48 research outputs found
Observation of different charge transport regimes and large magnetoresistance in graphene oxide layers
We report a systematic study on charge transport properties of thermally reduced graphene
oxide (rGO) layers, from room temperature to 2 K and in presence of magnetic fields up to
7 T. The most conductive rGO sheets follow different transport regimes: at room temperature
they show an Arrhenius-like behavior. At lower temperature they exhibits a thermally
activated behavior with resistance R following a R = R0exp(T0/T)p law with p = 1/3, consistently
with 2D Mott Variable Range Hopping (VRH) transport mechanism. Below a given
temperature Tc, we observe a crossover from VHR to another regime, probably due to a
shortening of the characteristic lengths of the disordered 2D system. The temperature Tc
depends on the reduction grade of the rGO. Magnetoresistance DR/R of our rGO films shows
as well a crossover between positive and negative and below liquid He temperature DR/R
reaches values larger than 60%, surprisingly high for a \u2013 nominally \u2013 non magnetic
material
Improved Biocompatibility of Amino‐Functionalized Graphene Oxide in Caenorhabditis elegans
International audienc
Interaction of graphene-related materials with human intestinal cells: an in vitro approach
Graphene-related materials (GRM) inherit unique combinations of physicochemical properties which offer a high potential for technological as well as biomedical applications. It is not clear which physicochemical properties are the most relevant factors influencing the behavior of GRM in complex biological environments. In this study we have focused on the interaction of GRM, especially graphene oxide (GO),and Caco-2 cells in vitro. We mimiked stomach transition by acid-treatment of two representative GRM followed by analysis of their physicochemical properties. No significant changes in the material properties or cell viability of exposed Caco-2 cells in respect to untreated GRM could be detected. Furthermore, we explored the interaction of four different GO and Caco-2 cells to identify relevant physicochemical properties for the establishment of a material property–biological response relationship. Despite close interaction with the cell surface and the formation of reactive oxygen species (ROS), no acute toxicity was found for any of the applied GO (concentration range 0–80 μg ml−1) after 24 h and 48 h exposure. Graphene nanoplatelet aggregates led to low acute toxicity at high concentrations, indicating that aggregation, the number of layers or the C/O ratio have a more pronounced effect on the cell viability than the lateral size alone
effect of charge, dipole and molecular structure
We study the mechanism of surface adsorption of organic dyes on graphene, and
successive exfoliation in water of these dye-functionalized graphene sheets. A
systematic, comparative study is performed on pyrenes functionalized with an
increasing number of sulfonic groups. By combining experimental and modeling
investigations, we find an unambiguous correlation between the graphene–dye
interaction energy, the molecular structure and the amount of graphene flakes
solubilized. The results obtained indicate that the molecular dipole is not
important per se, but because it facilitates adsorption on graphene by a
“sliding” mechanism of the molecule into the solvent layer, facilitating the
lateral displacement of the water molecules collocated between the aromatic
cores of the dye and graphene. While a large dipole and molecular asymmetry
promote the adsorption of the molecule on graphene, the stability and pH
response of the suspensions obtained depend on colloidal stabilization, with
no significant influence of molecular charging and dipole
Graphene oxide doped polysulfone membrane adsorbers for the removal of organic contaminants from water
This work explored polysulfone (PS) – graphene oxide (GO) based porous membranes (PS-GO) as adsorber of seven selected organic contaminants of emerging concern (EOCs) including pharmaceuticals, personal care products, a dye and a surfactant from water. PS-GO was prepared by phase inversion method starting from a PS and GO mixture (5% w/w of GO). The porous PS-GO membranes showed asymmetric and highly porous micrometer sized pores on membrane top (diameter ≈20 μm) and bottom (diameter ≈2–5 μm) surfaces and tens of microns length finger like pores in the section. Nanomechanical mapping reveals patches of a stiffer material with Young modules comprised in the range 15–25 GPa, not present in PS pure membranes that are compatible with the presence of GO flakes on the membrane surfaces. PS-GO was immersed in EOCs spiked tap water and the adsorbance efficiency at different contact times and pH evaluated by HPLC analysis. Ofloxacin (OFLOX), benzophenone-3 (BP-3), rhodamine b (Rh), diclofenac (DCF) and triton X-100 (TRX) were removed with efficiency higher than 90% after 4 h treatments. Regeneration of PS-GO and reuse possibilities were demonstrated by washing with ethanol. The adsorption efficiencies toward OFLOX, Rh, DCF and carbamazepine (CBZ) were significantly higher than those of pure PS membrane. Moreover, PS-GO outperformed a commercial granular activated carbon (GAC) at low contact times and compared well at longer contact time for OFLOX, Rh, BP-3 and TRX suggesting the suitability of the newly introduced material for drinking water treatment
Benchmarking of graphene-based materials: real commercial products versus ideal graphene
There are tens of industrial producers claiming to sell graphene and related materials (GRM), mostly as solid powders. Recently the quality of commercial GRM has been questioned, and procedures for GRM quality control were suggested using Raman Spectroscopy or Atomic Force Microscopy. Such techniques require dissolving the sample in solvents, possibly introducing artefacts.A more pragmatic approach is needed, based on fast measurements and not requiring any assumption on GRM solubility. To this aim, we report here an overview of the properties of commercial GRM produced by selected companies in Europe, USA and Asia. We benchmark: (A) size, (B) exfoliation grade and (C) oxidation grade of each GRM versus the ones of ‘ideal’ graphene and, most importantly, versus what reported by the producer. In contrast to previous works, we report explicitly the names of the GRM producers and we do not re-dissolve the GRM in solvents, but only use techniques compatible with industrial powder metrology.A general common trend is observed: products having low defectivity (%sp2 bonds >95%) feature low surface area (<200 m2 g−1), while highly exfoliated GRM show a lower sp2 content, demonstrating that it is still challenging to exfoliate GRM at industrial level without adding defects
Biomimetic graphene for enhanced interaction with the external membrane of astrocytes
Graphene and graphene substrates display huge potential as material interfaces for devices and
biomedical tools targeting the modulation or recovery of brain functionality. However, to be considered
reliable neural interfaces, graphene-derived substrates should properly interact with astrocytes, favoring
their growth and avoiding adverse gliotic reactions. Indeed, astrocytes are the most abundant cells in
the human brain and they have a crucial physiological role to maintain its homeostasis and modulate
synaptic transmission. In this work, we describe a new strategy based on the chemical modification of
graphene oxide (GO) with a synthetic phospholipid (PL) to improve interaction of GO with brain
astroglial cells. The PL moieties were grafted on GO sheets through polymeric brushes obtained by
atom-transfer radical-polymerization (ATRP) between acryloyl-modified PL and GO nanosheets modified
with a bromide initiator. The adhesion of primary rat cortical astrocytes on GO–PL substrates increased
by about three times with respect to that on glass substrates coated with standard adhesion agents
(i.e. poly-D-lysine, PDL) as well as with respect to that on non-functionalized GO. Moreover, we show
that astrocytes seeded on GO–PL did not display significant gliotic reactivity, indicating that the material
interface did not cause a detrimental inflammatory reaction when interacting with astroglial cells. Our
results indicate that the reported biomimetic approach could be applied to neural prosthesis to improve
cell colonization and avoid glial scar formation in brain implants. Additionally, improved adhesion could
be extremely relevant in devices targeting neural cell sensing/modulation of physiological activity