• 2D Hexagonal Boron Nitride (2D-hBN) Explored as a Potential Electrocatalyst for the Oxygen Reduction Reaction

      Khan, Aamar F.; Brownson, Dale A. C.; Ji, Xiaobo; Smith, Graham C.; Banks, Craig E.; Manchester Metropolitan University (Khan, Brownson, Banks); University of Chester (Smith); Central South University Changsha (Ji) (Wiley, 2016-09-28)
      Crystalline 2D hexagonal Boron Nitride (2D-hBN) is explored as a potential electrocatalyst towards the oxygen reduction reaction (ORR) when electrically wired via a drop-casting approach upon a range of carbon based electrode surfaces; namely, glassy carbon (GC), boron-doped diamond (BDD), and screen-printed graphitic electrodes (SPEs). We consider the ORR in acidic conditions and critically evaluate the performance of unmodified and 2D-hBN modified electrodes, implementing coverage studies (commonly neglected in the literature) in order to ascertain the true impact of this novel nanomaterial. The behaviour of 2D-hBN towards the ORR is shown to be highly dependent upon both the underlying carbon substrate and the coverage/mass utilised. 2D-hBN modified SPEs are found to exhibit the most beneficial response towards the ORR, reducing the peak potential by ca. 0.28 V when compared to an unmodified/bare SPE. Such improvements at this supporting substrate are inferred due to favourable 2D-hBN interaction with ridged surfaces exposing a high proportion of edge regions/sites, where conversely, we show that relatively smooth substrate surfaces (such as GC) are less conducive towards successful 2D-hBN immobilisation. In this paper, we reveal for the first time (in the specific case of using a rough supporting substrate) that 2D-hBN gives rise to beneficial electrochemical behaviour towards the ORR. Unfortunately, this material is not considered an electrocatalyst for use within fuel cells given that the estimated number of electrons transferred during the ORR ranges between 1.90–2.45 for different coverages, indicating that the ORR at 2D-hBN predominantly produces hydrogen peroxide. 2D-hBN does however have potential and should be explored further by those designing, fabricating and consequently electrochemically testing modified electrocatalysts towards the ORR.
    • 2D Hexagonal Boron Nitride (2D-hBN) Explored for the Electrochemical Sensing of Dopamine

      Khan, Aamar F.; Brownson, Dale A. C.; Randviir, Edward P.; Smith, Graham C.; Banks, Craig E.; Manchester Metropolitan University (Khan, Brownson, Randviir, Banks); University of Chester (Smith) (American Chemical Society, 2016-09-23)
      Crystalline 2D hexagonal boron nitride (2D-hBN) nanosheets are explored as a potential electrocatalyst toward the electroanalytical sensing of dopamine (DA). The 2D-hBN nanosheets are electrically wired via a drop-casting modi fication process onto a range of commercially available carbon supporting electrodes, including glassy carbon (GC), boron-doped diamond (BDD), and screen-printed graphitic electrodes (SPEs). 2D-hBN has not previously been explored toward the electrochemical detection/electrochemical sensing of DA. We critically evaluate the potential electrocatalytic performance of 2D-hBN modified electrodes, the effect of supporting carbon electrode platforms, and the effect of “mass coverage” (which is commonly neglected in the 2D material literature) toward the detection of DA. The response of 2D-hBN modified electrodes is found to be largely dependent upon the interaction between 2D-hBN and the underlying supporting electrode material. For example, in the case of SPEs, modification with 2D-hBN (324 ng) improves the electrochemical response, decreasing the electrochemical oxidation potential of DA by ∼ 90 mV compared to an unmodified SPE. Conversely, modification of a GC electrode with 2D-hBN (324 ng) resulted in an increased oxidation potential of DA by ∼ 80 mV when compared to the unmodified electrode. We explore the underlying mechanisms of the aforementioned examples and infer that electrode surface interactions and roughness factors are critical considerations. 2D-hBN is utilized toward the sensing of DA in the presence of the common interferents ascorbic acid (AA) and uric acid (UA). 2D-hBN is found to be an effective electrocatalyst in the simultaneous detection of DA and UA at both pH 5.0 and 7.4. The peak separations/resolution between DA and UA increases by ∼ 70 and 50 mV (at pH 5.0 and 7.4, respectively, when utilizing 108 ng of 2D-hBN) compared to unmodified SPEs, with a particularly favorable response evident in pH 5.0, giving rise to a significant increase in the peak current of DA. The limit of detection (3σ) is found to correspond to 0.65 μM for DA in the presence of UA. However, it is not possible to deconvolute the simultaneous detection of DA and AA. The observed electrocatalytic effect at 2D-hBN has not previously been reported in the literature when supported upon carbon or any other electrode. We provide valuable insights into the modifier −substrate interactions of this material, essential for those designing, fabricating, and consequently performing electrochemical experiments utilizing 2D-hBN and related 2D materials.
    • 2D Molybdenum Disulphide (2D-MoS2) Modified Electrodes Explored Towards the Oxygen Reduction Reaction

      Rowley-Neale, Samuel J.; Fearn, Jamie; Brownson, Dale A. C.; Smith, Graham C.; Ji, Xiaobo; Banks, Craig E.; Manchester Metropolitan University (Rowley-Neale, Fearn, Brownson, Banks); University of Chester (Smith); Central South University Changsha (Ji) (Royal Society of Chemistry, 2016-07-11)
      Two-dimensional molybdenum disulphide nanosheets (2D-MoS2)have proven to be an effective lectro- catalyst, with particular attention being focused on their use towards increasing the efficiency of the reac-tions associated with hydrogen fuel cells. Whilst the majority of research has focused on the Hydrogen Evolution Reaction (HER), herein we explore the use of 2D-MoS2 as a potential electrocatalyst for the much less researched Oxygen Reduction Reaction (ORR). We stray from literature conventions and perform experiments in 0.1 M H2SO4 acidic electrolyte for the first time, evaluating the electrochemical performance of the ORR with 2D-MoS2 electrically wired/immobilised upon several carbon based elec-trodes (namely; Boron Doped Diamond (BDD), Edge Plane Pyrolytic Graphite (EPPG), Glassy Carbon (GC) and Screen-Printed Electrodes (SPE)) whilst exploring a range of 2D-MoS2 coverages/masses. Conse-quently, the findings of this study are highly applicable to real world fuel cell applications. We show that significant improvements in ORR activity can be achieved through the careful selection of the under-lying/supporting carbon materials that electrically wire the 2D-MoS2and utilisation of an optimal mass of 2D-MoS2. The ORR onset is observed to be reduced to ca.+0.10 V for EPPG, GC and SPEs at 2D-MoS2 (1524 ng cm−2 modification), which is far closer to Pt at +0.46 V compared to bare/unmodified EPPG, GC and SPE counterparts. This report is the first to demonstrate such beneficial electrochemical responses in acidic conditions using a 2D-MoS2 based electrocatalyst material on a carbon-based substrate (SPEs in this case). Investigation of the beneficial reaction mechanism reveals the ORR to occur via a 4 electron process in specific conditions; elsewhere a 2 electron process is observed. This work offers valuable insights for those wishing to design, fabricate and/or electrochemically test 2D-nanosheet materials towards the ORR
    • 2D nanosheet molybdenum disulphide (MoS2) modified electrodes explored towards the hydrogen evolution reaction

      Rowley-Neale, Samuel J.; Brownson, Dale A. C.; Smith, Graham C.; Satwell, David A. G.; Kelly, Peter J.; Banks, Craig E.; Faculty of Science and Engineering, Manchester Metropolitain University, Manchester M 5GD, UK (Rowley-Neale, Brownson, Satwell, Kelly & Banks); Department of Natural Sciences, University of Chester, Thornton Science Park, Chester CH2 4NU (Smith) (Royal Society of Chemistry, 2015-10-06)
      We explore the use of two-dimensional (2D) MoS2 nanosheets as an electro-catalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode support materials, namely edge plane pyrolytic graphite (EPPG), glassy carbon (GC), boron-doped diamond (BDD) and screen-printed graphite electrodes (SPE), we critically evaluate the reported electro-catalytic performance of unmodified and MoS2 modified electrodes towards the HER. Surprisingly, current literature focuses almost exclusively on the use of GC as an underling support electrode upon which HER materials are immobilised. 2D MoS2 nanosheet modified electrodes are found to exhibit a coverage dependant electrocatalytic effect towards the HER. Modification of the supporting electrode surface with an optimal mass of 2D MoS2 nanosheets results in a lowering of the HER onset potential by ca. 0.33, 0.57, 0.29 and 0.31 V at EPPG, GC, SPE and BDD electrodes compared to their unmodified counterparts respectively. The lowering of the HER onset potential is associated with each supporting electrodes individual electron transfer kinetics/properties. The effect of MoS2 coverage is also explored. We reveal that its ability to catalyse the HER is dependent on the mass deposited until a critical mass of 2D MoS2 nanosheets is achieved, after which its electrocatalytic benefits and/or surface stability curtail. The active surface site density and turn over frequency for the 2D MoS2 nanosheets is determined, characterised and found to be dependent on both the coverage of 2D MoS2 nanosheets and the underlying/supporting substrate. This work is essential for those designing, fabricating and consequently electrochemically testing 2D nanosheet materials for the HER.
    • 3D printed graphene based energy storage devices

      Foster, Christopher; Down, Michael; Zhang, Yan; Ji, Xiaobo; Rowley-Neale, Samuel; Smith, Graham C.; Kelly, Peter; Banks, Craig; Manchester Metropolitan University; University of Chester; Central South University Changsha (Springer Nature, 2017-03-03)
      3D printing technology provides a unique platform for rapid prototyping of numerous applications due to its ability to produce low cost 3D printed platforms. Herein, a graphene-based polylactic acid filament (graphene/PLA) has been 3D printed to fabricate a range of 3D disc electrode (3DE) configurations using a conventional RepRap fused deposition moulding (FDM) 3D printer, which requires no further modification/ex-situ curing step. To provide proof-of-concept, these 3D printed electrode architectures are characterised both electrochemically and physicochemically and are advantageously applied as freestanding anodes within Li-ion batteries and as solid-state supercapacitors. These freestanding anodes neglect the requirement for a current collector, thus offering a simplistic and cheaper alternative to traditional Li-ion based setups. Additionally, the ability of these devices’ to electrochemically produce hydrogen via the hydrogen evolution reaction (HER) as an alternative to currently utilised platinum based electrodes (with in electrolysers) is also performed. The 3DE demonstrates an unexpectedly high catalytic activity towards the HER (−0.46 V vs. SCE) upon the 1000th cycle, such potential is the closest observed to the desired value of platinum at (−0.25 V vs. SCE). We subsequently suggest that 3D printing of graphene-based conductive filaments allows for the simple fabrication of energy storage devices with bespoke and conceptual designs to be realised.
    • Aerosol Chemistry Resolved by Mass Spectrometry: Linking Field Measurements of Cloud Condensation Nuclei Activity to Organic Aerosol Composition

      Vogel, Alexander; Schneider, Johannes; Mueller-Tautges, Christina; Phillips, Gavin J.; Poehlker, Mira L.; Rose, Diana; Zuth, Christoph; Makkonen, Ulla; Hakola, Hannele; Crowley, John N.; Andreae, Meinrat O.; Poeschl, Ulrich; Hoffmann, Thorsten; Johannes Gutenberg-University; Max Planck Institute for Chemistry; Finnish Meteorological Insititute; Paul Scherrer Institute; University of Chester; Goethe University (American Chemical Society, 2016-10-06)
      Aerosol hygroscopic properties were linked to its chemical composition by using complementary online mass spectrometric techniques in a comprehensive chemical characterization study at a rural mountaintop station in central Germany in August 2012. In particular, atmospheric pressure chemical ionization mass spectrometry ((−)APCI-MS) provided measurements of organic acids, organosulfates, and nitrooxy-organosulfates in the particle phase at 1 min time resolution. Offline analysis of filter samples enabled us to determine the molecular composition of signals appearing in the online (−)APCI-MS spectra. Aerosol mass spectrometry (AMS) provided quantitative measurements of total submicrometer organics, nitrate, sulfate, and ammonium. Inorganic sulfate measurements were achieved by semionline ion chromatography and were compared to the AMS total sulfate mass. We found that up to 40% of the total sulfate mass fraction can be covalently bonded to organic molecules. This finding is supported by both on- and offline soft ionization techniques, which confirmed the presence of several organosulfates and nitrooxy-organosulfates in the particle phase. The chemical composition analysis was compared to hygroscopicity measurements derived from a cloud condensation nuclei counter. We observed that the hygroscopicity parameter (κ) that is derived from organic mass fractions determined by AMS measurements may overestimate the observed κ up to 0.2 if a high fraction of sulfate is bonded to organic molecules and little photochemical aging is exhibited.
    • Aging and condensed phase chemistry affects the hygroscopicity of ambient SOA

      Vogel, Alexander; Müller-Tautges, Christina; Krueger, Mira; Rose, Diana; Schneider, Johannes; Phillips, Gavin J.; Makkonen, Ulla; Hakola, Hannele; Crowley, John N.; Poeschl, Ulrich; Hoffmann, Thorsten; Johannes Gutenberg-University Mainz, Max Planck Institute for Chemistry, Finnish Meteorological Institute, CERN, Goethe University Frankfurt/Main, University of Chester (European Aerosol Assembly, 2015-09)
      Secondary inorganic and organic aerosol particles are ubiquitous constituents in the atmosphere. They are largely produced through the photo-oxidation of gaseous precursor molecules, such as SO2, NOx and VOCs, from both anthropogenic and natural sources. Once grown to atmospherically relevant sizes, they can act as cloud condensation nuclei (CCN) and thus affect earth’s climate (IPCC, 2013). However, their chemical composition can vary considerably over their atmospheric lifetime (up to one week) as a result of which, their physico-chemical properties may change significantly due to chemical transformation processes (Jimenez et al., 2009). One of these properties is hygroscopicity, which largely depends on the chemical composition. Linking both, measured chemical composition and hygroscopicity helps to advance our current understanding of the hygroscopicity parametrisation. In this work we investigated how photochemical aging of the organic aerosol fraction and chemical reactions between inorganic and organic compounds can affect the hygroscopicity parameter κ (Petters and Kreidenweis, 2007). The measurements were conducted at the semi-rural Taunus Observatory/ Germany during summer 2012. An extensive suite of particle phase characterizing instrumentation was applied for the detailed composition analysis of submicron aerosol: We used online atmospheric pressure chemical ionization mass spectrometry (APCI-MS) (Vogel et al., 2013), aerosol mass spectrometry (AMS), and filter sampling for laboratory based analysis using ultrahigh performance liquid chromatography coupled to electrospray ionization ultrahigh resolution (OrbitrapTM) mass spectrometry (UHPLC/ESI-UHRMS). The AMS allows quantification of total organics, sulfate and nitrate, whereas the APCI-MS can identify single organic species (organic acids, organosulfates, nitrooxy-organosulfates), both at a high measurement frequencies (< 1 minute). The UHPLC/ESI-UHRMS analysis of filter samples provides vital information helping to understand the complex online spectra of the APCI-MS by the unambiguous determination of the elemental composition of different organic compounds. Furthermore, we used a MARGA (Monitor for Aerosols and Gases in Ambient Air) to measure the concentration of purely inorganic sulfate in PM10. Finally a CCN counter coupled to a differential mobility analyser (DMA) and to a condensation particle counter (CPC) was used to measure size-resolved CCN efficiency spectra and to derive the hygroscopicity parameter κ. We determined the κ-value of the ambient aerosol from size resolved chemical composition measurements by the AMS and compared it to the measured values of the CCN efficiency spectra. The relative evolution of the aerosol aging was determined by measuring the ratio of two biogenic acids: the aging product 1,2,3-methyl-butane-tricarboxylic acid (MBTCA) and the first generation oxidation product pinic acid by the online APCI-MS. The occurrence of organosulfates and nitrooxy-organosulfates was observed by the ultrahigh resolution MS analysis and the online APCI-MS. Comparison of the total sulfate concentration measured by the AMS with the sulfate measurements by the MARGA allowed for the determination of the fraction of sulfate which is bonded to organic molecules. We observed that photochemical aging and the formation of (hydrophobic) nitrooxy-organosulfates is responsible for the observed bias between the predicted and measured κ-value.
    • Alternative selection of processing additives to enhance the lifetime of OPVs

      Kettle, Jeff; Waters, Huw; Horie, Masaki; Smith, Graham C.; University of Bangor (Kettle, Waters), National Tsing Hua University Taiwan (Horie), University of Chester (Smith) (IOP Publishing, 2016-01-27)
      The use of processing additives is known to accelerate the degradation of Organic Photovoltaics (OPVs) and therefore, this paper studies the impact of selecting alternative processing additives for PCPDTBT:PC71BM solar cells in order to improve the stability. The use of naphthalene-based processing additives has been undertaken, which is shown to reduce the initial power conversion efficiency by 23%-42%, primarily due to a decrease in the short-circuit current density, but also fill factor. However, the stability is greatly enhanced by using such additives, with the long term stability (T50%) enhanced by a factor of four. The results show that there is a trade-off between initial performance and stability to consider when selecting the initial process additives. XPS studies have provided some insight into the decreased degradation and show that using 1-chloronaphthalene (ClN) leads to reduced morphology changes and reduced oxidation of the thiophene-ring within the PCPDTBT backbone.
    • Angus I. Kirkland and Sarah J. Haigh (Eds.): Nanocharacterization, 2nd ed.

      Smith, Graham C.; Department of Natural Sciences, University of Chester (Springer, 2016-01)
      Book review of NanoCharacterisation, second edition, Editors Angus I. Kirkland and Sarah J. Haigh. Published by Royal Society of Chemistry ISBN: 978-1-84973-805-7
    • Anodic stripping voltammetry with graphite felt electrodes for the trace analysis of silver

      Davies, Trevor J.; University of Chester (Royal Society of Chemistry, 2016-05-31)
      Graphite felt (GF) is a mass produced porous carbon electrode material commonly used in redox flow batteries. Previous studies have suggested GF may have valuable applications in electroanalysis as a low cost disposable carbon electrode material, although most GF sensors have used flow cell arrangements. In this work, an elegant wetting technique is employed that allows GF electrodes to be used in quiescent solution to detect trace levels of silver in water via anodic stripping voltammetry. GF electrodes display good repeatability and a limit of detection of 25 nM of Ag+ in 0.1 M HNO3, with a linear range spanning two orders of magnitude. This compares to a value of around 140 nM when using conventional carbon electrodes. Combined with their low cost and disposable nature, the results suggest GF electrodes can make a valuable contribution to electroanalysis.
    • Atomic-layer-deposited aluminum and zirconium oxides for surface passivation of TiO 2 in High-Efficiency Organic Photovoltaics

      Vasilopoulou, Maria; Georgiadou, Dimitra G.; Soultati, Anastasia; Boukos, Nikos; Gardelis, Spyros; Palilis, Leonidas C.; Fakis, Mihalis; Skoulatakis, Georgios; Kennou, Stella; Botzakaki, Martha; Georga, Stavroula; Krontiras, Christoforos A.; Auras, Florian; Fattakhova-Rohlfing, Dina; Bein, Thomas; Papadopoulos, Theodoros A.; Davazoglou, Dimitrios; Argitis, Panagiotis; Institute of Renewable Energy and Environmental Technologies (IREET), Department of Engineering, University of Bolton; University of Chester; Institute of Nanoscience and Nanotechnology (INN); National Centre for Scientific Research “Demokritos”; 153 10 Aghia Paraskevi Attikis Athens Greece; Institute of Nanoscience and Nanotechnology (INN); National Centre for Scientific Research “Demokritos”; 153 10 Aghia Paraskevi Attikis Athens Greece; Institute of Nanoscience and Nanotechnology (INN); National Centre for Scientific Research “Demokritos”; 153 10 Aghia Paraskevi Attikis Athens Greece; Institute of Nanoscience and Nanotechnology (INN); National Centre for Scientific Research “Demokritos”; 153 10 Aghia Paraskevi Attikis Athens Greece; Institute of Nanoscience and Nanotechnology (INN); National Centre for Scientific Research “Demokritos”; 153 10 Aghia Paraskevi Attikis Athens Greece; Department of Physics; University of Patras; 26500 Patras Greece; Department of Physics; University of Patras; 26500 Patras Greece; Surface Science Laboratory, Department of Chemical Engineering; University of Patras; 26500 Patras Greece; Surface Science Laboratory, Department of Chemical Engineering; University of Patras; 26500 Patras Greece; Department of Physics; University of Patras; 26500 Patras Greece; Department of Physics; University of Patras; 26500 Patras Greece; Department of Physics; University of Patras; 26500 Patras Greece; Department of Chemistry and Center for Nanoscience (CeNS); University of Munich (LMU); 81377 Munich Germany; Department of Chemistry and Center for Nanoscience (CeNS); University of Munich (LMU); 81377 Munich Germany; Department of Chemistry and Center for Nanoscience (CeNS); University of Munich (LMU); 81377 Munich Germany; Institute of Renewable Energy and Environmental Technologies (IREET); Department of Engineering; University of Bolton; Deane Rd. BL3 5AB Bolton UK; Institute of Nanoscience and Nanotechnology (INN); National Centre for Scientific Research “Demokritos”; 153 10 Aghia Paraskevi Attikis Athens Greece; Institute of Nanoscience and Nanotechnology (INN); National Centre for Scientific Research “Demokritos”; 153 10 Aghia Paraskevi Attikis Athens Greece (Wiley, 2014-10-28)
      The reduction in electronic recombination losses by the passivation of surfaces is a key factor enabling high-efficiency solar cells. Here we investigate a strategy to passivate surface trap states of TiO 2 films used as cathode interlayers in organic photovoltaics (OPVs) through applying alumina (Al2O3) or zirconia (ZrO2) insulating nanolayers by thermal atomic layer deposition (ALD). Our results suggest that the surface traps in TiO 2 are oxygen vacancies, which cause undesirable recombination and high electron extraction barrier, reducing the open-circuit voltage and the short-circuit current of the complete OPV device. It was found that the ALD metal oxides enable excellent passivation of the TiO2 surface followed by a downward shift of the conduction band minimum. OPV devices based on different photoactive layers and using the passivated TiO2 electron extraction layers exhibited a significant enhancement of more than 30% in their power conversion efficiencies (PCEs) as compared to their reference devices without the insulating metal oxide nanolayers as a result of significant suppression of charge recombination and enhanced electron extraction rates at the TiO2/ALD metal-oxide/organic interface.
    • Avoiding ambient air and light induced degradation in high-efficiency polymer solar cells by the use of hydrogen-doped zinc oxide as electron extraction material

      Polydorou, Ermioni; Sakelis, Elias; Soultati, Anastasia; Kaltzoglou, Andreas; Papadopoulos, Theodoros A.; Briscoe, Joe; Tsikritzis, Dimitris; Fakis, Mihalis; Palilis, Leonidas C.; Kennou, Stella; Argitis, Panagiotis; Falaras, Polycarpos; Davazoglou, Dimitris; Vasilopoulou, Maria; National Center for Scientific Research Demokritos; University of Patras; University of Athens; National Technical University of Athens; University of Chester; Queen Mary University of London (Elsevier, 2017-02-24)
      Polymer solar cells have undergone rapid development in recent years. Their limited stability to environmental influence and during illumination, however, still remains a major stumbling block to the commercial application of this technology. Several attempts have been made to address the instability issue, mostly concentrated on the insertion of charge transport interlayers in the device stack. Although zinc oxide (ZnO) is one of the most common electron transport materials in those cells, the presence of defects at the surface and grain boundaries significantly affects the efficiency and stability of the working devices. To address these issues, we herein employ hydrogen-doping of ZnO electron extraction material. It is found that devices based on photoactive layers composed of blends of poly(3-hexylthiophene) (P3HT) with electron acceptors possessing different energy levels, such as [6,6]-phenyl-C70butyric acid methyl ester (PC70BM) or indene-C60 bisadduct (IC60BA) essentially enhanced their photovoltaic performance when using the hydrogen-doped ZnO with maximum power conversion efficiency (PCE) reaching values of 4.62% and 6.65%, respectively, which are much higher than those of the cells with the pristine ZnO (3.08% and 4.51%). Most significantly, the degradation of non-encapsulated solar cells when exposed to ambient or under prolonged illumination is studied and it is found that devices based on un-doped ZnO showed poor environmental stability and significant photo-degradation while those using hydrogen-doped ZnO interlayers exhibited high long-term ambient stability and maintained nearly 80–90% of their initial PCE values after 40 h of 1.5 AM illumination. All mechanisms responsible for this enhanced stability are elucidated and corresponding models are proposed. This work successfully addresses and tackles the instability problem of polymer solar cells and the key findings pave the way for the upscaling of these and, perhaps, of related devices such as perovskite solar cells.
    • Bioinspired bactericidal surfaces with polymer nanocone arrays

      Hazell, Gavin; Fisher, Leanne E.; Murray, W. Andrew; Nobbs, Angela H.; Su, Bo; University of Chester; University of Bristol (Elsevier, 2018-05-28)
      Infections resulting from bacterial biofilm formation on the surface of medical devices are challenging to treat and can cause significant patient morbidity. Recently, it has become apparent that regulation of surface nanotopography can render surfaces bactericidal. In this study, poly(ethylene terephthalate) nanocone arrays are generated through a polystyrene nanosphere-mask colloidal lithographic process. It is shown that modification of the mask diameter leads to a direct modification of centre-to-centre spacing between nanocones. By altering the oxygen plasma etching time it is possible to modify the height, tip width and base diameter of the individual nanocone features. The bactericidal activity of the nanocone arrays was investigated against Escherichia coli and Klebsiella pneumoniae. It is shown that surfaces with the most densely populated nanocone arrays (center-to-center spacing of 200 nm), higher aspect ratios (>3) and tip widths <20 nm kill the highest percentage of bacteria (∼30%).
    • Chemical and device degradation in PCPDTBT: PCBM solar cells using XPS and ToF-SIMS

      Kettle, Jeff; Waters, Huw; Ding, Ziqian; Smith, Graham C.; Bangor University ; Bangor University ; Bangor University ; University of Chester (2015-04-20)
      Analysis of the degradation routes for PCPDTBT-based solar cells under illumination and in the presence of air have been conducted using a combination of X-ray Photoelectron Spectroscopy (XPS), Time-Of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) and solar cell device data. After ageing, XPS studies show that PCPDTBT appears as an oxygen-containing polymer, with data indicating that a break-up in the aromatic rings, formation of sulphates at the thiophene ring, chain scission in the polymer backbone and also loss of side chains. XPS studies on active layers blends of PCPDTBT and PCBM also show significant changes in the vertical composition during ageing, with increased enrichment of PCPDTBT observed at the top surface and that the use of a processing additive (ODT) has a negative impact on the morphological stability. TOF-SIMS has been used to study electrode degradation during ageing experiments leads to migration of indium and tin ions into the active layer in non-inverted devices, but is eliminated for inverted devices.
    • Chemical changes in PCPDTBT:PCBM solar cells using XPS and TOF-SIMS and use of inverted device structure for improving lifetime performance

      Kettle, Jeff; Waters, Huw; Ding, Ziqian; Horie, Masaki; Smith, Graham C.; School of Electronic Engineering University of Bangor (Kettle, Waters, Ding), Department of Chemical Engineering National Tsing Hua University Taiwan (Horie), Department of Natural Sciences University of Chester (Smith) (Elsevier, 2015-06-10)
      Analysis of the degradation routes for poly[(4,4-bis(2-ethylhexyl)-cyclopenta-[2,1-b;3,4-b′]dithiophene)-2,6-diyl-alt-2,1,3-benzothiadiazole-4,7-diyl] (PCPDTBT)-based solar cells under illumination and in the presence of air have been conducted using a combination of X-ray Photoelectron Spectroscopy (XPS), Time-Of-Flight Secondary Ion Mass Spectrometry (TOF-SIMs) and solar cell device data. After ageing, XPS studies show that PCPDTBT appears as an oxygen-containing polymer, with data indicating that a break-up in the aromatic rings, formation of sulphates at the thiophene ring, chain scission in the polymer backbone and also loss of side chains. XPS studies have also been conducted on Phenyl-C71-butyric acid methyl ester (PC71BM) films and show a breakage of the fullerene cage, loss of molecular shape and oxidation of carbon atoms in the fullerene cage and side chains after ageing. XPS studies on active layers blends of PCPDTBT and PCBM also show significant changes in the vertical composition during ageing, with increased enrichment of PCPDTBT observed at the top surface and that the use of a processing additive (ODT) has a negative impact on the morphological stability. Based on these studies, it shown that inverted structures are better suited than non-inverted devices for PCPDTBT:PCBM solar cells. An additional advantage of inverted devices is shown using TOF-SIMS; electrode degradation during ageing experiments leads to migration of indium and tin ions into the active layer in non-inverted devices, but is eliminated for inverted devices.
    • Chemical ionization quadrupole mass spectrometer with an electrical discharge ion source for atmospheric trace gas measurement

      Eger, Philipp G.; Helleis, Frank; Schuster, Gerhard; Phillips, Gavin J.; Lelieveld, Jos; Crowley, John N.; Max Planck Institute for Chemistry; University of Chester (Copernicus Publications, 2019-03-26)
      We present a chemical ionization quadrupole mass spectrometer (CI-QMS) with a radio-frequency (RF) discharge ion source through N2∕CH3I as a source of primary ions. In addition to the expected detection of PAN, peracetic acid (PAA) and ClNO2 through well-established ion–molecule reactions with I− and its water cluster, the instrument is also sensitive to SO2, HCl and acetic acid (CH3C(O)OH) through additional ion chemistry unique to our ion source. We present ionization schemes for detection of SO2, HCl and acetic acid along with illustrative datasets from three different field campaigns underlining the potential of the CI-QMS with an RF discharge ion source as an alternative to 210Po. The additional sensitivity to SO2 and HCl makes the CI-QMS suitable for investigating the role of sulfur and chlorine chemistry in the polluted marine and coastal boundary layer.
    • ClNO2 and nitrate formation via N2O5 uptake to particles: Derivation of N2O5 uptake coefficients from ambient datasets

      Phillips, Gavin J.; Thieser, Jim; Tang, Mingjin; Sobanski, Nicolas; Fachinger, Johannes; Drewnick, Frank; Lelieveld, Jos; Crowley, John N.; Max Planck Institute for Chemistry/University of Chester ; Max Planck Institute for Chemistry ; Max Planck Institute for Chemistry ; Max Planck Institute for Chemistry ; Max Planck Institute for Chemistry ; Max Planck Institute for Chemistry ; Max Planck Institute for Chemistry; Max Planck Institute for Chemistry (Copernicus Publications, 2015-02-25)
      We present estimates of the uptake coefficient of N2O5 using ambient measurements of the trace gases N2O5 and ClNO2 and particle composition and surface area at the Kleiner Feldberg observatory, near Frankfurt, SW Germany, during the PARADE campaign (summer 2011). Three methods used to extract gamma(N2O5) from the datasets were found to be in reasonable agreement, generating values between 0.001 and 0.4. Gamma (N2O5) displayed a significant dependence on relative humidity (RH), the largest values obtained, as expected, at high RH. No significant dependence of gamma(N2O5) on particle organic content or sulphate-to-organic ratio was observed. The variability in gamma(N2O5) is however large, indicating that humidity is not the sole factor determining the uptake coefficient. There is also an indication that the yield of ClNO2 with respect to N2O5 uptake is larger with lower concentrations of PM1 total organics. Our results will be compared to existing uptake coefficients from laboratory studies and those derived from field observations.
    • Comment on “Observations of ammonia, nitric acid, and fine particles in a rural gas production region” by Yi Li, Florian M. Schwandnera, H. James Sewell, Angela Zivkovich, Mark Tigges, Suresh Raja, Stephen Holcomb, John V. Molenar, Lincoln Sherman, Cassie Archuleta, Taehyoung Lee and Jeffrey L. Collett Jr. Atmospheric Environment (in press)

      Phillips, Gavin J.; University of Chester (Elsevier, 2014-01)
      Peer reviewed commentary on a research paper. An artefact of the detection of nitric acid (HNO3) by denuder methods is discussed. This artefact arises from the likely reaction of dinitrogen pentoxide (N2O5) on the denuder train resulting in the report of some fraction of N2O5 as HNO3.
    • Computational benchmarking for ultrafast electron dynamics: wavefunction methods vs density functional theory

      Oliveira, Micael J. T.; Mignolet, Benoit; Kus, Tomasz; Papadopoulos, Theodoros A.; Remacle, Francoise; Verstraete, Matthieu J.; University of Chester (American Chemical Society, 2015-05-12)
      Attosecond electron dynamics in small- and medium-sized molecules, induced by an ultrashort strong optical pulse, is studied computationally for a frozen nuclear geometry. The importance of exchange and correlation effects on the nonequilibrium electron dynamics induced by the interaction of the molecule with the strong optical pulse is analyzed by comparing the solution of the time-dependent Schrodinger equation based on the correlated field-free stationary electronic states computed with the equation-of-motion coupled cluster singles and doubles and the complete active space multi-configurational self-consistent field methodologies on one hand, and various functionals in real-time time-dependent density functional theory (TD-DFT) on the other. We aim to evaluate the performance of the latter approach, which is very widely used for nonlinear absorption processes and whose computational cost has a more favorable scaling with the system size. We focus on LiH as a toy model for a nontrivial molecule and show that our conclusions carry over to larger molecules, exemplified by ABCU (C10H19N). The molecules are probed with IR and UV pulses whose intensities are not strong enough to significantly ionize the system. By comparing the evolution of the time-dependent field-free electronic dipole moment, as well as its Fourier power spectrum, we show that TD-DFT performs qualitatively well in most cases. Contrary to previous studies, we find almost no changes in the TD-DFT excitation energies when excited states are populated. Transitions between states of different symmetries are induced using pulses polarized in different directions. We observe that the performance of TD-DFT does not depend on the symmetry of the states involved in the transition.
    • Control of the dipole layer of polar organic molecules adsorbed on metal surfaces via different charge-transfer channels

      Lin, Meng-Kai; Nakayama, Yasuo; Zhuang, Ying-Jie; Su, Kai-Jun; Wang, Chin-Yung; Pi, Tun-Wen; Metz, Sebastian; Papadopoulos, Theodoros A.; Chiang, Tai-Chang; Ishii, Hisao; Tang, Shu-Jung; University of Chester (American Physical Society, 2017-02-17)
      Organic molecules with a permanent electric dipole moment have been widely used as a template for further growth of molecular layers in device structures. Key properties of the resulting organic films such as energy level alignment (ELA), work function, and injection/collection barrier are linked to the magnitude and direction of the dipole moment at the interface. Using angle-resolved photoemission spectroscopy (ARPES), we have systematically investigated the coverage-dependent work function and spectral line shapes of occupied molecular energy states (MES) of chloroaluminium-phthalocyanine (ClAlPc) grown on Ag(111). We demonstrate that the dipole orientation of the first ClAlPc layer can be controlled by adjusting the deposition rate and post annealing conditions; the ELA at the interface differs by ~0.4 eV between the Cl-up and -down configurations of the adsorbed ClAlPc molecules. These observations are rationalized by density-functional-theory (DFT) calculations based on a realistic model of the ClAlPc/Ag(111) interface, which reveal that the different orientations of the ClAlPc dipole layer lead to different charge-transfer channels between the adsorbed ClAlPc and Ag(111) substrate. Our findings provide a useful framework towards method development for ELA tuning.