Calum Dickinson

University of Limerick, Luimneach, Munster, Ireland

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Publications (17)100.39 Total impact

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    ABSTRACT: Multilayer assemblies of two crown-type type heteropolyanions (HPA) [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- and Ni4(P8W48O148)(WO2)]28- have been immobilized onto glassy carbon electrode surfaces via the layer-by-layer (LBL) technique employing polycathion-stabilized silver nanoparticles (AgNP) as the cationic layer within the resulting thin films characterized by electrochemical and physical methods. The redox behaviours of both HPA monitored during LBL assembly with cyclic voltammetry and impedance spectroscopy revealed significant changes by immobilization. The presence of AgNPs led to retention of film porosity and electronic conductivity, which has been shown with impedance and voltammeric studies of film permeabilities towards reversible redox probes. The resulting films have been characterized by physical methods. Finally, the electrocatalytic performance of obtained films to nitrite and nitrate electrocatalytic reduction have been comparatively studied for both catalysts. Nickel atoms entrapped inside HPA showed higher specific activity for reduction.
    Langmuir 02/2015; 31(8). DOI:10.1021/la503889j · 4.46 Impact Factor
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    ABSTRACT: A new class of platinum-silver nanomaterial for the catalytic electrooxidation of methanol is considered here. The material was synthesised on a carbon nanochips platform via a combination of chemical reduction to form a particulate bimetallic alloy (Pt2Ag1/f-CNC) and an anodic-etching process to form a unique porous core-shell platinum-silver nanoparticle (np-Pt2Ag1/f-CNC). Morphology, structural and compositional characterisations of the alloy were performed using transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) techniques. Data confirms average particle size of 2.07 nm (median 1.73 nm). The alloy nature of the nanoparticle was confirmed by XRD and TEM/EDX analysis. The np-Pt2Ag1/f-CNC material was examined in electrochemical studies as a catalyst for the oxidation of methanol in sulfuric acid electrolyte. Catalytic efficiency is reported in terms of oxidation current density, 134.8 mA mg−1 (platinum mass) and a current ratio, If/Ib=0.86. The electrochemical data is indicative of high catalytic rates for methanol conversion, as well as the effectiveness of porous core-shell platinum-silver particles to resist carbon monoxide poisoning. The work demonstrates improved long-term catalytic performance of a novel nanomaterial electrode offering promising energy applications.
    Electroanalysis 11/2014; 27(1). DOI:10.1002/elan.201400434 · 2.50 Impact Factor
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    ABSTRACT: The electrocatalytic ability of the iron-substituted crown-type polyoxometalate (POM) Li4K16[P8W48O184Fe16(OH)28(H2O)4]·66H2O·2KCl (P8W48Fe16) towards the reduction of both nitrite and hydrogen peroxide reduction has been studied in both the solution and immobilized states for the POM. P8W48Fe16 was surface immobilised onto carbon electrode surfaces through employment of the layer-by-layer technique (LBL) using pentaerythritol-based Ru(II)-metallodendrimer [RuD](PF6)8 as the cationic layer within the resulting films. The constructed multilayer films have been extensively studied by various electrochemical techniques and surface based techniques. Cyclic voltammetry and impedance spectroscopy have been utilized to monitor the construction of the LBL film after the deposition of each monolayer. The electrochemical behaviour of both a cationic and anionic redox probes at the LBL films has been undertaken to give indications as to the film's porosity. The elemental composition and the surface morphology of the LBL films was conifmrde through the employment of AFM, XPS and SEM.
    Electrochimica Acta 05/2014; 134C:450-458. DOI:10.1016/j.electacta.2014.03.099 · 4.50 Impact Factor
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    ABSTRACT: A tetra Ru-substituted polyoxometalate Na10[{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2] (Ru4POM) has been successfully immobilised onto glassy carbon electrodes and indium tin oxide (ITO) coated glass slides through the employment of a conducting polypyrrole matrix and the layer-by-layer (LBL) technique. The resulting Ru4POM doped polypyrrole films showed stable redox behaviour associated with the Ru centres within the Ru4POM, whereas, the POM's tungsten-oxo redox centres were not accessible. The films showed pH dependant redox behaviour within the pH range 2 to 5 whilst exhibiting excellent stability towards redox cycling. The layer-by-layer assembly was constructed onto poly(diallyldimethylammonium chloride) (PDDA) modified carbon electrodes by alternate depositions of Ru4POM and a RuII metallodendrimer. The resulting Ru4POM assemblies showed stable redox behaviour for the redox processes associated with Ru4POM in the pH range 2 to 5. The charge transfer resistance of the LBL films was calculated through AC-Impedance. Surface characterisation of both the polymer and LBL Ru4POM films was carried out using atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Initial investigations into the ability of the Ru4POM LBL films to electrocatalytically oxidise water at pH 7 have also been conducted.
    ACS Applied Materials & Interfaces 04/2014; 6(11). DOI:10.1021/am405295c · 6.72 Impact Factor
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    Emma Mullane · Tadhg Kennedy · Hugh Geaney · Calum Dickinson · Kevin M. Ryan
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    ABSTRACT: Silicon and germanium nanowires are grown in high density directly from a tin layer evaporated on stainless steel. The nanowires are formed in low cost glassware apparatus using the vapor phase of a high boiling point organic solvent as the growth medium. HRTEM, DFSTEM, EELS, and EDX analysis show the NWs are single crystalline with predominant 111 growth directions. Investigation of the seed/nanowire interface shows that in the case of Si an amorphous carbon interlayer occurs that can be removed by modifying the growth conditions. Electrochemical data shows that both the tin metal catalyst and the semiconductor nanowire reversibly cycle with lithium when the interface between the crystalline phases of the metal and semiconductor is abrupt. The dually active nanowire arrays were shown to exhibit capacities greater than 1000 mAh g–1 after 50 charge/discharge cycles.
    Chemistry of Materials 05/2013; 25(9-9):1816-1822. DOI:10.1021/cm400367v · 8.54 Impact Factor
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    ABSTRACT: Here, we report the formation of high density arrays of Cu15Si4 nanowires using a high boiling point organic solvent based method. The reactions were carried out using Cu foil substrates as the Cu source with nanowire growth dependent upon the prior formation of Cu15Si4 crystallites on the surface. The method shows that simple Si delivery to metal foil can be used to grow high densities of silicide nanowires with a tight diameter spread at reaction temperatures of 460 °C. The nanowires were characterized by high-resolution transmission electron microscopy (HRTEM), high-resolution scanning electron microscopy (HRSEM), and X-ray photoelectron spectroscopy (XPS), and electrical analysis showed that they possess low resistivities.
    Chemistry of Materials 11/2012; 24(22-22):4319-4325. DOI:10.1021/cm302066n · 8.54 Impact Factor
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    ABSTRACT: Herein, we describe the growth of Si nanowires (NWs) in the vapor phase of an organic solvent medium on various substrates (Si, glass, and stainless steel) upon which an indium layer was evaporated. Variation of the reaction time allowed NW length and density to be controlled. The NWs grew via a predominantly root-seeded mechanism with discrete In catalyst seeds formed from the evaporated layer. The NWs and substrates were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The suitability of the indium seeded wires as anode components in Li batteries was probed using cyclic voltammetric (CV) measurements. The route represents a versatile, glassware-based method for the formation of Si NWs directly on a variety of substrates.
    Chemistry of Materials 05/2012; 24(11). DOI:10.1021/cm301023j · 8.54 Impact Factor
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    Ajay Singh · Calum Dickinson · Kevin M Ryan
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    ABSTRACT: Vertical nanorod assembly over three dimensions is shown to result in the formation of Moiré interference patterns arising from rotational offsets between respective monolayer sheets. Six distinct patterns are observed in HRTEM and angular dark-field STEM (DF-STEM) images, allowing the exact angle of rotation to be determined from their respective size and repeat order. At large rotation angles approaching 30°, the aperiodicity in the structure of the nanorod supercrystals becomes apparent, resulting in 12-fold ordering characteristics of a quasicrystal. The rotational offsets are further elucidated from Fourier transform and small angle electron diffraction, allowing interpretation of several multilayers when combined with DF-STEM and SEM. Pattern formation owing to angular rotation is differentiated from those occurring from a lateral shift, providing an important insight into the complex multilayered structures in assembled rods that may have an impact on their collective electronic or photonic properties. We also show how random tetrapods when present at low concentrations in colloidal nanorod solutions act as termination points for 2D sheet crystallization, impacting the size and shape of the resultant assemblies. The occurrence of Moiré patterns in rod assemblies demonstrates the extraordinary order achievable in their assembly and offers a nondestructive technique to precisely map the placement of each nanorod in this important nanoarchitecture.
    ACS Nano 03/2012; 6(4):3339-45. DOI:10.1021/nn300331x · 12.88 Impact Factor
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    Baljit Singh · Eithne Dempsey · Calum Dickinson · Fathima Laffir
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    ABSTRACT: A highly efficient and reproducible approach for effective Pt nanoparticles dispersion and excellent decoration (inside/outside) of functionalised carbon nanofibers (f-CNF) is presented. The surface morphological, compositional and structural characterisations of the synthesised Pt(19.2)/f-CNF(80.8) material were examined using transmission electron microscopy (TEM/STEM/DF-STEM), energy-dispersive X-ray spectrometry (EDS), thermogravimetric analysis (TGA/DTG), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) was employed in order to confirm the typical electrochemical response for Pt. The aim of the work was to improve the utility of both the supporting matrix (via the use of both inner/outer surfaces of nanofibers) and precious Pt, together with the sensitive glucose determination. TEM data indicated successful nanoparticle decoration with average Pt particle size 2.4 nm. The studies demonstrated that utilisation of the inner surface of the nanofibers, together with the modified outer surface characteristics using chemical treatment, enables excellent decoration, effective dispersion and efficient impregnation of Pt nanoparticles on carbon nanofibers. Pt(19.2)/f-CNF(80.8) exhibited excellent amperometric response (sensitivity = 22.7 μAmM(-1)cm(-2) and LoD = 0.42 μM) towards direct glucose sensing, over the range 0-10 mM glucose, in neutral conditions (pH 7.4). The improved carbon surface area for nanoparticle decoration, inner surface structure and morphology of nanofibers together with the presence of functional groups provided strong interactions and stability. These features together with the effective nanoparticle dispersion and decoration resulted in excellent catalytic response. The decorated nanoscaled material (Pt(19.2)/f-CNF(80.8)) is capable of large scale production, providing sensing capability in neutral conditions, while eliminating the temperature sensitivity, pH and lifetime issues associated with glucose enzymatic sensors and holds great promise in the quantification of glucose in real clinical samples.
    The Analyst 03/2012; 137(7):1639-48. DOI:10.1039/c2an16146j · 4.11 Impact Factor
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    ABSTRACT: A conducting polymer was used for the immobilization of various transition metal ion-substituted Dawson-type polyoxometalates (POMs) onto glassy carbon electrodes. Voltammetric responses of films of different thicknesses were stable within the pH domain 2-7 and reveal redox processes associated with the conducting polymer, the entrapped POMs and incorporated metal ions. The resulting POM doped polypyrrole films were found to be extremely stable towards redox switching between the various redox states associated with the incorporated POM. An amperometric sensor for hydrogen peroxide detection based upon the POM doped polymer films was investigated. The detection limits were 0.3 and 0.6 μM, for the Cu(2+)- and Fe(3+)-substituted POM-doped polypyrrole films respectively, with a linear region from 0.1 up to 2 mM H(2)O(2). Surface characterization of the polymer films was carried out using atomic force microscopy, X-ray photoelectron spectroscopy and scanning electron microscopy.
    The Analyst 12/2011; 137(3):624-30. DOI:10.1039/c1an15665a · 4.11 Impact Factor
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    ABSTRACT: Herein, we describe the growth of highly dense germanium nanowire mats directly on copper foil by a self-induced, solid seeded protocol. The existence of Cu(3)Ge tips on each of the nanowires indicates that growth proceeds via a solid catalyzed route, dependent on the in situ formation of the germanide intermediate. The nanowires show a tight diameter distribution and typically < 110 > growth directions resulting from similarities in the d spacings between the nanowire and the catalyst seed. The nanowires and substrates were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), and electron backscatter diffraction (EBSD).
    Chemistry of Materials 10/2011; 23(21). DOI:10.1021/cm202276m · 8.54 Impact Factor
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    ABSTRACT: Pt based mono/bi/tri-metallic nanocomposites on different carbon based supports (activated carbon (AC), carbon nanotubes (CNTs) and carbon nanofibers (CNFs)) were synthesised and Pt surface enrichment achieved. The overall theoretical metallic content (Pt + Au + Sn) was 20% (w/w) in all mono/bi/tri-metallic nanocomposites and was found to be uniformly distributed in the supporting matrix (80%). The surface morphology and composition of the synthesised materials was characterised using scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), while cyclic voltammetry was employed in order to confirm their typical metallic electrochemical characteristics. Electrochemical measurements indicated that Pt(2)Au(1)Sn(1) trimetallic catalysts demonstrated a significantly higher electrochemically active surface area relative to activated carbon supported PtAu based bimetallic counterparts. The results show that the CNT based trimetallic catalyst (Pt(2)Au(1)Sn(1)/CNT) showed greatest electroactive surface area (49.3 m(2)/g) and current density for methanol oxidation in acidic (490 mA mg(-1) Pt) as well as basic (1700 mA mg(-1) Pt) conditions. Results demonstrated that in comparison to Au/C and Sn/C (no/negligible response), the presence of a small amount of Pt in the Au and Sn based nanocomposites, significantly modified the catalytic properties. The activated carbon supported bimetallic (Pt(1)Au(3)/C) catalyst showed reasonably good response (260 mA mg(-1) Pt) among all bimetallic nanomaterials examined. The current response achieved for Pt(2)Au(1)Sn(1)/CNT was 1.9 times (in acidic media) and 2.1 times (in basic media) that for synthesised Pt/C in terms of per mg Pt activity. Overall the methanol oxidation studies demonstrated that the presence of Au and Sn in Pt based catalysts strongly indicated their capacity to reduce the precious Pt content required for this application, demonstrating the role of Au in improving current/potential response and signifying the importance of supporting matrices.
    Nanoscale 06/2011; 3(8):3334-49. DOI:10.1039/c1nr10273g · 7.39 Impact Factor
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    ABSTRACT: Here we show the impact of preferred growth directions and defects in the formation of complex Ge nanowire (NW) structures grown by a simple organic medium based synthesis. Various types of NWs are examined including: straight defect free NWs; periodically bent NWs with precise angles between the NW segments; NWs with mutually exclusive lateral or longitudinal faults; and more complex "wormlike" structures. We show that choice of solvent and reaction temperature can be used to tune the morphology of the NWs formed. The various types of NWs were probed in depth using transmission electron microscopy (TEM), scanning electronic microscopy (SEM), selected area electron diffraction (SAED), and dark field TEM (DFTEM).
    Crystal Growth & Design 06/2011; 11(7-7):3266-3272. DOI:10.1021/cg200510y · 4.56 Impact Factor
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    Crystal Growth & Design 04/2011; 11. · 4.56 Impact Factor
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    ABSTRACT: Novel Co-Ni based catalysts on activated carbon support were prepared using NaBH4 as a reducing agent in aqueous conditions and examined with respect to direct amperometric uric acid detection. The surface morphology and composition of the synthesised materials were examined using transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) was employed in order to confirm the typical metallic electrochemical response of the Co, Ni and Co-Ni based materials. The combination of metal hydroxides/oxides and nanoparticles in the carbon supported Co-Ni based materials were found to play a key role in uric acid determination. Upon surface confinement of the Co1Ni1/C material, uric acid sensitivity 248.2 µA mM−1 cm−2 and limit of detection 0.08 µM at Eapp=+0.4 V vs. Ag/AgCl was found by hydrodynamic amperometry over the range 0–250 µM (r2=0.9992). The sensor provided linear and reproducible behaviour over a wide range (25–575 µM) of uric acid. The composite materials showed excellent selectivity with respect to commonly found interferences with no response even at 10-fold concentration of urea, glucose and oxalate, and minimal influence of ascorbic acid (2 fold concentration). Overall, these materials are excellent candidates for direct uric acid detection in a stable, sensitive and very specific fashion over relevant physiological ranges, eliminating the pH, temperature sensitivity and lifetime issues associated with enzyme based systems. The materials are very promising for a range of applications including wound care/management and as non-enzymatic disposable uric acid test strips.
    Electroanalysis 01/2011; 23(1):79 - 89. DOI:10.1002/elan.201000444 · 2.50 Impact Factor
  • Dhanraj Rathod · Calum Dickinson · Denise Egan · Eithne Dempsey
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    ABSTRACT: Nanocomposites of ethylene glycol protected platinum nanoparticles were prepared in the presence of activated carbon (AC), multi-walled carbon nanotubes (MWNTs) and carbon nanofibres (CNFs) at 20% (w/w) Pt loading and their potential in non-enzymatic glucose sensing evaluated. Physical and electrochemical characterization of these hybrid materials was enabled using transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and cyclic voltammetry. The average platinum nanoparticle diameters, as determined from TEM and XRD measurements, were 2 ± 1 to 3 ± 1 nm. The electrochemically active surface area of the platinum nanoparticles were found to be 91, 78 and 128 m2 g−1 for Pt-C, Pt-MWCNT and Pt-CNF respectively, as determined by the hydrogen adsorption/desorption phenomenon, using cyclic voltammetry in H2SO4. The nanomaterials were applied to the direct non-enzymatic quantization of glucose over its physiological range in the absence of the enzyme glucose oxidase. Hydrodynamic amperometric at Eapp = 0.55 V vs. Ag/AgCl in phosphate buffer (pH 7.4) was employed and the materials responded linearly to glucose (at pH 7.4, 298 K) over the range 2–20 mM (R2 = 0.99) with sensitivity 1.07, 1.10 and 0.52 μA mM−1 cm−2 for Pt-C, Pt-MWCNT and Pt-CNF respectively.
    Sensors and Actuators B Chemical 01/2010; 143(2-143):547-554. DOI:10.1016/j.snb.2009.09.064 · 4.29 Impact Factor
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    ABSTRACT: Silicon nanocrystals were synthesized at high temperatures and high pressures by the thermolysis of diphenylsilane using a combination of supercritical carbon dioxide and phosphonic acid surfactants. Size and shape evolution from pseudo-spherical silicon nanocrystals to well-faceted tetrahedral-shaped silicon crystals with edge lengths in the range of 30-400 nm were observed with sequentially decreasing surfactant chain lengths. The silicon nanocrystals were characterized by transmission electron microscopy (TEM), energy-dispersive x-ray spectroscopy (EDX), x-ray diffraction (XRD), photoluminescence (PL), scanning electron microscopy (SEM) and Raman scattering spectroscopy.
    Nanotechnology 08/2009; 20(27):275605. DOI:10.1088/0957-4484/20/27/275605 · 3.67 Impact Factor

Publication Stats

178 Citations
100.39 Total Impact Points

Institutions

  • 2010–2015
    • University of Limerick
      • • Materials and Surface Science Institute (MSSI)
      • • Department of Chemical and Environmental Science
      Luimneach, Munster, Ireland