Highly concentrated and stable few-layers graphene suspensions in pure and volatile organic solvents

Highly stable graphene suspensions in pure organic solvents, including volatile solvents such as ethanol, tetrahydrofurane, chloroform, acetone or toluene have been prepared by re-dispersion of a graphene-powder. Such re-dispersable solid is produced by precipitation or solvent elimination from graphene suspensions obtained by sonication of graphite in several organic solvent-water mixtures. Re-dispersion is feasible in a wide range of pure organic solvents, obtaining high quality few-layers graphene flakes stable in suspension for months. As a proof-of-concept, on-glass spray deposition of some of these suspensions, e.g. ethanol or tetrahydrofuran, results on electrically conductive transparent coatings. These results suggest industrial potential use of the scalable technology here developed to fabricate low-cost devices with many different potential applicationsThis research was financially supported by Abengoa Co., the Spanish Ministry of Economy and Competitiveness (MAT2013-46753-C2-1-P and RYC2012-09864) and Comunidad de Madrid (CAM 09-S2009_MAT-1467

Towards robust alkane oxidation catalysts: electronic variations in non-heme iron(II) complexes and their effect in catalytic alkane oxidation

A series of non-heme iron(II) bis(triflate) complexes containing linear and tripodal tetradentate ligands has been prepared. Electron withdrawing and electron donating substituents in the para position of the pyridine ligands as well as the effect of pyrazine versus pyridine and sulfur or oxygen donors instead of nitrogen donors have been investigated. The electronic effects induced by these substituents influence the strength of the ligand field. UV-vis spectroscopy and magnetic susceptibility studies have been used to quantify these effects and VT 1H and 19F NMR spectroscopy as well as X-ray diffraction have been used to elucidate structural and geometrical aspects of these complexes. The catalytic properties of the iron(II) complexes as catalysts for the oxidation of cyclohexane with hydrogen peroxide have been evaluated. In the strongly oxidising environment required to oxidise alkanes, catalyst stability determines the overall catalytic efficiency of a given catalyst, which can be related to the ligand field strength and the basicity of the ligand and its propensity to undergo oxidation

Hydrodynamic slip can align thin nanoplatelets in shear flow

The large-scale processing of nanomaterials such as graphene and MoS2 relies on understanding the flow behaviour of nanometrically-thin platelets suspended in liquids. Here we show, by combining non-equilibrium molecular dynamics and continuum simulations, that rigid nanoplatelets can attain a stable orientation for sufficiently strong flows. Such a stable orientation is in contradiction with the rotational motion predicted by classical colloidal hydrodynamics. This surprising effect is due to hydrodynamic slip at the liquid-solid interface and occurs when the slip length is larger than the platelet thickness; a slip length of a few nanometers may be sufficient to observe alignment. The predictions we developed by examining pure and surface-modified graphene is applicable to different solvent/2D material combinations. The emergence of a fixed orientation in a direction nearly parallel to the flow implies a slip-dependent change in several macroscopic transport properties, with potential impact on applications ranging from functional inks to nanocomposites.Energy Technolog

Van der Waals heterostructures

Research on graphene and other two-dimensional atomic crystals is intense and likely to remain one of the hottest topics in condensed matter physics and materials science for many years. Looking beyond this field, isolated atomic planes can also be reassembled into designer heterostructures made layer by layer in a precisely chosen sequence. The first - already remarkably complex - such heterostructures (referred to as 'van der Waals') have recently been fabricated and investigated revealing unusual properties and new phenomena. Here we review this emerging research area and attempt to identify future directions. With steady improvement in fabrication techniques, van der Waals heterostructures promise a new gold rush, rather than a graphene aftershock

Supramolecular attachment of metalloporphyrins to graphene oxide and its pyridine-containing derivative

Functionalized with porphyrins: The interactions of metalloporphyrins with graphene oxide and pyridine‐substituted graphene oxide have been probed (see figure). The interactions elucidated offer unprecedented tools in the quest for functional nanostructured materials.Funding support from MICINN (MAT2010‐20843‐C02‐01 and CTQ2012‐37420‐C02‐02) and Comunidad de Madrid (CAM2009‐S2009‐MAT‐1467 and CC10‐UAM/MAT‐5881) is acknowledged. R.M.‐B. thanks M.E.C. for funding through the “Ramón y Cajal” program.Peer Reviewe