Leigh Aldous | King's College London (original) (raw)
Papers by Leigh Aldous
The Journal of Physical Chemistry C, 2013
ABSTRACT The oxygen reduction reaction (ORR) has been studied at platinum, gold, and glassy carbo... more ABSTRACT The oxygen reduction reaction (ORR) has been studied at platinum, gold, and glassy carbon electrodes using cyclic voltammetry and potential-step chronoamperometry in 11 room temperature protic ionic liquids (PILs). The diffusion coefficient and solubility of oxygen in seven PILs were determined by nonlinear curve fitting of potential-step chronoamperometry at a platinum microelectrode. The diffusion coefficient of oxygen in the PILs was consistently on the order of 10–6 cm2 s–1. The ORR in the PILs was found to largely follow an electrochemical–chemical–electrochemical–chemical (ECEC) mechanism, as demonstrated by digital simulation of cyclic voltammograms at platinum, gold, and glassy carbon electrodes. The influence of electrode material on peak potential, heterogeneous rate constant, and transfer coefficient was studied. The influence of temperature on kinetics and thermodynamic properties like activation energy of ORR, activation energy of diffusion, and enthalpy of dissolution of oxygen in ethylammonium nitrate, bis(methoxyethyl)ammonium benzoate, and bis-(methoxyethyl)ammonium sulfamate was also investigated.
The electrochemistry of chloride in water-containing hydrophobic ([Emim][NTf2] and [BmPyrr][NTf2]... more The electrochemistry of chloride in water-containing hydrophobic ([Emim][NTf2] and [BmPyrr][NTf2]) and
hydrophilic ([Emim][OAc]) ionic liquids (ILs) has been described in detail for the first time. Cyclic
voltammetric studies at a glassy carbon electrode note the significant effect of ambient water on the electrochemistry
of chloride, with different outcomes based upon the hydrophilicity (c.f. water content) of the hygroscopic
ILs. Added hydroxide highlighted this as a reactive species. Evaluation of chloride, hypochlorite,
chlorite, chlorate and perchlorate electrochemistry (chlorine oxidation states −1, +1, +3, +5 and +7)
was performed. Ultimately, the electrochemically formed chlorine (Cl2) was determined to react with
water or hydroxide to yield higher oxidation state species via oxychloride intermediates (e.g. hypochlorite)
through multiple EC steps, likely resulting in chlorate as the final product.
Combining ferrocene and iodine results in enhanced thermoelectrochemical (or thermogalvanic) wast... more Combining ferrocene and iodine results in enhanced thermoelectrochemical
(or thermogalvanic) waste heat harvesting abilities,
for both the Seebeck coefficient and the overall power output.
All systems displayed a mixture of ferrocene, ferrocenium, iodine
and triiodide. The observed enhancement correlates with lower
electron-density on the ferrocene; the synergistic improvement
observed for mixtures of substituted ferrocenes and iodine is attributed
to the formation of charge-transfer complexes. Combining
dibutanoylferrocene and iodine resulted in the highest Seebeck
coefficient of 1.67 mV K1.
The effect of ionic liquids upon the mechanical and (bio)chemical integrity of macadamia nut shel... more The effect of ionic liquids upon the mechanical
and (bio)chemical integrity of macadamia nut shells (from
Macadamia integrifolia) has been investigated. Whole macadamia nuts-in-shell are notoriously difficult to crack, and the Australian macadamia nut shells used in this study required
2240 ± 430 N of force to crack. Ionic liquids were screened for
their solubility values, with 1-ethyl-3-methylimidazolium
acetate ([Emim][OAc]) able to dissolve 5.5 ± 0.5 wt %
macadamia nut shell. Treatment with small quantities of
[Emim][OAc] resulted in weakened whole nut-in-shells that
could be cracked with only ca. 46% of the displacement (0.67
± 0.16 mm), ca. 34% of the force (760 ± 240 N) and ca. 15%
of the energy (0.25 ± 0.10 J per shell) relative to no treatment. Further treatment by dissolution and precipitation of macadamia nut shell, followed by enzymatic hydrolysis with cellulase, resulted in the release of 80 ± 15% of the expected glucose content, relative to 1.3 ± 1.0% before any pretreatment.
In this study, a “membrane-less and spill-less” gas-sensing device has been evaluated for the ele... more In this study, a “membrane-less and spill-less” gas-sensing device has been evaluated for the electrochemical detection of oxygen. Iron oxide magnetic nanoparticles were prepared by chemical co-precipitation and used to prepare an aqueous ferrofluid. The iron oxide nanoparticles were subsequently stabilised and passivated with a cationic polymer, namely, poly(diallyldimethyl ammonium chloride). The resulting ferrofluid was evaluated as an electrolyte for the analytical quantification of oxygen on screen-printed carbon electrodes. An applied magnetic field immobilised the ferrofluid electrolyte in place to result in a “membrane-less and spill-less” ferrofluid-based gas sensor. The polymer poly(diallyldimethyl ammonium chloride) was found to result in an apparent enhancement in the electrocatalysis of the system towards the oxygen reduction reaction. Furthermore, as the strength of the applied magnetic field was increased, the oxygen reduction current also increased owing to the response of the polymer-coated nanoparticles. The oxygen reduction current was linear from 0 to 100 % oxygen content.
The effect of ionic liquids upon the mechanical and (bio)chemical integrity of macadamia nut shel... more The effect of ionic liquids upon the mechanical and (bio)chemical integrity of macadamia nut shells (from Macadamia integrifolia) has been investigated. Whole macadamia nuts-in-shell are notoriously difficult to crack, and the Australian macadamia nut shells used in this study required 2240 ± 430 N of force to crack. Ionic liquids were screened for their solubility values, with 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) able to dissolve 5.5 ± 0.5 wt % macadamia nut shell. Treatment with small quantities of [Emim][OAc] resulted in weakened whole nut-in-shells that could be cracked with only ca. 46% of the displacement (0.67 ± 0.16 mm), ca. 34% of the force (760 ± 240 N) and ca. 15% of the energy (0.25 ± 0.10 J per shell) relative to no treatment. Further treatment by dissolution and precipitation of macadamia nut shell, followed by enzymatic hydrolysis with cellulase, resulted in the release of 80 ± 15% of the expected glucose content, relative to 1.3 ± 1.0% before any pretreatment.
A facile technique for the quantification of lignin solubility in ionic liquids has been establis... more A facile technique for the quantification of lignin solubility in ionic liquids has been established. This was used to examine the effect of the anionic and cationic components of ionic liquids on lignin solubility. Changing the cation was shown to have a significant effect on lignin solubility. Interaction of aromatic cations with the solute was significant in most, but not all, ionic liquids. The anion was required to have a minimum hydrogen bonding basicity value for lignin to dissolve, but after this point the anion effect on the overall lignin solubility was negligible relative to the cation.
Ionic liquids can be used as non-volatile, tunable solvents, extractants and electrolytes. This w... more Ionic liquids can be used as non-volatile, tunable solvents, extractants and electrolytes. This work investigates their ability to extract an organic analyte, capsaicin, from fresh Capsicum annuum Bird's eye chilli peppers (also known as Thai chillies), followed by the electroanalytical quantification of the extracted analyte. Ascorbic acid (vitamin C) was also extracted and quantified. Two ionic liquids were identified to extract capsaicin from fresh chilli more effectively than the conventional ethanol-based process; the inherently basic 1-ethyl-3-methylimidazolium acetate, [Emim][OAc], and the inherently acidic 1-ethyl-3-methylimidazolium hydrogen sulfate, [Emim][HSO4]. The ionic liquid extracts could be electrochemically quantified using a bare glassy carbon electrode either in the pure ionic liquid (one pot extraction and quantification) or after dilution with water/ethanol to assist resolution of the capsaicin (flavour indicator) and ascorbic acid (freshness indicator) features.
We present a review on the multifunctional use of ionic liquids with respect to lignin processing... more We present a review on the multifunctional use of ionic liquids with respect to lignin processing. In a biorefinery context, lignocellulosics could be used to provide sustainable sources of fuels such as bioethanol, and feedstock molecules for the chemical industry such as phenols and other aromatics. However, separation of lignin from cellulose and hemicellulose is a vital step. Ionic liquids can dissolve extensive quantities of biomass, and even be designed to be multifunctional solvents. We highlight the use of ionic liquids in selectively or non-selectively dissolving lignin, the depolymerization reactions that have been attempted on lignin in ionic liquids, and the effect ionic liquids have been observed to have on such processes. Finally, we present some of the challenges and issues that must be addressed before the informed and large-scale application of ionic liquids can be realized for lignin processing.
http://dx.doi.org/10.1071/CH12324
Herein, we report the synthesis of three covalently linked superparamagnetic nanocrystal-multi-wa... more Herein, we report the synthesis of three covalently linked superparamagnetic nanocrystal-multi-walled carbon nanotube (MWCNT) composites. A generic strategy for amphiphilic polymer coating of nanocrystals and further functionalization for amide bond formation with the MWCNTs is discussed. This approach can in principle allow attachment of any colloidal nanocrystal to the MWCNTs. The materials were characterized at each stage of the syntheses using DLS, zeta-potential measurements, FT-IR, TEM, and XPS techniques. The practicality of this linkage is demonstrated by the reversible magnetic immobilization of these materials on an electrode during non-aqueous electrochemistry.
http://dx.doi.org/10.1016/j.jcis.2012.06.028
The Hydrogen evolution reaction has been quantitatively investigated at a Pt electrode in series ... more The Hydrogen evolution reaction has been quantitatively investigated at a Pt electrode in series of room temperature ionic liquids vs. Ag/Ag+ redox couple. The measured formal potentials of the H2/H+(HNTf2) redox couple in each RTIL reveals a dependence on the nature of anion, suggesting significant interaction between proton and anion.
The reduction of oxygen on boron-doped diamond (BDD) and glassy carbon (GC) electrodes was studie... more The reduction of oxygen on boron-doped diamond (BDD) and glassy carbon (GC) electrodes was studied in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(2)mim][NTf(2)]. O(2) reduction at both electrodes was found to involve the 1e(-) reduction of oxygen to superoxide. The formation of superoxide was verified by repeating the oxygen reduction on BDD in the presence of benzoic acid, resulting in a shift from the 1e(-) reduction observed in the absence of benzoic acid to a 2e(-) reduction yielding the hydroperoxyl anion. The reduction of O(2) was found to be quasi-reversible on GC and irreversible on BDD. The significantly slower kinetics observed on the BDD electrode are likely due to the lower electronic density of states in BDD.
http://dx.doi.org/10.1016/j.jelechem.2011.10.004
The electrochemistry of elemental sulfur (S(8)) and the polysulfides Na(2)S(4) and Na(2)S(6) has ... more The electrochemistry of elemental sulfur (S(8)) and the polysulfides Na(2)S(4) and Na(2)S(6) has been studied for the first time in nonchloroaluminate ionic liquids. The cyclic voltammetry of S(8) in the ionic liquids is different to the behavior reported in some organic solvents, with two reductions and one oxidation peak observed. Supported by in situ UV-vis spectro-electrochemical experiments, the main reduction products of S(8) in [C(4)mim][DCA] ([C(4)mim] = 1-butyl-3-methylimidazolium; DCA = dicyanamide) have been identified as s(6)(2-) and S(4)(2-), and plausible pathways for the formation of these species are proposed. Dissociation and/or disproportionation of the polyanions S(6)(2-) and S(4)(2-) appears to be slow in the ionic liquid, with only small amounts of the blue radical species S3(center dot-) formed in the solutions at r.t., in contrast with that observed in most molecular solvents.
http://dx.doi.org/10.1021/jp208159v
After 35 years the hunt for improved anthracycline antibiotics is unabated but has yet to achieve... more After 35 years the hunt for improved anthracycline antibiotics is unabated but has yet to achieve the levels of clinical success desired. Electrochemical techniques provide a large amount of kinetic and thermodynamic information, but the use of such procedures is hindered by issues of sensitivity and selectivity. This work demonstrates how by harnessing the mechanism of catalytic reduction of oxygen by the quinone functionality present within the anthracycline structure it is possible to study the reactive moiety in nanomolar concentration. This methodology allows electrochemical investigation of the intercalation of quinizarin into DNA and, in particular, the quinone oxidation and degradation mechanism. The reversible reduction of the quinizarin, which in the presence of oxygen leads to the formation of reactive oxygen species, is found to occur at -0.535 V (vs. SCE) pH 6.84 and the irreversible oxidation leading to the molecules degradation occurs at +0.386 V (vs. SCE) pH 6.84.
http://dx.doi.org/10.1073/pnas.1113615108
The volatilisation of a range of ferrocene compounds from a range of room temperature ionic liqui... more The volatilisation of a range of ferrocene compounds from a range of room temperature ionic liquids (RTILs) into a flow of nitrogen gas was investigated. Namely, n-butylferrocene, 1,1'-dimethylferrocene and ferrocene were investigated in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide ([C(4)mpyrr][NTf2]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C(2)mim][NTf2]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BF4]). Cyclic voltammetric and chronoamperometric monitoring of the ferrocene compound concentration allowed quantification of the rate constants of volatilisation, k, activation energies of volatilisation, E-a, and entropies of activation, Delta S double dagger. The rate of volatilisation was found to be ferrocene > 1,1'-dimethylferrocene > n-butylferrocene, and trends in the rate constant of the volatilisation process as a function of molecular size and ionic liquid surface tension were investigated. These indicate that the transition state for the volatilisation is when the solute is located in the liquid surface, and that the creation of a cavity of some sort in the liquid surface is necessary to allow volatilisation.
http://dx.doi.org/10.1039/c2nj20704d
The voltammetric response of the quinone species 'quinizarin' (QZ) and its electrocatalytic reduc... more The voltammetric response of the quinone species 'quinizarin' (QZ) and its electrocatalytic reduction of oxygen are studied at a boron doped diamond electrode (BDD). It is demonstrated that, contrary to the widespread belief that adsorption of organic molecules on BDD is minimal, not only does QZ readily adsorb to the electrodes surface but this adsorption is also influenced at low surface coverages by the pre-exposure of the electrode to organic solvents. Furthermore, the nature of this adsorbed QZ species is investigated and a potential dependent phase transition is observed. This is to the authors knowledge the first system to exhibit a phase transition of an adsorbed species on a boron doped diamond surface. At low scan rates the system is found to oscillate; these oscillations are ascribed to the presence of a 'negative differential resistance'.
http://dx.doi.org/10.1039/c2cp23380k
The electrodeposition of rubidium from an ionic liquid (IL) N-butyl-N-methylpyrrolidium bis(trifl... more The electrodeposition of rubidium from an ionic liquid (IL) N-butyl-N-methylpyrrolidium bis(trifluoromethylsulfonyl)imide ([C(4)mpyrr][NTf(2)]) has been performed and monitored at a Nickel mesh electrode by using in situ electrochemical-X-ray Photoelectron Spectroscopy (XPS) measurements. At extremely high current values during the deposition of the metal, the solvent breakdown was also observed. By choosing suitable low current values, electrodeposition of Rb can be promoted over the IL degradation. IL degradation was characterised by carbonisation of the electrode-IL-vacuum interface, with the loss of fluorine being relatively pronounced, consistent with reduction of the [NTf(2)] anion.
http://dx.doi.org/10.1016/j.cplett.2011.10.017
First, the electrochemical characteristics of Fenton's reagent (Fe(III), Fe(II) and hydrogen pero... more First, the electrochemical characteristics of Fenton's reagent (Fe(III), Fe(II) and hydrogen peroxide), including its catalytic (EC') behaviour were investigated. Second, the electrogeneration of hydrogen peroxide by a two-electron reduction of dissolved oxygen was conducted at a carbon electrode in a divided electrolysis cell and the concentration of hydrogen peroxide obtained was determined by the titration. The two approaches were then combined to give a one-pot, relatively green approach to aromatic hydroxylation reactions, with the electro-Fenton method allowing the iron to be used catalytically and the oxygen/water employed as the hydroxylation reagent by the in situ production of hydrogen peroxide. In particular, the preparative-scale hydroxylation of salicylic acid has been studied in an oxygen-saturated 0.1 M Na2SO4 pH 3.0 solution containing 5 mM Fe(II) and 5 mM salicylic acid at the controlled potential of 1.0 V vs. SCE. The study showed that after the attack of the hydroxyl radical produced in situ by the electro-Fenton process on salicylic acid, 2,3- and 2,5-dihydroxybenzoic acids were detected as primary monohydroxylated products with the highest yield of ca. 21.6 +/- 2.5%.
http://dx.doi.org/10.1039/c2nj21007j
Carbon black (CB) nanoparticles modified with fluorescein, a highly fluorescent molecule, were pr... more Carbon black (CB) nanoparticles modified with fluorescein, a highly fluorescent molecule, were prepared using a facile and efficient methodology. Simply stirring CB in aqueous solution containing fluorescein resulted in the strong physisorption of fluorescein onto the CB surface. The resulting Fluorescein/CB was then characterised by means of X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), fluorescence microscopy and fluorescence spectroscopy. The optimum experimental conditions for fluorescence of Fluorescein/CB viz. fluorescence excitation and emission wavelengths, O-2 removal and the amount of Fluorescein/CB used, were investigated. The Fluorescein/CB was used as a fluorescent probe for the sensitive detection of Pd(II) in water, based on fluorescence quenching. The results demonstrated that the fluorescence intensity of Fluorescein/CB decreased with increasing Pd(II) concentration, and the fluorescence quenching process could be described by the Stern-Volmer equation. The limit of detection (LOD) for the fluorescence quenching of Fluorescein/CB by Pd(II) in aqueous solution was found to be 1.07 mu M (based on 3 sigma). Last, approaches were studied for the removal of Fe(III) which interferes with the fluorescence quenching of Fluorescein/CB. Complexation of Fe(III) with salicylic acid was used to enhance and control the selectivity of Fluorescein/CB sensor towards Pd(II) in the presence of Fe(III).
http://dx.doi.org/10.1039/c2an16261j
The Journal of Physical Chemistry C, 2013
ABSTRACT The oxygen reduction reaction (ORR) has been studied at platinum, gold, and glassy carbo... more ABSTRACT The oxygen reduction reaction (ORR) has been studied at platinum, gold, and glassy carbon electrodes using cyclic voltammetry and potential-step chronoamperometry in 11 room temperature protic ionic liquids (PILs). The diffusion coefficient and solubility of oxygen in seven PILs were determined by nonlinear curve fitting of potential-step chronoamperometry at a platinum microelectrode. The diffusion coefficient of oxygen in the PILs was consistently on the order of 10–6 cm2 s–1. The ORR in the PILs was found to largely follow an electrochemical–chemical–electrochemical–chemical (ECEC) mechanism, as demonstrated by digital simulation of cyclic voltammograms at platinum, gold, and glassy carbon electrodes. The influence of electrode material on peak potential, heterogeneous rate constant, and transfer coefficient was studied. The influence of temperature on kinetics and thermodynamic properties like activation energy of ORR, activation energy of diffusion, and enthalpy of dissolution of oxygen in ethylammonium nitrate, bis(methoxyethyl)ammonium benzoate, and bis-(methoxyethyl)ammonium sulfamate was also investigated.
The electrochemistry of chloride in water-containing hydrophobic ([Emim][NTf2] and [BmPyrr][NTf2]... more The electrochemistry of chloride in water-containing hydrophobic ([Emim][NTf2] and [BmPyrr][NTf2]) and
hydrophilic ([Emim][OAc]) ionic liquids (ILs) has been described in detail for the first time. Cyclic
voltammetric studies at a glassy carbon electrode note the significant effect of ambient water on the electrochemistry
of chloride, with different outcomes based upon the hydrophilicity (c.f. water content) of the hygroscopic
ILs. Added hydroxide highlighted this as a reactive species. Evaluation of chloride, hypochlorite,
chlorite, chlorate and perchlorate electrochemistry (chlorine oxidation states −1, +1, +3, +5 and +7)
was performed. Ultimately, the electrochemically formed chlorine (Cl2) was determined to react with
water or hydroxide to yield higher oxidation state species via oxychloride intermediates (e.g. hypochlorite)
through multiple EC steps, likely resulting in chlorate as the final product.
Combining ferrocene and iodine results in enhanced thermoelectrochemical (or thermogalvanic) wast... more Combining ferrocene and iodine results in enhanced thermoelectrochemical
(or thermogalvanic) waste heat harvesting abilities,
for both the Seebeck coefficient and the overall power output.
All systems displayed a mixture of ferrocene, ferrocenium, iodine
and triiodide. The observed enhancement correlates with lower
electron-density on the ferrocene; the synergistic improvement
observed for mixtures of substituted ferrocenes and iodine is attributed
to the formation of charge-transfer complexes. Combining
dibutanoylferrocene and iodine resulted in the highest Seebeck
coefficient of 1.67 mV K1.
The effect of ionic liquids upon the mechanical and (bio)chemical integrity of macadamia nut shel... more The effect of ionic liquids upon the mechanical
and (bio)chemical integrity of macadamia nut shells (from
Macadamia integrifolia) has been investigated. Whole macadamia nuts-in-shell are notoriously difficult to crack, and the Australian macadamia nut shells used in this study required
2240 ± 430 N of force to crack. Ionic liquids were screened for
their solubility values, with 1-ethyl-3-methylimidazolium
acetate ([Emim][OAc]) able to dissolve 5.5 ± 0.5 wt %
macadamia nut shell. Treatment with small quantities of
[Emim][OAc] resulted in weakened whole nut-in-shells that
could be cracked with only ca. 46% of the displacement (0.67
± 0.16 mm), ca. 34% of the force (760 ± 240 N) and ca. 15%
of the energy (0.25 ± 0.10 J per shell) relative to no treatment. Further treatment by dissolution and precipitation of macadamia nut shell, followed by enzymatic hydrolysis with cellulase, resulted in the release of 80 ± 15% of the expected glucose content, relative to 1.3 ± 1.0% before any pretreatment.
In this study, a “membrane-less and spill-less” gas-sensing device has been evaluated for the ele... more In this study, a “membrane-less and spill-less” gas-sensing device has been evaluated for the electrochemical detection of oxygen. Iron oxide magnetic nanoparticles were prepared by chemical co-precipitation and used to prepare an aqueous ferrofluid. The iron oxide nanoparticles were subsequently stabilised and passivated with a cationic polymer, namely, poly(diallyldimethyl ammonium chloride). The resulting ferrofluid was evaluated as an electrolyte for the analytical quantification of oxygen on screen-printed carbon electrodes. An applied magnetic field immobilised the ferrofluid electrolyte in place to result in a “membrane-less and spill-less” ferrofluid-based gas sensor. The polymer poly(diallyldimethyl ammonium chloride) was found to result in an apparent enhancement in the electrocatalysis of the system towards the oxygen reduction reaction. Furthermore, as the strength of the applied magnetic field was increased, the oxygen reduction current also increased owing to the response of the polymer-coated nanoparticles. The oxygen reduction current was linear from 0 to 100 % oxygen content.
The effect of ionic liquids upon the mechanical and (bio)chemical integrity of macadamia nut shel... more The effect of ionic liquids upon the mechanical and (bio)chemical integrity of macadamia nut shells (from Macadamia integrifolia) has been investigated. Whole macadamia nuts-in-shell are notoriously difficult to crack, and the Australian macadamia nut shells used in this study required 2240 ± 430 N of force to crack. Ionic liquids were screened for their solubility values, with 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) able to dissolve 5.5 ± 0.5 wt % macadamia nut shell. Treatment with small quantities of [Emim][OAc] resulted in weakened whole nut-in-shells that could be cracked with only ca. 46% of the displacement (0.67 ± 0.16 mm), ca. 34% of the force (760 ± 240 N) and ca. 15% of the energy (0.25 ± 0.10 J per shell) relative to no treatment. Further treatment by dissolution and precipitation of macadamia nut shell, followed by enzymatic hydrolysis with cellulase, resulted in the release of 80 ± 15% of the expected glucose content, relative to 1.3 ± 1.0% before any pretreatment.
A facile technique for the quantification of lignin solubility in ionic liquids has been establis... more A facile technique for the quantification of lignin solubility in ionic liquids has been established. This was used to examine the effect of the anionic and cationic components of ionic liquids on lignin solubility. Changing the cation was shown to have a significant effect on lignin solubility. Interaction of aromatic cations with the solute was significant in most, but not all, ionic liquids. The anion was required to have a minimum hydrogen bonding basicity value for lignin to dissolve, but after this point the anion effect on the overall lignin solubility was negligible relative to the cation.
Ionic liquids can be used as non-volatile, tunable solvents, extractants and electrolytes. This w... more Ionic liquids can be used as non-volatile, tunable solvents, extractants and electrolytes. This work investigates their ability to extract an organic analyte, capsaicin, from fresh Capsicum annuum Bird's eye chilli peppers (also known as Thai chillies), followed by the electroanalytical quantification of the extracted analyte. Ascorbic acid (vitamin C) was also extracted and quantified. Two ionic liquids were identified to extract capsaicin from fresh chilli more effectively than the conventional ethanol-based process; the inherently basic 1-ethyl-3-methylimidazolium acetate, [Emim][OAc], and the inherently acidic 1-ethyl-3-methylimidazolium hydrogen sulfate, [Emim][HSO4]. The ionic liquid extracts could be electrochemically quantified using a bare glassy carbon electrode either in the pure ionic liquid (one pot extraction and quantification) or after dilution with water/ethanol to assist resolution of the capsaicin (flavour indicator) and ascorbic acid (freshness indicator) features.
We present a review on the multifunctional use of ionic liquids with respect to lignin processing... more We present a review on the multifunctional use of ionic liquids with respect to lignin processing. In a biorefinery context, lignocellulosics could be used to provide sustainable sources of fuels such as bioethanol, and feedstock molecules for the chemical industry such as phenols and other aromatics. However, separation of lignin from cellulose and hemicellulose is a vital step. Ionic liquids can dissolve extensive quantities of biomass, and even be designed to be multifunctional solvents. We highlight the use of ionic liquids in selectively or non-selectively dissolving lignin, the depolymerization reactions that have been attempted on lignin in ionic liquids, and the effect ionic liquids have been observed to have on such processes. Finally, we present some of the challenges and issues that must be addressed before the informed and large-scale application of ionic liquids can be realized for lignin processing.
http://dx.doi.org/10.1071/CH12324
Herein, we report the synthesis of three covalently linked superparamagnetic nanocrystal-multi-wa... more Herein, we report the synthesis of three covalently linked superparamagnetic nanocrystal-multi-walled carbon nanotube (MWCNT) composites. A generic strategy for amphiphilic polymer coating of nanocrystals and further functionalization for amide bond formation with the MWCNTs is discussed. This approach can in principle allow attachment of any colloidal nanocrystal to the MWCNTs. The materials were characterized at each stage of the syntheses using DLS, zeta-potential measurements, FT-IR, TEM, and XPS techniques. The practicality of this linkage is demonstrated by the reversible magnetic immobilization of these materials on an electrode during non-aqueous electrochemistry.
http://dx.doi.org/10.1016/j.jcis.2012.06.028
The Hydrogen evolution reaction has been quantitatively investigated at a Pt electrode in series ... more The Hydrogen evolution reaction has been quantitatively investigated at a Pt electrode in series of room temperature ionic liquids vs. Ag/Ag+ redox couple. The measured formal potentials of the H2/H+(HNTf2) redox couple in each RTIL reveals a dependence on the nature of anion, suggesting significant interaction between proton and anion.
The reduction of oxygen on boron-doped diamond (BDD) and glassy carbon (GC) electrodes was studie... more The reduction of oxygen on boron-doped diamond (BDD) and glassy carbon (GC) electrodes was studied in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(2)mim][NTf(2)]. O(2) reduction at both electrodes was found to involve the 1e(-) reduction of oxygen to superoxide. The formation of superoxide was verified by repeating the oxygen reduction on BDD in the presence of benzoic acid, resulting in a shift from the 1e(-) reduction observed in the absence of benzoic acid to a 2e(-) reduction yielding the hydroperoxyl anion. The reduction of O(2) was found to be quasi-reversible on GC and irreversible on BDD. The significantly slower kinetics observed on the BDD electrode are likely due to the lower electronic density of states in BDD.
http://dx.doi.org/10.1016/j.jelechem.2011.10.004
The electrochemistry of elemental sulfur (S(8)) and the polysulfides Na(2)S(4) and Na(2)S(6) has ... more The electrochemistry of elemental sulfur (S(8)) and the polysulfides Na(2)S(4) and Na(2)S(6) has been studied for the first time in nonchloroaluminate ionic liquids. The cyclic voltammetry of S(8) in the ionic liquids is different to the behavior reported in some organic solvents, with two reductions and one oxidation peak observed. Supported by in situ UV-vis spectro-electrochemical experiments, the main reduction products of S(8) in [C(4)mim][DCA] ([C(4)mim] = 1-butyl-3-methylimidazolium; DCA = dicyanamide) have been identified as s(6)(2-) and S(4)(2-), and plausible pathways for the formation of these species are proposed. Dissociation and/or disproportionation of the polyanions S(6)(2-) and S(4)(2-) appears to be slow in the ionic liquid, with only small amounts of the blue radical species S3(center dot-) formed in the solutions at r.t., in contrast with that observed in most molecular solvents.
http://dx.doi.org/10.1021/jp208159v
After 35 years the hunt for improved anthracycline antibiotics is unabated but has yet to achieve... more After 35 years the hunt for improved anthracycline antibiotics is unabated but has yet to achieve the levels of clinical success desired. Electrochemical techniques provide a large amount of kinetic and thermodynamic information, but the use of such procedures is hindered by issues of sensitivity and selectivity. This work demonstrates how by harnessing the mechanism of catalytic reduction of oxygen by the quinone functionality present within the anthracycline structure it is possible to study the reactive moiety in nanomolar concentration. This methodology allows electrochemical investigation of the intercalation of quinizarin into DNA and, in particular, the quinone oxidation and degradation mechanism. The reversible reduction of the quinizarin, which in the presence of oxygen leads to the formation of reactive oxygen species, is found to occur at -0.535 V (vs. SCE) pH 6.84 and the irreversible oxidation leading to the molecules degradation occurs at +0.386 V (vs. SCE) pH 6.84.
http://dx.doi.org/10.1073/pnas.1113615108
The volatilisation of a range of ferrocene compounds from a range of room temperature ionic liqui... more The volatilisation of a range of ferrocene compounds from a range of room temperature ionic liquids (RTILs) into a flow of nitrogen gas was investigated. Namely, n-butylferrocene, 1,1'-dimethylferrocene and ferrocene were investigated in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide ([C(4)mpyrr][NTf2]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C(2)mim][NTf2]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BF4]). Cyclic voltammetric and chronoamperometric monitoring of the ferrocene compound concentration allowed quantification of the rate constants of volatilisation, k, activation energies of volatilisation, E-a, and entropies of activation, Delta S double dagger. The rate of volatilisation was found to be ferrocene > 1,1'-dimethylferrocene > n-butylferrocene, and trends in the rate constant of the volatilisation process as a function of molecular size and ionic liquid surface tension were investigated. These indicate that the transition state for the volatilisation is when the solute is located in the liquid surface, and that the creation of a cavity of some sort in the liquid surface is necessary to allow volatilisation.
http://dx.doi.org/10.1039/c2nj20704d
The voltammetric response of the quinone species 'quinizarin' (QZ) and its electrocatalytic reduc... more The voltammetric response of the quinone species 'quinizarin' (QZ) and its electrocatalytic reduction of oxygen are studied at a boron doped diamond electrode (BDD). It is demonstrated that, contrary to the widespread belief that adsorption of organic molecules on BDD is minimal, not only does QZ readily adsorb to the electrodes surface but this adsorption is also influenced at low surface coverages by the pre-exposure of the electrode to organic solvents. Furthermore, the nature of this adsorbed QZ species is investigated and a potential dependent phase transition is observed. This is to the authors knowledge the first system to exhibit a phase transition of an adsorbed species on a boron doped diamond surface. At low scan rates the system is found to oscillate; these oscillations are ascribed to the presence of a 'negative differential resistance'.
http://dx.doi.org/10.1039/c2cp23380k
The electrodeposition of rubidium from an ionic liquid (IL) N-butyl-N-methylpyrrolidium bis(trifl... more The electrodeposition of rubidium from an ionic liquid (IL) N-butyl-N-methylpyrrolidium bis(trifluoromethylsulfonyl)imide ([C(4)mpyrr][NTf(2)]) has been performed and monitored at a Nickel mesh electrode by using in situ electrochemical-X-ray Photoelectron Spectroscopy (XPS) measurements. At extremely high current values during the deposition of the metal, the solvent breakdown was also observed. By choosing suitable low current values, electrodeposition of Rb can be promoted over the IL degradation. IL degradation was characterised by carbonisation of the electrode-IL-vacuum interface, with the loss of fluorine being relatively pronounced, consistent with reduction of the [NTf(2)] anion.
http://dx.doi.org/10.1016/j.cplett.2011.10.017
First, the electrochemical characteristics of Fenton's reagent (Fe(III), Fe(II) and hydrogen pero... more First, the electrochemical characteristics of Fenton's reagent (Fe(III), Fe(II) and hydrogen peroxide), including its catalytic (EC') behaviour were investigated. Second, the electrogeneration of hydrogen peroxide by a two-electron reduction of dissolved oxygen was conducted at a carbon electrode in a divided electrolysis cell and the concentration of hydrogen peroxide obtained was determined by the titration. The two approaches were then combined to give a one-pot, relatively green approach to aromatic hydroxylation reactions, with the electro-Fenton method allowing the iron to be used catalytically and the oxygen/water employed as the hydroxylation reagent by the in situ production of hydrogen peroxide. In particular, the preparative-scale hydroxylation of salicylic acid has been studied in an oxygen-saturated 0.1 M Na2SO4 pH 3.0 solution containing 5 mM Fe(II) and 5 mM salicylic acid at the controlled potential of 1.0 V vs. SCE. The study showed that after the attack of the hydroxyl radical produced in situ by the electro-Fenton process on salicylic acid, 2,3- and 2,5-dihydroxybenzoic acids were detected as primary monohydroxylated products with the highest yield of ca. 21.6 +/- 2.5%.
http://dx.doi.org/10.1039/c2nj21007j
Carbon black (CB) nanoparticles modified with fluorescein, a highly fluorescent molecule, were pr... more Carbon black (CB) nanoparticles modified with fluorescein, a highly fluorescent molecule, were prepared using a facile and efficient methodology. Simply stirring CB in aqueous solution containing fluorescein resulted in the strong physisorption of fluorescein onto the CB surface. The resulting Fluorescein/CB was then characterised by means of X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), fluorescence microscopy and fluorescence spectroscopy. The optimum experimental conditions for fluorescence of Fluorescein/CB viz. fluorescence excitation and emission wavelengths, O-2 removal and the amount of Fluorescein/CB used, were investigated. The Fluorescein/CB was used as a fluorescent probe for the sensitive detection of Pd(II) in water, based on fluorescence quenching. The results demonstrated that the fluorescence intensity of Fluorescein/CB decreased with increasing Pd(II) concentration, and the fluorescence quenching process could be described by the Stern-Volmer equation. The limit of detection (LOD) for the fluorescence quenching of Fluorescein/CB by Pd(II) in aqueous solution was found to be 1.07 mu M (based on 3 sigma). Last, approaches were studied for the removal of Fe(III) which interferes with the fluorescence quenching of Fluorescein/CB. Complexation of Fe(III) with salicylic acid was used to enhance and control the selectivity of Fluorescein/CB sensor towards Pd(II) in the presence of Fe(III).
http://dx.doi.org/10.1039/c2an16261j
The storage and transport of hydrogen presents many challenges when compared to the current syste... more The storage and transport of hydrogen presents many challenges when compared to the current systems utilised for dealing with energy dense liquid hydrocarbons such as oil. Formic acid, HCOOH, is relatively dense in hydrogen (4.4 % w/w, ca. 53 g L-1, with potentially ca. 600 L H2 per L of HCOOH at atmospheric pressure), and thus makes an attractive compound in terms of molecular storage of hydrogen. Hydrazine, N2H4 is another potential compound, possessing ca. 12.6 % w/w H. Both are also being extensively investigated separately for application in fuel cells.
The electrochemistry of mixtures of HCOOH and N2H4 will be discussed. HCOOH is known to poison various electrocatalytic metals due to the formation of CO and other adsorbed products. However, the voltammetry of N2H4 displays a constant current density regardless of the presence or absence of HCOOH, e.g. HCOOH electrode poisoning does not poison N2H4 electrooxidation at the same electrode.
This interesting observation will be discussed, covering a range of pH values and electrolytes, comparison made with methanol and carbon monoxide voltammetry, and the reason for this behaviour suggested. The possible application of HCOOH / N2H4 mixtures to high power density and more gravimetrically efficient fuel cells will be noted.
The electrolysis of these mixtures will also be detailed, which was found to efficiently yield H2 gas at the cathode (with N2 and CO2 at the anode).
Cyclic voltammetric experiments were carried out on Li+, Na+, K+, Rb+ and Cs+ in ionic liquids (I... more Cyclic voltammetric experiments were carried out on Li+, Na+, K+, Rb+ and Cs+ in ionic liquids (ILs). Alloy formation was noted at Pt microelectrodes, but not at Ni. A range of ILs was investigated to identify the best IL to study the M/M+ redox couples, and bulk electrodeposition of all metals was observed in at least one IL, N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpyrr][NTf2]). Mathematical simulation of the CVs in this IL was conducted as a function of temperature. The diffusion coefficients, D, of the five metal ions were determined. The formal potential, Ef0 (vs. Fc/Fc+) of the five M/M+ couples was quantified, as well as the electrochemical rate constants, k0, and transfer coefficients, α. The activation energies of diffusion, Ea,dif, of Li+ and Na+ ions, and electron transfer, Ea, of Li/Li+ and Na/Na+ were determined, and ΔS0 (vs. Fc/Fc+) estimated for the Na/Na+ couple. The trends within the group are discussed.
http://link.aip.org/link/ECSTF8/v33/i7/p523/s1
The electrochemistry of various gases, including oxygen, carbon dioxide, hydrogen, ammonia, hydro... more The electrochemistry of various gases, including oxygen, carbon dioxide, hydrogen, ammonia, hydrogen sulfide, sulfur dioxide and nitrogen dioxide, in room temperature ionic liquids (RTILs) is reviewed. The application of RTILs to gas sensor design and development is highlighted.