20 research outputs found
Structure and stability of charged clusters
When a cluster or nanodroplet bears charge, its structure and thermodynamics
are altered and, if the charge exceeds a certain limit, the system becomes
unstable with respect to fragmentation. Some of the key results in this area
were derived by Rayleigh in the nineteenth century using a continuum model of
liquid droplets. Here we revisit the topic using a simple particle-based
description, presenting a systematic case study of how charge affects the
physical properties of a Lennard-Jones cluster composed of 309 particles. We
find that the ability of the cluster to sustain charge depends on the number of
particles over which the charge is distributed---a parameter not included in
Rayleigh's analysis. Furthermore, the cluster may fragment before the charge is
strong enough to drive all charged particles to the surface. The charged
particles in stable clusters are therefore likely to reside in the cluster's
interior even without considering solvation effects.Comment: 15 pages, 6 figure
Palladium catalysed C-H arylation of pyrenes: access to a new class of exfoliating agents for water-based graphene dispersions.
From Europe PMC via Jisc Publications RouterHistory: ppub 2020-01-01, epub 2020-01-28Publication status: PublishedFunder: Engineering and Physical Sciences Research Council; Grant(s): 1781838, EP/P00119X/1A new and diverse family of pyrene derivatives was synthesised via palladium-catalysed C-H ortho-arylation of pyrene-1-carboxylic acid. The strategy affords easy access to a broad scope of 2-substituted and 1,2-disubstituted pyrenes. The C1-substituent can be easily transformed into carboxylic acid, iodide, alkynyl, aryl or alkyl functionalities. This approach gives access to arylated pyrene ammonium salts, which outperformed their non-arylated parent compound during aqueous Liquid Phase Exfoliation (LPE) of graphite and compare favourably to state-of-the-art sodium pyrene-1-sulfonate PS1. This allowed the production of concentrated and stable suspensions of graphene flakes in water
Raman Fingerprints of Graphene Produced by Anodic Electrochemical Exfoliation
Electrochemical exfoliation is one of the most promising methods for scalable
production of graphene. However, limited understanding of its Raman spectrum as
well as lack of measurement standards for graphene strongly limit its
industrial applications. In this work we show a systematic study of the Raman
spectrum of electrochemically exfoliated graphene, produced using different
electrolytes and different types of solvents in varying amounts. We demonstrate
that no information on the thickness can be extracted from the shape of the 2D
peak as this type of graphene is defective. Furthermore, the number of defects
and the uniformity of the samples strongly depend on the experimental
conditions, including post-processing. Under specific conditions, formation of
short conductive trans-polyacetylene chains has been observed. Our Raman
analysis provides guidance for the community on how to get information on
defects coming from electrolyte, temperature and other experimental conditions,
by making Raman spectroscopy a powerful metrology tool.Comment: This document is the unedited Author's version of a Submitted Work
that was subsequently accepted for publication in Nano Letters, American
Chemical Society after peer review. To access the final edited and published
work, included the SI, see DOI: 10.1021/acs.nanolett.0c0033
Self-Catalytic Membrane Photo-Reactor made of Carbon Nitride Nanosheets
In this study we use a membrane photo-reactor (MPR) made of nanosheets of graphitic carbon nitride (g-C3N4), assembled by vacuum filtration, to make low-cost, efficient, easy-to-produce self-catalytic photo-reactors for water treatment under visible light.</p
Palladium Catalysed C–H Arylation of Pyrenes: Access to a New Class of Exfoliating Agents for Water-Based Graphene Dispersions
A new and diverse family of pyrene derivatives was synthesised via palladium-catalysed C–H ortho-arylation of pyrene-1-carboxylic acid. The strategy affords easy access to a broad scope of 2-substituted and 1,2-disubstituted pyrenes. The C1-substituent can be easily transformed into carboxylic acid, iodide, alkynyl, aryl or alkyl functionalities. This approach gives access to arylated pyrene ammonium salts, which outperformed their non-arylated parent compound during aqueous Liquid Phase Exfoliation (LPE) of graphite and compare favourably to state-of-the-art sodium pyrene-1-sulfonate PS1. This allowed the production of concentrated and stable suspensions of graphene flakes in water
Enhancing the Liquid-Phase Exfoliation of Graphene in Organic Solvents upon Addition of n-Octylbenzene
Due to a unique combination of electrical and thermal conductivity, mechanical stiffness, strength and elasticity, graphene became a rising star on the horizon of materials science. This two-dimensional material has found applications in many areas of science ranging from electronics to composites. Making use of different approaches, unfunctionalized and non-oxidized graphene sheets can be produced; among them an inexpensive and scalable method based on liquid-phase exfoliation of graphite (LPE) holds potential for applications in opto-electronics and nanocomposites. Here we have used n-octylbenzene molecules as graphene dispersion-stabilizing agents during the graphite LPE process. We have demonstrated that by tuning the ratio between organic solvents such as N-methyl-2-pyrrolidinone or ortho-dichlorobenzene, and n-octylbenzene molecules, the concentration of exfoliated graphene can be enhanced by 230% as a result of the high affinity of the latter molecules for the basal plane of graphene. The LPE processed graphene dispersions were further deposited onto solid substrates by exploiting a new deposition technique called spincontrolled drop casting, which was shown to produce uniform highly conductive and transparent graphene films