Adsorption of bismuth ions on graphite chemically modified with gallic acid

Graphite modified with gallic acid to form 'gallic acid-carbon' is demonstrated to be efficient for the removal of bismuth(III) ions from aqueous solutions. The uptake is demonstrated to be rapid but not to follow standard adsorption isotherm models. Instead, the uptake was found to be further promoted by the presence of the adsorbed metal. Additionally, the bismuth uptake showed linear dependence on the square of its concentration suggesting the possible formation of polymeric bismuth species. The gallic acid-carbon shows great promise as a relatively inexpensive material for solid-phase extraction and water purification with extraction efficiency close to 98%.     

Derivatised carbon powder electrodes: reagentless pH sensors

In this report, we derivatise carbon powder with anthracene, azobenzene, diphenylamine, 9,10-diphenylanthracene, methylene blue, 3-nitrofluoranthene, 6-nitrochrysene, 9-nitroanthracene, 9,10-phenanthraquinone (PAQ), thionin, and fast black K (2,5-dimethoxy-4-[(4-nitrophenyl)azo]benzenediazonium chloride) and separately immobilise the resulting material onto a bppg electrode. We use cyclic voltammetry (CV) to demonstrate that the observed voltammetric response for each derivatised carbon is consistent with that of an immobilised species. Further, we use CV and square wave voltammetry (SWV) to investigate the effect of pH on the peak potentials of each compound studied over the range pH 1-12 and at elevated temperatures up to 70 °C in order to demonstrate the versatility of derivatised carbon electrodes as reagentless pH sensors.     

Abrasively immobilised multiwalled carbon nanotube agglomerates: a novel electrode material approach for the analytical sensing of pH.

We demonstrate for the first time that agglomerates of multiwalled carbon nanotubes (MWCNTs) can be formed in which the binder in the agglomerate is itself a redox-active molecular solid. Two separate agglomerates were formed by dissolving 9,10-phenanthraquinone (PAQ) or 1,2-napthaquinone (NQ) in acetone together with MWCNTs and adding an excess of aqueous solution to cause precipitation of agglomerates, approximately 10 microns in dimension, which consist of bundles of nanotubes running into and throughout the amorphous molecular solid that binds the agglomerate together. The nature of this structure, when immobilised on a substrate electrode and in contact with aqueous electrolyte solutions, gives rise to many three-phase boundaries, electrolyte|agglomerate|conductor, which is advantageous to the solid-state analytical electrochemistry of such a material as it imparts a larger electroactive surface area than other modified carbon electrodes. The two agglomerates each gave a voltammetrically measurable response to changes in pH; when abrasively immobilised on a basal plane pyrolitic graphite electrode a plot of peak potential against pH produced a linear response for both MWCNT-PAQ and MWCNT-NQ agglomerates over the pH range pH 1-12 and over the temperature range 20-70 degrees C.     

Carbon nanotube-based electrochemical sensors for quantifying the 'heat' of chilli peppers: the adsorptive stripping voltammetric determination of capsaicin

A sensitive electroanalytical methodology for the determination of capsaicin using adsorptive stripping voltammetry (AdsSV) at a multiwalled carbon nanotube modified basal plane pyrolytic graphite electrode (MWCNT-BPPGE) is presented. This analytical method is then further developed using a multiwalled carbon nanotube screen-printed electrode (MWCNT-SPE) demonstrating the proof-of-concept that this approach can easily be incorporated into a sensing device which is both facile to use and inexpensive to produce. Capsaicin is the chemical responsible for the hot taste of chilli peppers, and measuring the concentration of capsaicin is an indicator of how hot any given chilli pepper, hot sauce and other related foodstuffs are. Standard additions plots for AdsSV of capsaicin at open circuit potential at a MWCNT-BPPGE exhibits two linear ranges, from 0.5 to 15 microM and from 15 to 60 microM. Using the first range of calibration curve, a detection limit of 0.31 microM (based on 3sigma) is obtained. The plot of standard additions of capsaicin determined using the disposable MWCNT-SPE shows a linear range between 0.5 and 35 microM and a detection limit of 0.45 microM. MWCNT-BPPGE and MWCNT-SPE are successfully utilized for the determination of capsaicin in real samples, such as a few commercially available hot pepper sauces, and the determined values are in excellent agreement and correlation with the average Scoville unit values reported in the literature for these sauces. To the best of our knowledge, this is the first electroanalytical method using MWCNT-BPPGE or MWCNT-SPE reported for the determination of capsaicin. This method offers advantages such as precision and objectivity over the well-known but potentially subjective Scoville method (based on organoleptic testing by human tasting panels) and is facile and inexpensive compared to existing HPLC methods.     

The influence of edge-plane defects and oxygen-containing surface groups on the voltammetry of acid-treated, annealed and “super-annealed” multiwalled carbon nanotubes

The role of edge-plane-like defects at the open ends of multiwalled carbon nanotubes (MWCNTs) and at hole defects in the tube walls is explored using cyclic voltammetry with two charged redox probes, namely potassium ferrocyanide and hexaamineruthenium(III) chloride in unbuffered aqueous solutions, and one neutral redox probe, norepinephrine, in pH 5.7 buffer. Further, the presence of oxygen-containing functional groups (such as phenol, quinonyl and carboxyl groups), which decorate the edge-plane defect sites on the voltammetric response of the MWCNTs, is also explored. To this end, three different pre-treatments were performed on the pristine MWCNTs made using the arc-discharge method (arc-MWCNTs). These were (a) arc-MWCNTs were subjected to acid oxidation to form acid-MWCNTs—open-ended MWCNTs also possessing numerous hole defects revealing a large number of edge-plane-like sites heavily decorated with surface functional groups; (b) acid-MWCNTs, which were subsequently vacuum-annealed at 900 °C to remove the functional groups but leaving the many undecorated edge-plane-like sites exposed (ann-MWCNTs); (c) ann-MWCNTs, which were subjected to a further vacuum “super-annealing” stage at 1,750 °C (sup-MWCNTs), which caused the hole defects to close and also closed the tube ends, thereby, restoring the original, pristine, almost edge-plane defect-free MWCNTs structure. The results of the voltammetric characterisation of the acid-, ann- and sup-MWCNTs provide further evidence that edge-plane-like sites are the electroactive sites on MWCNTs. The presence of oxygen-containing surface groups is found to inhibit the rate of electron transfer at these sites under the conditions used herein. Finally, the two charged, “standard” redox probes used were found to undergo strong interactions with the oxygen-containing surface groups present. Thus, we advise caution when using these redox probes to attempt to voltammetrically characterise MWCNTs, and by extension, graphitic carbon surfaces.     

Metal‐Free Dihydrogen Oxidation by a Borenium Cation: A Combined Electrochemical/Frustrated Lewis Pair Approach

In order to use H₂ as a clean source of electricity, prohibitively rare and expensive precious metal electrocatalysts, such as Pt, are often used to overcome the large oxidative voltage required to convert H₂ into 2 H⁺ and 2 e^?. Herein, we report a metal‐free approach to catalyze the oxidation of H₂ by combining the ability of frustrated Lewis pairs (FLPs) to heterolytically cleave H₂ with the in situ electrochemical oxidation of the resulting borohydride. The use of the NHC‐stabilized borenium cation [(IiPr₂)(BC₈H₁₄)]⁺ (IiPr₂=C₃H₂(NiPr)₂, NHC=N‐heterocyclic carbene) as the Lewis acidic component of the FLP is shown to decrease the voltage required for H₂ oxidation by 910 mV at inexpensive carbon electrodes, a significant energy saving equivalent to 175.6 kJ mol^?1. The NHC–borenium Lewis acid also offers improved catalyst recyclability and chemical stability compared to B(C₆F₅)₃, the paradigm Lewis acid originally used to pioneer our combined electrochemical/frustrated Lewis pair approach.     

The Fabrication and Characterization of a Bismuth Nanoparticle Modified Boron Doped Diamond Electrode and Its Application to the Simultaneous Determination of Cadmium(II) And Lead(II)

We report the simultaneous electroanalytical determination of Pb²⁺ and Cd²⁺ by square‐wave anodic stripping voltammetry (SWASV) using a bismuth nanoparticle modified boron doped diamond (Bi‐BDD) electrode. Bi deposition was performed in situ with the analytes, from a solution of 0.1 mM Bi(NO₃)₃ in 0.1 M HClO₄ (pH 1.2), and gave detection limits of 1.9 μg L^?1 and 2.3 μg L^?1 for Pb(II) and Cd(II) respectively. Pb²⁺ and Cd²⁺ could not be detected simultaneously at a bare BDD electrode, whilst on a bulk Bi macro electrode (BiBE) the limits of detection for the simultaneous determination of Pb²⁺ and Cd²⁺ were ca. ten times higher.     

The Electrocatalytic Properties of Arc‐MWCNTs and Associated ‘Carbon Onions’

For the first time we report on the electrochemical characteristics of nanometer sized polyhedral graphite onions dispersed amongst arc‐MWCNTs. These are formed during the electric arc discharge method of producing ultrapure MWCNTs (arc‐MWCNTs). The carbon onions are randomly dispersed amongst the arc‐MWCNTs which are produced with very little amorphous carbon deposits or other unwanted impurities and are formed as closed‐ended tubes. By comparison with commercially available open‐ended hollow‐tube multiwalled carbon nanotubes made using the chemical vapor deposition method (cvd‐MWCNTs), a glassy carbon electrode (GCE), an edge‐plane pyrolytic graphite electrode (eppg) and basal plane pyrolytic graphite (bppg) electrode, we can speculate that it is the edge‐plane‐like defect sites that are the electroactive sites responsible for the apparent ‘electrocatalysis’ seen with a wide range of analytes including: ferrocyanide, ruthenium hexaamine(III), nicotinamide adenosine dinucleotide (NADH), epinephrine, norepinephrine, cysteine, and glutathione. The arc‐MWCNTs themselves are produced as closed‐ended tubes with very few, if any, edge‐plane‐like defect sites evident in their HRTEM characterization. Therefore we speculate that it is the carbon onions dispersed amongst the arc‐MWCNTs which have incomplete graphite shells or a rolled‐up ‘Swiss‐roll’ structures that posses the edge‐plane‐like defect sites and are responsible for the observed voltammetric responses. Carbon onions are no more or no less ‘electrocatalytic’ than open‐ended MWCNTs which in turn are no more electrocatalytic than an eppg electrode. As the carbon onions are ubiquitous in MWCNTs formed using the arc‐discharge method the authors advise that caution should be taken before assigning any electrocatalytic behavior to the MWCNTs themselves as any observed electrocatalysis likely arises from the carbon onion impurities.     

Applications of a travelling wave-based radio-frequency-only stacked ring ion guide

The use of radio-frequency (RF)-only ion guides for efficient transport of ions through regions of a mass spectrometer where the background gas pressure is relatively high is widespread in present instrumentation. Whilst multiple collisions between ions and the background gas can be beneficial, for example in inducing fragmentation and/or decreasing the spread in ion energies, the resultant reduction of ion axial velocity can be detrimental in modes of operation where a rapidly changing influx of ions to the gas-filled ion guide needs to be reproduced at the exit. In general, the RF-only ion guides presently in use are based on multipole rod sets. Here we report investigations into a new mode of ion propulsion within an RF ion guide based on a stack of ring electrodes. Ion propulsion is produced by superimposing a voltage pulse on the confining RF of an electrode and then moving the pulse to an adjacent electrode and so on along the guide to provide a travelling voltage wave on which the ions can surf. Through appropriate choice of the travelling wave pulse height, velocity and gas pressure it will be shown that the stacked ring ion guide with the travelling wave is effective as a collision cell in a tandem mass spectrometer where fast mass scanning or switching is required, as an ion mobility separator at pressures around 0.2 mbar, as an ion delivery device for enhancement of duty cycle on an orthogonal acceleration time-of-flight (oa-TOF) mass analyser, and as an ion fragmentation device at higher wave velocities.