Determination of nanomolar lead (II) using H<Subscript>2</Subscript>O<Subscript>2</Subscript>-oxidized activated carbon modified electrode

The virgin activated carbon (AC) was oxidized by 30% H₂O₂ under the ultrasonic condition for 6 h (denoted as AC-6). The electrochemical response of Pb²⁺ at the AC-6 modified paste electrode was investigated, suggesting that AC-6 shows much higher accumulation efficiency to trace levels of Pb²⁺. Based on this, a sensitive and convenient electrochemical method was developed for the determination of Pb²⁺ utilizing the excellent properties of AC-6. In pH 3.6 HAc-NaAc buffer, Pb²⁺ was easily accumulate at the surface of AC-6 modified paste electrode, then reduced to Pb at −1.20 V. During the following anodic sweep, the reduced Pb was oxidized and resulted in an oxidation stripping peak at −0.58 V. The stripping peak current is proportional to the concentration of Pb²⁺ over the range from the 8.0 × 10⁻⁹ to 2.0 × 10⁻⁶ mol l⁻¹, and the limit of detection is as low as 2.0 × 10⁻⁹ mol l⁻¹. Finally, this newly-developed method was successfully employed to determine Pb²⁺ in water samples.     

Hydrogen generation from H<Subscript>2</Subscript>O/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/MnWO<Subscript>4</Subscript> system

Hydrogen gas as a clear energy resource was found to be largely bubbled from a H₂O/H₂O₂/MnWO₄ system. MnWO₄ powder was fabricated by an aqueous reaction method. The powder was characterized with X-ray diffraction (XRD), transmission electron microscope (TEM), and X-ray photoelectron spectrometry (XPS). The efficiency of the hydrogen generation increases with an increase in initial pH in the appropriate range, H₂O₂ proportion, MnWO₄ proportion, and intensity of light resource. Calcining at 400 °C for 1 h can make the MnWO₄ powder synthesized by an aqueous reaction more effective for H₂ generation and more stable in higher initial pH. The MnWO₄ catalyst shows a long-term stability for photocatalytic H₂ generation. A mechanism was suggested for the hydrogen generation from the H₂O/H₂O₂/MnWO₄ system together with XPS analysis.     

In-situ growth of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles on mesoporous carbon nanofibers: a new nanocomposite for nonenzymatic amperometric sensing of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

The paper describes a nonenzymatic amperometric H₂O₂ sensor that uses a nanocomposite consisting of Co₃O₄ nanoparticles (NPs) and mesoporous carbon nanofibers (Co₃O₄-MCNFs). The Co₃O₄ NPs were grown in situ on the MCNFs by a solvothermal procedure. The synergetic combination of the electrocatalytic activity of the Co₃O₄ NPs and the electrical conductivity of MCNFs as an immobilization matrix enhance the sensing ability of the hybrid nanostructure. The oxidation current, best measured at 0.2 V (vs. SCE) is linear in the 1 to 2580 μM H₂O₂ concentration range, with a 0.5 μM lower detection limit (at an S/N ratio of 3). The sensor is highly selective even in the presence of common electroactive interferents. It was applied to the determination of H₂O₂ in spiked milk samples.

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Graphical abstract Schematic of the synthesis of a nanocomposite consisting of Co₃O₄ nanoparticles (NPs) and mesoporous carbon nanofibers (Co₃O₄-MCNFs) by a solvothermal procedure. It was used as electrocatalyst for direct oxidation of H₂O₂.

     

Glassy carbon electrode modified with hemin and new melamine compounds for H<Subscript>2</Subscript>O<Subscript>2</Subscript> amperometric detection

In an attempt to increase the stability and efficiency of hemin-modified electrodes, the present work reports the preparation of a new modified glassy carbon electrode obtained by immobilization of hemin (Hm) on the electrode surface together with a new N-substituted melamine (2,4,6-triamino-1,3,5-triazine) based G-2 dendrimer comprising p-aminophenol as peripheral unit (Den) or with one of its analogues, a melamine G-0 dimer (Dim). Basic structural features, able to determine intimate relationships between Hm and Dim (or Den) at room temperature in solid state, were evidenced with the use of vibrational analysis carried out by FT-IR. This method revealed contacts between Hm and Dim or Den respectively as H-bond interactions, proton-interchange, and π-π stacking interactions. The new modified electrodes were characterized by cyclic voltammetry and electrochemical impedance spectroscopy and tested for amperometric detection of H₂O₂. In this purpose, GC/Hm-Dim electrode exhibited better catalytic properties than GC/Hm-Den electrode, but lower stability.     

Immobilization of hemoglobin on SBA-15 applied to the electrocatalytic reduction of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

The direct electron transfer between hemoglobin (Hb) and an electrode was realized by first immobilizing the protein onto SBA-15.The results of the immobilization showed that the adsorption was pH-dependent with a maximum adsorption near the isoelectric point of the protein, and SBA-15 with a larger pore diameter showed greater adsorption capacity for Hb. UV–vis spectroscopy and nitrogen adsorption analysis indicated that Hb was adsorbed within the channel of SBA-15 and no significant denaturation occurred to the protein. The Hb/SBA-15 composite obtained was used for the fabrication of a Hb biosensor to detect hydrogen peroxide. A pair of well-defined redox peaks at −0.337 and −0.370 V on the Hb/SBA-15 composite modified glassy carbon electrode was observed, and the electrode reactions showed a surface-controlled process with a single proton transfer at a scan rate range from 20 to 1,000 mV/s. The sensor showed a fast amperometric response, a low detection limit (2.3 × 10⁻⁹ M) and good stability for the detection of H₂O₂. The electrochemical results indicated that the immobilized Hb still retained its biological activity.     

Advanced Bi<Subscript>2</Subscript>O<Subscript>2.7</Subscript>/Bi<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> composite film with enhanced visible-light-driven activity for the degradation of organic dyes

Bi₂O_2.7/Bi₂Ti₂O₇ composite photocatalyst films are synthesized by sol–gel dip-coating. The ratio of adding Bi and Ti precursors can be controlled during the preparation process. The phase structure is confirmed by X-ray diffraction. The UV–visible diffuse reflectance spectrum shows that the composite catalysts present light absorption in the visible region. The obtained Bi₂O_2.7/Bi₂Ti₂O₇ composite films possess superior photocatalytic degradation of rhodamine B, owing to the visible light response of Bi₂O_2.7 and the separation of photogenerated electrons and holes between the two components. As a result, the Bi₂O_2.7/Bi₂Ti₂O₇ (Bi/Ti = 1:1) displays the highest photocatalytic activity under visible light or UV light irradiation for the degradation of different organic dyes, including methyl blue, methyl orange and acid orange 7.     

Dimethyl phthalate (DMP) degradation in aqueous solution by gamma-irradiation/H<Subscript>2</Subscript>O<Subscript>2</Subscript>

This work includes the applications of radiation processing to decompose dimethyl phthalate (DMP) with gamma and gamma/H₂O₂ processes. Changes in amounts of DMP, dissolved oxygen, total acidity and formaldehyde with irradiation dose were followed. The qualitative analysis of the DMP and the intermediates were determined by using a gas chromatography combined to mass spectrometry and ion chromatography. The results indicated that degradation rate of DMP was affected by H₂O₂ concentration, irradiation dose and removal efficiency of 25 mg L^?1 DMP can reach 100% for 1.42 kGy irradiation dose in the concentration of 4.8 mM H₂O₂, respectively.     

Preparation and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> submicron-belts synthesized by a sol–gel H<Subscript>2</Subscript>O<Subscript>2</Subscript> route

One-dimensional (1D) submicron-belts of V₂O₅ have been prepared by a sol–gel route using V₂O_5, H₂O₂ and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement and cyclic voltammeter. The results showed that the synthesized V₂O₅ appeared to be submicron-belts and orthorhombic structure. The V₂O₅ submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge rate in the potential region 1.8–4.0 V.     

Synthesis of peroxy-radical condensates from mixtures of H<Subscript>2</Subscript>+O<Subscript>2</Subscript>

One of the methods for the synthesis of peroxy-radical condensates is the condensation at liquid nitrogen temperature of an H₂+O₂ mixture dissociated in an electrical discharge at low pressure. Peroxy-radical condensates are thought to contain substantial quantities of higher hydrogen peroxides H₂O₃ and H₂O₄. The present work investigates the influence of experimental parameters on the synthesis of peroxy-radical condensates from an H₂+O₂ mixture, analyses the relevant literature, and recommends the optimal experimental conditions for the synthesis. The synthesis is carried out in a U-tube electrical discharge reactor (inner diameter ∼15 mm), immersed in liquid nitrogen, at rather low pressure (0.5–1 Torr). The maximum conversion of initial O₂ into higher hydrogen peroxides was observed at a composition of initial gas mixture of 66.7% H₂ + 33.3% O₂.     

Kinetics of the oxidation of diethyl sulfide in the B(OH)<Subscript>3</Subscript>-H<Subscript>2</Subscript>O<Subscript>2</Subscript>/H<Subscript>2</Subscript>O system

Data obtained for the kinetics of oxidation of diethyl sulfide (Et₂S) by hydrogen peroxide in aqueous solution catalyzed by boric acid indicate that monoperoxoborates B(O₂H)(OH) ₃ ⁻ and diperoxoborates B(O₂H)₂(OH) ₂ ⁻ are the active species. The rates of the reactions of Et₂S with B(O₂H)(OH) ₃ ⁻ and B(O₂H)₂(OH) ₂ ⁻ are 2.5 and 100 times greater than with H₂O₂. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 38–42, January–February, 2007.     

Synthesis and study of (hexacaprolactam)trionium dodecamolybdophosphate (C<Subscript>6</Subscript>H<Subscript>11</Subscript>NO)<Subscript>6</Subscript>H<Subscript>3</Subscript>[PMo<Subscript>12</Subscript>O<Subscript>40</Subscript>]

(Hexacaprolactam)trionium dodecamolybdophosphate (C₆H₁₁NO)₆H₃[PMo₁₂O₄₀] has been prepared and studied by means of chemical and X-ray diffraction analysis as well as NMR and IR spectroscopy.     

Subsolidus phase relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Li<Subscript>2</Subscript>O-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> (Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>) systems

The phase composition has been studied and an equilibrium phase diagram has been designed for the Al₂O₃-Li₂O-R₂O₅ (R = Ta or Nb) systems in the subsolidus region up to 1000°C and 85 mol % Li₂O. New phases with the composition Li_1+x Al_1?x O_2?x , where x = 0–0.67, have been found.     

An ITO electrode modified with electrodeposited graphene oxide and gold nanoclusters for detecting the release of H<Subscript>2</Subscript>O<Subscript>2</Subscript> from bupivacaine-injured neuroblastoma cells

This study describes an amperometric sensor for hydrogen peroxide (H₂O₂) that uses an ITO glass electrode which was modified with a nanocomposite consisting of electrochemically reduced graphene oxide and gold nanoclusters (AuNCs). The sensor was used to quantify extracellular H₂O₂ released from human neuroblastoma cells of type SH-SY5Y. The calibration plot, established best at a working voltage of ?0.4 V (vs. Ag/AgCl) is linear in the 40 nmol?L^?1 to 2 μmol?L^?1 concentration range, and the detection limit is 20 nmol?L^?1 (at a signal-to-noise ratio of 3). The method was further applied to study bupivacaine-induced cell damage and the protective effects of α-lipoic acid. The study indicated that pretreatment of the cells with lipoic acid retards cell damage induced by bupivacaine. The sensor can be easily fabricated, is disposable and highly sensitive. The sensor is perceived to represent an alternative for studying the interactions of drugs with cells, and as an effective tool to quantify cell-secreted H₂O₂.

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Graphical abstract One-step electrochemical synthesis of graphene oxide and gold nanoclusters on an ITO electrode for studying the release of H₂O₂ from SH-SY5Y cells and for evaluation of drug-induced cell damage

     

Deposition of Prussian blue on nanoporous gold film electrode and its electrocatalytic reduction of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

Prussian blue-modified nanoporous gold film (PB-NPGF) electrode was fabricated in this study. The fabrication was realized through electrodeposition of Prussian blue nanoparticles on the skeleton of a nanoporous gold film electrode without destroying the porous structure of NPGF electrode. The resulting PB-NPGF composite electrode showed very high electrocatalytic activity, repeatability, and stability to the reduction of H₂O₂. For instance, its activity was about twenty times that of the PB-modified polished gold electrode. More importantly, the sensitivity of the PB-NPGF composite electrode reaches as high as 10.6 μA μM⁻¹ cm⁻². This PB-NPGF composite electrode is very promising in the fields of catalysis, analysis, and so on.     

Core-shell like Cu<Subscript>2</Subscript>O nanocubes enfolded with Co(OH)<Subscript>2</Subscript> on reduced graphene oxide for the amperometric detection of caffeine

The authors report on the fabrication of Co(OH)₂-enfolded Cu₂O nanocubes on reduced graphene oxide (rGO), and the use of this material in an electrochemical caffeine sensor. The rGO/Cu₂O/Co(OH)₂ composite was characterized by X-ray powder diffraction pattern analysis, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy. A rotating disc glassy carbon electrode covered with the nanocomposite displays enhanced electrocatalytic activity towards the electro-oxidation of caffeine. The peak oxidation potential is at 1.4  V (vs. Ag/AgCl) and hence is strongly shifted to the negative side when compared to other modified electrodes. The calibration plot is linear in the 0.83 to 1200 μM concentration range, with a 0.4 μM detection limit (at a signal-to-noise ratio of 3). The modified electrode is sensitive, selective and stable. It was successfully applied to the determination of caffeine in (spiked) caffeine-containing beverages and coffee powder and gave recoveries that ranged from 95.7 to 98.3 %.

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Graphical abstract Co(OH)₂ enfolded Cu₂O nanocubes on reduced graphene oxide (rGO) for the caffeine sensor

     

Study on chemisorption of H<Subscript>2</Subscript>, O<Subscript>2</Subscript>, CO and C<Subscript>2</Subscript>H<Subscript>4</Subscript>on Pt-Ag/SiO<Subscript>2</Subscript>catalysts by microcalorimetry and FTIR

Adsorption microcalorimetry has been employed to study the interaction of ethylene with the reduced and oxidized Pt-Ag/SiO₂catalysts with different Ag contents to elucidate the modified effect of Ag towards the hydrocarbon processing on platinum catalysts. In addition, microcalorimetric adsorption of H₂, O₂, CO and FTIR of CO adsorption were conducted to investigate the influence of Ag on the surface structure of Pt catalyst. It is found from the microcalorimetric results of H₂and O₂adsorption that the addition of Ag to Pt/SiO₂leads to the enrichment of Ag on the catalyst surface which decreases the size of Pt surface ensembles of Pt-Ag/SiO₂catalysts. The microcalorimetry and FTIR of CO adsorption indicates that there still exist sites for linear and bridged CO adsorption on the surface of platinum catalysts simultaneously although Ag was incorporated into Pt/SiO₂. The ethylene microcalorimetric results show that the decrease of ensemble size of Pt surface sites suppresses the formation of dissociative species (ethylidyne) upon the chemisorption of C₂H₄on Pt-Ag/SiO₂. The differential heat vs. uptake plots for C₂H₄adsorption on the oxygen-preadsorbed Pt/SiO₂and Pt-Ag/SiO₂catalysts suggest that the incorporation of Ag to Pt/SiO₂could decrease the ability for the oxidation of C₂H₄.     

Synthesis of nanocrystalline ZnO by the thermal decomposition of [Zn(H<Subscript>2</Subscript>O)(O<Subscript>2</Subscript>C<Subscript>5</Subscript>H<Subscript>7</Subscript>)<Subscript>2</Subscript>] in isoamyl alcohol

It was studied how the conditions of heat treatment of a [Zn(H₂O)(O₂C₅H₇)₂] solution in isoamyl alcohol at 120–140°C for 2–60 min affect the precursor decomposition mechanism and the characteristics of the obtained nanocrystalline zinc oxide. In all the cases, the product was a crystalline substance with the wurtzite structure and a size of crystallites of 14–18 nm, which was independent of the synthesis conditions. The thermal behavior and microstructure of the separated and dried nanostructured ZnO powder were investigated. It was determined how the duration and temperature of the heat treatment of the precursor solution affects the microstructure of ZnO coatings dip-coated onto glass substrates using dispersions produced at 120 and 140°C. The nanosized ZnO application procedure was shown to be promising for creating a gas-sensing layer of chemical gas sensors for detecting 1% H₂ (\(R_0 /R_{H_2 } \) was 58 ± 2 at an operating temperature of 300°C) and 4 ppm NO₂ (\(R_{NO_2 } /R_0\) were 15 ± 1 and 1.9 ± 0.1 at operating temperatures of 200 and 300°C, respectively).     

Mid-temperature solid oxide fuel cells with thin film ZrO<Subscript>2</Subscript>: Y<Subscript>2</Subscript>O<Subscript>3</Subscript> electrolyte

Data on the mid-temperature solid-oxide fuel cells (SOFC) with thin-film ZrO₂-Y₂O₃ (YSZ) electrolyte are shown. Such a fuel cell comprises a carrying Ni-YSZ anode, a YSZ electrolyte 3–5 μm thick formed by vacuum ion-plasma methods, and a LaSrMnO₃ cathode. It is shown that the use of a combined method of YSZ electrolyte deposition, which involves the magnetron deposition of a 0.5–1.5-μm thick sublayer and its pulse electron-beam processing allows a dense nanostructured electrolyte film to be formed and the SOFC working temperature to be lowered down as the result of a decrease in both the solid electrolyte Ohmic resistance and the Faradaic resistance to charge transfer. SOFC are studied by the methods of voltammentry and impedance spectroscopy. The maximum power density of the SOFC under study is 250 and 600 mW/cm⁻² at temperatures of 650 and 800°C, respectively.     

A novel amperometric immunosensor based on Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic nanoparticles/chitosan composite film for determination of ferritin

A novel amperometric immunosensor was developed by immobilizing ferritin antibody (FeAb) on the surface of Fe₃O₄ magnetic nanoparticles/chitosan composite film modified glassy carbon electrode (GCE). This material combined the advantages of inorganic Fe₃O₄ nanoparticles with the organic polymer chitosan. The stepwise assembly procedure of the immunosensor was characterized by means of differential pulse voltammetry (DPV) and ac impedance. The K₃Fe(CN)₆/K₄Fe(CN)₆ was used as a marker to probe the interface and to determinate ferritin. The factors that could influence the performance of the resulting immunosensor were studied in detail. After the immunosensor was incubated with ferritin for 32 min at 35 °C, the DPV current decreased linearly with the logarithm of ferritin concentration in the range from 20 to 500 ng mL⁻¹ with a correlation coefficient of 0.995 and a detection limit of 7.0 ng mL⁻¹. This immunosensor was used to analyze ferritin in human serum samples. The analytical results showed that the developed immunoassay was comparable with the radioimmunoassay (RIA), and the studied immunosensor exhibited good accuracy, high sensitivity, and long-term stability for 3 weeks, which implies a promising alternative approach for detecting ferritin in clinical diagnosis.     

The stability and structure of (N<Subscript>2</Subscript>)<Subscript>j</Subscript>(H<Subscript>2</Subscript>O)<Subscript>i</Subscript> and (Ar)<Subscript>j</Subscript>(H<Subscript>2</Subscript>O)<Subscript>i</Subscript> clusters

The stability and structure of water clusters absorbing nitrogen molecules or argon atoms was analyzed by molecular dynamics simulation at 233 K. The (?μ/?i)_{V, T} derivative of the chemical potential, a value characterizing the stability of a cluster with respect to its size, depends linearly on the number of molecules i. According to this criterion, the clusters under study become stable near i = 40. The average length of H-bonds increases monotonically in the growing cluster of pure water and exhibits oscillatory behavior if the growing cluster contains N₂ molecules or Ar atoms. The number of H-bonds per molecule oscillates between one and six as the cluster size changes. These oscillations are damped in pure water and sustained for clusters containing impurities, especially argon.