are synthesized and characterized by UV-vis absorption, powder X-ray diffraction, FT-IR, scanning electron microscopy with energy dispersive X-ray analysis and elemental mapping, transmission electron microscopy and atomic force microscopy. Oxidation of nitrite is effectively electrocatalyzed at Au-MOF-5 with significant increase in oxidation current (41 and 38% in comparison with bare glassy carbon (GC) and MOF-5 coated GC (GC/MOF-5) electrodes, respectively) and with considerable decrease in the oxidation potential (0. 17 and 0.25 V in comparison with bare GC and GC/MOF-5 electrodes, respectively). The electrocatalytic reduction of nitrobenzene at GC/Au-MOF-5 is confirmed by an appreciable increase in the reduction current (79 and 36% in comparison with bare GC and GC/MOF-5 electrodes, respectively) and a small shift in the reduction potential (20 mV in comparison with GC/MOF-5). The detection limit is calculated as 1.0 μM with a sensitivity of 0.23 μAμM −1 cm −2 for nitrite and 15.3 μM with a sensitivity of 0.43 μAμM −1 cm −2 for nitrobenzene determinations. The Au-MOF-5 based electrochemical sensing platform shows high stability and selectivity even in the presence of several interferences (including phenols, inorganic ions and biologically important molecules) with a broad calibration range. Certain kinetic parameters of nitrite oxidation and nitrobenzene reduction have also been studied by hydrodynamic voltammetry. [ABSTRACT FROM AUTHOR]