Imperial College London

Prof Milo Shaffer

Faculty of Natural SciencesDepartment of Chemistry

Professor of Materials Chemistry
 
 
 
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Contact

 

+44 (0)20 7594 5825m.shaffer Website

 
 
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Assistant

 

Mr John Murrell +44 (0)20 7594 2845

 
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Location

 

M221Royal College of ScienceSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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277 results found

Thong AZ, Shaffer MS, Horsfield AP, 2017, HOMO-LUMO coupling: the fourth rule for highly effective molecular rectifiers, Nanoscale, Vol: 9, Pages: 8119-8125, ISSN: 2040-3372

Three rules for creating highly effective unimolecular rectifiers that utilize asymmetric anchoring groups have been proposed by Van Dyck and Ratner [Ratner et al., Nano Lett., 2015, 15, 1577–1584]. This study investigates their proposed rectification mechanism in a functionalised azafullerene system (4TPA–C60) and identifies a fourth rule. NEGF-DFT shows that 4TPA–C60 fulfills the three design rules and finds that a saturated bridge is not required to fulfil the third rule, contrary to previous belief. Instead a twisted-π bridge decouples the donor and acceptor states whilst still providing a high conductance pathway. The molecular junction has a calculated rectification ratio of 145 at a bias of ±1 V and the U-type rectification mechanism is driven by the pinning of the HOMO to the LUMO when the device is forward biased, but not when reverse biased. The switching behaviour is a result of a charge dipole forming at different interfaces for different bias directions. An additional design rule is thus proposed: charge transport should allow bias dependent coupling of filled to unfilled states. The findings in this work not only help in understanding charge transport in molecular rectifiers, but also have wider implications for the design of molecular resonant tunneling devices.

Journal article

Robinson RK, Birrell MA, Adcock JJ, Wortley MA, Dubuis ED, Chen S, McGilvery CM, Hu S, Shaffer MSP, Bonvini SJ, Maher SA, Mudway IS, Porter AE, Carlsten C, Tetley TD, Belvisi MGet al., 2017, Mechanistic link between diesel exhaust particles and respiratory reflexes, Journal of Allergy and Clinical Immunology, Vol: 141, Pages: 1074-1084.e9, ISSN: 1097-6825

BackgroundDiesel exhaust particles (DEPs) are a major component of particulate matter in Europe's largest cities, and epidemiologic evidence links exposure with respiratory symptoms and asthma exacerbations. Respiratory reflexes are responsible for symptoms and are regulated by vagal afferent nerves, which innervate the airway. It is not known how DEP exposure activates airway afferents to elicit symptoms, such as cough and bronchospasm.ObjectiveWe sought to identify the mechanisms involved in activation of airway sensory afferents by DEPs.MethodsIn this study we use in vitro and in vivo electrophysiologic techniques, including a unique model that assesses depolarization (a marker of sensory nerve activation) of human vagus.ResultsWe demonstrate a direct interaction between DEP and airway C-fiber afferents. In anesthetized guinea pigs intratracheal administration of DEPs activated airway C-fibers. The organic extract (DEP-OE) and not the cleaned particles evoked depolarization of guinea pig and human vagus, and this was inhibited by a transient receptor potential ankyrin-1 antagonist and the antioxidant N-acetyl cysteine. Polycyclic aromatic hydrocarbons, major constituents of DEPs, were implicated in this process through activation of the aryl hydrocarbon receptor and subsequent mitochondrial reactive oxygen species production, which is known to activate transient receptor potential ankyrin-1 on nociceptive C-fibers.ConclusionsThis study provides the first mechanistic insights into how exposure to urban air pollution leads to activation of guinea pig and human sensory nerves, which are responsible for respiratory symptoms. Mechanistic information will enable the development of appropriate therapeutic interventions and mitigation strategies for those susceptible subjects who are most at risk.

Journal article

Pike SD, White ER, Regoutz A, Sammy N, Payne DJ, Williams CK, Shaffer MSPet al., 2017, Reversible Redox Cycling of Well-Defined, Ultrasmall Cu/Cu2O Nanoparticles, ACS Nano, Vol: 11, Pages: 2714-2723, ISSN: 1936-0851

Exceptionally small and well-defined copper (Cu) and cuprite (Cu2O) nanoparticles (NPs) are synthesized by the reaction of mesitylcopper(I) with either H2 or air, respectively. In the presence of substoichiometric quantities of ligands, namely, stearic or di(octyl)phosphinic acid (0.1–0.2 equiv vs Cu), ultrasmall nanoparticles are prepared with diameters as low as ∼2 nm, soluble in a range of solvents. The solutions of Cu NPs undergo quantitative oxidation, on exposure to air, to form Cu2O NPs. The Cu2O NPs can be reduced back to Cu(0) NPs using accessible temperatures and low pressures of hydrogen (135 °C, 3 bar H2). This striking reversible redox cycling of the discrete, solubilized Cu/Cu(I) colloids was successfully repeated over 10 cycles, representing 19 separate reactions. The ligands influence the evolution of both composition and size of the nanoparticles, during synthesis and redox cycling, as explored in detail using vacuum-transfer aberration-corrected transmission electron microscopy, X-ray photoelectron spectroscopy, and visible spectroscopy.

Journal article

Gonzalez Carter DA, Leo BF, Ruenraroengsak P, Chen S, Goode A, Theodorou I, Chung KF, Carzaniga R, Shaffer M, Dexter D, Ryan M, Porter Aet al., 2017, Silver nanoparticles reduce brain inflammation and related neurotoxicity through induction of H2S-synthesizing enzymes, Scientific Reports, Vol: 7, ISSN: 2045-2322

Silver nanoparticles (AgNP) are known to penetrate into the brain and cause neuronal death. However, there is a paucity in studies examining the effect of AgNP on the resident immune cells of the brain, microglia. Given microglia are implicated in neurodegenerative disorders such as Parkinson’s disease (PD), it is important to examine how AgNPs affect microglial inflammation to fully assess AgNP neurotoxicity. In addition, understanding AgNP processing by microglia will allow better prediction of their long term bioreactivity. In the present study, the in vitro uptake and intracellular transformation of citrate-capped AgNPs by microglia, as well as their effects on microglial inflammation and related neurotoxicity were examined. Analytical microscopy demonstrated internalization and dissolution of AgNPs within microglia and formation of non-reactive silver sulphide (Ag2S) on the surface of AgNPs. Furthermore, AgNP-treatment up-regulated microglial expression of the hydrogen sulphide (H2S)-synthesizing enzyme cystathionine-γ-lyase (CSE). In addition, AgNPs showed significant anti-inflammatory effects, reducing lipopolysaccharide (LPS)-stimulated ROS, nitric oxide and TNFα production, which translated into reduced microglial toxicity towards dopaminergic neurons. Hence, the present results indicate that intracellular Ag2S formation, resulting from CSE-mediated H2S production in microglia, sequesters Ag+ ions released from AgNPs, significantly limiting their toxicity, concomitantly reducing microglial inflammation and related neurotoxicity.

Journal article

Hodge SA, Buckley D, Yau HC, Skipper N, Howard C, Shaffer MSPet al., 2017, Chemical routes to discharging graphenides, Nanoscale, Vol: 9, Pages: 3150-3158, ISSN: 2040-3372

Chemical and electrochemical reduction methods allow the dispersion, processing, and/or functionalization of discrete sp2-hybridised nanocarbons, including fullerenes, nanotubes and graphenes. Electron transfer to the nanocarbon raises the Fermi energy creating nanocarbon anions, thereby activating an array of possible covalent reactions. The Fermi level may then be partially or fully lowered by intended functionalization reactions, but in general, techniques are required to removeexcess charge without inadvertent covalent reactions that potentially degrade the nanocarbon properties of interest. Here, simple and effective chemical discharging routes are demonstrated for graphenide polyelectrolytes and are expected to apply to other systems, particularly nanotubides. Thedischarging process is inherently linked to the reduction potentials of such chemical discharging agents and the unusual fundamental chemistry of charged nanocarbons.

Journal article

Garcia-Trenco A, White ER, Regoutz A, Payne DJ, Shaffer MSP, Williams CKet al., 2017, Pd2Ga-Based Colloids as Highly Active Catalysts for the Hydrogenation of CO2 to Methanol, ACS Catalysis, Vol: 7, Pages: 1186-1196, ISSN: 2155-5435

Colloidal Pd2Ga-based catalysts are shown to catalyze efficiently the hydrogenation of CO2 to methanol. The catalysts are produced by the simple thermal decomposition of Pd(II) acetate in the presence of Ga(III) stearate, which leads to Pd0 nanoparticles (ca. 3 nm), and the subsequent Pd-mediated reduction of Ga(III) species at temperatures ranging from 210 to 290 °C. The resulting colloidal Pd2Ga-based catalysts are applied in the liquid-phase hydrogenation of carbon dioxide to methanol at high pressure (50 bar). The intrinsic activity is around 2-fold higher than that obtained for the commercial Cu-ZnO-Al2O3 (60.3 and 37.2 × 10–9 molMeOH m–2 s–1), respectively, and 4-fold higher on a Cu or Pd molar basis (3330 and 910 μmol mmolPd or Cu–1 h–1). Detailed characterization data (HR-TEM, STEM/EDX, XPS, and XRD) indicate that the catalyst contains Pd2Ga nanoparticles, of average diameters 5–6 nm, associated with a network of amorphous Ga2O3 species. The proportion of this Ga2O3 phase can be easily tuned by adjusting the molar ratio of the Pd:Ga precursors. A good correlation was found between the intrinsic activity and the content of Ga2O3 surrounding the Pd2Ga nanoparticles (XPS), suggesting that methanol is formed by a bifunctional mechanism involving both phases. The increase in the reaction temperature (190–240 °C) leads to a gradual decrease in methanol selectivity from 60 to 40%, while an optimum methanol production rate was found at 210 °C. Interestingly, unlike the conventional Cu-ZnO-Al2O3, which experienced approximately 50% activity loss over 25 h time on stream, the Pd2Ga-based catalysts maintain activity over this time frame. Indeed, characterization of the Pd/Ga mixture postcatalysis revealed no ripening of the nanoparticles or changes in the phases initially present.

Journal article

Mattevi C, 2016, Graphitic carbon nitride as a catalyst support in fuel cells and electrolyzers, Electrochimica Acta, Vol: 222, Pages: 44-57, ISSN: 1873-3859

Electrochemical power sources, such as polymer electrolyte membrane fuel cells (PEMFCs), require the use of precious metal catalysts which are deposited as nanoparticles onto supports in order to minimize their mass loading and therefore cost. State-of-the-art/commercial supports are based on forms of carbon black. However, carbon supports present disadvantages including corrosion in the operating fuel cell environment and loss of catalyst activity. Here we review recent work examining the potential of different varieties of graphitic carbon nitride (gCN) as catalyst supports, highlighting their likely benefits, as well as the challenges associated with their implementation. The performance of gCN and hybrid gCN-carbon materials as PEMFC electrodes is discussed, as well as their potential for use in alkaline systems and water electrolyzers. We illustrate the discussion with examples taken from our own recent studies.

Journal article

Lee W, CLANCY A, KONTTURI E, BISMARCK A, SHAFFER Met al., 2016, Strong and Stiff: High-Performance Cellulose Nanocrystal/Poly(vinyl alcohol) Composite Fibers, ACS Applied Materials & Interfaces, Vol: 8, Pages: 31500-31504, ISSN: 1944-8244

Mechanical properties of rod7like cellulose nanocrystals (CNCs) offer great potential as bioderived reinforcement in (nano)composites. Polyvinyl alcohol (PVOH) is a useful industrial material and very compatible with CNC chemistry. High performance CNC/PVOH composite fibers were produced coaxial coagulation spinning, followed by hot7drawing. DSC and WAXS showed that CNCs increase the alignment and crystallinity of PVOH, as well as providing direct reinforcement, leading to enhanced fiber strength and stiffness. At 40 wt.% CNC loading, the strength and stiffness reached 880 MPa and 29.9 GPa, exceeding the properties of most other nanocellulose based composite fibers previously reported.

Journal article

Beesley DJ, Price BK, Hunter S, Shaffer MSP, de Mello JCet al., 2016, Direct dispersion of SWNTs in highly conductive solvent-enhanced PEDOT:PSS films, Nanocomposites, Vol: 2, Pages: 135-140, ISSN: 2055-0332

Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) is shown to be an effective dispersant for single-wall carbon nanotubes (SWNTs), enabling uniform aqueous suspensions to be obtained at weight loadings of up to 0.23 mg/ml (>1% by weight relative to PEDOT:PSS) without recourse to additional surfactants. Thin films spin-coated from PEDOT:PSS/SWNT suspensions exhibited sheet resistances of 90 Ω/sq. at 80 % transmittance, slightly higher than equivalent films of pure PEDOT:PSS which exhibited sheet resistances of 70 Ω/sq. at the same transmittance.

Journal article

Pike S, White E, Shaffer M, Williams CKet al., 2016, Simple Phosphinate Ligands Access New Zinc Clusters Identified in the Synthesis of Zinc Oxide Nanoparticles, Nature Communications, Vol: 7, ISSN: 2041-1723

The bottom-up synthesis of ligand-stabilised functional nanoparticles from molecular precursors is widely applied but difficult to study mechanistically. Here, we use 31P NMR spectroscopy to follow the trajectory of phosphinate ligands during the synthesis of a range of new ligated zinc oxo clusters, containing 4, 6 and 11 zinc atoms. Using an organometallic route, the clusters interconvert rapidly, and self-assemble in solution based on thermodynamic equilibria, rather than nucleation kinetics. These clusters are also identified, in situ, during the synthesis of phosphinate-capped zinc oxide nanoparticles. Unexpectedly, the ligand is sequestered to a stable Zn11 cluster during the majority of the synthesis and only becomes coordinated to the nanoparticle surface, in the final step. As well as a versatile and accessible route to new (optionally doped) zinc clusters, the findings provide a new understanding of the role of well-defined molecular precursors during the synthesis of small (2-4 nm) nanoparticles.

Journal article

Sweeney S, Hu S, Ruenraroengsak P, Chen S, Gow A, Schwander S, Zhang JJ, Chung KF, Ryan MP, Porter AE, Shaffer MS, Tetley TDet al., 2016, Carboxylation of multiwalled carbon nanotubes reduces their toxicity in primary human alveolar macrophages, Environmental Science: Nano, Vol: 3, Pages: 1340-1350, ISSN: 2051-8153

Surface functionalisation of multiwalled carbon nanotubes (MWCNT) is commonly used to facilitate their various and diverse applications. Inhaled nanomaterials, such as MWCNTs, have a high deposition rate in the alveolar units of the deep lung, where alveolar macrophages (AM) provide the front line of cellular immune defence by removing foreign matter (microbes, particles etc.). The toxicity of MWCNTs (with or without functionalisation) towards primary human AMs is not known. We investigated the physicochemical characteristics and toxicity of two MWCNT materials: acid purified ‘Purified-MWCNT’ and concentrated acid functionalised ‘COOH-MWCNT’. We hypothesised that the bioreactivity with primary human AM would differ between the materials. Full characterisation of the MWCNTs revealed that –COOH functionalisation yielded shorter MWCNTs, accompanied by a greater occurrence of framework defects, in comparison to Purified-MWCNT. In agreement with our hypothesis that the bioreactivity would differ, Purified-MWCNT were significantly more toxic as measured by reduced cell viability and increased inflammatory mediator release. For example, IL-1β and IL-8 release by AMs significantly increased 3.5- and 2.4-fold, respectively (P < 0.05), 24 hours after treatment with Purified-MWCNT. In contrast, IL-1β and IL-8 release by AMs did not significantly change 24 hours after treatment with COOH-MWCNT. We determined that the mechanism of this toxicity is likely due to activation of the inflammasome, as lipopolysaccharide priming of primary human AMs was necessary to see the inflammatory response and this was accompanied by lysosomal disruption and increased generation of reactive oxygen species. This study contributes further to our understanding of the effects of MWCNTs and surface modification on highly relevant human lung AMs; the findings have important implications for the manufacture, application and use of MWCNTs. In particular, this is

Journal article

Mansor N, Jia J, Miller TS, Suter T, Jorge AB, Gibbs C, Shearing P, McMillan PF, Mattevi C, Shaffer M, Brett DJLet al., 2016, Graphitic carbon nitride-graphene hybrid nanostructure as a catalyst support for polymer electrolyte membrane fuel cells, ECS Transactions, Vol: 75, Pages: 885-897, ISSN: 1938-5862

Graphitic carbon nitrides form a class of semiconducting graphene-like polymeric materials with visible light absorption and photocatalytic properties. In addition to high nitrogen content and tunable structure, it was shown that graphitic carbon nitride based on polytrazine imide (PTI) sheets exhibit excellent anti-corrosion ability in ex-situ fuel cell environments. However, in bulk form, their low surface area and poor conductivity limits their applications in fuel cells. In this work, PTI was exfoliated to form an ink made from single to few-layer nanosheets. The ink was then processed to produce 3D networks of carbon nitride nanosheets/reduced graphene oxide (PTI-rGO) hybrid aerogel with large interconnecting pores for fast mass transport of reactants and high surface area. The material was decorated with platinum nanoparticles, and then investigated for its electrochemical properties and applications as a catalyst support for polymer electrolyte membrane (PEM) fuel cells. Initial results show that the cathode catalytic activity of Pt/rGO-PTI hybrid is significantly improved in comparison to Pt/PTI or Pt/rGO. In addition, the in-situ fuel cell performance of Pt/PTI as anode catalyst is comparable to commercial Pt/C especially at low densities, making it attractive as an alternative, durable anode catalyst support material to conventional carbon black.

Journal article

Zhang JJ, Lee KB, He L, Seiffert J, Subramaniam P, Yang L, Chen S, Maguire P, Mainelis G, Schwander S, Tetley T, Porter A, Ryan M, Shaffer M, Hu S, Gong J, Chung KFet al., 2016, Effects of a nanoceria fuel additive on the physicochemical properties of diesel exhaust particles., Environmental Science: Processes & Impacts, Vol: 18, Pages: 1333-1342, ISSN: 2050-7887

Nanoceria (i.e., CeO2 nanoparticles) fuel additives have been used in Europe and elsewhere to improve fuel efficiency. Previously we have shown that the use of a commercial fuel additive Envirox™ in a diesel-powered electricity generator reduced emissions of diesel exhaust particle (DEP) mass and other pollutants. However, such additives are currently not permitted for use in on-road vehicles in North America, largely due to limited data on the potential health impact. In this study, we characterized a variety of physicochemical properties of DEPs emitted from the same engine. Our methods include novel techniques such as Raman spectrometry for analyzing particle surface structure and an assay for DEP oxidative potential. Results show that with increasing Envirox™ concentrations in the fuel (0×, 0.1×, 1×, and 10× of manufacturer recommended 0.5 mL Envirox™ per liter fuel), DEP sizes decreased from 194.6 ± 20.1 to 116.3 ± 14.8 nm; the zeta potential changed from -28.4 mV to -22.65 mV; DEP carbon content decreased from 91.8% to 79.4%; cerium and nitrogen contents increased from 0.3% to 6.5% and 0.2% to 0.6%, respectively; the ratio of organic carbon (OC) to elemental carbon (EC) increased from 22.9% to 38.7%; and the ratio of the disordered carbon structure to the ordered carbon structure (graphitized carbon) in DEPs decreased. Compared to DEPs emitted from 0×, 0.1×, and 1× fuels, DEPs from the 10× fuel had a lower oxidative potential likely due to the increased ceria content because pure ceria nanoparticles exhibited the lowest oxidative potential compared to all the DEPs. Since the physicochemical parameters tested here are among the determinants of particle toxicity, our findings imply that adding ceria nanoparticles into diesel may alter the toxicity of DEPs. The findings from the present study, hence, can help future studies that will examine the impact of nanoceria additives on DEP to

Journal article

Sehmi SK, Noimark S, Pike SD, Bear JC, Peveler WJ, Williams CK, Shaffer MSP, Allan E, Parkin IP, MacRobert AJet al., 2016, Enhancing the Antibacterial Activity of Light-Activated Surfaces Containing Crystal Violet and ZnO Nanoparticles: Investigation of Nanoparticle Size, Capping Ligand, and Dopants, ACS OMEGA, Vol: 1, Pages: 334-343, ISSN: 2470-1343

Journal article

Clancy ARJ, White E, Tay HH, Yau HC, Shafferet al., 2016, Systematic Comparison of Conventional and Reductive Single-walled Carbon Nanotube Purifications, Carbon, Vol: 108, Pages: 423-432, ISSN: 0008-6223

As-synthesised single-walled carbon nanotubes (SWCNTs) are often contaminated withamorphous carbon and residual catalyst particles. These contaminants have a detrimental effecton the effective mechanical and electronic properties, limiting their performance in manyapplications. A comparative series of SWCNT purifications including acid treatments, gasphase purifications and recently-developed reductive purifications have been conducted usinga single commercial SWCNT type (Tuball™). Each of the purification procedures was selectedfor its potential scalability to bulk quantities and evaluated for the extent of impurity removal,SWCNT damage, and overall yield. Raman spectra confirmed that reductive purification usingsodium naphthalide gave the lowest D/G ratio, suggesting that the sp2carbon framework wasmost effectively preserved, while removing a large percentage of the metal impurities.Conversely, nitric acid treatment was most effective at removing catalytic impurities, but thesp2carbon framework was most heavily damaged in the process. The development of scalable,one pot, reductive separations provides a useful new approach to SWCNT purification.

Journal article

Garcia Trenco A, White E, Shaffer M, Williams CKet al., 2016, A one-step Cu/ZnO Quasi-Homogeneous Catalyst for DME Production from Syn-gas, Catalysis Science & Technology, Vol: 6, Pages: 4389-4397, ISSN: 2044-4753

A simple one-pot synthetic method allows the preparation of hybrid catalysts, based on colloidal Cu/ZnO nanoparticles(NPs), used for the liquid phase synthesis of DME from syngas. The method obviates the high temperature calcinations andpre-reduction treatments typically associated with such catalysts. The hybrid catalysts are applied under typicalindustrially relevant conditions. The nature of the hybrid catalysts, the influence of the acid component, mass ratiobetween components, and Cu/Zn composition are assessed. The best catalysts comprise a colloidal mixture of Cu/ZnONPs, as the methanol synthesis component, and -Al2O3, as the methanol dehydration component. These catalysts showhigh DME selectivity (65-70 %C). Interestingly, the activity (relative to Cu content) is up to three times higher than that forthe reference hybrid catalyst based on the commercial Cu/ZnO/Al2O3 methanol synthesis catalyst. The hybrid catalysts arestable for at least 20 h time-on-stream, not showing any significant sintering of the Cu0phase. Post-catalysis,TEM/EDXshows that the hybrid catalysts consist of Cu0and ZnO NPs with an average size of 5-7 nm with -Al2O3 particles in closeproximity.

Journal article

Blaker JJ, Anthony DB, Tang G, Shamsuddin SR, Kalinka G, Weinrich M, Abdolvand A, Shaffer MSP, Bismarck Aet al., 2016, Property and shape modulation of carbon fibers using lasers, ACS Applied Materials & Interfaces, Vol: 8, Pages: 16351-16358, ISSN: 1944-8244

An exciting challenge is to create unduloid-reinforcing fibers with tailored dimensions to produce synthetic composites with improved toughness and increased ductility. Continuous carbon fibers, the state-of-the-art reinforcement for structural composites, were modified via controlled laser irradiation to result in expanded outwardly tapered regions, as well as fibers with Q-tip (cotton-bud) end shapes. A pulsed laser treatment was used to introduce damage at the single carbon fiber level, creating expanded regions at predetermined points along the lengths of continuous carbon fibers, whilst maintaining much of their stiffness. The range of produced shapes was quantified and correlated to single fiber tensile properties. Mapped Raman spectroscopy was used to elucidate the local compositional and structural changes. Irradiation conditions were adjusted to create a swollen weakened region, such that fiber failure occurred in the laser treated region producing two fiber ends with outwardly tapered ends. Upon loading the tapered fibers allow for viscoelastic energy dissipation during fiber pull-out by enhanced friction as the fibers plough through a matrix. In these tapered fibers, diameters were locally increased up to 53%, forming outward taper angles of up to 1.8°. The tensile strength and strain to failure of the modified fibers were significantly reduced, by 75% and 55%, respectively, ensuring localization of the break in the expanded region; however, the fiber stiffness was only reduced by 17%. Using harsher irradiation conditions, carbon fibers were completely cut, resulting in cotton-bud fiber end shapes. Single fiber pull-out tests performed using these fibers revealed a 6.75 fold increase in work of pull-out compared to pristine carbon fibers. Controlled laser irradiation is a route to modify the shape of continuous carbon fibers along their lengths, as well as to cut them into controlled lengths leaving tapered or cotton-bud shapes.

Journal article

Liberti E, Menzel R, Shaffer MS, McComb DWet al., 2016, Probing the size dependence on the optical modes of anatase nanoplatelets using STEM-EELS, Nanoscale, Vol: 8, Pages: 9727-9735, ISSN: 2040-3372

Anatase titania nanoplatelets with predominantly exposed {001} facets have been reported to have enhanced catalytic properties in comparison with bulk anatase. To understand their unusual behaviour, it is essential to fully characterize their electronic and optical properties at the nanometer scale. One way of assessing these fundamental properties is to study the dielectric function. Valence electron energy-loss spectroscopy (EELS) performed using a scanning transmission electron microscope (STEM) is the only analytical method that can probe the complex dielectric function with both high energy (<100 meV) and high spatial (<1 nm) resolution. By correlating experimental STEM-EELS data with simulations based on semi-classical dielectric theory, the dielectric response of thin (<5 nm) anatase nanoplatelets was found to be largely dominated by characteristic (optical) surface modes, which are linked to surface plasmon modes of anatase. For platelets less than 10 nm thick, the frequency of these optical modes varies according to their thickness. This unique optical behaviour prompts the enhancement of light absorption in the ultraviolet regime. Finally, the effect of finite size on the dielectric signal is gradually lost by stacking consistently two or more platelets in a specific crystal orientation, and eventually suppressed for large stacks of platelets.

Journal article

Menzel R, Iruretagoyena D, Wang Y, Bawaked SM, Mokhtar M, Al-Thabaiti SA, Basahel SN, Shaffer MSPet al., 2016, Graphene oxide/mixed metal oxide hybrid materials for enhanced adsorption desulfurization of liquid hydrocarbon fuels, Fuel, Vol: 181, Pages: 531-536, ISSN: 0016-2361

A series of mixed metal oxides (MMOs) adsorbents (MgAl-, CuAl- and CoAl-MMOs) were supported on graphene oxide (GO) through in-situ precipitation of layered double hydroxides (LDHs) onto exfoliated GO, followed by thermal conversion. The study shows that GO is an excellent support for the LDH-derived MMOs due to matching geometry and charge complementarity, resulting in a strong hybrid effect, evidenced by significantly enhanced adsorption performance for the commercially important removal of heavy thiophenic compounds from hydrocarbons. Fundamental liquid-phase adsorption characteristics of the MMO/GO hybrids are quantified in terms of adsorption equilibrium isotherms, selectivity and adsorbent regenerability. Upon incorporation of as little as 5 wt% GO into the MMO material, the organosulfur uptake was increased by up to 170%, the recycling stability was markedly improved and pronounced selectivity for thiophenic organosulfurs over sulfur-free aromatic hydrocarbons was observed.

Journal article

Herceg TM, Abidin MSZ, Greenhalgh ES, Shaffer MSP, Bismarck Aet al., 2016, Thermosetting hierarchical composites with high carbon nanotube loadings: En route to high performance, Composites Science and Technology, Vol: 127, Pages: 134-141, ISSN: 0266-3538

A wet powder impregnation route to manufacture carbon fibre reinforced thermoplastic composites was adapted to accommodate thermosetting matrices reinforced with high fractions (20 wt%/13.6 vol%) of multiwalled carbon nanotubes (CNTs). The produced carbon fibre prepregs were consolidated into laminates with fibre volume fractions of 50–58% and up to 6.1 vol% CNTs. Microscopic imaging confirmed successful consolidation at intermediate CNT loadings, but some voidage at the highest CNT loading due to the highly viscoelastic uncured matrix. Nonetheless, through-thickness electrical conductivity and Mode I interlaminar fracture toughness were enhanced by as much as 152% and 24% to unprecedented values of σ = 53 S m−1 and GIC = 840 J m−2, respectively. Fractographic characterisation indicated that crack deflection was the mechanism responsible for the improved fracture toughness. The material properties were shown to be strongly dependent on the microstructure of the matrix.

Journal article

Sweeney S, Leo BF, Chen S, Abraham-Thomas N, Thorley AJ, Gow A, Schwander S, Zhang JJ, Shaffer MS, Chung KF, Ryan MP, Porter AE, Tetley TDet al., 2016, Pulmonary surfactant mitigates silver nanoparticle toxicity in human alveolar type-I-like epithelial cells., Colloids and Surfaces B - Biointerfaces, Vol: 145, Pages: 167-175, ISSN: 1873-4367

Accompanying increased commercial applications and production of silver nanomaterials is an increased probability of human exposure, with inhalation a key route. Nanomaterials that deposit in the pulmonary alveolar region following inhalation will interact firstly with pulmonary surfactant before they interact with the alveolar epithelium. It is therefore critical to understand the effects of human pulmonary surfactant when evaluating the inhalation toxicity of silver nanoparticles. In this study, we evaluated the toxicity of AgNPs on human alveolar type-I-like epithelial (TT1) cells in the absence and presence of Curosurf(®) (a natural pulmonary surfactant substitute), hypothesising that the pulmonary surfactant would act to modify toxicity. We demonstrated that 20nm citrate-capped AgNPs induce toxicity in human alveolar type I-like epithelial cells and, in agreement with our hypothesis, that pulmonary surfactant acts to mitigate this toxicity, possibly through reducing AgNP dissolution into cytotoxic Ag(+) ions. For example, IL-6 and IL-8 release by TT1 cells significantly increased 10.7- and 35-fold, respectively (P<0.01), 24h after treatment with 25μg/ml AgNPs. In contrast, following pre-incubation of AgNPs with Curosurf(®), this effect was almost completely abolished. We further determined that the mechanism of this toxicity is likely associated with Ag(+) ion release and lysosomal disruption, but not with increased reactive oxygen species generation. This study provides a critical understanding of the toxicity of AgNPs in target human alveolar type-I-like epithelial cells and the role of pulmonary surfactant in mitigating this toxicity. The observations reported have important implications for the manufacture and application of AgNPs, in particular for applications involving use of aerosolised AgNPs.

Journal article

Ruenraromgsak P, Chen S, Hu S, Melbourne J, Sweeney S, Thorley AJ, Skepper JN, Shaffer MSP, Tetley TD, Porter AEet al., 2016, Translocation of functionalized multi-walled carbon nanotubes across human pulmonary alveolar epithelium: dominant role of epithelial type 1 cells, ACS Nano, Vol: 10, Pages: 5070-5085, ISSN: 1936-086X

Uptake and translocation of short functionalized multi-walled carbon nanotubes (short-fMWCNTs) through the pulmonary respiratory epithelial barrier depend on physicochemical property and cell type. Two monoculture models, immortalized human alveolar epithelial type 1 (TT1) cells and primary human alveolar epithelial type 2 cells (AT2), which constitute the alveolar epithelial barrier, were employed to investigate the uptake and transport of 300 and 700 nm in length, poly(4-vinylpyridine)-functionalized, multi-walled carbon nanotubes (p(4VP)-MWCNTs) using quantitative imaging and spectroscopy techniques. The p(4VP)-MWCNT exhibited no toxicity on TT1 and AT2 cells, but significantly decreased barrier integrity (*p < 0.01). Uptake of p(4VP)-MWCNTs was observed in 70% of TT1 cells, correlating with compromised barrier integrity and basolateral p(4VP)-MWCNT translocation. There was a small but significantly greater uptake of 300 nm p(4VP)-MWCNTs than 700 nm p(4VP)-MWCNTs by TT1 cells. Up to 3% of both the 300 and 700 nm p(4VP)-MWCNTs reach the basal chamber; this relatively low amount arose because the supporting transwell membrane minimized the amount of p(4VP)-MWCNT translocating to the basal chamber, seen trapped between the basolateral cell membrane and the membrane. Only 8% of AT2 cells internalized p(4VP)-MWCNT, accounting for 17% of applied p(4VP)-MWCNT), with transient effects on barrier function, which initially fell then returned to normal; there was no MWCNT basolateral translocation. The transport rate was MWCNT length modulated. The comparatively lower p(4VP)-MWCNT uptake by AT2 cells is proposed to reflect a primary barrier effect of type 2 cell secretions and the functional differences between the type 1 and type 2 alveolar epithelial cells.

Journal article

Leese HS, Govada L, Saridakis E, Khurshid S, Menzel R, Morishita T, Clancy ARJ, White E, Chayen NE, Shaffer MSPet al., 2016, Reductively PEGylated carbon nanomaterials andtheir use to nucleate 3D protein crystals:a comparison of dimensionality, Chemical Science, Vol: 7, Pages: 2916-2923, ISSN: 2041-6539

A range of carbon nanomaterials, with varying dimensionality, were dispersed by a non-damaging and versatile chemical reduction route, and subsequently grafted by reaction with methoxy polyethylene glycol (mPEG) monobromides. The use of carbon nanomaterials with different geometries provides both a systematic comparison of surface modification chemistry and the opportunity to study factors affecting specific applications. Multi-walled carbon nanotubes, single-walled carbon nanotubes, graphite nanoplatelets, exfoliated few layer graphite and carbon black were functionalized with mPEG-Br, yielding grafting ratios relative to the nanocarbon framework between ca. 7 and 135 wt%; the products were characterised by Raman spectroscopy, TGA-MS, and electron microscopy. The functionalized materials were tested as nucleants by subjecting them to rigorous protein crystallization studies. Sparsely functionalized flat sheet geometries proved exceptionally effective at inducing crystallization of six proteins. This new class of nucleant, based on PEG grafted graphene-related materials, can be widely applied to promote the growth of 3D crystals suitable for X-ray crystallography. The association of the protein ferritin with functionalized exfoliated few layer graphite was directly visualized by transmission electron microscopy, illustrating the formation of ordered clusters of protein molecules critical to successful nucleation.

Journal article

Ferguson A, Khan U, Walsh M, Lee KY, Bismarck A, Shaffer MS, Coleman JN, Bergin SDet al., 2016, Understanding the dispersion and assembly of bacterial cellulose in organic solvents, Biomacromolecules, Vol: 17, Pages: 1845-1853, ISSN: 1526-4602

The constituent nanofibrils of bacterial cellulose are of interest to many researchers because of their purity and excellent mechanical properties. Mechanisms to disrupt the network structure of bacterial cellulose (BC) to isolate bacterial cellulose nanofibrils (BCN) are limited. This work focuses on liquid-phase dispersions of BCN in a range of organic solvents. It builds on work to disperse similarly intractable nanomaterials, such as single-walled carbon nanotubes, where optimum dispersion is seen for solvents whose surface energies are close to the surface energy of the nanomaterial; bacterial cellulose is shown to disperse in a similar fashion. Inverse gas chromatography was used to determine the surface energy of bacterial cellulose, under relevant conditions, by quantifying the surface heterogeneity of the material as a function of coverage. Films of pure BCN were prepared from dispersions in a range of solvents; the extent of BCN exfoliation is shown to have a strong effect on the mechanical properties of BC films and to fit models based on the volumetric density of nanofibril junctions. Such control offers new routes to producing robust cellulose films of bacterial cellulose nanofibrils.

Journal article

Shaffer MSP, Diba M, Fam DWH, Boccaccini Aet al., 2016, Electrophoretic deposition of graphene-related materials: A review of the fundamentals, Progress in Materials Science, Vol: 82, Pages: 83-117, ISSN: 1873-2208

The Electrophoretic Deposition (EPD) of graphene-related materials (GRMs) is an attractive strategy for a wide range of applications. This review paper provides an overview of the fundamentals and specific technical aspects of this approach, highlighting its advantages and limitations, in particular considering the issues that arise specifically from the behaviour and dimensionality of GRMs. Since obtaining a stable dispersion of charged particles is a pre-requisite for successful EPD, the strategies for suspending GRMs in different media are discussed, along with the resulting influence on the deposited film. Most importantly, the kinetics involved in the EPD of GRMs and the factors that cause deviation from linearity in Hamaker’s Law are reviewed. Side reactions often influence both the efficiency of deposition and the nature of the deposited material; examples include the reduction of graphene oxide (GO) and related materials, as well as the decomposition of the suspension medium at high potentials. The microstructural characteristics of GRM deposits, including their degree of reduction and orientation, strongly influence their performance in their intended function. These factors will also determine, to a large extent, the commercial potential of this technique for applications involving GRMs, and are therefore discussed here.

Journal article

De Marco MDM, Markoulidis F, Menzel R, Bawaked S, Mokhtar M, Al-Thabaiti S, Basahel S, Shaffer Met al., 2016, Cross-linked single-walled carbon nanotube aerogel electrodes via reductive coupling chemistry, Journal of Materials Chemistry A, Vol: 4, Pages: 5385-5389, ISSN: 2050-7496

Single-walled carbon nanotube (SWCNT) anions can be cross-linked by a dielectrophile to form covalent, carbon-bonded organogels. Freeze-drying produces cryogels with low density (2.3 mg cm−3), high surface area (766 m2 g−1), and high conductivity (9.4 S m−1), showing promise as supercapacitor electrodes. Counterion concentration controls debundling, grafting ratio, as well as all the resulting properties.

Journal article

Herceg TM, Yoon S-H, Abidin MSZ, Greenhalgh ES, Bismarck A, Shaffer MSPet al., 2016, Thermosetting nanocomposites with high carbon nanotube loadings processed by a scalable powder based method, Composites Science and Technology, Vol: 127, Pages: 62-70, ISSN: 0266-3538

A powder based processing route was developed to allow manufacturing of thermosettingnanocomposites with high (20 wt%) carbon nanotube (CNT) loading fractions. Adaptation ofhigh shear mixing methods, as used in thermoplastic processing, ensured that the CNTs werewell distributed and dispersed even at the highest loadings. By minimising flow distances,compression moulding of powders ensured that the CNTs did not agglomerate duringconsolidation, and yielded a percolated CNT network in a nanocomposite with excellentelectrical and thermal conductivities of 67 S m-1and 0.77 W m-1 K-1, respectively. Unusually,the CNTs provided effective mechanical reinforcement at even the highest loadings;embrittlement is minimised by avoiding large scale inhomogeneities and the maximummeasured Young’s modulus (5.4 GPa) and yield strength (90 MPa) could make thenanocomposite an attractive matrix for continuous fibre composites. The macromechanicalmeasurements were interpolated using micromechanical models that were previouslysuccessfully applied at the nanoscale.

Journal article

Chayen N, shaffer, govada, Khurshid, Kassen, Leese H S, Hu S, Menzel, Chain B, Saridakiset al., 2016, Exploring Carbon Nanomaterial Diversity for Nucleation of Protein Crystals, Scientific Reports, Vol: 6, ISSN: 2045-2322

Controlling crystal nucleation is a crucial step in obtaining high quality protein crystals for structure determination by X-ray crystallography. Carbon nanomaterials (CNMs) including carbon nanotubes, graphene oxide, and carbon black provide a range of surface topographies, porosities and length scales; functionalisation with two different approaches, gas phase radical grafting and liquid phase reductive grafting, provide routes to a range of oligomer functionalised products. These grafted materials, combined with a range of controls, were used in a large-scale assessment of the effectiveness for protein crystal nucleation of 20 different carbon nanomaterials on five proteins. This study has allowed a direct comparison of the key characteristics of carbon-based nucleants: appropriate surface chemistry, porosity and/or roughness are required. The most effective solid system tested in this study, carbon black nanoparticles functionalised with poly(ethylene glycol) methyl ether of mean molecular weight 5000, provides a novel highly effective nucleant, that was able to induce crystal nucleation of four out of the five proteins tested at metastable conditions.

Journal article

Woodward RT, Fam DWH, Anthony DB, Hong J, McDonald TO, Petit C, Shaffer MSP, Bismarck Aet al., 2016, Hierarchically porous carbon foams from pickering high internal phase emulsions, Carbon, Vol: 101, Pages: 253-260, ISSN: 0008-6223

Carbon foams were produced from a macroporous poly(divinylbenzene) (poly(DVB) precursor, synthesized by polymerizing the continuous but minority phase of water-in-oil high internal phase emulsions (HIPEs) stabilized by molecular and/or particulate emulsifiers. Both permeable and non-permeable hierarchically porous carbon foams, or ‘carboHIPEs’, were prepared by carbonization of the resulting macroporous polymers at 800 °C. The carbon yields were as high as 26 wt.% of the original polymer. CarboHIPEs retain the pore structure of the macroporous polymer precursor, but with surface areas of up to 505 m2/g and excellent electrical conductivities of 81 S/m. Contrary to some previous reports, the method does not require further modification, such as sulfonation or additional crosslinking of the polyHIPE prior to carbonization, due to the inherently crosslinked structure of poly(DVB). The use of a pourable, aqueous emulsion-template enables simple moulding, minimises waste and avoids the strong acid treatments used to remove many conventional solid-templates. The retention of the macroporous structure is coupled with the introduction of micropores during carbonization, producing hierarchically porous carboHIPEs, suitable for a wide range of applications as sorbents and electrodes.

Journal article

Anthony DB, Shaffer MSP, 2016, Process for producing carbon-nanotube grafted substrate, WO 2016009207 A1

The present invention relates to a process for producing a carbon nanotube-grafted substrate, the process comprising: providing a substrate having catalytic material deposited thereon; and synthesising carbon nanotubes on the substrate by a chemical vapour deposition process in a reaction chamber; characterised in that the process comprises providing a counter electrode, applying a potential difference to the substrate in relation to the counter electrode and maintaining the potential difference of the substrate in relation to the counter electrode during the chemical vapour deposition process.

Patent

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