A copolymerized dodecacarborane anion as covalently attached cation exchanger in ion-selective sensors

The traditional cation exchangers used in ion-selective electrodes and optodes are tetraphenylborate derivatives, which are generally adequate for most analytical applications but may in some cases suffer from decomposition by acid hydrolysis, oxidants, and light. Recently, halogenated dodecacarboranes were found to be improved cation exchangers in terms of lipophilicity and chemical stability. This forms the basis for the convenient covalent attachment of the cation exchanger to the polymeric backbone of the sensing material. This is a challenge that has not satisfactorily been solved and which is especially important in view of developing ultraminiaturized sensing arrays. Here, a C-derivative of the closo-dodecacarborane anion (CB(11)H(12)(-)) with a polymerizable group was synthesized as a chemically stable cation exchanger. This new derivative was copolymerized with methyl methacrylate and decyl methacrylate (MMA-DMA) to fabricate a plasticizer-free polymer with cation-exchange properties. This polymer could be conveniently blended with traditional plasticized poly(vinyl chloride) or with noncrosslinked methacrylic polymers to give solvent cast films that appear to be clear and homogeneous and that could be doped with ionophores. Optode leaching experiments supported the covalent grafting of the carborane anions. Ion-selective membranes and optode thin films were evaluated in terms of response function, response time, and selectivity. In all cases, the new material exhibited behavior similar to free tetraphenylborate derivative-based membranes. As a result of these studies, an all-polymeric plasticizer-free calcium-selective membrane was fabricated on the basis of the covalently attached carborane, a recently introduced grafted calcium ionophore, and an MMA-DMA polymer matrix. The resulting ion-selective electrodes showed Nernstian response slopes and rapid response times, demonstrating that covalent grafting of all sensing components is a feasible approach to the development of ion sensors.     

Polyacrylamide thorium (IV) phosphate as an important lead selective fibrous ion exchanger: synthesis, characterization and removal study

The objective of the present research was to synthesize, characterize and to investigate the removal efficiency of lead (II) ion from synthetic lead solution by a hybrid fibrous ion exchanger. In the present study polyacrylamide thorium (IV) phosphate was synthesized by co-precipitation method and was characterized using SEM, XRD, FTIR and TGA-DSC. To know the practical applicability, a detailed removal study of lead ion was carried out. The removal of lead was 52.9% under neutral condition, and using 0.4 g of adsorbent in 100 mL of lead solution having initial concentration of 100 mg/L. Adsorption kinetic study revealed that the adsorption process followed first order kinetics. Adsorption data were fitted to linearly transformed Langmuir isotherm with R(2) (correlation coefficient)>0.99. Thermodynamic parameters were also calculated to study the effect of temperature on the removal process. In order to understand the adsorption type, equilibrium data were tested with Dubinin-Radushkevich isotherm. The percentage removal was found to increase gradually with increase in pH and 99% removal was achieved at pH 10. The process was rapid and equilibrium was established within first 30 min.     

Quasi-one dimensional metal oxide semiconductors: Preparation, characterization and application as chemical sensors

The continuous evolution of nanotechnology in these years led to the production of quasi-one dimensional (Q1D) structures in a variety of morphologies such as nanowires, core-shell nanowires, nanotubes, nanobelts, hierarchical structures, nanorods, nanorings. In particular, metal oxides (MOX) are attracting an increasing interest for both fundamental and applied science. MOX Q1D are crystalline structures with well-defined chemical composition, surface terminations, free from dislocation and other extended defects. In addition, nanowires may exhibit physical properties which are significantly different from their coarse-grained polycrystalline counterpart because of their nanosized dimensions. Surface effects dominate due to the increase of their specific surface, which leads to the enhancement of the surface related properties, such as catalytic activity or surface adsorption: key properties for superior chemical sensors production.High degree of crystallinity and atomic sharp terminations make nanowires very promising for the development of a new generation of gas sensors reducing instabilities, typical in polycrystalline systems, associated with grain coalescence and drift in electrical properties. These sensitive nanocrystals may be used as resistors, and in FET based or optical based gas sensors.This article presents an up-to-date review of Q1D metal oxide materials research for gas sensors application, due to the great research effort in the field it could not cover all the interesting works reported, the ones that, according to the authors, are going to contribute to this field’s further development were selected and described.     

Ceramic-based chemical sensors, probes and field-tests in automobile engines

The monitoring and control of combustion-related emissions is a top priority in many industries. The major methods used to detect combustion gases fall short of practical applications for in-situ measurements in industrial environments involving high temperature and chemical contaminants. The real challenge is not only to develop highly sensitive and selective sensors, but to maintain long-term stability in such aggressive environments. This article presents an overview of a multidisciplinary research effort in ceramic-based chemical sensors, highlighting opportunities as well as challenges. The group of sensors (CO, NO _x , O₂, and CO₂) selected for this article can, in general, be used to determine the state of combustion in a wide variety of applications. Fabrication of sensor probes and their field-test results in automobile engines are also presented.     

Alternately pulsed nanoelectrospray ionization/atmospheric pressure chemical ionization for ion/ion reactions in an electrodynamic ion trap

The alternate operation of nanoelectrospray ionization and atmospheric pressure chemical ionization, using a common atmosphere/vacuum interface and ion path, has been implemented to facilitate ion/ion reaction experiments in a linear ion trap-based tandem mass spectrometer. The ion sources are operated in opposite polarity modes whereby one of the ion sources is used to form analyte ions while the other is used to form reagent ions of opposite polarity. This combination of ion sources is well-suited to implementation of experiments involving multiply charged ions in reaction with singly charged ions of opposite polarity. Three analytically useful ion/ion reaction types are illustrated: the partial deprotonation of a multiply protonated protein, the partial protonation of a multiply deprotonated oligonucleotide, and electron transfer to a multiply protonated peptide. The approach described herein is attractive in that it enables both single proton-transfer and single electron-transfer ion/ion reaction experiments to be implemented without requiring major modifications to the tandem mass spectrometer hardware. Furthermore, a wide range of reactant ions can be formed with these ionization methods and the pulsed nature of operation appears to lead to no significant compromise in the performance of either ion source.     

Studies of removal of platinum(IV) ion microquantities from the model solutions of aluminium, copper, iron, nickel and zinc chloride macroquantities on the anion exchanger Duolite S 37

Platinum has been widely applied in catalytic industry and the recovery of noble metals from industrial wastes becomes an economic issue. The laboratory studies of platinum(IV) microquantities removal from 1M aluminium, copper, iron, nickel and zinc chloride solutions in 0.1M hydrochloric acid solutions on the anion exchanger Duolite S 37 of the functional secondary and tertiary amine groups were carried out. For this anion exchanger the fraction extracted values (%E, Pt(IV)) as well as the sorption isotherms were determined depending on the kind of aqueous phase and phase contact time. Moreover, the bed and weight distribution coefficients as well as working and total ion-exchange capacities were calculated from the platinum(IV) breakthrough curves. Kinetic parameters were determined.     

Direct chemical analysis of solids by laser ablation in an ion storage time-of-flight mass spectrometer

A laser ablation/ionization mass spectrometer system is described for the direct analysis of solids, particles, and fibers. The system uses a quadrupole ion trap operated in an ion storage mode, coupled with a reflectron time-of-flight mass spectrometer). The sample is inserted radially into the ring electrode, and an imaging system allows direct viewing and selected analysis of the sample. Measurements identified trace contaminants of Ag, Sn, and Sb in a Pb target with single laser shot experiments. Resolution (m/Delta m) of 1500 and detection limits of approximately 10 pg have been achieved with a single laser pulse. The system configuration and related operating principles for accurately measuring low concentrations of isotopes are described.     

Optical nanosensors for chemical analysis inside single living cells. 1. Fabrication, characterization, and methods for intracellular delivery of PEBBLE sensors

Spherical optical nanosensors, or PEBBLEs (probes encapsulated by biologically localized embedding), have been produced in sizes including 20 and 200 nm in diameter. These sensors are fabricated in a microemulsion and consist of fluorescent indicators entrapped in a polyacrylamide matrix. A generalized polymerization method has been developed that permits production of sensors containing any hydrophilic dye or combination of dyes in the matrix. The PEBBLE matrix protects the fluorescent dye from interference by proteins, allowing reliable in vivo calibrations of dyes. Sensor response times are less than 1 ms. Cell viability assays indicate that the PEBBLEs are biocompatible, with negligible biological effects compared to control conditions. Several sensor delivery methods have been studied, including liposomal delivery, gene gun bombardment, and picoinjection into single living cells.     

Hydrogenated vanadium oxides as an advanced anode material in lithium ion batteries

Current research on vanadium oxides in lithium ion batteries (LIBs) considers them as cathode materials, whereas they are rarely studied for use as anodes in LIBs because of their low electrical conductivity and rapid capacity fading. In this work, hydrogenated vanadium oxide nanoneedles were prepared and incorporated into freeze-dried graphene foam. The hydrogenated vanadium oxides show greatly improved charge-transfer kinetics, which lead to excellent electrochemical properties. When tested as anode materials (0.005–3.0 V vs. Li/Li⁺) in LIBs, the sample activated at 600 °C exhibits high specific capacity (～941 mA·h·g^?1 at 100 mA·g^?1) and high-rate capability (～504 mA·h·g^?1 at 5 A·g^?1), as well as excellent cycling performance (～285 mA·h·g^?1 in the 1,000^th cycle at 5 A·g^?1). These results demonstrate the promising application of vanadium oxides as anodes in LIBs.

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锂离子电池正极材料LiFe_(1-2x)Mn_xMg_xPO_4/C的电化学性能研究

通过高温固相合成法以MnCO3为锰源、(MgCO3)4·Mg(OH)·5H2O为镁源,葡萄糖为碳源,在氩气气氛下合成二元掺杂Mn、Mg的LiFe0.8Mn0.1Mg0.1PO4/C和LiFePO4/C正极材料,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、红外光谱仪(FT-IR)进行结构表征,通过恒电流充放电实验研究了LiFe0.8Mn0.1Mg0.1PO4/C和LiFePO4/C电化学性能。结果表明,二元掺杂Mn、Mg的LiFe0.8Mn0.1Mg0.1PO4/C呈现橄榄石结构,无杂质产生。与未掺杂的LiFePO4/C相比,掺杂后LiFe0.8Mn0.1Mg0.1PO4/C提高了电导率,0.1C倍率下放电可逆容量为131mAh/g,表现出良好的电化学性能。     

Near ideal electrical switching in fast ion conducting glasses: Evidence for an electronic process with chemical origin

Bulk AgI based fast ion conducting (FIC) glasses have been prepared by a novel microwave technique. Electrical switching characteristics of these glasses have been investigated for the first time. It has been found that AgI based FIC glasses exhibit a current-controlled high speed memory electrical switching behaviour. SEM, EDAX and ESR investigations have been performed on the virgin and switched sampies to understand the nature of the conducting state. A chemical model is proposed to explain the switching behaviour of these glasses, which is consistent with the observed results.     

Quantitative chemical identification of four gases in remote infrared (9-11 mum) differential absorption lidar experiments

A combined experimental and computational approach utilizing tunable CO(2) lasers and chemometric analysis was employed to detect chemicals and their concentrations in the field under controlled release conditions. We collected absorption spectra for four organic gases in the laboratory by lasing 40 lines of the laser in the 9.3-10.8-mum range. The ability to predict properly the chemicals and their respective concentrations depends on the nature of the target, the atmospheric conditions, and the round-trip distance. In 39 of the 45 field experiments, the identities of the released chemicals were identified correctly without predictions of false positives or false negatives.     

HgO as an internal oxygen source in Y1Ba2Cu3O7-δ

This paper reports an alternative technique for preparing Y₁Ba₂Cu₃O_7-δ with uniform oxygen stoichiometry which eliminates the need for flowing oxygen during sintering. Our studies show that when HgO is added to the YBaCuO system it provides an abundant source of oxygen during sintering. Mercury diffuses out of the system leaving the crystal structure intact. We have thus been able to obtain a T _c (zero resistivity) of 90 K consistently in HgO doped YBaCuO specimens and sintered in air. An optimum value of HgO leads to a strongly coupled grain material. Resistivity, X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and a.c. susceptibility data are reported. This revised version was published online in November 2006 with corrections to the Cover Date.     

Determination of the ionization state of 11-thioundecyl-1-phosphonic acid in self-assembled monolayers by chemical force microscopy

The present article describes the preparation and preliminary characterization of a novel phosphate-functionalized self-assembled monolayer (SAM) and the determination of the surface ionization states of the phosphate headgroup in aqueous solutions by chemical force microscopy (CFM). The phosphate headgroup used was PO(OH)2, a diprotic acid. The adhesion force between an AFM probe and a flat substrate, both of which were chemically modified with the same phosphate SAM, was also measured as a function of pH and ionic strength. At low ionic strength (10(-4) M), two peaks were observed in the force titration curve (adhesion force versus pH) at pH 4.5 and 8.4. The two peaks are positioned 2.4 and 1.2 pH units higher, respectively, than the acid dissociation constants obtained for the phosphate group free in aqueous solution. At high ionic strength (10(-1) M), the adhesion forces were reduced by 1 order of magnitude and the peaks were replaced by shoulders similar to those previously reported for acid force titrations. On the basis of JKR theory, the surface pKa values of the phosphate group in high ionic strength solutions were found to be 4.5 and 7.7, respectively. However, in light of the effects of ionic strength on the force titration curves, we discuss the applicability of JKR theory to nanoscopic measurements of adhesion force and surface pKa.     

Methyldichloroborane evidenced as an intermediate in the chemical vapour deposition synthesis of boron carbide

The most recent ceramic-matrix composites (CMC) considered for long-life applications as thermostructural parts in aerospace propulsion contain, among others, boron-rich phases like boron carbide. This compound is prepared by thermal Chemical Vapour Infiltration (CVI), starting from precursors like boron halides and hydrocarbons. We present a study aiming at a precise knowledge of the gas-phase composition in a hot-zone LPCVD reactor fed with BCl3, CH4 and H2, which combines experimental and theoretical approaches. This work has brought strong evidences of the presence of Methydichloroborane (MDB, BCl2CH3) in the process. It is demonstrated that this intermediate, the presence of which had never been formally proved before, appears for processing temperatures slightly lower than the deposition temperature of boron carbide. The study features quantum chemical computations, which provide several pieces of information like thermochemical and kinetic data, as well as vibration and rotation frequencies, reaction kinetics computations, and experimental gas-phase characterization of several species by FTIR, for several processing parameter sets. The main results are presented, and the place of MDB in the reaction scheme is discussed.     

Synthesis of calcium peroxide nanoparticles as an innovative reagent for in situ chemical oxidation

Chemical oxidation is one of the many different methods of site remediation that has emerged lately as an alternative method to traditional techniques. According to this research calcium peroxide is suitable choice for contaminant biodegradation in soil and ground water but speed of oxidation reaction between calcium peroxide and contaminant is slow. Synthesis of calcium peroxide in nano size by increased ratio of surface to volume can increase the speed of reaction and solve the problem. We have developed a simple surface modification technique to avoid irreversible agglomeration of calcium peroxide nanoparticles. The technique is based on hydrolysis-precipitation procedure, using CaCl₂ as a precursor. Polyethylene glycol 200 (PEG200) is used as a surface modifier. CaO₂ was identified and studied by characterization techniques, including XRD and TEM. The results indicate the ability of this method for synthesis of new reagent in nano size and improve quality of in situ chemical oxidation. Size determination by TEM image indicates the size of calcium peroxide nanoparticles approximately 15-25 nm.     

An investigation on oxidation/carburisation of 9Cr-1Mo steel heat exchanger tube in an AGR environment

Abstract

9Cr–1Mo steels have been used extensively in the power generation industry. In this study, a wide range of experimental samples exposed at different times and temperatures in a CO₂ environment were analysed to look at the development of the metal and oxides over time. The main objective of this work was to obtain a better understanding of the carburisation and oxidation behaviour of 9Cr 1Mo steels as a function of temperature/time, with special attention paid to the transition from protective to breakaway oxidation. In addition, experiments were also carried out to investigate any links between oxidation transition and carburisation behaviour of these materials.