Positive graphene by chemical design: Tuning supramolecular strategies for functional surfaces

Article abstract of DOI:10.1039/c3cc47056c

A diazonium based-arylation reaction was efficiently used for the covalent addition of 4-amino-N,N,N-trimethylbenzene ammonium to stable dispersions of few layer graphene (FLG) yielding an innovative FLG platform with positive charges to immobilize inorganic polyanions. The Royal Society of Chemistry.

Full text of DOI:10.1039/c3cc47056c

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Positive graphene by chemical design: tuning
supramolecular strategies for functional surfaces†
Cite this: Chem. Commun., 2014,
0, 885
5
a
b
c
c
Caroline Hadad, Xiaoxing Ke, Mauro Carraro, Andrea Sartorel,
d
b
c
e
Received 15th September 2013,
Accepted 6th November 2013
Carla Bittencourt, Gustaaf Van Tendeloo, Marcella Bonchio,* Mildred Quintana
and Maurizio Prato*
a
DOI: 10.1039/c3cc47056c
www.rsc.org/chemcomm
A diazonium based-arylation reaction was efficiently used for the Unfortunately, oxidation disrupts the electronic structure of
covalent addition of 4-amino-N,N,N-trimethylbenzene ammonium to the carbon lattice making GO an insulator rather than a semi-
stable dispersions of few layer graphene (FLG) yielding an innovative metal. Alternatively, ultrasonication-based procedures can be
FLG platform with positive charges to immobilize inorganic polyanions. used to prepare stable dispersions of few layer graphene (FLG)
9
on a preparative scale, and to enable an efficient chemical
1
The outstanding physical and chemical properties of graphene
modification by covalent organic reactions yielding functionalized
10
hold great potential in the preparation of emerging materials FLG (f-FLG). f-FLG has the advantage of being easily tuned for
2
with advanced functions. Graphene provides a 2D confined integration into new composite materials since tailored graphene
space to anchor active sub-units and trigger enhanced optical, architectures can be specifically designed to host other functional
mechanical, catalytic, and/or magnetic properties of the composites. molecules or nanostructures avoiding major structural damage to
3
11
Some examples are found in the preparation of energy materials,
the p-surface compared to GO. Herein, we report a successful
4
5
6
sensors, reinforced polymer matrices, drug delivery systems, and synthetic protocol to introduce a vast coverage of permanent
cleaning materials for the removal of metal particles and organic positive charges that disrupt the hydrophobic surface of pristine
pollutants from water. Graphene-integrated functional effectors graphene. The aim is twofold: (i) to increase solubility and disper-
7
include inorganic compounds, organic molecules, polymers, metals, sion by inter-layer electrostatic repulsion and (ii) to intercalate
1
2,13
metal oxides, and magnetic nanoparticles. A widely used procedure functional anions by complementary charge interaction.
for the synthesis of graphene composites exploits graphene oxide For this purpose, we have expressly synthesized the positively
8
(
GO). This material consists of graphene-like sheets, chemically charged 4-amino-N,N,N-trimethylbenzene ammonium (3), see ESI.†
functionalized with moieties such as carboxyl, hydroxyl and Then, FLG was covalently functionalized with 3 (see ESI†) by a
14
epoxides, which stabilize the graphene layers in polar solvents diazonium-based arylation reaction expected to have an impact
2
like water and allow its interaction with other materials.
on the electronic structure of FLG by doping and opening a band
15
gap. As the final step, the positively charged f-FLG has been
exposed to a totally inorganic polyanionic cluster, in order to probe
its surface anchoring properties. In particular we have investigated
the electrostatic immobilization of the ruthenium polyoxometalate
a
Center of Excellence for Nanostructured Materials (CENMAT) and INSTM, Unit of
Trieste, Dipartimento di Scienze Chimiche e Farmaceutiche, University of Trieste,
Piazzale Europa 1, I-34127 Trieste, Italy. E-mail: prato@units.it;
Fax: +39 040 52572; Tel: +39 040 558 7883
10À
12
{
Ru (m-O) (m-OH) (H O) [g-SiW O ] }
(Ru POM), Scheme 1.
4
4
4
2
2
4
10 36 2
b
The resulting material, Ru POM@f-FLG, is relevant for the mole-
Electron Microscopy for Materials Research (EMAT), University of Antwerp,
4
Groenenborgerlaan 171, B-2020 Antwerp, Belgium
cular design of nanostructured multi-electron catalysts enabling
c
ITM-CNR and Dipartimento di Scienze Chimiche, University of Padova,
oxygen evolution from aqueous solutions by direct water oxidation
via F. Marzolo 1, 35131 Padova, Italy. E-mail: marcella.bonchio@unipd.it;
13
2 2
or H O dismutation. The in situ production of nascent gas can
Fax: +39 049 8275239; Tel: +39 049 8275670
d
be conveniently exploited with surface anti-fouling/self-cleaning
activity, and avoiding the graphene-flake aggregation/clustering.
FLG was produced by the ultrasonication of graphite in DMF
Chemistry of Interaction Plasma Surface (ChiPS), University of Mons,
Rue du Parc 20, B-7000 Mons, Belgium
e
Instituto de F ´ı sica, Universidad Autonoma de San Luis Potos ´ı , Manuel Nava 6,
Zona Universitaria, 78290 San Luis Potosi, SLP, Mexico. Fax: +52 444 8133874;
Tel: +52 444 8262362 ext. 130
(
1 g in 200 mL) at room temperature (see ESI† for the detailed
protocol). The concentration of FLG in the dispersion was
†
Electronic supplementary information (ESI) available: Complete experimental
1
6
À1
determined by UV-vis spectroscopy to be 0.3 mg mL . This
dispersion was stable for several weeks. The covalent reaction
with 3 (2.5 equiv. per FLG carbon) was performed in aqueous
details of the synthesis of 4-amino-N,N,N-trimethylbenzene ammonium iodide (3),
NMR and ESI-MS spectra, TGA, Raman, TEM images and X-ray photoelectron
spectroscopy analysis of graphene compounds. See DOI: 10.1039/c3cc47056c
This journal is ©The Royal Society of Chemistry 2014
Chem. Commun., 2014, 50, 885--887 | 885

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Scheme 1 Synthesis of Ru
4
POM@f-FLG. Reagents and conditions: (a)
Fig. 1 Raman spectra of FLG (black curve), Ru
4
POM@f-FLG (red curve),
4
-amino-N,N,N-trimethylbenzene ammonium, 3-methylbutyl nitrite, DMF/
and Ru
of Ru
4
POM (blue curve). In the inset, the superimposed spectral features
À1
H
2
O at 80 1C; (b) Ru POM, H O (pH 4) at r.t.
4
2
4
POM@f-FLG and Ru
4
POM up to 1000 cm are shown.
DMF (DMF/H
2
O, 5 : 1) in the presence of 3-methylbutyl nitrite
D G
The ratio of the intensities of the D and G bands (I /I ) is
(
5 equiv. per FLG carbon) at 80 1C overnight. After cooling down often used as an indication of the chemical modification
1
1
to room temperature, the suspension was diluted with DMF extent. The ID/IG ratios in FLG, f-FLG, and Ru POM@f-FLG
4
(
100 mL), filtered (PTFE membrane, 0.45 mm) and washed turn out to be 0.29, 0.46 and 0.43, respectively. The increase in
several times with DMF and MeOH. the D band signal observed for the modified graphene surface
The successful covalent functionalization of f-FLG was verified by compared to that of pristine FLG is consistent with the covalent
7
2
different characterization techniques, such as thermogravimetric functionalization of the carbon lattice (Fig. S12, ESI†). The Ru-(H O)
À1
analysis (TGA), transmission electron microscopy (TEM), and stretching modes are clearly recognized at 250–400 cm
,
17
À1
Raman spectroscopy. The temperature modulated curves for together with the tetraruthenate core vibrations at 450–500 cm
12
FLG and f-FLG (see ESI,† Fig. S10 and S11) indicate that FLGs have (Fig. 1, inset).
not been damaged by the ultrasonication treatments, whereas f-FLG Finally, the morphology of the Ru POM@f-FLG nanohybrid
4
presents a weight loss of 6.7% at 450 1C. This weight loss is was investigated by TEM and HRTEM showing the inorganic
attributed to the functional groups attached to the FLG surface. cluster domains well-distributed all over the graphene surface
TEM analysis shows no significant differences in the morphology of (Fig. 2a and b). High resolution images acquired with a dose of
À
À2 À1
f-FLG compared to FLG (ESI,† Fig. S13–S15).
The self-assembly of the Ru POM@f-FLG nanohybrid was inorganic domains anchored on the positive graphene nano-
induced by the straightforward metathesis in water. f-FLG flakes with atomic resolution (Fig. 2c). Aberration-corrected
approximately 1000 e
Å
s
allow the inspection of the
4
(
(
2
1 mg) was added to an aqueous solution of Ru
4
POM TEM is able to image the Ru
10 mol L , 2 mL) at pH 4. The mixture was sonicated for accelerating voltage of 80 kV reduces the beam damage to the
min and let under stirring overnight. Ru POM@f-FLG was graphene-based nanohybrids. Simulation of the Ru POM molecular
4
POM at the atomic scale whereas an
À4
À1
4
4
washed several times yielding a stable suspension in water structure addresses its conformational mobility upon 2D confine-
À1
(
0.1 mg mL , pH 4). X-Ray photoelectron spectroscopy (XPS), ment on f-FLG, as a function of time (Fig. 2d). Interestingly, during
Raman spectroscopy, TEM, and HRTEM techniques were the acquisition time of 37 s, only 5 different projections are
instrumental for the material characterization. identified from the image series, which indicate a strong electro-
The non-covalent binding of the Ru POM@f-FLG nanohybrid static adhesion to the nano-carbon surface, and a limited mobility.
4
was detected by XPS (see ESI,† Fig. S16–S19). The W 4f peak The latter depends on the nature of the graphene-linker. Indeed,
characteristic of the Ru POM confirms its attachment on f-FLG. a spatially protruding dendrimer, with multiple ammonium
4
The N 1s peak shifted about 0.4 eV towards lower binding terminals, displaying a long-range, flexible grip on the molecular
energies after the grafting of the Ru
reproduced using 5 components indicating the presence of carbon during 70 s, under the same experimental conditions.
atoms at 5 different chemical environments: component 1 centered The benzene ammonium linker 3 is likely to act with a
at 283.4 eV was associated with carbon atoms in the hexagonal shorter-radius, and combined surface-assisted confinement of
4
POM. The C 1s peak can be anion, allowed the registration of over 25 different orientations
2
1
1
8
units near defect-like vacancies. Component 2 at 284.6 eV is the Ru
4
POM is likely to take place, limiting the conformational
generated by photoelectrons emitted from carbon atoms in the freedom. Polyoxometalate ions have been shown to interact
1
9
CQC bonding. Components 3, 4 and 5 at 285.1 eV, 286.0 eV with the electronic density of the GO platform in response to
2
0
22
and 287.8 eV are due to carbon atoms in 3.
As expected, Raman spectra in Fig. 1 show the specific the interplay of electrostatic forces and p-electron clouds on
features of Ru POM in the Ru POM@f-FLG nanohybrid and graphene results in the tight immobilization of the inorganic
H-bonding type interactions.
Our study confirms that
4
4
the signal peaks corresponding to D, G and 2D peaks of f-FLG at polyanion, displaying a lower motion frequency and remaining
À1
11,17
1
350, 1586 and 2715 cm , respectively.
statics for a longer time.
8
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Financial support of Trieste University, the EU-FP7 ERC-
008-AdG-227135, MIUR (Cofin prot. 2010N3T9M4 and FIRB
prot. RBAP11ETKA) and Fondazione CARIPARO (NanoMode,
010) is acknowledged. MQ thanks CONACYT project 166914.
MQ and CB acknowledge the project 193257 Bilateral Coopera-
tion Mexico (CONACYT) – Belgium (F.R.S.– FNRS). XK and GVT
acknowledge funding from the EU-FP7-ERC Grant (No 246791).
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This journal is ©The Royal Society of Chemistry 2014
Chem. Commun., 2014, 50, 885--887 | 887