Calomel Electrode Research Articles

Spectroelectrochemical and ESR investigation of free radicals derived from indotricarbocyanine dyes for photodynamic therapy

Cyclic voltammetry, UV–Vis absorption spectroscopy, and electron spin resonance are applied to study the properties of indotricarbocyanine dyes and their radicals formed during electrooxidation. We use electrochemistry to generate relatively stable free radicals of the dyes under controlled conditions. The dyes undergo electrooxidation during the chronoamperometric electrolysis at 1.1 V (versus saturated calomel electrode) yielding radical dications. The radicals exhibit an absorption band that is blue-shifted relative to the parent dye (561 nm versus 714 nm). In acetonitrile solutions, the radicals are characterized by a lifetime of ca. 20 min and a g factor of 2.002. The oxidation potential of the dyes is slightly greater than that of bromide ions allowing the radicals of the dyes to interact with bromide ions. The ability of the indotricarbocyanine dyes to sensitize generation of highly reactive bromine radicals might play an important role in their photodynamic activity.

(Digital Presentation) Activated Carbon Supported Ni-Co Layered Double Hydroxides Nanowires: An Effective and Low-Cost Electrocatalyst Towards Ethanol Oxidation Reaction in Alkaline Media

Developing nanostructured architectures using non-noble, low-cost transition metals with good electrocatalytic activity and durability to replace noble electrocatalysts such as Pt and Pd have gained considerable attention in the field of sustainable and clean energy production technology. To address this, we adopted a facile synthesis route to synthesize Ni-Co layered double hydroxides (NiCo-LDH) nanowires supported on Activated Carbon (AC) via a one-pot hydrothermal synthesis method. The resulting NiCo-LDH nanowires, possessing a crystallite size of ~16.15 nm and a Surface area of 100.81 m2/g, have been utilized as a bifunctional electrocatalyst for ethanol oxidation reaction (EOR) in an alkaline medium. The electrochemical performance of the synthesized catalyst was investigated by Cyclic Voltammetry (CV), Chronoamperometry (CA), and Electrochemical Impedance Spectroscopy (EIS) techniques at room temperature. Impressively, NiCo-LDH/AC exhibited good electrocatalytic activity of 9.79 mA.cm-2 at 1.51 V vs. Saturated Calomel Electrode (SCE) and retained remarkable stability even after 200 cycles in 0.1 M NaOH with 1 M EtOH. The better electrocatalytic activity of NiCo/AC catalyst can be attributed to the presence of active sites and porous structures as well as the good electron transfer conductivity of AC. The attractive performance and facile synthesis of NiCo-LDH supported on AC highlights its potential application as an anodic material in direct ethanol fuel cells (DEFCs).

(Digital Presentation) Vanadium Intercalated Cobalt Trimesic MOF Composite for Enhanced Solid-State Asymmetric Supercapacitor Storage

Metal organic framework (MOF) is a supramolecular coordination material composed of metal ions coordination, nodes, and organic ligands. MOFs were used as active materials for chemical capacitors to realize the high electrochemical performance, providing adequate redox sites and accelerating ion diffusion rate. Using MOF as a template to fabricate a novel platform can deliver large specific surface areas and abundant oxidation-active sites to augment electrical conductivity. The electrode material based on a MOF has a unique morphology that can significantly shorten charge transport paths to alleviate the electron transport and diffusion, thus strengthening the catalytic performance of the electrode materials. Also, the incorporation of vanadium in the intermediate leads to a broad impact on the morphology and the electrochemical energy storage of Cobalt-Trimesic matrix worked as a base for fabricating the composite. The DMF is a solvent to prepare the vanadium cobalt oxide composite derived using the MOF matrix. Trimesic acid is used as an initial organic linker precursor to initiate the formation of MOF of cobalt in DMF solvent. Then the vanadium ion is integrated into the same material matrix. In this study, the impact of organic system precursors and the integration of annealing play a pivotal role in alleviating the enhanced electrochemical storage response. After analyzing through XRD, the corresponding MOF crystal peaks are prominently affirmed. The high intensified peaks in the obtained patterns symbolize the oxide phase of cobalt vanadium and confirm the formation derived from MOF. The FTIR spectroscopy investigation depicted the proper presence of cobalt, vanadium, carbon, and nitrogen. The observed FESEM morphology illustrated the dissimilar structure and involved in the charge storage likewise. The morphology significantly impacts surface-dependent charge storage with having porosity introduced. High-temperature annealing also consists of the crystal orientation of the bi-metallic MOF matrix and creates porosity on the effective surface area.The Co-MOF-V oxide composite is thoroughly investigated individually in three-electrode arrangements for analyzing the electrochemical charge storage in 2MKOH represented in Fig.1 (c-d). Firstly, the oxide is scrutinized as working positive electrodes and measured in the potential window of -0.2 to 0.6 V w.r.t the saturated calomel reference electrode. The accomplished specific capacitance value from the cyclic voltammetry plot is 549 F/g at 2mV/s scan rate. Furthermore, the charge-discharge analysis of the composite delineated an admirable discharge time at 3mA/cm2 current density. It portrayed 349 F/g specific capacitance, leading to higher specific energy and specific power of 31.02Wh/kg and 159.53W/kg at the value of the same current density. The Nyquist plot corroborates that the electrode resistance, electrode-electrolyte interfacing resistance, and the value of diffuse layer resistance are significantly less. This study can bestow a greater pathway of ion transportation from the electrolyte to active electrode material that abetted to conversate superior storage using complete morphology. The transition metal possesses a variational oxidation state that directly contributes to this MOF composite's pseudocapacitive charge storage process. Alternatively, comparable analysis is directed over anode material that is lignocellulose derived activated porous carbon. It is depicted in Fig.1(e-f) in the potential window of -1 to 0v w.r.t the Ag/AgCl electrode in 2M KOH. The gained specific capacitance from the cyclic voltammetry analysis is 426 F/g at a 2mV/s scan rate. Besides, the charge-discharge study of the same carbon depicted admirable discharge time at 0.5A/g current density and portrayed 565 F/g specific capacitance. The specific energy and power of 78.47Wh/kg and 282W/kg at the same current density. Also, the integrated porous system with the high active surface area, which significantly comes from the MOF matrix, provides an added phase to strengthen the amount of storage like EDLC formation.Furthermore, combining both of those active materials, the asymmetric supercapacitor storage is made up [Fig.1 (g-h)]. That system works upon 0 to 1.4V windows. The attained areal capacitance is 0.54 F/cm2, and volumetric capacitance is 0.68 F/cm3 in the current density of 4mA/cm2. The Ragone plot shows its perfect positioning in the region of asymmetric storage. This ASC system delineated coulombic efficiency 79% of capacitive retention 75% after the 10,000 long cycle stability study. From the electrochemical impedance spectroscopy analysis, the obtained interfacing and electrode resistance diffuse layer resistance is found significantly lesser and upwards. Figure 1

The choice of the copper concentration favoring the production of stoichiometric CuSbS2 and Cu12Sb4S13 thin films co-electrodeposited on FTO

In order to elaborate stoichiometric CuSbS 2 and Cu 12 Sb 4 S 13 (CAS) thin films by co-electrodeposition on FTO substrates, the copper concentration was varied between 0.015 M and 0.030 M at − 0.98 mV co-electrodeposition potential (vs. saturated calomel electrode (SCE)). After a sulfurization step in a quartz tube at 410 °C under an argon flow for 45 min, the samples formed are analyzed by different techniques: The XRD technique has shown the existence of characteristic peaks of the CuSbS 2 phase at 28.53, 28.79, 29.73 and 29.99° clearly for the 0.015 M concentration, but this XRD spectrum has shifted to that of Cu 12 Sb 4 S 13 phase when the copper concentration increases to 0.030 M. Likewise the Raman spectroscopy has indicated the principal peak of CuSbS 2 located at 337 cm −1 on the spectrum of the 0.015 M concentration, but this peak have disappeared for the 0.030 M concentration and was replaced by a new principal peak of Cu 12 Sb 4 S 13 at 317 cm −1 . This effect was confirmed by the UV-Visible spectrophotometry technique which shows an increase of optical gap from 1.46 eV (CuSbS 2 ) to 1.81 eV (Cu 12 Sb 4 S 13 ) when the copper concentration passes from 0.015 M to 0.030 M. The morphological study and EDS analysis have proved that the layers CuSbS 2 and Cu 12 Sb 4 S 13 were elaborated with good stoichiometry. • Stoichiometric CuSbS 2 and Cu 12 Sb 4 S 13 thin films were synthesized for the first time by co-electrodeposition in aqueous medium. • XRD and Raman analysis shows a transition from CuSbS 2 to Cu 12 Sb 4 S 13 when Cu passes from 0.015 M to 0.030 M. • An increase of the optical gap was estimated from 1.46 to 1.58 eV for CuSbS 2 and from 1.71 to 1.81 eV for Cu 12 Sb 4 S 13 .

CdS Quantum Dots as Potent Photoreductants for Organic Chemistry Enabled by Auger Processes.

Strong reducing agents (<-2.0 V vs saturated calomel electrode (SCE)) enable a wide array of useful organic chemistry, but suffer from a variety of limitations. Stoichiometric metallic reductants such as alkali metals and SmI2 are commonly employed for these reactions; however, considerations including expense, ease of use, safety, and waste generation limit the practicality of these methods. Recent approaches utilizing energy from multiple photons or electron-primed photoredox catalysis have accessed reduction potentials equivalent to Li0 and shown how this enables selective transformations of aryl chlorides via aryl radicals. However, in some cases, low stability of catalytic intermediates can limit turnover numbers. Herein, we report the ability of CdS nanocrystal quantum dots (QDs) to function as strong photoreductants and present evidence that a highly reducing electron is generated from two consecutive photoexcitations of CdS QDs with intermediate reductive quenching. Mechanistic experiments suggest that Auger recombination, a photophysical phenomenon known to occur in photoexcited anionic QDs, generates transient thermally excited electrons to enable the observed reductions. Using blue light-emitting diodes (LEDs) and sacrificial amine reductants, aryl chlorides and phosphate esters with reduction potentials up to -3.4 V vs SCE are photoreductively cleaved to afford hydrodefunctionalized or functionalized products. In contrast to small-molecule catalysts, QDs are stable under these conditions and turnover numbers up to 47 500 have been achieved. These conditions can also effect other challenging reductions, such as tosylate protecting group removal from amines, debenzylation of benzyl-protected alcohols, and reductive ring opening of cyclopropane carboxylic acid derivatives.

Photogenerated cathodic protection properties of Ag/Ag3PO4/TiO2 nanocomposites

Using immersion-deposition and photoreduction methods, high-purity Ag3PO4 and Ag nanoparticles were compounded on the surface of TiO2 nanowires. The cathodic protection effect of Ag/Ag3PO4/TiO2 nanocomposites on 304 stainless steel, as well as the morphology, composition, and optical absorption characteristics of the material were studied. When the number of impregnation-deposition cycles of Ag3PO4 was 6 and the concentration of AgNO3 in the photoreduction process was 0.1 M, the prepared Ag/Ag3PO4/TiO2 nanocomposites provided the best cathodic protection to 304 stainless steel. Relative to the saturated calomel electrode, the protection potential reached −900 mV, and the protection current reached 130 µA/cm2.

Study of Electrical Output in Photogalvanic Cell for Solar Energy Conversion and Storage: Lauryl Glucoside-Tartrazine-D-Fructose System

Objective: The present study is focusing on the role of surfactant in photogalvanic cells and how photons from sunlight can be used as a driving force for energy solar energy conversion and storage. Methods: An H shaped cell was designed for study of electrical output in solar transformations. Electrical circuit was proposed by using of dye, reductant, surfactant, NaOH, double distilled water (DDW), multi-meter, calomel electrode, 250 k roistered, saturated calomel electrode, platinum electrode, carbon pot, resistance key, digital pH meter, microammeter, and 200 W tungsten bulb. A detailed reaction mechanism for the proposed photogalvanic cell (PG Cell) for generating photocurrent and photocurrent has been studied. PG Cells were studied for the solar energy transformation system. Findings: PG Cells were studied by using different parameters via photocurrent, photopotential, conversion efficiency, fill factor and cell performance. The above values are as follows: 388.0 □A, 1141.0 mV, 0.7995%, 0.5389 and 129.0 minutes. Electrical output of the cell has also been observed for tartrazine, D-Fructose and lauryl glucoside systems. Potential at power point, Potential at open circuit, power point of cell (pp) and current at short circuit were also studied. The obtained values are as follows: 1133 mV, 1523 mV, 435.321 and 544mA. Novelty: The photogalvanic is an emerging field of research for conversion and storage of solar energy. This study employs lauryl glucoside-tartrazine-D-fructose system for better electrical output which is also an eco-friendly natural dye system. The observed results are better in cell performance (t1=2) and reduction in cost (INR 9531.38 / USD 125) of the photogalvanic cell for its commercial viability. Keywords: Photogalvanic cells; solar energy conversion; storage; lauryl glucoside; tartrazine

Electrochemical Redox Behaviors of Sulfur Mustard at Different Platinum Electrodes

A bare platinum (Pt) plate electrode, two composite Pt electrodes of Pt/polypyrrole/glassy carbon electrode (Pt/pPy/GCE) and Pt nanoparticles/CeO2 microspheres/GCE (Pt NPs/CeO2/GCE) were prepared to investigate the electrochemical redox behaviors of sulfur mustard (HD). Cyclic voltammetry (CV) measurements revealed two irreversible oxidation peaks and an irreversible reduction peak. All three Pt electrodes had two oxidation peaks at 1.02 V (vs. saturated calomel electrode (SCE)) and 1.26 V (vs. SCE), indicating the formation of bis(2-chloroethyl) sulfoxide and bis(2-chloroethyl) sulfone on all the electrode surfaces. The reduction peak at 1.16 V (vs. SCE) attributed to the cleaving of HD was observed on both Pt/pPy/GCE and Pt NPs/CeO2/GCE, but not on the bare Pt-plate electrode, which revealed that Pt/pPy and Pt NPs/CeO2 materials were more conducive for catalyzing degradation of HD. Fourier transform infrared (FT-IR) and high performance liquid chromatography-mass spectrometry (HPLC-MS) measurements were taken, which further supported the presence of sulfoxide, sulfone, hydroxyl structure, and 2,2′-sulfonyldi[ethanol]. Furthermore, this work proposes the integral redox process of HD on Pt NPs/CeO2.

N–TiO2 crystal seeds incorporated in amorphous matrix for enhanced solar hydrogen generation: Experimental & first-principles analysis

We present here a combined study on the photoelectrochemical activity of highly active Nitrogen doped titanium dioxide thin-film using experiments and First principle density (DFT) based calculation. Hybridization of N 2p with O 2p and localized valence band upshifting leads to the reduction in band-gap of N–TiO2. To validate theoretical findings, the role of nitrogen in TiO2 is revisited with a focus on partial crystallinity. The best-case photoelectrode, nanostructured partially crystalline nitrogen-doped titanium dioxide (PCNDTO) offered photocurrent density of 24.3 mA/cm2 at 1 V versus saturated calomel electrode (SCE). The absence of well-defined peaks and long-range order in XRD pattern and Raman spectrum respectively suggests partially crystallinity. High-resolution transmission electron microscopy (HR-TEM) images confirm the presence of TiO2 crystals in the amorphous matrix. High photoelectrochemical response can be attributed to the abundance of hydroxyl groups, high electrochemical active surface area, reduced charge transfer resistance, and reduced charge carrier recombination rate.

Sulfite food additive electrochemical determination by nucleophilic addition on poly(4-aminodiphenylamine)-4-aminothiophenol-Au composite electrode

Realizing reagentless selective sodium sulfite (SO32−) food-additive sensors for real-time applications is challenging. Regular SO32− additive monitoring is necessary for providing harmless food to consumers. In this study, Au nanoparticles were prepared by electrodepositing Au3+ (+0.75 V vs. saturated calomel electrode) on a glassy carbon (GC) surface. An Au/GC surface self-assembled 4-aminothiophenol (4-ATP) (denoted as 4-ATP-Au/GC). The 4-ATP head group (-SH) was chemisorbed on S-Au/GC, while tail –NH2 was functionalized using 4-aminodiphenylamine (ADPA) via a chemical/electrochemical approach. The as-prepared p-ADPA-4-ATP-Au/GC was thoroughly investigated stepwise by cyclic voltammetry traces and ex situ spectroscopy. We propose an E→CE→-mechanism-based SO32− determination: p-ADPA-4-ATP-Au/GC was electrochemically oxidized to a quinonimine unit and chemically sulfonated by the nucleophilic addition reaction by SO32−. This product was further electrochemically oxidized. The sulfonation of the polymer chains was confirmed using ex situ X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and electrochemical impedance spectroscopy. The p-ADPA-4-ATP-Au/GC composite electrode exhibited a wide linear range of SO32− detection, from 5 to 160 μM. The sensitivity and detection limit were 0.0176 μA μM−1 and 1.5 μM, respectively. Finally, the p-ADPA-4-ATP-Au/GC was used in food samples containing SO32−, which yielded a recovery in the range of 101.3–102.6%.

Controlled Growth Interface of Charge Transfer Salts of Nickel-7,7,8,8-Tetracyanoquinodimethane on Surface of Graphdiyne

Controlled Growth Interface of Charge Transfer Salts of Nickel-7,7,8,8-Tetracyanoquinodimethane on Surface of Graphdiyne

Cobalt(III) Complexes for Light-Activated Delivery of Acetylacetonate-BODIPY, Cellular Imaging, and Photodynamic Therapy.

Cobalt(III) complexes [Co(TPA)(L1)](ClO4)2 (1), [Co(4-COOH-TPA)(L1)](ClO4)2 (2), [Co(TPA)(L2)]Cl2 (3), and [Co(4-COOH-TPA)(L2)]Cl2 (4) having acetylacetonate-linked boron-dipyrromethene ligands (L1, acac-BODIPY; L2, acac-diiodo-BODIPY) were prepared and characterized, and their utility as bioimaging and phototherapeutic agents was evaluated (TPA, tris-(2-pyridylmethyl)amine; 4-COOH-TPA, 2-((bis-(2-pyridylmethyl)amino)methyl)isonicotinic acid). HL1, HL2, and complex 1 were structurally characterized by X-ray crystallography. Complexes 1 and 2 on photoactivation or in a reducing environment (excess GSH, ascorbic acid, and 3-mercaptopropionic acid) released the acac-BODIPY ligand. They exhibited strong absorbance near 501 nm (ε ∼ (5.2-5.8) × 104 M-1 cm-1) and emission bands near 513 nm (ΦF ∼ 0.13, λex = 490 nm) in dimethyl sulfoxide (DMSO). Complexes 3 and 4 with absorption maxima at ∼536 and ∼538 nm (ε ∼ (1.2-1.8) × 104 M-1 cm-1), respectively, afforded high singlet oxygen quantum yield (ΦΔ ∼ 0.79) in DMSO. Complexes 1-4 showed Co(III)-Co(II) redox responses near -0.2 V versus saturated calomel electrode (SCE) in dimethylformamide (DMF)-0.1 M tetrabutylammonium perchlorate (TBAP). The photocleavage of pUC19 DNA by complex 4 revealed the formation of both singlet oxygen and superoxide anion radicals as the reactive oxygen species (ROS). Confocal fluorescence microscopy showed the selective accumulation of complex 1 in the endoplasmic reticulum (ER) in A-549 cells. Complex 4 exhibited a high phototherapeutic index value (PI > 7000) in HeLa cancer cells (IC50 ∼ 0.007 μM in visible light of 400-700 nm, total dose ∼5 J cm-2). The ancillary ligands in the complexes demonstrated a structure-activity relationship and modulated the Co(III)-Co(II) redox potential, the complex solubility, acac-BODIPY ligand release kinetics, and phototherapeutic efficacy.

Nitrate-reducing-bacteria assisted hydrogen embrittlement of X80 steel in a near-neutral pH solution

The effect of nitrate-reducing bacteria (NRB) on the hydrogen embrittlement of X80 steel in a near-neutral pH solution was studied by various tests. NRB promote the formation of numerous pits under static load after 120 days and enlarge the polarization current at the same polarization potential. The increasing probability of hydrogen penetration into the biotic medium further leads to hydrogen embrittlement higher than 7–17% of the sterile medium. Under the same failure risk of 40%, NRB can cause hydrogen deterioration of steel, and the safe cathodic potential range will be narrowed from − 0.79–− 1.08 V to − 0.79–− 0.86 V (saturated calomel electrode).

A core-shell NiCu@NiCuOOH 3D electrode induced by surface electrochemical reconstruction for the ammonia oxidation reaction

A direct ammonia microfluidic fuel cell is a potential portable carbon-free clean energy device. In this work, a NiCu-based core-shell 3D electrode is obtained by electrodeposition and surface electrochemical reconstruction on the nickel foam substrate. The physical characterization results confirm the core-shell structure with NiCu as the core and Cu(OH)2 and NiOOH as the shell. In the 3D electrode, the metal core continuously transfers charge to the surface to transform into active species (NiCu hydroxides), thus accelerating the slow ammonia oxidation reaction kinetics. Furthermore, the 3D porous structure is conducive to the rapid diffusion and transport of ions, which effectively improves the fuel depletion boundary layer problem. Consequently, electrochemical tests indicate that the NiCu@NiCuOOH-NF electrode show excellent ammonia oxidation reaction activity and good stability, reaching a maximum current density of 90 mA cm−2 at the potential of 0.7 V vs. saturated calomel electrode (SCE). When 2 M NaOH + 3 M NH4Cl is adopted as fuel for the DAMFC, an open circuit voltage of 0.72 V and a peak power density of 17.1 mW cm−2 can be obtained, while the limiting current density is as high as 102 mA cm−2.

Nanoporous Cauliflower-like Pd-Loaded Functionalized Carbon Nanotubes as an Enzyme-Free Electrocatalyst for Glucose Sensing at Neutral pH: Mechanism Study.

In this work, we propose a novel functionalized carbon nanotube (f-CNT) supporting nanoporous cauliflower-like Pd nanostructures (PdNS) as an enzyme-free interface for glucose electrooxidation reaction (GOR) in a neutral medium (pH 7.4). The novelty resides in preparing the PdNS/f-CNT biomimetic nanocatalyst using a cost-effective and straightforward method, which consists of drop-casting well-dispersed f-CNTs over the Screen-printed carbon electrode (SPCE) surface, followed by the electrodeposition of PdNS. Several parameters affecting the morphology, structure, and catalytic properties toward the GOR of the PdNS catalyst, such as the PdCl2 precursor concentration and electrodeposition conditions, were investigated during this work. The electrochemical behavior of the PdNS/f-CNT/SPCE toward GOR was investigated through Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV), and amperometry. There was also a good correlation between the morphology, structure, and electrocatalytic activity of the PdNS electrocatalyst. Furthermore, the LSV response and potential-pH diagram for the palladium–water system have enabled the proposal for a mechanism of this GOR. The proposed mechanism would be beneficial, as the basis, to achieve the highest catalytic activity by selecting the suitable potential range. Under the optimal conditions, the PdNS/f-CNT/SPCE-based biomimetic sensor presented a wide linear range (1–41 mM) with a sensitivity of 9.3 µA cm−2 mM−1 and a detection limit of 95 µM (S/N = 3) toward glucose at a detection potential of +300 mV vs. a saturated calomel electrode. Furthermore, because of the fascinating features such as fast response, low cost, reusability, and poison-free characteristics, the as-proposed electrocatalyst could be of great interest in both detection systems (glucose sensors) and direct glucose fuel cells.

Enhanced anodic electrochemiluminescence due to efficient exchange recombination and its sensing application

To obtain semiconductor nanocrystals (NCs) with strong anodic electrochemiluminescence (ECL) remains a challenge due to their insufficiency to resist following corrosion upon holes injection to the NCs. Herein, we report strong and stable anodic ECL generated from 0.8 at% Mn2+ doped CdS NC films on indium tin oxide (ITO) electrode in the presence of coreactant triethanolamine (TEOA) under potential scan to +1.5 V vs. saturated calomel electrode (SCE), which is much more negative than the valence band potential of host NCs. The Mn2+ doping leads to an 8-fold enhancement in anodic ECL intensity in comparison with undoped CdS NC films due to efficient Mn excitation via nonradiative recombination energy transfer, i.e., exchange recombination. The efficiency is dependent on Mn2+ doping amount as well as applied potential for holes injection with the maximum obtained when the charge transfer to Mn dopants is possible and the energy gap between conduction band and applied potential matches with Mn excitation. This anodic ECL was used to detect dopamine, a model analyte, showing a wide linear range from 5 nM to 1 μM with a detection limit of 1 nM at S/N=3. This work provides a new insight into ECL generation in doped semiconductor NCs. The Mn2+ doped CdS NCs passivated by carboxylic groups display great potential in future development of biosensors.

Rapid direct cathodic voltammetric determination of insecticide flonicamid by renewable silver-amalgam film electrode

ABSTRACT The voltammetric characterisation and determination of insecticide flonicamid (N-cyanomethyl-4-(trifluoromethyl)nicotinamide) were performed for the first time using a simple electrochemical sensor, renewable silver-amalgam film electrode (Hg(Ag)FE). During the development of the direct cathodic square wave voltammetric method (SWV) for the determination of flonicamid, a voltammetric behaviour of a target analyte in aqueous Britton-Robinson buffer solution from pH 2.0 to pH 11.98 was examined. In the investigated pH range, the peak which appeared in the potential span between −0.86 V and −1.56 V vs. saturated calomel electrode depending on the applied pH value was chosen for analytical purposes. As optimal pH for the determination of flonicamid, pH 2.5 was selected. Cyclic voltammetric measurements at pH 2.5 confirmed that the electrode reaction mechanism is an irreversible reduction controlled by the diffusion of flonicamid at Hg(Ag)FE. The optimised Hg(Ag)FE-SWV method resulted in good linearity in the concentration range of 1.96–41.2 µg mL−1 while the relative standard deviation of the method was 0.30%. Flonicamid was successfully determined in commercial formulation Teppeki 500 WG® and spiked river water sample by the developed method using the standard addition procedure. The average value of flonicamid amount found in a commercial formulation based on three repetitions was 497.8 ± 0.9 g kg−1, which is in good agreement with the manufacturer’s declaration (500 ± 25 g kg−1) and with comparative high-performance liquid chromatographic measurements with diode array detection where a found average value of flonicamid content was 497.5 ± 11.5 g kg−1. The obtained results also indicate that the developed SWV procedure using Hg(Ag)FE was appropriate for the determination of flonicamid in a spiked river water sample with the recovery of 92.86% and RSD of 6.19%.

Cyclometalated Rhodium and Iridium Complexes Containing Masked Catecholates: Synthesis, Structure, Electrochemistry, and Luminescence Properties.

Two neutral cyclometalated rhodium and iridium coordination assemblies [(F2ppy)2M(η-Cat)], M = Rh, (2) and M = Ir, (3) (F2ppy: 2,4-difluorophenylpyridine), displaying a masked catecholate (η-Cat = η-O∧O) are described. The catecholate ligand is π-bonded to an organometallic Cp*Ru(II) moiety. The latter brings stability to the whole system in solution and suppresses the formation of the related paramagnetic semiquinone complex. The determination of the molecular structure of the iridium complex [(F2ppy)2Ir(η-Cat)] (3) corroborates the formation of the target compound and reveals the generation of a rare two-dimensional (2D) honeycomb supramolecular architecture in the solid state, in which the Δ-enantiomer self-assembles with the Λ-enantiomer through encoded π-π interactions among individual units. The electrochemistry of complexes 2 and 3 was investigated and showed that reduction occurs at very negative potentials (∼-2.2 V versus saturated calomel electrode (SCE)), while oxidation of the cyclometalated Rh and Ir centers occurs at 0.8 and 0.86 V. In contrast to complexes with 1,2-dioxolene chelates, which are nonemissive, the heterodinuclear diamagnetic complexes 2 and 3 were found to be emissive at room temperature both in solution and in the solid state. Moreover, at 77 K in a solid state, both compounds display opposite emission behavior, for instance, complex 3 displays a blue-shifted emission, while rhodium compound 2 exhibits red-shifted emission to lower energy.

Trinuclear Nickel Catalyst for Water Oxidation: Intramolecular Proton-Coupled Electron Transfer Triggered Trimetallic Cooperative O–O Bond Formation

Trinuclear Nickel Catalyst for Water Oxidation: Intramolecular Proton-Coupled Electron Transfer Triggered Trimetallic Cooperative O–O Bond Formation

Electroreduction of Nitrate to Ammonia on Palladium-Cobalt-Oxygen Nanowire Arrays.

Developing high-efficiency electrocatalysts for the selective reduction of nitrate to valuable ammonia is of great significance. Herein, Pd-PdO-modified Co3O4 nanowire arrays on nickel foam (PdCoO/NF) are fabricated by a facile cation-exchange reaction. Pd and PdO can facilitate the generation of adsorbed hydrogen, and abundant oxygen vacancies can promote nitrate activation. Therefore, the PdCoO/NF exhibits a superior nitrate conversion rate (89.3%), Faradaic efficiency (88.6%), and ammonium selectivity (95.3%) at -1.3 V versus a saturated calomel electrode. The source of the produced ammonia is confirmed by 15N isotope labeling experiments and 1H magnetic resonance. This presented synthetic method provides a powerful strategy for the preparation of nanowire arrays with controllable compositions for selective nitrate electroreduction to ammonia.