Preparation of nickel oxide and carbon nanosheet array and its application in glucose sensing

Nickel oxide and carbon (NiO/C) nanosheet array was fabricated on Ti foil for the first time by calcining the precursor, which was synthesized through the hydrothermal reaction of nickel acetate, urea and glucose. The slow release of OH⁻ by the hydrolysis of urea aided in the direct nucleation and adhesion of precursor seeds on Ti substrate. The presence of carbon ensured a large specific surface area and good conductivity of the final NiO/C composite. The prepared NiO/C nanosheet array exhibited higher catalytic oxidation activity of glucose compared with the pure NiO nanosheet at a detection limit of 2 μM, linear range up to 2.6 mM (R²=0.99961), and sensitivity of 582.6 μAm M⁻¹ cm⁻². With good analytical performance, simple preparation and low cost, this composite is promising for nonenzymatic glucose sensing.     

The Role of Substitutional Defects in Order/Disorder Phenomena of OH− Ions in Hydroxyapatite

We report on density functional quantum mechanical calculations of hydroxyapatite. The central focus is dedicated to the local arrangement of hydroxide ions in proximity of defects originating from substituting OH^? by F^? or O^2? ions. At ambient conditions the preferred structure of bulk hydroxyapatite exhibits an ordering of OH^? ions oriented in rows along the [001] direction. From zero Kelvin geometry optimizations the orientation inversion of a hydroxide ion was found to be disfavored by 0.165 eV. This picture changes dramatically when replacing one of the OH^? ions by a fluoride ion. The preferred hydroxide ion arrangement next to the F^? defect was identified as an OH^?··F^?··HO^? constellation, which implies the orientation inversion of one of the neighboring hydroxide ions. An analogous phenomenon was observed for O^2? defects.     

Performance study of palladium modified platinum anode in direct ethanol fuel cells: A green power source

The direct ethanol fuel cell is a green and renewable power source alternative to fossil fuels and produces less emissions compared to a combustion engine. Ethanol can be generated in great quantity from renewable resources like biomass through a fermentation process. Bio-generated ethanol is thus attractive fuel since growing crops for biofuels absorbs much of the carbon dioxide emitted into the atmosphere from the oxidation of ethanol. The platinum and palladium were co-deposited on graphite substrate by the galvanostatic technique and employed as anode catalyst for ethanol electrooxidation. The information on surface morphology, structural characteristics and bulk composition of the catalyst was obtained using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) spectroscopy. The cyclic voltammetry (CV) were used for the estimation of the electrochemically active surface area (ECSA) of the synthesized catalysts in alkaline medium. The CVs for ethanol oxidation revealed superior catalytic activity of Pt–Pd/C compared to Pd/C and Pt/C. The effect of OH^? on ethanol oxidation at Pt–Pd/C catalyst was studied using cyclic voltammetry, quasisteady-state polarization, chronoamperometry, and electrochemical impedance spectroscopy (EIS). The Pt–Pd/C catalyst shows good stability and enhanced electrocatalytic activity is ascribed to the synergistic effect of higher electrochemical surface area, preferred OH^? adsorption on the surface and palladium ad-atom contribution on the alloyed surface.     

A Novel Bioelectrochemical Sensor Based on Immobilized Urease on the Surface of Nickel Oxide Nanoparticle and Polypyrrole Composite Modified Pt Electrode

Nickel oxide nanoparticle (NiO?NP) and polypyrrole (PPy) composite were deposited on a Pt electrode for fabrication of a urea biosensor. To develop the sensor, a thin film of PPy?NiO composite was deposited on a Pt substrate that serves as a matrix for the immobilization of enzyme. Urease was immobilized on the surface of Pt/PPy?NiO by a physical adsorption. The response of the fabricated electrode (Pt/PPy?NiO/Urs) towards urea was analyzed by chronoamperometry and cyclic voltammetry (CV) techniques. Electrochemical response of the bio‐electrode was significantly enhanced. This is due to electron transfer between Ni²⁺ and Ni³⁺ as the electro‐catalytic group and the reaction between polypyrrole and the urease‐liberated ammonium. The fabricated electrode showed reliable and demonstrated perfectly linear response (0.7–26.7 mM of urea concentration, R²= 0.993), with high sensitivity (0.153 mA mM^?1 cm^?2), low detection of limit (1.6 μM), long stability (10 weeks), and low response time (～5 s). The developed biosensor was highly selective and obtained data were repeatable and reproduced using PPy‐NiO composite loaded with immobilized urease as urea biosensors.     

Urea Assisted Synthesis of Flower Like CuO Nanostructures and Their Chemical Sensing Application for the Determination of Cadmium Ions

The novel nanostructures of CuO with improved morphology are strongly required for the development of devices with enhanced performance. In this study flower like nanostructures of CuO are synthesized by hydrothermal method using urea as tuning material for the morphology of CuO during the growth process. Scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques were used for the characterization of these nanostructures. The nanostructures are highly dense, uniform and well aligned on the gold coated glass substrate. Moreover, CuO nanostructures exhibited pure phase of CuO. These novel CuO nanostructures were potentially used for the construction of cadmium ion sensor by functionalizing with tetrathia‐12‐crown‐4 a selective cadmium ion ionophore. The proposed cadmium ion sensor has detected the wide range of cadmium ion concentrations from 1.0×10^?9–1.0×10^?1 M with a sensitivity of 29.3±0.3 mV/decade and also a fast response time of less than 10.0 s is demonstrated. CuO nanostructures based cadmium ion selective electrode has also shown excellent reproducibility, repeatability, selectivity, and stability. The sensor electrode was also used as indicator electrode for the confirmation of practical utility and the obtained result describes the good behavior of the sensor in the potentiometric titration for the determination of cadmium ions.     

Unsupported palladium nanoparticles for ethanol cyclic voltammetric sensing in alkaline media

Carbon-supported palladium nanostructures have had a recent rise in their use for ethanol oxidation applications. In this work, we present the use of unsupported palladium nanoparticles (PdNPs), synthesized by sodium borohydride chemical reduction method, for ethanol electrochemical sensing. The unsupported PdNPs were studied for ethanol oxidation in alkaline media by cyclic voltammetry, and additionally were characterized using transmission electron microscopy, and x-ray photoelectron spectroscopy. The performance of unsupported PdNP-modified glassy carbon electrodes for the electrochemical ethanol oxidation in 1.0 M potassium hydroxide (KOH) solution was studied by cyclic voltammetry. These electrochemical results demonstrated that the unsupported PdNPs have very promising catalytic activity towards the oxidation of ethanol in alkaline media with good detection performance in the concentration range of 2304 to 288 ppm (i.e., 50.00 to 6.25 mM). The detection limit and linear correlation coefficient were 49.3 ppm (1.10 mM) and 0.9998, respectively. The unsupported PdNP-modified glassy carbon electrodes presented good cyclic voltammetric stability for ethanol sensing application in alkaline media.     

Ag/ZnO Catalysts with Different ZnO Nanostructures for Non‐enzymatic Detection of Urea

Silver coated ZnO nanorods and nanoflakes with different crystallographic orientations were synthesized by a combination of sputter deposition and solution growth process. Catalytic properties of morphology‐dependent Ag/ZnO nanostructures were then investigated for urea sensors without enzyme. Ag/ZnO nanorods on carbon electrodes exhibit a higher catalytic activity and an improved efficiency than Ag/ZnO nanoflakes on carbon electrodes. Ag/ZnO nanorod catalysts with more electrochemically surface area (169 cm² mg^?1) on carbon electrode facilitate urea electrooxidation due to easier electron transfer, which further promotes the urea electrolysis. The Ag/ZnO nanorod catalysts also show a significant reduction in the onset voltage (0.410 V vs. Ag/AgCl) and an increase in the current density (12.0 mA cm^?2 mg^?1) at 0.55 V vs Ag/AgCl. The results on urea electrooxidation show that Ag/ZnO nanostructures can be a potential catalyst for non‐enzymatic biosensors and fuel cells.     

pH‐Dependent Degradation of Layered Black Phosphorus: Essential Role of Hydroxide Ions

The practical application of layered black phosphorus (LBP) is compromised by fast decomposition in the presence of H₂O and/or O₂. The role of H₂O is controversial. Herein, we propose a hydroxide ion (OH^?)‐initiated degradation mechanism for LBP to elucidate the role of H₂O. We found that LBP degraded faster in alkaline solutions than in neutral or acidic solutions with or without O₂. Degradation rates of LBP increased linearly from pH 4 to 10. Density functional theory (DFT) calculations showed that OH^? initiated the decomposition of LBP through breaking the P?P bond and forming a P?O bond. The detection of hypophosphite, generated from OH^? reacting with P atoms, confirmed the hypothesis. Protons acted in a way distinctive from OH^?, by inducing deposition/aggregation or forming a cation–π layer to protect LBP from degradation. This work reveals the degradation mechanism of LBP and thus facilitates the development of effective stabilization technologies.     

Kinetic analysis of the disproportionation of aqueous glyoxal

Rates of disproportionation of 0.015–0.4 mM aqueous glyoxal toglycolic acid were measured at 0.24–75 mM NaOH and constant ionic strength, leading to the empirical rate expression r = (a₁[OH^?] + a₂[OH^?]²) [G_T]/(1 + a₃[OH^?]), where [G_T] is the total glyoxal concentration. These results were confirmed in bicarbonate/carbonate buffer and at 2–20 mM [G_T]. The rate form is in contradiction to earlier work on glyoxal, which suggested a second-order dependence on [OH^?], but agrees with the rate equation for phenylglyoxal disproportionation. The kinetic data can be explained by a mechanism postulating the presence of monohydrated and dihydrated forms of glyoxal in equilibrium, with the rate-limiting steps being intramolecular hydride ion transfers to the unhydrated carbonyl carbon of the mono- and divalent anions of glyoxal monohydrate.     

A study of some reactions of acetylacetonatobis(ethylenediamine)cobalt(III) ion in sodium hydroxide solution

The reactions of acetylacetonato cobalt (III) ion in sodium hydroxide solutions have been studied spectrophotometrically over a range of temperatures and hydroxide ion concentrations. The activation enthalpy, ΔH^≠ was 70.6 kJ mol^?1 and the activation entropy, ΔS^≠ was ? 119 JK^?1mol^?1, with a rate law of k_obs = k₂ [OH^?]². A mechanism involving initial de-chelation of the acetylacetone ligand is suggested. The rate of exchange of methyl hydrogen of the acetylacetone ligand was studied, using proton nuclear magnetic resonance. The rate law was k_obs = k [OH^?]. Initial de-chelation is also suggested as a mechanism for this process. The ¹³C nuclear magnetic resonance spectrum of the complex is reported.     

Mild Synthesis of Pt/SnO2/Graphene Nanocomposites with Remarkably Enhanced Ethanol Electro‐oxidation Activity and Durability

We have designed a new Pt/SnO₂/graphene nanomaterial by using L ‐arginine as a linker; this material shows the unique Pt‐around‐SnO₂ structure. The Sn²⁺ cations reduce graphene oxide (GO), leading to the in situ formation of SnO₂/graphene hybrids. L ‐Arginine is used as a linker and protector to induce the in situ growth of Pt nanoparticles (NPs) connected with SnO₂ NPs and impede the agglomeration of Pt NPs. The obtained Pt/SnO₂/graphene composites exhibit superior electrocatalytic activity and stability for the ethanol oxidation reaction as compared with the commercial Pt/C catalyst owing to the close‐connected structure between the Pt NPs and SnO₂ NPs. This work should have a great impact on the rational design of future metal–metal oxide nanostructures with high catalytic activity and stability for fuel cell systems.     

Quantum chemical models of alkali metal hydroxide-water-dimethylsulfoxide superbasic media (MOH-H<Subscript>2</Subscript>O-DMSO,M = Li,Na, K)

Models of alkali metal hydroxide-water-dimethylsulfoxide superbasic media have been constructed using Hartree Fock and DFT (B3LYP) quantum chemical methods; the structure and energies of anion complexes are considered. The hydroxide anion in the models is stabilized as complexes of OH^?·H₂O and OH^?· 2H₂O types.     

Gas phase reactions induced by OH− ion

The site of proton abstraction by OH^? ion in some 4-substituted-3,5,6-triphenyl-Δ′-cyclohexenes has been established from labelling studies. The further fragmentation mode of (M-H)^? ion depends on its structure and stereochemistry. The $\text{exo}$ and $\text{endo}$ nitro isomers exhibit stereochemical differences in the elimination of HNO₂ while the amino and cyano analogues show stereochemically controlled RDA fragmentation mode.     

Electron transfer to trans-dihydroxotetraoxoosmate(VIII). II. Kinetics of the oxidation of dimethylsulfoxide in aqueous alkaline media

The kinetics of the oxidation of dimethylsulfoxide by oxohydroxoosmate(VIII) complex ions in alkaline media follow pseudo-first-order disappearance in Os(VIII). The values of the observed pseudo-first-order rate constant are linearly dependent on initial dimethylsulfoxide concentrations in a fortyfold range, and increase with increasing [OH^?], leveling off at higher relative [OH^?]. The results are interpreted in terms of outer sphere interactions involving dimethylsulfoxide and various species of the Os(VIII) complex. The more nucleophilic dihydroxotetraoxoosmate(VIII) ion reacts about 50 times faster than the trihydroxotrioxoosmate(VIII) species.     

Abiotic C?C bond formation under environmental conditions: Kinetics of the aldol condensation of acetaldehyde in water catalyzed by carbonate ions (CO32−)

The role of C? C bond‐forming reactions such as aldol condensation in the degradation of organic matter in natural environments is receiving a renewed interest because naturally occurring ions, ammonium ions, NH⁺₄, and carbonate ions, CO₃^2?, have recently been reported to catalyze these reactions. While the catalysis of aldol condensation by OH^? has been widely studied, the catalytic properties of carbonate ions, CO₃^2?, have been little studied, especially under environmental conditions. This work presents a study of the catalysis of the aldol condensation of acetaldehyde in aqueous solutions of sodium carbonate (0.1–50 mM) at T = 295 ± 2 K. By monitoring the absorbance of the main product, crotonaldehyde, instead of that of acetaldehyde, interferences from other reaction products and from side reactions, in particular a known Cannizzaro reaction, were avoided. The rate constant was found to be first order in acetaldehyde in the presence of both CO₃^2? and OH^?, suggesting that previous studies reporting a second order for this base‐catalyzed reaction were flawed. Comparisons between the rate constants in carbonate solutions and in sodium hydroxide solutions ([NaOH] = 0.3–50 mM) showed that, among the three bases present in carbonate solutions, CO₃^2?, HCO₃^?, and OH^?, OH^? was the main catalyst for pH ≤ 11. CO₃^2? became the main catalyst at higher pH, whereas the catalytic contribution of HCO₃^? was negligible over the range of conditions studied (pH 10.3–11.3). Carbonate‐catalyzed condensation reactions could contribute significantly to the degradation of organic matter in hyperalkaline natural environments (pH ≥ 11) and be at the origin of the macromolecular matter found in these environments. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 676–686, 2010     

Kinetics and mechanism of oxidation of the drug mephenesin by bis(hydrogenperiodato)argentate(III) complex anion

Mephenesin is being used as a central‐acting skeletal muscle relaxant. Oxidation of mephenesin by bis(hydrogenperiodato)argentate(III) complex anion, [Ag(HIO₆)₂]^5?, has been studied in aqueous alkaline medium. The major oxidation product of mephenesin has been identified as 3‐(2‐methylphenoxy)‐2‐ketone‐1‐propanol by mass spectrometry. An overall second‐order kinetics has been observed with first order in [Ag(III)] and [mephenesin]. The effects of [OH^?] and periodate concentration on the observed second‐order rate constants k′ have been analyzed, and accordingly an empirical expression has been deduced: k′ = (k_a + k_b[OH^?])K₁/{f([OH^?])[IO^?₄]_tot + K₁}, where [IO^?₄]_tot denotes the total concentration of periodate, k_a = (1.35 ± 0.14) × 10^?2M^?1s^?1 and k_b = 1.06 ± 0.01 M^?2s^?1 at 25.0°C, and ionic strength 0.30 M. Activation parameters associated with k_a and k_b have been calculated. A mechanism has been proposed to involve two pre‐equilibria, leading to formation of a periodato‐Ag(III)‐mephenesin complex. In the subsequent rate‐determining steps, this complex undergoes inner‐sphere electron transfer from the coordinated drug to the metal center by two paths: one path is independent of OH^? whereas the other is facilitated by a hydroxide ion. In the appendix, detailed discussion on the structure of the Ag(III) complex, reactive species, as well as pre‐equilibrium regarding the oxidant is provided. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 440–446, 2007     

Pt–NiCo Nanostructures with Facilitated Electrocatalytic Activities for Sensitive Determination of Intracellular Thiols with Long‐Term Stability

A Pt–NiCo nanomaterial has been synthesized for developing the sensitive electrochemical determination of biological thiols that include L ‐cysteine (CySH), homocysteine (HCySH), and gluthione (GSH) with high sensitivity and long‐term stability, in which the Pt nanoparticles are well supported on amorphous NiCo nanofilms. The electrochemical oxidation of thiols has been successfully facilitated on the optimized Pt–NiCo nanostructures, that is, two oxidation peaks of CySH have been clearly observed at potentials of +0.06 and +0.45 V. The experimental results demonstrate that the first peak for CySH oxidation may be attributed to a direct oxidation from CySH to L ‐cystine (CySSCy), whereas the second peak possibly results from a sequential oxidation from CySSCy to cysteic acid (CySO₃H), together with a direct oxidation of CySH into CySO₃H. The enhanced electrocatalytic activities at the Pt₂₃–NiCo nanostructures have provided a methodology to determine thiols at a very low potential of 0.0 V with relatively high sensitivity (637 nA μM cm^?2), a low detection limit (20 nM ), and a broad linear range. The striking analytical performance, together with the characteristic properties of the Pt–NiCo nanomaterial itself, including long‐term stability and strong antipoisoning ability, has established a reliable and durable approach for the detection of thiols in liver cancer cells, Hep G2.     

An Automatic Molecular Dispenser of Chloride

The combined activity of the 1.1.1‐cryptand and of a dicopper(II) bistren cryptate complex including chloride makes the Cl^? ion be continuously and slowly delivered to the solution, without any external intervention. The 1.1.1‐cryptand slowly releases OH^? ions, according to a defined kinetics, and each OH^? ion displaces a Cl^? ion from the cryptate. Chloride displacement induces a sharp colour change from bright yellow to aquamarine and can be conveniently monitored spectrophotometrically, even in diluted solutions. The 1.1.1‐cryptand is the motor of a molecular dispenser (the dicopper(II) cryptate) delivering chloride ion automatically, from the inside of the solution.     

Synthesis of Sheet Like Nanostructures of NiO Using Potassium Dichromate as Surface Modifying Agent for the Sensitive and Selective Determination of Amlodipine Besylate (ADB) Drug

The monitoring of hypertension drugs is very critical and important to sustain a healthy life. In this study, we have synthesized nickel oxide (NiO) nanostructures using potassium dichromate as surface modifying agent by hydrothermal method. These NiO nanostructures were found highly active for the oxidation of ADB besylate (ADB). The unit cell structure and morphology were investigated by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) techniques. The SEM study has confirmed the nano sheet like morphology and XRD analysis has described the cubic unit arrays of NiO. After the physical characterization, NiO nanostructures were used to modify the surface of glassy carbon electrode (GCE) by drop casting method. Then cyclic voltammetry (CV) was used to characterize the electrochemical activity of NiO nanostructures in the0.1 M phosphate buffer solution of pH 10.0 and a well resolved oxidation peak was identified at 0.70 V. The linear range for the NiO nanostructures was observed from 20–90 nM with a regression coefficient of 0.99 using CV. The calculated limit of detection (LOD) was 2.125 nM and the limit of quantification (LOQ) was 4.08 nM. Further to validate the CV calibration plot, an amperometry experiment was performed on the NiO nanostructures and sensors exhibited a linear range of 10 nM to 115 nM with LOD of 1.15 nM. The proposed approach was successfully used for the determination of ADB from commercial tablets and it reveals that the sensor could be capitalized to monitor ADB concentrations from pharmaceutical products. The use of potassium dichromate as a surface modifying agent for the metal oxide nanostructures may be of great interest to manipulate their crystal and surface properties for the extended range of biomedical and energy related applications.     

Ultra‐sensitive Amperometric Hydrazine Sensing via Dimethyl Glyoxomat Derived NiO Nanostructures

Here we report the synthesis of NiO nanostructures via glyoxomat assisted precipitation protocol using hydrothermal route under the influence of ammonia followed by annealing at 450 ^oC. These nanostructures were characterized via Scanning Electron Microscopy (SEM) and X‐ray Diffraction (XRD) method. The morphological investigation of the finally prepared NiO revealed foam‐like porous nanostructures. These NiO nanostructures were immobilized onto glassy carbon electrode (GCE) with nafion as binding material and used as highly sensitive and selective sensor for determining hydrazine in the range of 100–500 nM and 600–1600 nM with a calculated limit of detection (LOD) equal to 5 nM. The as prepared sensor was tested for the presence of various interfering species such as Na⁺, Cu²⁺, uric acid, hydrogen peroxide and glucose in the presence of equimolar concentration of hydrazine and negligible interference was noticed. The sensor was further tested for hydrazine detection using square wave voltammetry (SWV) however it only worked in the range of 50–1200 μM. Finally the sensor was successfully implemented for hydrazine determination in real water samples using amperometric protocol.