Determination of hydrogen sulfide in gasoline by Au nanoclusters modified glassy carbon electrode

A promising hydrogen sulfide (H₂S) sensor was prepared by electrodeposition of Au nanoclusters on glassy carbon electrode (GCE) and the surface structure was characterized by SEM and EDAX. These flower-like form Au nanoclusters, which were made up of highly dense clustering Au nanorods with an average diameter of 20 nm and length up to 80 nm, had an average size about 600 nm and uniformly distributed on the GCE surface. The electrocatalytic oxidation of H₂S in gasoline was performed on this modified electrode, which had a satisfactory liner response to H₂S in the range of 1–80 ppm and a detection limit of 0.45 ppm (s/n = 3). This sensor was sensitive, selective and stable.     

Microwave-irradiated synthesized platinum nanoparticles/carbon nanotubes for oxidative determination of trace arsenic(III)

Platinum nanoparticles/carbon nanotubes (Pt_nano/CNTs) were rapidly synthesized by microwave radiation, and applied for the oxidative determination of arsenic(III). The transmission electron microscopy (TEM) revealed the size of synthesized Pt nanoparticles with nominal diameter of 15 ± 3 nm. Pt_nano/CNTs modified glassy carbon electrode (Pt_nano/CNTs/GCE) exhibited better performance for arsenic(III) analysis than that of Pt nanoparticles modified GCE (Pt_nano/GCE) by electrochemical deposition or Pt foil electrode. Excellent reproducibility of the Pt_nano/CNTs/GCE was obtained with the relative standard deviation (RSD) of 3.5% at 20 repeated analysis of 40 μM As(III), while the RSD was 9.8% for Pt_nano/GCE under the same conditions. The limit of determination (LOD) of the Pt_nano/CNTs/GCE was 0.12 ppb, which was 1–2 orders of magnitude lower than that of Pt_nano/GCE or Pt foil electrode.     

Choline biosensors based on a bi-electrocatalytic property of MnO2 nanoparticles modified electrodes to H2O2

An interesting mode of reactivity of MnO₂ nanoparticles modified electrode in the presence of H₂O₂ is reported. The MnO₂ nanoparticles modified electrodes show a bi-direction electrocatalytic ability toward the reduction/oxidation of H₂O₂. Based on this property, a choline biosensor was fabricated via a direct and facile electrochemical deposition of a biocomposite that was made of chitosan hydrogel, choline oxidase (ChOx) and MnO₂ nanoparticles onto a glassy carbon (GC) electrode. The biocomposite is homogeneous and easily prepared and provides a shelter for the enzyme to retain its bioactivity. The results of square wave voltammetry showed that the electrocatalytic reduction currents increased linearly with the increase of choline chloride concentration in the range of 1.0 × 10⁻⁵ –2.1 × 10⁻³ M and no obvious interference from ascorbic acid and uric acid was observed. Good reproducibility and stability were obtained. A possible reaction mechanism was proposed.     

Hydrothermal synthesis and thermochemistry of metalloborophosphate of Na2[CuB3P2O11(OH)]·0.67H2O

The pure hydrated metalloborophosphate sample, Na₂[CuB₃P₂O₁₁(OH)]·0.67H₂O, has been synthesized and characterized by XRD, FT-IR, DTA-TG techniques, and chemical analysis. The molar enthalpies of solution of Na₂[CuB₃P₂O₁₁(OH)]·0.67H₂O(s) in 1 mol · dm^?3 HCl (aq), of Cu(OH)₂ (s) in (HCl + H₃BO₃) (aq), and of NaH₂PO₄·2H₂O (s) in (HCl + H₃BO₃ + Cu(OH)₂) (aq) were measured, respectively. With the incorporation of the previously determined enthalpy of solution of H₃BO₃ (s) in 1 mol · dm^?3 HCl (aq), together with the use of the standard molar enthalpies of formation for NaH₂PO₄·2H₂O (s), Cu(OH)₂ (s), H₃BO₃ (s), and H₂O (l), the standard molar enthalpy of formation of ?(4988.4 ± 2.5) kJ · mol^?1 for Na₂[CuB₃P₂O₁₁(OH)]·0.67H₂O at T = 298.15 K was obtained on the basis of the appropriate thermochemical cycle.     

Electrodeposition of monodispersed metal nanoparticles in a nafion film: Towards highly active nanocatalysts

We have explored a new and facile method for the fabrication of metal nanoparticles on the electrode surface. The approach for fabricating metal nanoparticles was carried out by two steps consisting of ion-exchange in nafion film coated on the electrode and subsequent reduction of metal ions to metallic nanoparticles by electrochemical method. The results of characterization by TEM show that metal nanoparticles were nearly monodispersed in the whole nafion film. The average diameters of Cu, Co and Ni nanoparticles were statistically measured to be 5.1 nm ± 0.2 nm, 4.6 nm ± 0.2 nm and 4.7 nm ± 0.2 nm, respectively. The amount of metal nanoparticles can be readily controlled by the amount of nafion coated on the electrode. By performing the H₂O₂ reduction at the obtained Cu nanoparticles, the high electrocatalytic activity of metal nanoparticles fabricated has been confirmed.     

Enthalpy of formation of zinc acetate dihydrate

The enthalpy of formation of zinc acetate dihydrate (Zn(CH₃COO)₂ · 2H₂O) was measured with respect to crystalline zinc oxide (ZnO), glacial acetic acid (CH₃COOH) and liquid water by room temperature solution calorimetry. The enthalpy of formation was verified by utilizing two independent thermodynamic cycles, using enthalpy of solution measurements in 5 mol · L^?1 sodium hydroxide (NaOH) and in 5 mol · L^?1 hydrochloric acid (HCl) solutions. The enthalpy of the reaction ZnO (cr) + 2CH₃COOH (l) + H₂O (l) to form Zn(CH₃COO)₂ · 2H₂O (cr) is –(65.78 ± 0.36) kJ · mol^?1 for measurements in 5 mol · L^?1 NaOH and –(66.25 ± 0.17) kJ · mol^?1 for measurements in 5 mol · L^?1 HCl. The standard enthalpy of formation of Zn(CH₃COO)₂ · 2H₂O from the elements is –(1669.35 ± 1.30) kJ · mol^?1. This work provides the first calorimetric measurement of the enthalpy of formation of Zn(CH₃COO)₂ · 2H₂O.     

Influence of Pt and Au nanophases on electrochromism of WO3 in nanostructure thin-film electrodes

We report electrochromic properties of WO₃ in Au–WO₃ and Pt–WO₃ nanostructure thin-film electrodes prepared by co-sputtering deposition method. The nanostructure electrodes consisted of Au or Pt metallic nanophase and a tungsten oxidative phase, indicating the formation of crystalline metallic nanophases in the amorphous oxide matrix. In particular, due to metallic nanophases, the modified electrochromic properties of WO₃ were observed in the Au–WO₃ and Pt–WO₃. The nanostructure electrodes showed a reverse optical modulation with respect to applied potentials in H₂SO₄ solution compared to that of pure WO₃ electrode. However, due to an excellent electrocatalytic activity of platinum for methanol electrooxidation at 25 °C, the electrochromism of the Pt–WO₃ in contrast with that of the Au–WO₃ was affected by the potentials for methanol electrooxidation in 2 M CH₃OH and 0.5 M H₂SO₄.     

Direct electrochemistry and electrocatalysis of hemoglobin entrapped in composite matrix based on chitosan and CaCO3 nanoparticles

The direct electron transfer between hemoglobin (Hb) and the underlying glassy carbon electrode (GCE) can be readily achieved via a high biocompatible composite system based on biopolymer chitosan (CHT) and inorganic CaCO₃ nanoparticles (nano-CaCO₃). Cyclic voltammetry of Hb-CHT/nano-CaCO₃/GCE showed a pair of stable and quasi-reversible peaks for HbFe(III)/Fe(II) redox couple in pH 7.0 buffer. The electrochemical reaction of Hb immobilized in CHT/nano-CaCO₃ composite matrix exhibited a surface-controlled process accompanied by electron and proton transfer. The electron transfer rate constant was estimated to be 1.8 s⁻¹. This modified electrode showed a high thermal stability up to 60 °C. The apparent Michaelis–Menten constant was calculated to be 7.5 × 10⁻⁴ M, indicating a high catalytic activity of the immobilized Hb toward H₂O₂. The interaction between Hb and this nano-hybrid material was also investigated using FT-IR and UV–vis spectroscopy, indicating that Hb retained its native structure in this hybrid matrix.     

Amperometric biosensors based on deposition of gold and platinum nanoparticles on polyvinylferrocene modified electrode for xanthine detection

In this study, new xanthine biosensors, XO/Au/PVF/Pt and XO/Pt/PVF/Pt, based on electroless deposition of gold(Au) and platinum(Pt) nanoparticles on polyvinylferrocene(PVF) coated Pt electrode for detection of xanthine were presented. The amperometric responses of the enzyme electrodes were measured at the constant potential, which was due to the electrooxidation of enzymatically produced H₂O₂. Compared with XO/PVF/Pt electrode, XO/Au/PVF/Pt and XO/Pt/PVF/Pt exhibited excellent electrocatalytic activity towards the oxidation of the analyte. Effect of Au and Pt nanoparticles was investigated by monitoring the response currents at the different deposition times and the different concentrations of KAuCl₄ and PtBr₂. Under the optimal conditions, the calibration curves of XO/Au/PVF/Pt and XO/Pt/PVF/Pt were obtained over the range of 2.5 × 10^?3 to 0.56 mM and 2.0 × 10^?3 to 0.66 mM, respectively. The detection limits were 7.5 × 10^?4 mM for XO/Au/PVF/Pt and 6.0 × 10^?4 mM for XO/Pt/PVF/Pt. The effects of interferents, the operational and the storage stabilities of the biosensors and the applicabilities of the proposed biosensors to the drug samples analysis were also evaluated.     

Synthesis of new substituted benzaldazine derivatives,hydrogen bonding-induced supramolecular structures and luminescent properties

Syntheses of three benzaldazine compounds 1–3 with the general formula Ar₁(CH = N–N = HC)Ar₂ (Ar₁ = Ar₂ = 2-OH-3,5-^tBu₂C₆H₂ (1), Ar₁ = Ar₂ = 2-BrC₆H₄ (2), Ar₁ = ortho-C₆H₄(NHC₆H₃-Me₂-2,6), Ar₂ = C₆H₄F-2 (3)) are described. All compounds were characterized by elemental analysis, ¹H NMR, ¹³C NMR, IR spectroscopy and single-crystal X-ray crystallography. The different supramolecular structures were obtained through different weak interactions (C ? H···O, O ? H···N and π···π interactions for 1; C ? H···Br and Br···Br interactions for 2; C ? H···F and C ? H···N interactions for 3). Compound 1 shows solvent-dependent fluorescent properties with blue to green emission on the increasing of the solvent polarity. Compounds 2, 3 show blue photoluminescence in different solvents.     

Electrocatalytic oxidation of NADH based on bicontinuous gyroidal mesoporous carbon with low overpotential

The electrochemical oxidation of β-nicotinamide adenine dinucleotide (NADH) is studied at a glassy carbon electrode (GCE) modified with bicontinuous gyroidal mesoporous carbon (BGMC). Due to the large surface area and remarkable electrocatalytic properties of BGMC, the BGMC/GCE exhibits potent electrocatalytic activity toward the electro-oxidation of NADH. A substantial decrease of 649 mV in the overpotential of NADH oxidation reaction is achieved compared with a bare GCE. The anodic peak currents increase steadily with the concentration of NADH in a broad range from 3.0 × 10^?6 to 1.4 × 10^?3 M with a low detection limit of 1.0 × 10^?6 M under the optimal condition.     

Direct electron transfer of cytochrome c and its biosensor based on gold nanoparticles/room temperature ionic liquid/carbon nanotubes composite film

A robust and effective composite film based on gold nanoparticles (GNPs)/room temperature ionic liquid (RTIL)/multi-wall carbon nanotubes (MWNTs) modified glassy carbon (GC) electrode was prepared by a layer-by-layer self-assembly technique. Cytochrome c (Cyt c) was successfully immobilized on the RTIL-nanohybrid film modified GC electrode by electrostatic adsorption. Direct electrochemistry and electrocatalysis of Cyt c were investigated. The results suggested that Cyt c could be tightly adsorbed on the modified electrode. A pair of well-defined quasi-reversible redox peaks of Cyt c was obtained in 0.10 M, pH 7.0 phosphate buffer solution (PBS). RTIL-nanohybrid film showed an obvious promotion for the direct electron transfer between Cyt c and the underlying electrode. The immobilized Cyt c exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis currents increased linearly to the H₂O₂ concentration in a wide range of 5.0 × 10⁻⁵– 1.15 × 10⁻³ M. Based on the multilayer film, the third-generation biosensor could be constructed for the determination of H₂O₂.     

Preparation and characterization of NiO(core)/Fe2O3(shell) composite particles

A novel hydrothermal coating process has been developed to deposit amorphous Ni(OH)₂·H₂O over octahedral α-Fe₂O₃ particles by treating aqueous dispersion of the preformed cores in Ni(NO₃)₂/CH₃COONa solution. NiO_(core)/Fe₂O_3(shell) composite particles were prepared by air sintering of the Ni(OH)₂·H₂O_(shell)/Fe₂O_3(core) particles at 200–500°C for 1–6 h. The changes of morphology, structure and weight of the hydrothermal and sintering products were studied by means of TEM, XRD, XPS, TG and IR analyzers. The nucleation and growth model was suggested for the non-isothermal decomposition of Ni(OH)₂·H₂O coatings and the kinetic equation was derived from the non-linear regression of the TG data. The activation in the thermal-decomposition process is 73.8 kJ mol⁻¹ and the pre-exponential factor is 1.95×10⁴ s⁻¹.     

Hydrothermal synthesis and thermodynamic properties of 2ZnO · 3B2O3 · 3H2O

The important zinc borate of 2ZnO · 3B₂O₃ · 3H₂O has been synthesized and characterized by means of chemical analysis, XRD, FT-IR, and DTA–TG techniques. The molar enthalpies of solution of H₃BO₃(s) in HCl · 54.561H₂O, of ZnO(s) in the mixture of HCl · 54.561H₂O and calculated amount of H₃BO₃, and of 2ZnO · 3B₂O₃ · 3H₂O(s) in HCl · 54.604H₂O were measured, respectively. With the use of the standard molar enthalpies of formation for ZnO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of ?(5561.7 ± 4.9) kJ · mol^?1 for 2ZnO · 3B₂O₃ · 3H₂O(s) was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method.     

Controlled-potential electrosynthesis of glucosaminic acid from glucosamine at a gold electrode

The electrocatalytic oxidation of d-glucosamine (2-amino-2-deoxy-d-glucose) in alkaline and neutral solutions was examined using a carbon felt electrode modified with 2 nm core sized gold nanoparticles (Au_2 nm nanoparticles) and a gold plate electrode. The electrocatalytic voltammetric oxidation curves of d-glucosamine were obtained in both solutions. The voltammetric responses for the electrocatalytic oxidation at a Au_2 nm nanoparticle-modified electrode in both alkaline and neutral solutions were almost the same to those at a gold plate electrode. The oxidized product was identified to be d-glucosaminic acid (2-amino-2-deoxy- d-gluconic acid) generated by the 2-electron oxidation product of d-glucosamine by electrospray ionization time-of-flight mass spectra (ESI TOF-MS). The HPLC results also indicated that the oxidation product was d-glucosaminic acid.The controlled-potential electrolysis of d-glucosamine was performed at the Au_2 nm nanoparticle-modified carbon felt electrodes in both alkaline and neutral solutions. In the alkaline solution, at a potential of −0.2 V, d-glucosaminic acid was formed with a current efficiency of 100%. In the neutral solution, electrolysis at 0.4 V on d-glucosaminic acid was obtained with current efficiencies of 70%.     

Drastically enhanced cycle life of Co-B alloy electrode by 8-hydroxyquinoline at elevated temperature

The effect 8-hydroxyquinoline (8-HQ) additive in electrolyte on the cyclic stability of Co-B alloy electrode was investigated at elevated temperature (55 °C). Charge–discharge measurements show that 8-HQ can drastically enhance the cycle life of Co-B alloy electrode. Specifically, in the electrolyte containing 0.028 M 8-HQ additive, the discharge capacity of Co-B alloy electrode after 100 cycles are still up to 385.8 mAh/g at 55 °C. However, for the electrode in 8-HQ-free electrolyte, its discharge capacity is sharply decreased to only 138.5 mAh/g after 100 cycles. ICP-OES, XRD and ATR/FT-IR measurements were used to clarify the reason of the improvement in the cyclic stability. These results show that beneficial effect of 8-HQ on cycle life of Co-B alloy electrode can be attributed to the formation of insoluble complex (8-HQ)₂Co(II)·2H₂O protective layer that can suppress the dissolution of Co(OH)₂ into electrolyte at elevated temperature.     

Thermodynamic properties of chloropinnoite

The molar enthalpies of solution of 2MgO · 2B₂O₃ · MgCl₂ · 14H₂O in approximately 1 mol · dm⁻³ aqueous hydrochloric acid (HCl) and of MgCl₂ · 6H₂O(s) in aqueous (approximately 1 mol · dm⁻³ HCl + MgCl₂ + H₃BO₃) at T=298.15 K were determined. From a combination of these results with measured enthalpies of solution of boric acid (H₃BO₃) in HCl(aq) and of magnesium oxide (MgO) in aqueous (HCl + H₃BO₃) solution, together with the standard molar enthalpies of formation of MgO(s), H₃BO₃(s), MgCl₂ · 6H₂O(s) and H₂O(l), the standard molar enthalpy of formation of −(8812 ± 3) kJ · mol⁻¹ of 2MgO · 2B₂O₃ · MgCl₂ · 14H₂O was obtained. Thermodynamic properties of this compound were also calculated by group contribution method.     

Electrografting of amino-TEMPO on graphene oxide and electrochemically reduced graphene oxide for electrocatalytic applications

4-Amino-2,2,6,6-tetramethyl-1-piperridine N-oxyl (4-amino-TEMPO), an electroactive nitroxide radical, was attached to the surface of graphene oxide (GO) and electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode by a simple, rapid and green electrografting method. The electroactive interfaces were analyzed by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The calculated surface coverage for 4-amino-TEMPO is up to 1.55 × 10^− 9 mol·cm^− 2. The modified electroactive interface exhibited excellent electrocatalytic activity towards the electro-oxidation of reduced glutathione (GSH) and hydrogen peroxide (H₂O₂).     

Improved direct electron transfer and electrocatalytic activity of horseradish peroxidase immobilized on gemini surfactant–polyvinyl alcohol composite film

The voltammetric and electrocatalytic behavior of horseradish peroxidase (HRP) immobilized on a cationic gemini surfactant (i.e. C₁₂H₂₅N(CH₃)₂–C₁₂H₂₄–N(CH₃)₂C₁₂H₂₅Br₂, C₁₂–C₁₂–C₁₂)–polyvinyl alcohol (PVA) composite film-coated glassy carbon electrode (GCE) has been studied. It is found that on the novel composite film HRP presents excellent electroactivity and can exhibit a pair of well-defined voltammetric peaks in 0.10 M pH 7.0 phosphate buffer solution (PBS). The immobilized HRP also presents good bioelectrocatalytic activity, and it can catalyze the reduction of oxygen (O₂), hydrogen peroxide (H₂O₂), nitrite ion (NO₂^?) and trichloroacetic acid (TCA). For H₂O₂ the catalytic current is linear to its concentration in the range of 0.195–97.5 μM, and the detection limit is down to 6.5 × 10^?8 M. The response shows Michaelis–Menten feature and the apparent Michaelis–Menten constant is estimated to be 110.5 μM. Similarly, the electrode can sense NO₂^? and TCA. In addition, it is observed that the spacer group of gemini surfactant affects the electroactivity of HRP significantly. A spacer group with higher flexibility and hydrophility is favorable to the electron transfer of HRP. UV–vis spectrum indicates that the structure of HRP in the PVA–C₁₂–C₁₂–C₁₂ film is similar to that of native HRP. Thus the C₁₂–C₁₂–C₁₂–PVA composite possesses good biocompatibility and has promising application in fabricating biosensor and bioelectronics.