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Electrochemical and micro-imaging analysis of a commercial graphite-composite material is presented following electro-oxidation with β-methylumbelliferone. Charge-transfer surface modification was observed for the graphite electrode, presumed to have arisen from adsorbed interfacial umbelliferone moieties. The molecular permeability of the new surface towards a range of similar, yet size-variable (23 Å3–136 Å3) molecular redox probes is discussed. Red-shift fluorescence in confocal microscopy offers further support for the presence of a surface-bound umbelliferone layer. An SEM-platinum profiling technique was used as an imaging tool to map the umbelliferone surface and size-distribution of electroactive sites.

Engineered nanoparticles (NPs) entering the environment are subject to various transformations that in turn influence how particles are presented to, and taken up by, organisms. To understand the effect of soil properties on the toxicity of nanosilver to Caenorhabditis elegans, toxicity assays were performed in porewater extracts from natural soils with varying organic matter content and pH using 3-8 nm unfunctionalized silver (Ag 3-8Unf), 52-nm polyvinylpyrrolidone (PVP)-coated Ag NPs (Ag 52PVP), and AgNO3 as ionic Ag. Effects on NP agglomeration and stability were investigated using ultraviolet-visible (UV-vis) spectroscopy and asymmetric flow field-flow fractionation (AF4); Ag+ showed greater overall toxicity than nanosilver, with little difference between the NP types. Increasing soil organic matter content significantly decreased the toxicity of Ag 3-8Unf, whereas it increased that of AgNO3 . The toxicity of all Ag treatments significantly decreased with increasing porewater pH. Dissolution of both NPs in the porewater extracts was too low to have contributed to their observed toxic effects. The UV-vis spectroscopy revealed low levels of agglomeration/aggregation independent of soil properties for Ag 3-8Unf, whereas higher organic matter as well as low pH appeared to stabilize Ag 52PVP. Overall, both soil organic matter content and pH affected NP fate as well as toxicity to C. elegans; however, there appears to be no clear connection between the measured particle characteristics and their effect. Environ Toxicol Chem 2018;37:2609-2618. © 2018 SETAC.

Silver nanoparticles (AgNPs) are widely used worldwide, most likely leading to their release into the environment and a subsequent increase of environmental concentrations. Studies of their deleterious effects on organisms is crucial to understand their environmental impacts. The freshwater snail Physa acuta was chosen to evaluate the potential deleterious effects of AgNPs and their counterpart AgNO3 , through water-only exposures. The toxicity of AgNPs is greatly influenced by medium composition. Thus, 2 media were tested: artificial pond water (APW) and modified APW (adapted by removing calcium chloride). Acute tests (96 h) were performed with juvenile and adult snails in both media to assess lethality, and egg mass chronic tests were conducted with APW medium only to assess embryo viability and mortality, carried out until 90% hatching success was reached in the control. Acute toxicity increased with decreasing shell length for both silver forms (ion and nanoparticle); that is, juveniles were more sensitive than adults. Different test media led to dissimilar median lethal concentrations, with chloride playing an important role in toxicity, most likely by complexation with silver ions, which would reduce the bioavailability, uptake, and toxicity of silver. Chronic tests showed that hatching success was more sensitive to silver in the ionic form than in the particulate form. Different forms of silver, exposure media, and life cycle stages led to different patterns of toxicity, highlighting an impairment in the snails' life cycle. Environ Toxicol Chem 2017;36:243-253. © 2016 SETAC.

Filamentous hyphae of the human pathogen, Candida albicans, invade mucosal layers and medical silicones. In vitro, hyphal tips reorient thigmotropically on contact with small obstacles. It is not known how surface topography is sensed but hyphae lacking the cortical marker, Rsr1/Bud1, are unresponsive. We show that, on surfaces, the morphology of hyphal tips and the position of internal polarity protein complexes are asymmetrically skewed towards the substratum and biased towards the softer of two surfaces. In nano-fabricated chambers, the Spitzenkorper (Spk) responded to touch by translocating across the apex towards the point of contact, where its stable maintenance correlated with contour-following growth. In the rsr1Δ mutant, the position of the Spk meandered and these responses were attenuated. Perpendicular collision caused lateral Spk oscillation within the tip until after establishment of a new growth axis, suggesting Spk position does not predict the direction of growth in C. albicans. Acute tip reorientation occurred only in cells where forward growth was countered by hyphal friction sufficient to generate a tip force of ∼ 8.7 μN (1.2 MPa), more than that required to penetrate host cell membranes. These findings suggest mechanisms through which the organization of hyphal tip growth in C. albicans facilitates the probing, penetration and invasion of host tissue.

Commercially available Cu foils are leading candidates as substrates employed for the generation of large-area graphene using chemical vapour deposition (CVD) techniques. However, the growth of high-quality graphene on Cu foils is often hindered by contamination particles, which will also be detrimental for many potential applications of graphene. Here we investigate the influence of typical substrate impurities on the formation of CVD graphene using as-received Cu foils of various purities from different suppliers and the same cleaned by popular methods. Analytical characterisation of the Cu foils revealed that contamination particles consist of calcium, aluminium, and silicon oxides. We show that contamination particles are present on foils with purities ranging between 99.8% and 99.9999% and that these particles influence the nucleation density, growth rate, and growth features of graphene domains. Based on our findings we propose new industrially applicable targeted cleaning procedures of immersion in purposely-selected HCl and KOH solutions to chemically dissolve the aforementioned impurities, bringing about improved growth of graphene.

To progress from the laboratory to commercial applications, it will be necessary to develop industrially scalable methods to produce large quantities of defect-free graphene. Here we show that high-shear mixing of graphite in suitable stabilizing liquids results in large-scale exfoliation to give dispersions of graphene nanosheets. X-ray photoelectron spectroscopy and Raman spectroscopy show the exfoliated flakes to be unoxidized and free of basal-plane defects. We have developed a simple model that shows exfoliation to occur once the local shear rate exceeds 10(4) s(-1). By fully characterizing the scaling behaviour of the graphene production rate, we show that exfoliation can be achieved in liquid volumes from hundreds of millilitres up to hundreds of litres and beyond. The graphene produced by this method performs well in applications from composites to conductive coatings. This method can be applied to exfoliate BN, MoS2 and a range of other layered crystals.

article i nfo Silver nanoparticles (AgNP) have gained attention over the years due to the antimicrobial function of silver, which has been exploited industrially to produce consumer goods that vary in type and application. Undoubtedly the in- crease of production and consumption of these silver-containing products will lead to the entry of silver com- pounds into the environment. In this study we have used Pseudokirchneriella subcapitata, Daphnia magna and Daniorerioas model organisms to investigate the toxicity of AgNP and AgNO3by assessing different biological end- points and exposure periods. Organisms were exposed following specific and standardized protocols for each spe- cies/endpoints, with modifications when necessary. AgNP were characterized in each test-media by Transmission Electron Microscopy (TEM) and experiments were performed by Dynamic Light Scattering (DLS)to investigate the aggregation and agglomeration behavior of AgNP under different media chemical composition and test-period. TEM images of AgNP in the different test-media showed dissimilar patterns of agglomeration, with some agglom- erates inside an organic layer, some loosely associated particles and also the presence of some individual particles. The toxicity of both AgNO3 and AgNP differ significantly based on the test species: we found no differences in toxicity for algae, a small difference for zebrafish and a major difference in toxicity for Daphnia magna.

Adipic acid was used in this work as a carbon-containing precursor for the HPHT synthesis of a carbon sample containing nano-diamond. The carbon sample consists of lamellar diamond nano-grains of about 30–50 nm embedded in an amorphous or poorly crystallized carbon matrix. The carbon sample comprises mainly sp 2 -hybrydized carbon in form of graphite or amorphous carbon.

Calcium phosphate (CaP) materials such as synthetic hydroxyapatite (HA, Ca 10 (PO 4 ) 6 (OH) 2 ) andβ-tricalcium phosphate ( -TCP, Ca 3 (PO 4 ) 2 ) are well-known for their potential in bone tissue engineeringand drug delivery applications. Processing such materials into submicrofibres might contribute toimprove their biocompatibility. This paper presents a new method for creating CaP submicrofibresthrough the electrospinning route. A thermal treatment at sintering temperature (1100 1C) was appliedto electrospun polymer fibres filled with hydroxyapatite nanoparticles to cause aggregation of thenanoparticles and vaporise the polymer matrix. The images taken by electron microscopy revealed thatthe treated samples maintained their submicrofibrous morphology. Moreover, Fourier transform infraredspectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy analysis confirmed that theresulting fibres are made of hydroxypatite and tricalcium phosphates.& 2013 The Authors. Published by Elsevier B.V. All rights reserved.

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

We investigated the effect of the reaction parameters on the structure of multi-walled carbon nanotubes containing different concentrations of nitrogen and boron. The nanotubes were produced using a 'standard' aerosol chemical vapour deposition technique in conjunction with benzylamine, triethylborane, hexane and toluene mixtures. These precursors were thermally decomposed between 800 and 1100 °C under argon at atmospheric pressure. By varying the precursor concentrations, the nitrogen and boron content of the nanotubes could be altered between 0-2.2 and 0-0.5 at.% respectively. Using a typical laboratory-sized 50 cm long tube furnace, yields between 0.3 and 1.5 g of nanotubes/10 min were relatively easily achieved. Moreover, we show that doping carbon nanotubes with heteroatoms, such as B and N, can be used to control nanotube diameters, change their defect density, and manipulate their oxidation resistance within a range of ca. 170 °C. Hence, we show that it is possible to tune nanotube properties within a certain interval and to produce nanotubes with relatively well defined properties in quantities usable for further characterisation and for studying their viability in applications such as composite materials, gas sensors, capacitors, and electronic components. © 2010 Elsevier Ltd. All rights reserved.

The effects from multigenerational exposures to engineered nanoparticles (ENPs) in their pristine and transformed states are currently unknown despite such exposures being an increasingly common scenario in natural environments. Here, we examine how exposure over 10 generations affects the sensitivity of the nematode Caenorhabditis elegans to pristine and sulfidized Ag ENPs and AgNO 3 . We also include populations that were initially exposed over six generations but kept unexposed for subsequent four generations to allow recovery from exposure. Toxicity of the different silver forms decreased in the order AgNO 3 , Ag ENPs and Ag 2 S ENPs. Continuous exposure to Ag ENPs and AgNO 3 caused pronounced sensitization (approx. 10-fold) in the F2 generation, which was sustained until F10. This sensitization was less pronounced for Ag 2 S ENP exposures, indicating different toxicity mechanisms. Subtle changes in size and lifespan were also measured. In the recovery populations, the sensitivity to Ag ENPs and AgNO 3 resulting from the initial multigenerational exposure persisted. Their response sensitivity for all endpoints was most closely related to the last ancestral exposed generation (F5), rather than unexposed controls. The mechanisms of transgenerational transfer of sensitivity are probably organized through the epigenome, and we encourage others to investigate such effects as a priority for mechanistic toxicology.

Monodisperse, size-controlled Ni-P nanoparticles were synthesised in a single step process using triphenyl-phosphane (TPP), oleylamine (OA), and Ni(ii)acetyl-acetonate. The nanoparticles were amorphous, contained ∼30 at% P and their size was controlled between 7-21 nm simply by varying the amount of TPP. They are catalytically active for tailored carbon nanotube growth. © 2011 The Royal Society of Chemistry.

Carbon powder modified with lead(IV) oxide was synthesised by a wet impregnation procedure from concentrated lead(II) nitrate solution. The impregnated powder was subsequently thermally treated at 823 K. Electrochemical and spectroscopic characterisation of the modified powder showed that lead(IV) oxide has been formed during the procedure. A novel composite lead(IV) oxide modified carbon powder epoxy electrode was developed for electrocatalytic sensing of gaseous, inorganic and organic analytes. The behaviour and analytical advantages of the composite electrode are evaluated with respect to determination of ammonia, nitrite ions and several different phenols. It has been demonstrated that the composite electrode can be used to analyze these analytes in standard aqueous solutions with competitively low limits of detection.

The electrochemical opening of closed-ended, pristine single-walled carbon nanotubes (SWCNTs) upon the application of either a sufficiently oxidizing or reducing electrode potential is reported. Hitherto, it has been unclear whether the side walls of SWCNTs are electrochemically active, or whether, like their multiwalled counterparts (MWCNTs), the electroactive sites on SWCNTs also reside at the edge-plane-like defects at the open ends of the tubes. Evidence is presented herein that suggests the latter case is true, i.e., that SWCNTs require edge-plane sites to be electroactive. Comparisons of the voltammetric response of end-closed SWCNTs (EC-SWCNTs), end-open (EO-SWCNTs), and SWCNTs encapsulating a metal halide filling (MX@SWCNTs, where MX represents either NaI or CuI) in aqueous electrolytes indicate that SWCNTs undergo electrochemical opening if the applied electrode potential is greater than +1.2 V vs SCE or less than -1.5 V vs SCE. This was further confirmed using ex situ X-ray photoelectron spectroscopy. The nonaqueous voltammetry of NaCl@SWCNTs, NaI@SWCNTs, CuI@SWCNTs, and ZnCl2@SWCNTs in dimethyl formamide (DMF) containing 0.1 M tetrabutyl ammonium perchlorate (TBAP) all exhibited voltammetric responses identical to that of EC-SWCNTs unless the potential was cycled beyond ca. +1.6 V vs Ag (+2.129 V vs the cobaltocene/ cobaltocenium redox couple) whereupon voltammetry corresponding to the filling material was observed, again indicating that the SWCNTs had become open-ended. Evidence for quantized charging of the EC-SWCNTs is presented in terms of the unusual "bow-tie" shape of the background charging current in DMF is also presented. © 2008 American Chemical Society.

We demonstrate with transmission electron microscopy and X-ray photoelectron spectroscopy that single-walled carbon nanotubes contain significant amounts of iron in the form of Fe(3)O(4), which even after acid washing, is not removed.

We describe the systematic study of multi-walled carbon nanotubes with different nitrogen doping produced by aerosol chemical vapor deposition. Benzylamine:toluene mixtures of 0:100, 5:95, 10:90, 25:75, 50:50, 75:25 and 100:0 were thermally decomposed at 800-900 °C under argon at atmospheric pressure, whereby the nitrogen content of the bulk material was varied between 0 and 2.2 at%. We also show how the presence of nitrogen in the precursor changed the nanotube morphology, i.e. nitrogen decreased the number of kinks incorporated into the carbon nanotubes, decreased their length and diameter and increased the proportion of 'bamboo' shaped nanotubes. Furthermore, due to the nitrogen doping, the oxidation resistance of the nanotube material was decreased. With concentrations above 10% benzylamine the increase of the reaction temperature had no significant effect on the quality of the nanotubes, however, at higher temperatures the nitrogen content was decreased. We demonstrate the control over the nanotube geometry, the nitrogen content and oxidation resistance of the nanotubes, and show that these properties are interlinked. © 2008 Elsevier Ltd. All rights reserved.

Effective preparation of clean GaN surfaces is vital for surface studies, and also has a key role to play in the development of nitride-based electronic devices, due to the importance of forming good metal-semiconductor contacts. We identify the effect of two common surface cleaning treatments (annealing in ammonia, and sputtering in nitrogen followed by in vacuo annealing) on surface reconstruction, morphology and stoichiometry, by employing a combination of in situ RHEED and scanning tunnelling microscopy (STM), and ex situ X-ray photoelectron spectroscopy (XPS). We show how the defect densities in as-treated GaN surfaces may be reduced by growing thin layers of GaN by low-pressure MBE, a technique compatible with most experimental surface science systems. By using a combination of in situ etching and low-pressure growth, we show that it is possible to obtain very similar surface structures to those obtained by full-scale MBE. © 2003 Elsevier Science B.V. All rights reserved.

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

The CO oxidation reaction has been studied on Au/TiO2 catalysts prepared by incipient wetness (IW) and deposition-precipitation (DP) methods, with a range of metal loadings from 0.1 to 5 wt% for the former. We have found that there are three types of CO2 production from fresh catalysts which have been calcined to only 120°C, namely noncatalytic (types I and II) and catalytic (type III). The DP catalysts are far more active for type III reaction, showing activity at room temperature, whereas the IW catalysts generally do not show steady-state conversion until > 120°C. However, IW catalysts with low loadings produce type I CO2 (that formed at room temperature), whereas higher loadings produce only type II (that formed when heating), with intermediate loadings showing both. We associate type I CO 2 production with monolayer Au catalysts, which have intimate contact with the TiO2, and are probably already in some oxidic form. Type II behavior we associate with three-dimensional oxidic Au, the surface of which is no longer in direct contact with the support. The poor performance of IW catalysts compared with DP catalysts is ascribed to the presence of chloride in the former, which induces a larger average particle size, and vulnerability to extensive sintering. © 2003 Elsevier Inc. All rights reserved.

L-Cysteine methyl ester modified glassy carbon powder (CysOMe-GC) has been shown to have potential for the removal of toxic heavy metal ions, such as copper(II), cadmium(II) and arsenic(III), from “real” water samples. To develop this material for environmental applications we must develop an understanding of the thermodynamic parameters controlling the uptake of metal ions by the modified carbon powder. Here we characterise the material using X-ray photoelectron spectroscopy (XPS), before investigating the effect of varying the solution pH, the concentration of copper(II) ions and the mass of CysOMe-GC powder added to the solution using square wave voltammetry (SWV). This data allows us to understand the thermodynamics controlling the copper(II) ion uptake and elucidate that the adsorption of copper(II) onto the CysOMe modified surface is controlled by a Freundlich isotherm.

Electrochemical processes, which underlie the use of conductive diamond electrodes for the simultaneous detection of two or more metal ions in solution by anodic stripping voltammetry (ASV), have been investigated. The model analyte system studied contains the two metal species, Ag+(aq) and Pb 2+(aq), and the experimental techniques employed include cyclic and square wave voltammetries, along with X-ray photoelectron spectroscopy and secondary electron microscopy. Although the bulk metallic forms of Ag and Pb are immiscible, several interactions in the system between the two metal species present are observed, which significantly influence the electrodeposition and electrodissolution processes which underlie ASV. The subsequent nucleation and growth of a given metal on the electrode surface is enhanced by the presence of the second metal on the surface. The encapsulation of one metal by the other, within the metal particulates that form on the electrode surface, significantly reduces the stripping yield at the potentials characteristic of the individual metals. The stripping potentials are also influenced by bonding interactions between deposited Ag and Pb, which broaden the characteristic stripping peaks in cyclic voltammetry, as well as producing underpotential deposition and stripping. Given these interactions, the extent to which ASV at diamond electrodes can be used to determine the solution concentrations of Ag +(aq) and Pb2+(aq) is considered. © The Owner Societies 2005.

The electron transfer kinetics of ferrocyanide, potassium hexachloroiridate(III), hexaammineruthenium(III) chloride, and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) have been examined at basal plane and edge plane pyrolytic graphite electrodes which have been allowed to oxidise in air for various periods of time. It is demonstrated via voltammetric and X-ray photoelectron spectroscopy (XPS) analysis that oxygenated species formed at edge plane sites/defects decrease the electron transfer kinetics of ferrocyanide but that the rates for potassium hexachloroiridate(III), hexaammineruthenium(III) chloride and TMPD are insensitive to the oxygenated species. The behaviour of the ferro-/ferricyanide couple contrasts with that seen on single-walled carbon nanotubes where oxygenation of the tube ends is known to speed up the electron transfer kinetics (A. Chou, T. Bocking, N. K. Singh, J. J. Gooding, Chem. Commun. 2005, 842); the possible reasons for this contrasting behaviour are discussed.

The electrochemical oxidation of 1-butyl-3-methylimidazolium nitrate [C4mim][NO3] was studied by cyclic voltammetry in the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C2mim][NTf2]. A sharp peak was observed on a Pt microelectrode (d = 10 μm), and a diffusion coefficient at infinite dilution of ca. 2.0 × 10-11 m 2 s-1 was obtained. Next, the cyclic voltammetry of sodium nitrate (NaNO3) and potassium nitrate (KNO3) was studied, by dissolving small amounts of solid into the RTIL [C2mim][NTf 2]. Similar oxidation peaks were observed, revealing diffusion coefficients of ca. 8.8 and 9.0 × 10-12 m2 s -1 and solubilities of 11.9 and 10.8 mM for NaNO3 and KNO3, respectively. The smaller diffusion coefficients for NaNO 3 and KNO3 (compared to [C4mim][NO 3]) may indicate that NO3- is ion-paired with Na+ or K+. This work may have applications in the electroanalytical determination of nitrate in RTIL solutions. Furthermore, a reduction feature was observed for both NaNO3 and KNO3, with additional anodic peaks indicating the formation of oxides, peroxides, superoxides and nitrites. This behaviour is surprisingly similar to that obtained from melts of NaNO3 and KNO3 at high temperatures (ca. 350-500°C), and this observation could significantly simplify experimental conditions required to investigate these compounds. We then used X-ray photoelectron spectroscopy (XPS) to suggest that disodium(i) oxide (Na2O), which has found use as a storage compound for hydrogen, was deposited on a Pt electrode surface following the reduction of NaNO3. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

International audience; The response of pristine, nitrogen and boron doped carbon nanotube (CNT) sensors to NO2, CO, C2H4 and H2O at ppm concentrations was investigated at both room temperature and 150 degrees C. N-doped CNTs show the best sensitivity to nitrogen dioxide and carbon monoxide, while B-doped CNTs show the best sensitivity to ethylene. All tubes (including undoped) show strong humidity response. Sensing mechanisms are determined via comparison with density functional calculations of gas molecule absorption onto representative defect structures in N and B-doped graphene. N-CNTs show decreased sensitivity with temperature, and detection appears to occur via gas physisorption. B-CNTs appear to react chemically with many of the absorbed species as shown by their poor baseline recovery and increasing sensitivity with temperature. This limits their cyclability. Overall gas sensitivity is as good or better than post-growth functionalised nanotubes, and used in combination, CNTs, N-CNTs and B-CNTs appear highly promising candidates for cheap, low power, room temperature gas sensing applications. (C) 2013 Elsevier Ltd. All rights reserved.

"Bamboo-like" multiwalled (b-MWCNT), "hollow-tube" multiwalled (h-MWCNT) and single-walled carbon nanotubes (SWCNT), chemically modified with 1-anthraquinonyl (AQ) or 4-nitrophenyl (NP) groups, are characterized using voltammetric, electron microscopic and Raman spectroscopic techniques. The pKa values of the AQ-modified CNTs are found to be shifted by greater than three units when compared to the pKa values of anthrahydroquinone (AHQ, the reduced form of AQ) in aqueous solution to beyond pH 14. These large changes in the surface pKa values of the modified CNTs are explored further by comparing the pKa values of CNTs modified with an anthraquinonyl-2-carboxylic acid group. These groups are attached to the CNT surface via the formation of an amide bond with an aminophenyl "spacer" unit derived from the chemical reduction of NP modified CNTs. The location of reactive sites on the CNT surface is investigated and their influence on the pKa of the modified materials is discussed. Comparison with modified pyrolytic graphite electrodes exposing pure edge-plane or pure basal-plane crystal faces indicates that the modifying aryl groups are predominantly located on edge-plane like defects at the tube ends of MWCNTs. The effect of polymer formation on electron transfer kinetics of b-MWCNTs and h-MWCNTs is also discussed. In contrast SWCNTs show both significant side-wall functionalisation and fast electron transfer kinetics which is attributed to their different electronic structure. This journal is © The Royal Society of Chemistry.

Graphite powder derivatised with 4-nitrophenyl moieties (NPcarbon) can be used to successively attach other chemical species to the graphite surface in a controlled and selective manner. Characterisation of these novel materials was undertaken using electrochemical and X-ray photoelectron spectroscopic (XPS) techniques. We demonstrate the proof of concept of this "building-block" chemistry by first reducing the nitro groups on the NPcarbon using a Sn-HCl reduction to the corresponding aniline-like moieties, and then coupling p-nitrobenzoic acid to these via an amide-linkage. Next we demonstrate the utility of this novel derivatisation method by coupling poly-S-benzyl-L-cysteine to the reduced NPcarbon in an analogous manner. After deprotection of the thiol groups using Na in liquid ammonia, the poly-L-cysteine derivatised carbon (PCcarbon) was found to complex cadmium(II) ions. Quantitative analysis of the uptake of Cd2+ from aqueous solutions at pH 5.0 by PCcarbon was carried out using stripping-voltammetry at a boron doped diamond (BDD) electrode and revealed that PCcarbon complexed 137 ± 20 mg of Cd2+ per gram of modified PCcarbon. © The Royal Society of Chemistry 2005.

All rights reserved.Metal-free growth of carbon nanotubes/fibers (CNT/Fs) using chemical vapor deposition (CVD) on semiconducting and insulating substrates is of interest in the context of the construction of nanoscale electronic devices. However, controllable synthesis of CNT/Fs without the aid of metal catalysts is an ongoing challenge. Here we report the direct CVD synthesis of CNT/Fs on the perovskite oxides SrTiO3 (STO) and Ba0.6Sr0.4TiO3 (BST). A variety of processing steps were used on STO (001) substrates to create a set of six patterns with varying atomic-scale surface roughnesses. These substrates were all subjected to the same CVD growth conditions, and a correlation was found between the surface roughness of the substrates and the density of CNT/Fs. This indicates that nanometer-scale asperities on the substrates act as the catalytically active sites for CNT/F growth. In a separate set of experiments the surfaces of polished polycrystalline BST samples were investigated. The random orientation of the exposed etched facets of the individual grains revealed significantly different catalytic activity for CNT/F growth. Our study demonstrates the great influence of the nature of the crystal surface condition on the catalytic activity of the substrates and is a critical first step towards perovskite oxide catalyst design.

Carbon black nanoparticles modified with palladium nanoparticles (Pd/CB) were prepared using a facile methodology. Stirring CB in an aqueous solution of palladium chloride was found to result in the spontaneous formation of Pd nanoparticles on the CB surface. The Pd/CB composite demonstrated high electrocatalytic activity towards hydrazine oxidation, with good stability and reproducibility. Three linear dynamic ranges of hydrazine determination were found between 5μM and 50mM. The limit of detection (LOD) for hydrazine was found to be 8.8μM (based on 3σ). The sensitivity of unmodified CB to trace metal impurities present in certain common electrolytes is also noted. © 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.

X-Ray Photoelectron Spectroscopy (XPS) was used to quantify the amount of bromide ions present in two samples of [C(4)mpyrr]Br dissolved in the room temperature ionic liquid (RTIL) [C(4)mpyrr][N(Tf)2]. One sample was of a known concentration (0.436 Br atom%); the other was a saturated solution. The results obtained from quantitative XPS analysis indicated that the saturated sample had a concentration, or solubility, of 0.90 Br atom% (746 mM) at 298 K, which was then independently confirmed by potential-step chronoamperometry of the same solution.

Negatively charged poly(lactic-co-glycolic acid) (PLGA) microspheres encapsulated with hydrophilic drugs have been successfully prepared by a solidin-oil-in-water (s/o/w) solvent evaporation method in the presence of anionic surfactants, sodium dodecyl sulfate (SDS), and dioctyl sodium sulfosuccinate (DSS), and nonionic surfactant polyvinyl alcohol (PVA). The effects of microencapsulation methods, surfactants types, and surfactant concentrations on the properties of microspheres were studied. Amoxicillin (AMX) was chosen as a hydrophilic model drug, and its encapsulation efficiency (EE) and in vitro release profiles were measured. The s/o/w method achieved higher EE of 40% in PLGA microspheres using surfactant SDS compared with the conventional water-in-oil-in-water (w/o/w) method (about 2%). Triphasic release profiles were observed for all PLGA microspheres (s/o/w) with slight drug burst, a slow diffusion-controlled release within the period of about 7 days and followed by the degradation-controlled sustained release for further 30 days. Smaller particle size and surface charge were achieved for s/o/w method than w/o/w method using the same anionic surfactants, and smooth surface and less porous interior matrix. The s/o/w method effectively encapsulated AMX into anionic PLGA microspheres using anionic surfactants, and these negatively charged PLGA microspheres represented an attractive approach for the controlled release of hydrophilic drugs. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association.

The fate of Ti was examined in an activated sludge plant serving over 200,000 people. These studies revealed a decrease of 30 to 3.2 μg/L of Ti

A method of constructing a "designer interface" consisting of either monolayers or multilayers of chemically modified microbeads is reported, whereby the shape of the interface as well as the interfacial chemistry imparts "diffusional protection" to the underlying surface material. © The Royal Society of Chemistry 2006.

Analytical expressions for the anodic stripping voltammetry of metallic nanoparticles from an electrode are provided. First, for reversible electron transfer, two limits are studied: that of diffusionally independent nanoparticles and the regime where the diffusion layers originating from each particle overlap strongly. Second, an analytical expression for the voltammetric response under conditions of irreversible electron transfer kinetics is also derived. These equations demonstrate how the peak potential for the stripping process is expected to occur at values negative of the formal potential for the redox process in which the surface immobilised nanoparticles are oxidised to the corresponding metal cation in the solution phase. This work is further developed by considering the surface energies of the nanoparticles and its effect on the formal potential for the oxidation. The change in the formal potential is modelled in accordance with the equations provided by Plieth [J. Phys. Chem., 1982, 86, 3166-3170]. The new analytical expressions are used to investigate the stripping of silver nanoparticles from a glassy carbon electrode. The relative invariance of the stripping peak potential at low surface coverages of silver is shown to be directly related to the surface agglomeration of the nanoparticles.

Herein, we report the synthesis of three covalently linked superparamagnetic nanocrystal-multi-walled carbon nanotube (MWCNT) composites. A generic strategy for amphiphilic polymer coating of nanocrystals and further functionalization for amide bond formation with the MWCNTs is discussed. This approach can in principle allow attachment of any colloidal nanocrystal to the MWCNTs. The materials were characterized at each stage of the syntheses using DLS, zeta-potential measurements, FT-IR, TEM, and XPS techniques. The practicality of this linkage is demonstrated by the reversible magnetic immobilization of these materials on an electrode during non-aqueous electrochemistry. © 2012 Elsevier Inc.

We herein report the synthesis of novel "Janus" calix[4]arenes bearing four "molecular tethering" functional groups on either the upper or lower rims of the calixarene. These enable facile multipoint covalent attachment to electrode surfaces with monolayer coverage. The other rim of the calixarenes bear either four azide or four ethynyl functional groups, which are easily modified by the copper(I)-catalyzed azide-alkyne cycloaddition reaction (CuAAC), either pre- or postsurface modification, enabling these conical, nanocavity reactor sites to be decorated with a wide range of substrates to impart desired chemical properties. Redox active species decorating the peripheral rim are shown to be electrically connected by the calixarene to the electrode surface in either "up" or "down" orientations of the calixarene.

A simple method for the synthesis of multi-walled carbon nanotubes (MWCNTs) containing Si, P-N and N is reported, and their gas sensing properties were investigated. The MWCNTs were synthesised by the thermal decomposition of aerosols containing mixtures of ferrocene/triphenylsilane, ferrocene/ triphenylphosphine/benzylamine, and ferrocene/benzylamine/toluene. Electron microscopy studies revealed that the addition of Si, P, and N alters the structure of CNTs dramatically. Gas sensing experiments were carried out using Si, P-N, N-containing MWCNTs, and were compared with pure MWCNTs synthesised at similar experimental conditions. These experiments showed that the gas sensitivity and selectivity of CNT-based sensors can be indeed tailored without any post-processing of the raw nanotubes. The efficient in situ tailoring of nanotube properties and functionality are important for nanotubes to become viable materials at the industrial scale where low cost processes are required. © 2012 Elsevier Ltd. All rights reserved.

In this letter, we present experimental data which challenges the model proposed since the mid-1990s that the reduction of C60 films in aqueous electrolytes involves the formation of [M+nC60n-] where M+ represents a metal cation or proton. Instead we provide voltammetric, XPS and UV-vis evidence that the reduction of "C60" films in aqueous media is instead the reduction of adventitious poly-epoxidated C60On with subsequent chemically irreversible loss of "O2-" as water, and that C60 is not reduced within the potential windows of aqueous electrolytes. © 2009 Elsevier B.V. All rights reserved.

ortho-Quinones can be differentiated from other oxygen-containing surface functional groups on the surfaces of graphite, glassy carbon, "bamboo-like", and "hollow-tube" multiwalled carbon nanotubes and single-walled carbon nanotubes by chemically labeling them with either an inorganic hexamminechromium(III) complex or organic 1,2-phenylenediamine derivatives. Both types of labels can be observed using cyclic voltammetry or by X-ray photoelectron spectroscopy and used to quantify the numbers and relative distribution of orifto-quinones from other oxygen-containing species on the surface including electroactive para-quinones which are not labeled. Labeling of ortho-quinones with 1,2-phenylenediamine derivatives results in the formation of phenazine-like adducts on the graphitic surface which have a distinct voltammetry particularly from that of the underivatized para-quinones. © 2007 American Chemical Society.

The combinatorial screening of different metallic nanoparticles as electrocatalysts was investigated and efficiently applied for the detection of hydrazine. In a first step, glassy carbon microspheres decorated with metallic nanoparticles (Au, Pd, and Ag) were abrasively attached on the surface of a basal plane pyrolytic electrode giving a 'multi-metal' nanoarray. In a second step, electrodes modified with only one type of metallic nanoparticles allowed the identification of Pd as the unique catalytic material. In addition, a carbon-epoxy composite electrode loaded with the Pd nanoparticles was then constructed for a practical use. The carbon-epoxy composite nanoarray electrode was found to have excellent characteristics as for the sensing of hydrazine with a limit of detection of 2 μM. © 2007 Wiley-VCH Verlag GmbH and Co. KGaA.

Principles and practical application of combinatorial electrochemistry in search for new electroactive materials in electroanalysis have been explored. Nanoparticles of three different metals: silver, gold and palladium have been independently synthesized on the glassy carbon spherical powder surface by electroless deposition process and characterized using both spectroscopic and electrochemical techniques. These three materials were then combined together onto basal plane pyrolytic graphite electrode surface and the application of the combinatorial approach to find the electrode material for bromide detection as model target analyte was demonstrated. The component electroactive for bromide detection was next identified and it was found that silver nanoparticles were the active ones. A composite electrode based on silver nanoparticle modified glassy carbon powder and epoxy resin was then fabricated and it was found to allow accurate determination of bromide. The electroactivity for the bromide determination of the composite electrode was compared with that of a bulk silver electrode and it was shown that the composite electrode is very efficient with a comparable electroactivity with only a portion of precious metals being used for its construction.

The result of acid washing multiwalled carbon bamboo nanotubes is explored with voltammetry and X-ray Photoelectron Spectroscopy; it is found that the presence of oxygenated species formed as a result at the ends of the nanotubes does not measurably change the heterogeneous charge transfer kinetics. © 2006 Wiley-VCH Verlag GmbH and Co. KGaA.

We report electrochemical composites of multi-walled carbon nanotubes (MWCNTs) with poly(vinylferrocene) (PVF). The polymeric architecture is prepared by first immobilising the MWCNTs onto a glassy carbon substrate, which acts to introduce electrical current into the composite, with the MWCNTs acting as 'molecular wires'. PVF films of varying surface coverages can be obtained by simply controlling the time a constant potential of +0.7 V (vs. Ag) wire is applied; with the characteristics of the derivatised MWCNTs examined by cyclic voltammetry and scanning electron microscopy. The application of the composite for glucose determination in aqueous solutions was investigated using linear sweep voltammetry, where it was found that the composites supported on glassy carbon substrates are superior to bare glassy carbon electrodes polymerised with PVF, likely due to the comparatively higher number of electrocatalytic centres in the former. This protocol was successfully transferred to prepare a PVF-MWCNT-paste electrode which was applied to glucose detection in diluted laked horse blood. The obtained results show potential and promising practical application for the polymer-derivatised MWCNT-modified electrodes in amperometric sensors for glucose determination.

Large-area synthesis of high-quality graphene by chemical vapour deposition on metallic substrates requires polishing or substrate grain enlargement followed by a lengthy growth period. Here we demonstrate a novel substrate processing method for facile synthesis of mm-sized, single-crystal graphene by coating polycrystalline platinum foils with a silicon-containing film. The film reacts with platinum on heating, resulting in the formation of a liquid platinum silicide layer that screens the platinum lattice and fills topographic defects. This reduces the dependence on the surface properties of the catalytic substrate, improving the crystallinity, uniformity and size of graphene domains. At elevated temperatures growth rates of more than an order of magnitude higher (120 μm min−1) than typically reported are achieved, allowing savings in costs for consumable materials, energy and time. This generic technique paves the way for using a whole new range of eutectic substrates for the large-area synthesis of 2D materials., Innovative substrate engineering is necessary to improve the quality of CVD-synthesized graphene. Here the authors demonstrate in situ fabrication of an eutectic Pt-Si alloy that forms a wetting liquid surface on polycrystalline Pt foils, allowing millimetre-sized graphene crystals to grow in minutes.

Filamentous hyphae of the human pathogen, Candida albicans, invade mucosal layers and medical silicones. In vitro, hyphal tips reorient thigmotropically on contact with small obstacles. It is not known how surface topography is sensed but hyphae lacking the cortical marker, Rsr1/Bud1, are unresponsive. We show that, on surfaces, the morphology of hyphal tips and the position of internal polarity protein complexes are asymmetrically skewed towards the substratum and biased towards the softer of two surfaces. In nano-fabricated chambers, the Spitzenkörper (Spk) responded to touch by translocating across the apex towards the point of contact, where its stable maintenance correlated with contour-following growth. In the rsr1Δ mutant, the position of the Spk meandered and these responses were attenuated. Perpendicular collision caused lateral Spk oscillation within the tip until after establishment of a new growth axis, suggesting Spk position does not predict the direction of growth in C. albicans. Acute tip reorientation occurred only in cells where forward growth was countered by hyphal friction sufficient to generate a tip force of ∼ 8.7 μN (1.2 MPa), more than that required to penetrate host cell membranes. These findings suggest mechanisms through which the organization of hyphal tip growth in C. albicans facilitates the probing, penetration and invasion of host tissue.

The importance of nanoparticle characterization for nanotoxicology has been extensively emphasized and it has been universally agreed that the most important parameters for characterizing nanomaterials are specific surface area and surface properties (chemistry, hydro-philicity/phobicity, charge etc.). This study is proposing the use of enthalpy of wetting which depends on both specific surface area and surface properties, is easily measurable and proves to be highly relevant for predicting nanoparticles' dispersion state and their interaction with the lungs. It also shows the conditioning effect of the lung surfactant main component, DPPC on the surface of particles when used in concentrations which mimic pulmonary exposure more closely. This journal is © the Partner Organisations 2014. ispartof: RSC ADVANCES vol:4 issue:39 pages:20573-20581 status: published

Electrodeposition methods are used to generate a sparse array of platinum nanoparticles on a glassy carbon electrode. Specifically electrodeposition from a 1 mM solution of H2PtCl6 in 0.5 M H2SO4 leads to surface coverages of 0.46% to 1.96% and nanoparticles of size 29 nm to 136 nm in diameter, using deposition times of 30 and 15 seconds. The reduction of oxygen at an array of 29 nm nanoparticles with a surface coverage of 0.46% showed voltammetric signals with a scan rate dependence consistent with a two electron reduction of O2 to H2O2 with the rate proportional to K0 exp(-α(E-Ef(0))/RT) and formal potential (Ef(0)) of -0.058 V vs. SHE, a standard electrochemical rate constant (k0) of ~10 cm s(-1) and a transfer coefficient (α) of 0.23. At higher Pt nanoparticle coverages, a scan rate dependence consistent with the partial further reduction of H2O2 to water becomes evident.

Transmission electron microscopy (TEM) is the only technique which can give accurate information on the individual size, shape and composition of NPs. However, in dilute forms it is difficult to collect a sufficient number of NPs on an electron microscope grid for TEM analysis without some means of concentrating the dispersion of NPs. This study introduces a novel TEM sampling technique which overcomes this shortcoming and allows for both the natural and engineered NPs in dilute dispersions as found in waste and contaminated waters to be selectively sampled, based on their electrical charge. The technique is based on the use of carefully functionalized collector surfaces built by using the layer-by-layer assembly of polyelectrolytes on TEM grids. The layers are electrically charged and the top layer will attract and retain oppositely charged sampled NPs from aqueous solutions. The ability of the collector to attract both single particles and particle aggregates on the top polyelectrolyte layer collected from dilute aqueous dispersions after a short sampling time is demonstrated from the TEM images. The nature of the particles attracted to the collector can be identified from the TEM images, their diffraction pattern and the EDX spectrum. Graphical Abstract: A large variety of equipment is nowadays being used worldwide for the detection and characterization of nanoparticles (NPs) dispersed in aqueous environmental liquids. To take advantage of these advanced analytical tools there is an increased need for the development of sampling technologies capable of collecting nanoparticle samples directly on suitable substrates (TEM grids or filters).[Figure not available: see fulltext.] © 2013 Springer Science+Business Media Dordrecht.

Consecutive electro-oxidation and reduction cycling of gold macroelectrodes in sulphuric acid medium is a widely-used cleaning and calibration procedure. In this paper this method is applied to electrodeposited nanoparticles revealing significant differences in the electro-oxidation process and the cleaning effectiveness. This suggests a higher density of surface defects on the nanoparticles.

The investigation of electrocatalytic nanoeffects is tackled via joint electrochemical measurements and computational simulations. The cyclic voltammetry of electrodes modified with metal nanoparticles is modeled considering the kinetics of the electrochemical process on the bulk materials of the different regions of the electrode, that is, the substrate (glassy carbon) and the nanoparticles (gold). Comparison of experimental and theoretical results enables the detection of changes in the electrode kinetics at the nanoscale due to structural and/or electronic effects. This approach is applied to the experimental assessment of electrocatalytic effects by gold nanoparticles (Au NPs) in the electrooxidation of nitrite and L-ascorbate. Glassy carbon electrode is modified with Au NPs via seed-mediated growth method. Divergence between the kinetics of these processes on gold macroelectrodes and gold nanoparticles is examined. Whereas claimed catalytic effects are not observed in the electrooxidation of nitrite, electrocatalytic nanoeffects are verified in the case of L-ascorbate. This is probably due to that the electron transfer process follows an adsorptive mechanism. The combination of simulation with experiments is commended as a general strategy of authentification, or not, of nanoelectrocatalytic effects.