Synthesis of stable aqueous dispersion of graphene/polyaniline composite mediated by polystyrene sulfonic acid

A facile method of producing stable aqueous dispersion of graphene/polyaniline (PANI) composite is described, which involves the in situ polymerization of aniline on the surface of graphene with the aid of polystyrene sulfonic acid (PSS). The prepared aqueous graphene/PANI composite dispersion was very stable and no aggregation or precipitation was observed for several weeks. The excellent aqueous dispersibility and stability of the graphene/PANI composite is attributed to the cooperative interactions of π stacking interaction between PSS, PANI, and the graphene basal planes, and the electrostatic repulsions between negatively charged PSS bound on graphene/PANI composite. Fourier transform‐infrared spectrometry (FTIR), ultraviolet‐visible spectra (UV–vis), and Raman spectra confirmed the interaction of PANI and graphene in the composite, which effectively delocalize the electrons. In addition, the composite showed three orders of magnitude of conductivity increase compared with pure PANI. This new approach is simple, fast, and straightforward, representing a significant improvement in the processing of graphene/PANI composites. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Assessing the Calibration of High-Dimensional Ensemble Forecasts Using Rank Histograms

Any decision-making process that relies on a probabilistic forecast of future events necessarily requires a calibrated forecast. This article proposes new methods for empirically assessing forecast calibration in a multivariate setting where the probabilistic forecast is given by an ensemble of equally probable forecast scenarios. Multivariate properties are mapped to a single dimension through a prerank function and the calibration is subsequently assessed visually through a histogram of the ranks of the observation’s preranks. Average ranking assigns a prerank based on the average univariate rank while band depth ranking employs the concept of functional band depth where the centrality of the observation within the forecast ensemble is assessed. Several simulation examples and a case study of temperature forecast trajectories at Berlin Tegel Airport in Germany demonstrate that both multivariate ranking methods can successfully detect various sources of miscalibration and scale efficiently to high-dimensional settings. Supplemental material in form of computer code is available online.     

A Novel Non-enzymatic Selective and Sensitive Glucose Sensor Based on Nickel-Copper Oxide@3D-rGO/MWCNTs

In this work, a modified 3D-rGO/MWCNT with nickel and copper oxide nanoparticles were synthesized. The structural properties of this nanocomposite were investigated by several techniques. The fabricated sensor at optimum condition potential of +0.60 V (vs. Ag/AgCl) and a rotational rate of 1800 rpm gave a detection limit of 0.04 μmol L⁻¹ with two dynamic ranges of 0.10–300 and 300–900 μmol L⁻¹ glucose with high stability. The good accuracy of the fabricated sensor was proved in the determination of glucose in a blood sample (with recoveries between 95 % to 105 % and RSDs of 1.2 to 2.5 %).     

Preparation,characterization and heterogeneous catalytic applications of GO/Fe3O4/HPW nanocomposite in chemoselective and green oxidation of alcohols with aqueous H2O2

Graphene oxide ‐ Fe₃O₄ ‐ NH₃⁺H₂PW₁₂O₄₀ ^‐ magnetic nanocomposite (GO/Fe₃O₄/HPW) was prepared by linking amino ‐ functionalized Fe₃O₄ nanoparticles (Fe₃O₄ ‐ NH₂) on the graphene oxide (GO), and then grafting 12 ‐ tungstophosphoric acid (H₃PW₁₂O₄₀) on the graphene oxide ‐ magnetite hybrid (GO ‐ Fe₃O₄ ‐ NH₂). The obtained GO/Fe₃O₄/HPW nanocomposite was well characterized with different techniques such as FT ‐ IR, TEM, SEM, XRD, EDX, TGA ‐ DTA, AGFM, ICP and BET measurements. The used techniques showed that the graphene oxide layers were well prepared and the various stages of preparation of the GO/Fe₃O₄/HPW nanocomposites successfully completed. This new nanocomposite displayed excellent performance as a heterogeneous catalyst in the oxidation of alcohols with H₂O₂. The as ‐ prepared GO/Fe₃O₄/HPW catalyst was more stable and recyclable at least five times without significantly reducing its catalytic activity.     

Distributing points uniformly on the unit sphere under a mirror reflection symmetry constraint

Uniformly distributed point sets on the unit sphere with and without symmetry constraints have been found useful in many scientific and engineering applications. Here, a novel variant of the Thomson problem is proposed and formulated as an unconstrained optimization problem. While the goal of the Thomson problem is to find the minimum energy configuration of N electrons constrained on the surface of the unit sphere, this novel variant imposes a new symmetry constraint – mirror reflection symmetry with the x–y plane as the plane of symmetry. Qualitative features of the two-dimensional projection of the optimal configurations are briefly mentioned and compared to the ground-state configurations of the two dimensional system of charged particles laterally confined by a parabolic potential well.     

Construction of a Graphene/Au‐Nanoparticles/Cucurbit[7]uril‐Based Sensor for Pb2+ Sensing

The development of highly sensitive and selective methods for the detection of lead ion (Pb²⁺) is of great scientific importance. In this work, we develop a new surface‐enhanced Raman scattering (SERS)‐based sensor for the selective trace measurement of Pb²⁺. The SERS‐based sensor is assembled from gold nanoparticles (AuNPs) and graphene using cucurbit[7]uril (CB[7]) as a precise molecular glue and a local SERS reporter. Upon the addition of Pb²⁺, CB[7] forms stronger complexes with Pb²⁺ and desorbs from AuNPs, resulting in a sensitive “turn‐off” of SERS signals. This SERS‐based assay shows a limit of detection (LOD) of 0.3 nm and a linear detection range from 1 nm to 0.3 μm for Pb²⁺. The feasibility of the assay is further demonstrated by probing Pb²⁺ in real water samples. This SERS‐based analytical method is highly sensitive and selective, and therefore holds promising applications in environmental analysis.