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Abstract: We have recently revised the oft-cited model of cation insertion into electroreduced C60 film-modified electrodes in aqueous, basic electrolytes [L. Xiao, G.G. Wildgoose, A. Crossley, R.G. Compton, The electroreduction of “C60” films in aqueous electrolyte does not lead to alkali metal ion insertion—evidence for the involvement of adventitious poly-epoxidated C60 (C60O n ), submitted for publication]. Instead we have proposed that the observed reduction corresponds to adventitious polyepoxidated C60O n within the starting material [L. Xiao, G.G. Wildgoose, A. Crossley, R.G. Compton, The electroreduction of “C60” films in aqueous electrolyte does not lead to alkali metal ion insertion—evidence for the involvement of adventitious poly-epoxidated C60 (C60O n ), submitted for publication]. In this paper, we further show, using scanning electron microscopy and cyclic voltammetry of ascorbic acid, how our alternative model can be used to explain both the voltammetric behaviour observed during the reduction of “C60” films in aqueous electrolytes, and how the structure of these films can give rise to misleading claims of apparent “electrocatalytic” behaviour. The latter arises due to restructuring of the deposited C60 film giving rise to a porous, partially blocked electrode, coupled with possible thin-layer effects. We find no evidence that C60 itself is reduced within the potential window offered by aqueous electrolytes, nor that it is involved in any form of electron mediation or electrocatalysis. [Copyright &y& Elsevier]

Abstract: In this letter, we present experimental data which challenges the model proposed since the mid-1990s that the reduction of C60 films in aqueous electrolytes involves the formation of [M+ n C60 n−] where M+ represents a metal cation or proton. Instead we provide voltammetric, XPS and UV–vis evidence that the reduction of “C60” films in aqueous media is instead the reduction of adventitious poly-epoxidated C60O n with subsequent chemically irreversible loss of “O2 −” as water, and that C60 is not reduced within the potential windows of aqueous electrolytes. [Copyright &y& Elsevier]

Gold nanoparticles (∼30–60 nm in diameter) were deposited onto the surface of glassy carbon microspheres (10–20 μm) through electroless plating to produce bulk (i.e., gram) quantities of nanoparticle surface-modified microspheres. The gold nanoparticle-modified powder was then characterized by means of scanning electron microscopy and cyclic voltammetry. The voltammetric response of a macroelectrode consisting of a film of gold nanoparticle-modified glassy carbon microspheres, bound together and ‘wired-up’ using multiwalled carbon nanotubes (MWCNTs), was investigated. We demonstrate that by intelligently exploiting both nano- and microchemical architectures and wiring up the electroactive centers using MWCNTs in this way, we can obtain macroelectrode voltammetric behavior while only using ∼1% by mass of the expensive gold material that would be required to construct the equivalent gold film macrodisk electrode. The potential utility of electrodes constructed using chemical architectures such as this was demonstrated by applying them to the analytical determination of arsenic-(III) concentration. An optimized limit of detection of 2.5 ppb was obtained. [ABSTRACT FROM AUTHOR]

A simple pH probe is developed based upon the covalent chemical derivatisation of carbon particles with anthraquinone. The amperometric response of electrodes constructed from this material is examined and shown to produce a Nernstian linear response to pH from 1 to 9, over a range of temperatures from 20 to 70 °C, consistent with a two-electron, two-proton electrochemical process. [Copyright &y& Elsevier]

The bond energy of the unsupported Au–Au bond in the Au(ii) dimer [(C∧N∧C)Au]2 and the difference between AuIII–OH and AuIII–H bond enthalpies have been determined experimentally by electrochemical methods, with Au–OH and Au–H complexes showing unexpected differences in their reduction pathways, supported by DFT modelling. [ABSTRACT FROM AUTHOR]

Abstract: The direct electrochemistry of a HRP–chi–[C4mim][BF4] film (where HRP = horseradish peroxidase, chi = chitosan, and [C4mim][BF4] = the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluoroborate) has been studied by cyclic voltammetry on a glassy carbon electrode. The mechanism for the electrochemical reaction of HRP is suggested to be EC for the reduction, and CE for the following re-oxidation, as the oxidative peak potential remained approximately unchanged across the scan rate range. The half wave potential of HRP reduction was found to be pH dependent, suggesting that a concomitant proton and electron transfer is occurring. Using theoretical simulations of the experimentally obtained peak positions, the standard electron transfer rate constant, k 0, was found to be 98 (±16) s−1 at 295 K in pH 7 phosphate buffer solution, which is very close to the value reported in the absence of ionic liquid. This suggests that the ionic liquid used here in the HRP–chi–[C4mim][BF4]/GC electrode does not enhance the rate of electron transfer. k 0 was found to increase systematically with increasing temperature and followed a linear Arrhenius relation, giving an activation energy of 14.20 kJ mol−1. The electrode kinetics and activation energies obtained are identical to those reported for HRP films in aqueous media. This leads us to question if the use of RTIL films provide any unique benefits for enzyme/protein voltammetry. Rather the films may likely contain aqueous zones in which the enzymes are located and undergo electron transfer. [Copyright &y& Elsevier]

Three structural isomers of tris{bis(trifluoromethyl)phenyl}borane have been studied as the acidic component of frustrated Lewis pairs. While the 3,5-substituted isomer is already known to heterolytically cleave H2 to generate a bridging-hydride; ortho-substituents in the 2,4- and 2,5-isomers quench such reactivity through electron donation into the vacant boron pz orbital and steric blocking of the boron centre; as shown by electrochemical, structural and computational studies. Electrochemical studies of the corresponding borohydrides identify that the two-electron oxidation of terminal-hydrides occurs at more positive potentials than observed for [HB(C6F5)3]−, while the bridging-hydride oxidizes at a higher potential still, comparable to that of free H2. [ABSTRACT FROM AUTHOR]

We herein explore whether tris(aryl)borane Lewis acids are capable of cleaving H 2 outside of the usual Lewis acid/base chemistry described by the concept of frustrated Lewis pairs (FLPs). Instead of a Lewis base we use a chemical reductant to generate stable radical anions of two highly hindered boranes: tris(3,5-dinitromesityl)borane and tris(mesityl)borane. NMR spectroscopic characterization reveals that the corresponding borane radical anions activate (cleave) dihydrogen, whilst EPR spectroscopic characterization, supported by computational analysis, reveals the intermediates along the hydrogen activation pathway. This radical-based, redox pathway involves the homolytic cleavage of H 2 , in contrast to conventional models of FLP chemistry, which invoke a heterolytic cleavage pathway. This represents a new mode of chemical reactivity for hydrogen activation by borane Lewis acids., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Herein, we extend our "combined electrochemical-frustrated Lewis pair" approach to include Pt electrode surfaces for the first time. We found that the voltammetric response of an electrochemical-frustrated Lewis pair (FLP) system involving the B(C6 F5 )3 /[HB(C6 F5 )3 ](-) redox couple exhibits a strong surface electrocatalytic effect at Pt electrodes. Using a combination of kinetic competition studies in the presence of a H atom scavenger, 6-bromohexene, and by changing the steric bulk of the Lewis acid borane catalyst from B(C6 F5 )3 to B(C6 Cl5 )3 , the mechanism of electrochemical-FLP reactions on Pt surfaces was shown to be dominated by hydrogen-atom transfer (HAT) between Pt, [PtH] adatoms and transient [HB(C6 F5 )3 ](⋅) electrooxidation intermediates. These findings provide further insight into this new area of combining electrochemical and FLP reactions, and proffers additional avenues for exploration beyond energy generation, such as in electrosynthesis., (© 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

A synthesis of graphite powder covalently modified with gallic acid (3,4,5-trihydroxybenzoic acid), via a 1,2-diaminoethane "linker" molecule, to form gallylaminoethylaminocarbonyl graphite (gallic-carbon) is reported. The synthesis was used as a model for a "ground-upwards building-block" approach to a primary dendrimer of gallic acid covalently attached to the surface of graphite powder, tris-(O-gallyl)-gallylaminoethylaminocarbonyl graphite (TGGA-carbon). The resulting modified carbon materials were characterized at each stage of the syntheses using X-ray photoelectron spectroscopy (XPS) analysis. The effects of increasing the modifier's structural complexity from monomeric gallic-carbon to the analogous primary dendrimer TGGA-carbon were explored by comparing each material's efficacy toward the adsorption of Al(III) ions from water. The uptake of Al(III) ions by gallic-carbon and TGGA-carbon was measured using UV-vis spectroscopy. In comparison to the case of monomeric gallic-carbon, the rate of adsorption of Al(III) ions by the TGGA-carbon was found to be 2.3 times more rapid. Furthermore, the total uptake of Al(III) ions was greater (reducing the concentration of 1000 ppb Al(III) solutions to below the WHO legal limit of 100 ppb in less than 5 min) and irreversible, in contrast to the gallic-carbon where the adsorption was found to be under thermodynamic control and to follow a Freundlich isotherm.

We demonstrate proof-of-concept that generator-collector experiments can be performed at a single macroelectrode and used to determine mechanistic information. The practical advantages of such a system over conventional generator-collector techniques are also outlined. The single-electrode generator-collector technique is applied to study the known mechanism of oxygen reduction in aqueous conditions as a model system. We seek to demonstrate that the single-electrode generator-collector approach is capable of detecting local pH changes, immediately adjacent to the electrode surface during a redox reaction. Experiments are performed using a molecular pH probe attached to the electrode surface. Comparison of experimental data with numerical simulations verifies that the reduction of oxygen at pH 6.8 proceeds via a two-electron, two-proton mechanism. Experiments were also performed with a molecular pH probe dissolved in the electrolyte solution in order to explore the feasibility of this approach, which is potentially applicable to a much wider range of electrochemical systems.

The pKa value of protonated Jeffamine (bis(3-aminopropyl) terminated polyethylene glycol) in solution and attached as a monolayer to graphite surfaces has been determined using potentiometric titration. The protonated Jeffamine was found to have a pKa value of 9.7 in solution at 25 degrees C, whereas this value decreases to 7.1 when it is attached to a graphite surface. Potentiometric titrations from 25 to 40 degrees C allowed us to determine the surface pKa of the protonated Jeffamine at each temperature studied and hence to determine the enthalpy, entropy and Gibbs energy changes associated with the deprotonation of the amino-terminated surface bound Jeffamine groups. It was found that the enthalpic contribution is negligibly small and the evaluation of these thermodynamic parameters controlling the shift in surface pKa value indicates that this process is controlled by entropic contribution arising from the ordering/disordering of solvent molecules at the carbon-water interface. This suggests that the long chain Jeffamine molecules are oriented on the carbon surface rather than existing in the bulk solution.

The thermodynamics of and the kinetic parameters controlling the sequestration of the toxic heavy-metal ion Cd(II) from aqueous media by using a novel material consisting of glassy carbon microspheres (10-20 microm in diameter) chemically modified with L-cysteine methyl ester are presented. In an effort to reduce the cost and increase the efficiency of toxic-metal-ion removal, this modification strategy was expanded to attach L-cysteine methyl chemically ester to less-expensive graphite powders (2-20 microm in diameter), and the thermodynamic and kinetic parameters of the sequestration of Cd(II), Cu(II), and As(III) toxic metal ions are presented. It was found that the use of chemically modified graphite powder greatly increased both the rate and the amount of metal ions removed from aqueous media. This work has important potential applications to filtration of drinking water and environmental remediation.