Immobilization of redox mediators on functionalized carbon nanotube: A material for chemical sensor fabrication and amperometric determination of hydrogen peroxide

Chemical functionalization of single-walled carbon nanotubes with redox mediators, namely, toluidine blue and thionin have been carried out and the performance of graphite electrode modified with functionalized carbon nanotubes is described. Mechanical immobilization of functionalized single-walled nanotube (SWNT) on graphite electrode was achieved by gently rubbing the electrode surface on carbon nanotubes supported on a glass slide. The electrochemical behaviour of the modified electrodes was investigated by cyclic voltammetry. The SWNT-modified electrodes showed excellent electrocatalytic effect for the reduction of hydrogen peroxide. A decrease in overvoltage was observed as well as an enhanced peak current compared to a bare graphite electrode for the reduction of hydrogen peroxide. The catalytic current was found to be directly proportional to the amount of hydrogen peroxide taken.     

Behavior of Prussian blue-based materials in presence of ammonia

Prussian blue and related materials, usually considered that behave as a zeolite for ammonia adsorption, when hydrated are unstable in the presence of this gaseous species. They remain stable only in the anhydrous form. In the decomposition products ammonium hexacyanometallates and an XRD amorphous iron(III) oxyhydroxide are detected. The crystallization and adsorbed water present in these solid materials participates in a decomposition reaction to give NH₄⁺ and OH⁻. The very basic OH⁻ anion removes the iron(III) cations from the complex to form Fe(OH)₃ and finally FeOOH, while the formed NH₄⁺ appears as the salt of the complex anion. As reference reactions, the interaction of ammonia with ferrocyanic acid and ferric chloride, both in solid state, were studied where crystalline ammonium ferrocyanide and ammonium chloride, respectively, are formed.     

A novel amperometric hydrogen peroxide biosensor based on pyrrole-PAMAM dendrimer modified gold electrode

Horseradish peroxidase (HRP) was immobilized into an electrochemically prepared copolymer of pyrrole–PAMAM (PAMAM; polyamidoamine) dendrimers for the construction of amperometric hydrogen peroxide biosensor. First, second, and third generation amidoamine–pyrrole dendrons having branched amine periphery and focal pyrrole functionality were synthesized via divergent pathway. Pyrrole dendrimers were covalently attached onto the electrode surface and polymerized by electrochemical copolymerization with pyrrole monomer. The synthesized dendrimers and copolymers have been characterized by FTIR-ATR and NMR. These copolymers have been utilized as conducting films for amperometric hydrogen peroxide sensing. The HRP retains its bioactivity after immobilization into the dendronized pyrrole-copolymers. Amperometric response was measured as a function of concentration of hydrogen peroxide, at fixed potential of +0.35 V vs. Ag/AgCl in a phosphate buffered saline (pH 7.5). The effect of pH and temperature of the medium, storage, and reusability properties were investigated. The results indicate an efficient immobilization of enzyme onto the PAMAM type dendrimer modified surface containing pyrrole monomer, which leads to high enzyme loading, and increased lifetime stability of the electrode.     

ZrO<Subscript>2</Subscript>/DNA-derivated polyion hybrid complex membrane for the determination of hydrogen peroxide in milk

An efficient biosensing substrate based on ZrO₂/DNA-derivated polyion complex (PIC) membrane has been developed for the determination of hydrogen peroxide (H₂O₂) in this study. To fabricate such a PIC membrane, ZrO₂ nanoparticles were initially electrodeposited on the bare gold electrode (ZrO₂/Au), and deoxyribonucleic acid (DNA)-doped hemoglobin mixture was then assembled onto the ZrO₂/Au surface. The double-strand DNA provided a biocompatible microenvironment for the immobilization of biomolecules, greatly amplified the surface coverage of biomolecules on the electrode surface, and improved the sensitivity of the biosensor. The fabricated procedure of the proposed biosensor was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. The performance and factors influencing the performance of the biosensor were also evaluated. Under optimal conditions, the developed biosensor exhibited a well-defined electrochemical behavior toward the reduction of H₂O₂ ranging from 1.1 μM to 2.3 mM with a detection limit of 0.5 μM (S/N = 3). The biosensor was applied to the determination of H₂O₂ in milk with satisfactory results. It is important to note that the PIC membrane provided an alternative substrate for the immobilization of other proteins.     

A hydrogen peroxide electrochemical sensor based on Ag nanoparticles grown on ITO substrate

In this article, the Ag nanoparticles were synthesized on indium tin oxide conducting glass (ITO) substrate using the electrochemical deposition method. The morphology analysis of the deposits using scanning electron microscope (SEM) reveals that the sizes and densities of the Ag nanoparticles were tuned by varying the time of electrodeposition. The structure of the deposits was characterized by X-ray diffraction (XRD). The prepared Ag nanoparticles electrode was then applied to detect hydrogen peroxide (H₂O₂) in 0.01 M pH 7.0 phosphate buffer medium. The present electrochemical sensing platform exhibited good electrocatalytic activity towards the reduction of H₂O₂. The detection sensitivity of the sensor was 0.237 mA mM⁻¹. This method is very simple, inexpensive, and undemanding, thus it should be extensively applied in many fields for the detection of H₂O₂.     

A proposed mechanisms for the transient suppression of bacterial luminescence by hydrogen peroxide

It has been shown previously that bacterial luminescence is reversibly suppressed in vivo and in vitro by both X-rays and hydrogen peroxide. The data presented here show that the mechanisms for this phenomenon is based on the transient oxidation of reduced flavin mononucleotide.     

A radiomimetic effect of hydrogen peroxide on bacterial luminescence

Hydrogen peroxide (H₂O₂) in appropriate doses was found to mimic the reversible X-ray suppression of bacterial luminescence. Catalase protected against this suppression both by X-rays and H₂O₂, but albumin did not. Luminescence did not recover until H₂O₂ was destroyed. These results support our hypothesis that reduced intermediates of the luminescent pathway are reversibly oxidized by both X-rays and H₂O₂. Cyanide enhanced the effects of both X-rays and H₂O₂ and this result suggests that endogenous catalase is important to the survival of cells exposed to ionizing radiation.     

Reaction of stannous fluoride in hydrogen peroxide

The reaction of SnF₂ stannous fluoride with aqueous solutions of H₂O₂ hydrogen peroxide was studied as a function of the molar ratio H₂O₂/SnF₂ in the range 0.02 to 5.00. The products were characterized by thermal analysis, X-ray diffraction and tin119 Mössbauer spectroscopy. The X-ray diffraction pattern of all samples shows only highly broadened lines, characteristic of microcrystalline SnO₂ (average particle diameter: 39 Å). Thermal analyses show that the material is hydrated. Mössbauer spectroscopy gives a broad single line at approximately 0 mm/s, characteristic of SnO₂ for all samples, and in some cases a tin(II) doublet with =3.1 mm/s and =1.9 mm/s.     

Ti-doped nano-porous graphene: A material for hydrogen storage and sensor

Clustering of Ti on carbon nanostructures has proved to be an obstacle in their use as hydrogen storagematerials. Using density functional theory we show that Ti atoms will not cluster at moderate concentrations when doped into nanoporous graphene. Since each Ti atom can bind up to three hydrogen molecules with an average binding energy of 0.54 eV/H₂, this material can be ideal for storing hydrogen under ambient thermodynamic conditions. In addition, nanoporous graphene is magnetic with or without Ti doping, but when it is fully saturated with hydrogen, the magnetism disappears. This novel feature suggests that nanoporous graphene cannot only be used for storing hydrogen, but also as a hydrogen sensor.     

A method of autonomous orbit determination for satellite using star sensor

1 Introduction Autonomous orbit determination of satellite means that orbit determination is solely finished on board, independent of the observation of ground system. Study on autono-mous orbit determination of satellite has been very hot in the field of orbit determination currently internationally due to its significance in application. There are two common ways of autonomous orbit determination internationally. One is autonomous orbit deter-mination based on navigation system, such as on-b…     

A study of the rotational-torsional spectrum of hydrogen peroxide between 80 and 700 GHz

One hundred and thirty-three new rotational transitions that occur between pairs of torsional sublevels in the ground vibrational state of hydrogen peroxide have been measured in the 80 to 700 GHz region of the spectrum. These data, in combination with the 50 previously measured lines, have been theoretically analyzed to within the expected experimental uncertainty (?0.1 MHz). The rotational constants for the τ = 1, 2 state are (in MHz): A = 301 878.857 ± 0.015, B = 26 211.9019 ± 0.0059, C = 25 099.1400 ± 0.0059, and for the τ = 3, 4 state: A = 301 583.825 ± 0.075, B = 26 156.337 ± 0.13, C = 25 185.771 ± 0.13. The splitting between the torsional levels is 342 885.03 ± 0.05. These measurements and analysis accurately characterize the nine branches that make substantial contributions in the spectral region below 700 GHz.     

The effects of hydrogen peroxide on the sonochemical degradation of phenol and bisphenol A

This report describes the effects of H₂O₂ concentration (0.01, 0.1, 1, and 10 mM) on the sonochemical degradation of phenol and bisphenol A (BPA) using an ultrasonic source of 35 kHz and 0.08 W/mL. The concentration of the target pollutants (phenol or BPA), total organic carbon (TOC), and H₂O₂ were monitored for each input concentration of H₂O₂. The effects of H₂O₂ on the sonochemical degradation of phenol was more significant than that of BPA because phenol has a high solubility and low octanol–water partition coefficient (K_ow) value and is subsequently very likely to remain in the aqueous phase, giving it a greater probability of reacting with H₂O₂. The removal of TOC was also enhanced by the addition of H₂O₂. Some intermediates of BPA have a high K_ow value and subsequently have a greater probability of pyrolyzing by the high temperatures and pressures inside of cavitation bubbles. Thus the removal efficiency of TOC in BPA was higher than that of phenol. The removal efficiencies of TOC were lower than the degradation efficiencies of phenol and BPA. This result is due to the fact that some intermediates cannot readily degrade during the sonochemical reaction. The H₂O₂ concentration decreased but was not completely consumed during the sonochemical degradation of pollutants. The initial H₂O₂ concentration and the physical/chemical characteristics of pollutants were considered to be important factors in determining the formation rate of the H₂O₂. When high concentration of H₂O₂ was added to the solution, the formation rates were relatively low compared to when low concentrations of H₂O₂ were used.     

探测氢气泄漏的布拉格光栅型传感器

介绍了布拉格光栅型氢传感器的工作原理,开发出一种新型的由布拉格光栅和溅射钯膜组成的氢气敏光纤传感器。分析了此传感器的应力传递过程,建立了最大波长漂移量与氢浓度关系的数学模型。通过试验研究了光栅的氢响应特性,理论模型预测的最大波长漂移量与试验结果十分吻合。     

Prediction and assignment of the FIR spectrum of hydrogen peroxide

Millimeter and submillimeter microwave studies are used to predict and assign the FIR rotational-torsional spectrum of hydrogen peroxide. Special attention is given to the strong Q-branch features that have recently been used by Traub and Chance to place an upper limit on the atmospheric abundance of hydrogen peroxide. In addition, 67 new transitions are reported in the 400–1000 GHz region.     

The role of hydrogen peroxide in the deposition of cerium-based conversion coatings

Cerium-based conversion coatings are progressing as an effective alternative to hazardous chromate-based systems used in the treatment of metal surfaces. However, there is still considerable debate over the mechanism by which these coatings are formed. Here, titrations of cerium-based conversion coating solutions were carried out in order to model the reactions that occur at the metal-solution interface during coating, with a particular emphasis on investigating the role of hydrogen peroxide (H₂O₂). The titration curves obtained support the proposed formation of Ce(III) peroxo complexes such as Ce(H₂O₂)³⁺ as an initial step, followed by deprotonation, oxidation and precipitation to form peroxo-containing Ce(IV) species such as Ce^(IV)(O₂)(OH)₂. The precipitates resulting from titrations were characterised by Raman spectroscopy, X-ray diffraction and thermogravimetric analysis, confirming the presence of peroxo bonds, and nano-sized CeO₂ crystallites that decreased in size with increasing H₂O₂ concentration. Characterisation of cerium conversion coatings on aluminium alloy surfaces confirmed the presence of peroxo species in the coatings, thereby supporting the titration model.     

Comparison of chemiluminescence methods for analysis of hydrogen peroxide and hydroxyl radicals

Assessment of alpha radiolysis influence on the chemistry of geologically disposed spent fuel demands analytical methods for radiolytic product determination at trace levels. Several chemiluminescence methods for the detection of radiolytic oxidants hydrogen peroxide and hydroxyl radicals are tested. Two of hydrogen peroxide methods use luminol, catalyzed by either μ-peroxidase or hemin, one uses 10-methyl-9-(p-formylphenyl)-acridinium carboxylate trifluoromethanesulfonate and one potassium periodate. All recipes are tested as batch systems in basic conditions. For hydroxyl radical detection luminophores selected are 3-hydroxyphthalic hydrazide and rutin. Both methods are tested as batch systems. The results are compared and the applicability of the methods for near-field dissolution studies is discussed.