Flow-induced ordering of particles and flow velocity profile transition in a tube flow of graphene oxide dispersions

We measured the S- and P-order parameters of flow-induced ordered graphene oxide (GO) particles and the flow velocity profiles for a flowing aqueous GO dispersion in a tube, by using an optical method. The order parameters clearly exhibit increasing concentric biaxial ordering as the flow velocity increases, with the exception of a disordered centre. Newtonian to non-Newtonian transition in the flow velocity profile is found, changing from a parabolic shape to a fuller shape at very low Reynolds numbers less than 10. This is attributed to the shear thinning effect (i.e., an ordering-induced reduction in viscosity). In the Newtonian flow, a uniaxial ordering was dominant; whereas a biaxial ordering sharply increased in the non-Newtonian flow, indicating that both the ordering of GO particles and the interparticle interactions influence the flow profile transition.     

Selenides and diselenides containing oxadiazoles: a new class of functionalised materials

A simple and efficient procedure for the synthesis of a new class of organoselenium liquid crystal compounds was developed. The coupling of aryl bromides with elemental selenium was catalysed using copper oxide nanopowder in the presence of potassium hydroxide employing dimethyl sulfoxide as the solvent. This is the first report of the synthesis and characterisation of liquid crystal-based diselenides. Their mesophases were characterised by polarising optical microscopy and differential scanning calorimetry. Compounds 1, 2 and 4b exhibited the smectic A phase. In addition, these compounds showed weak blue fluorescence in solution (λ_{max. em.} 350–405 nm) and a Stokes shift of around 90 nm.     

Synthesis and characterisation of a silicon oxide film solid-phase extraction system for lead traces determination: an all the way green analytical method

In this work, an all the way green analytical procedure based on a silicon oxide film-solid phase extraction system is proposed for lead traces determination. From the synthesis of a solid phase extraction (SPE) system and throughout the metal preconcentration and determination only aqueous media were employed. Characterisation of the film was carried out by Scanning Electron Microscopy and Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy. Preconcentration conditions, prior to Pb(II) Electrothermal Atomic Absorption Spectrometry (ETAAS) determination, such as adsorption and desorption time, pH and temperature, were optimised. Langmuir, Freundlich and Dubinin-Radushkevich isotherm models were analysed along with the evaluation of adsorption energy and standard free energy (ΔG ⁰). The greatest adsorption was obtained with incubation at pH 7 and 37°C. By using a small volume of 0.5?mol?L^?1 HNO₃ (0.5?mL) lead was desorbed from the silicon oxide film after 2?h incubation, generating low amount of waste. The films showed better adjustment for the Langmuir model (R^{2 ?}=?0.989). The detection limit (3.29σ) for Pb(II) was 0.228?µg?L^?1. The developed procedure is 10-fold more sensitive in comparison to direct ETAAS determination. Recovery values from soft tap-water and soft well-water were above 95%. When hard water was analysed, Pb(II) adsorption was found to be interfered by Mg²⁺ and Ca²⁺. After five preconcentration cycles relative recovery was found not to decay below 90%, indicating that the silicon oxide film could be used for multiple lead determinations.     

Graphene oxide reinforced polyamide nanocomposite coated on paper as a novel layered sorbent for microextraction by packed sorbent

ABSTRACT

In this work, a novel layered sorbent for microextraction by packed sorbent (MEPS) was introduced, which has been prepared by coating graphene oxide/polyamide (GO/PA) nanocomposite (NC) onto cellulose paper through solvent exchange method. Scanning electron microscopy (SEM) was applied to investigate the surface characteristic and morphology of PA and GO/PA NC coated on cellulose paper. The prepared MEPS device was used for extraction of organophosphorous pesticides (OPPs) including chlorpyrifos, fenthion, fenithrothion, ethion, edifenphos and phosalone in environmental aqueous samples followed by detection using gas chromatography-flame ionisation detector (GC-FID). Important parameters affecting the MEPS method including pH of sample solution, extraction draw-discard cycles, sorbent layers, desorption solvent volume and desorption draw-eject number were studied and optimised using central composite design (CCD). Based on the method validation, limits of detection (LODs) were in the range of 0.2–1 µg L^?1. The calibration graphs for chlorpyrifos, fenthion and edifenphos are linear in the concentration range of 1 to 500 µg L^?1; for ethion and phosalone are linear in the range of 1–1000 µg L^?1 and for fenithrothion is linear in the range of 3–1000 µg L^?1. The method precision (RSD %) with six replicates determinations was in the range of 3 to 9.4 % and 3.9 to 11.9% for distilled water and spiked river water sample, respectively, at the concentration level of 300 µg L^?1 . The developed method was applied successfully to determine OPP compounds in river, dam and tap water samples; accordingly, the relative recoveries (RR%) were obtained in the range of 77.8 to 113.3%.     

Single‐electron transfer‐living radical polymerization of oligo(ethylene oxide) methyl ether methacrylate in the absence and presence of air

The efficient Cu(0) wire‐catalyzed single‐electron transfer‐living radical polymerization (SET‐LRP) of oligo(ethylene oxide) methyl ether methacrylate (OEOMA) in DMSO and binary mixtures of DMSO with H₂O is reported. Addition of 10–80% H₂O to DMSO resulted in an increase in the apparent rate constant of propagation ( ), corresponding to an increase in the polarity and extent of disproportionation. At higher H₂O content, decreases, and in H₂O is slightly lower than that in DMSO. This unexpected behavior was attributed to the physical inaccessibility of Cu(0) wire catalyst to the hydrophobic reactive centers of OEOMA and initiator which self‐assemble in H₂O into micellar aggregates and vesicles. This hypothesis was confirmed by the faster polymerization in H₂O than in DMSO during catalysis with Cu(0) nanoparticles generated by disproportionation of CuBr. SET‐LRP of OEOMA can be performed in protic and dipolar aprotic solvents in air by the addition of hydrazine hydrate. The polymerization exhibited no induction period and identical as in the degassed experiment, and led to polymers with narrow molecular weigh distribution. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3110–3122     

Graphene Oxide Protected Nucleic Acid Probes for Bioanalysis and Biomedicine

Recently, the binding ability of DNA on GO and resulting nuclease resistance have attracted increasing attention, leading to new applications both in vivo and in vitro. In vivo, nucleic acids absorbed on GO can be effectively protected from enzymatic degradation and biological interference in complicated samples, making it useful for targeted delivery, gene regulation, intracellular detection and imaging with high uptake efficiencies, high intracellular stability, and very low toxicity. In vitro, the adsorption of ssDNA on GO surface and desorption of dsDNA or well‐folded ssDNA from GO surface result in the protection and deprotection of DNA from nucleic digestion, respectively, which has led to target‐triggered cyclic enzymatic amplification methods (CEAM) for amplified detection of analytes with sensitivity 2–3 orders of magnitude higher than that of 1:1 binding strategies. This Concept article explores some of the latest developments in this field.     

Unusual Inherent Electrochemistry of Graphene Oxides Prepared Using Permanganate Oxidants

Graphene and graphene oxides are materials of significant interest in electrochemical devices such as supercapacitors, batteries, fuel cells, and sensors. Graphene oxides and reduced graphenes are typically prepared by oxidizing graphite in strong mineral acid mixtures with chlorate (Staudenmaier, Hofmann) or permanganate (Hummers, Tour) oxidants. Herein, we reveal that graphene oxides pose inherent electrochemistry, that is, they can be oxidized or reduced at relatively mild potentials (within the range ±1 V) that are lower than typical battery potentials. This inherent electrochemistry of graphene differs dramatically from that of the used oxidants. Graphene oxides prepared using chlorate exhibit chemically irreversible reductions, whereas graphene oxides prepared through permanganate‐based methods exhibit very unusual inherent chemically reversible electrochemistry of oxygen‐containing groups. Insight into the electrochemical behaviour was obtained through cyclic voltammetry, chronoamperometry, and X‐ray photoelectron spectroscopy experiments. Our findings are of extreme importance for the electrochemistry community as they reveal that electrode materials undergo cyclic changes in charge/discharge cycles, which has strong implications for energy‐storage and sensing devices.     

Electrochemical‐Reduction‐Assisted Assembly of a Polyoxometalate/Graphene Nanocomposite and Its Enhanced Lithium‐Storage Performance

Herein, we present an electrochemically assisted method for the reduction of graphene oxide (GO) and the assembly of polyoxometalate clusters on the reduced GO (rGO) nanosheets for the preparation of nanocomposites. In this method, the Keggin‐type H₄SiW₁₂O₄₀ (SiW₁₂) is used as an electrocatalyst. During the reduction process, SiW₁₂ transfers the electrons from the electrode to GO, leading to a deep reduction of GO in which the content of oxygen‐containing groups is decreased to around 5 %. Meanwhile, the strong adsorption effect between the SiW₁₂ clusters and rGO nanosheets induces the spontaneous assembly of SiW₁₂ on rGO in a uniformly dispersed state, forming a porous, powder‐type nanocomposite. More importantly, the nanocomposite shows an enhanced capacity of 275 mAh g^?1 as a cathode active material for lithium storage, which is 1.7 times that of the pure SiW₁₂. This enhancement is attributed to the synergistic effect of the conductive rGO support and the well‐dispersed state of the SiW₁₂ clusters, which facilitate the electron transfer and lithium‐ion diffusion, respectively. Considering the facile, mild, and environmentally benign features of this method, it is reasonable as a general route for the incorporation of more types of functional polyoxometalates onto graphene matrices; this may allow the creation of nanocomposites for versatile applications, for example, in the fields of catalysis, electronics, and energy storage.