2 research outputs found
Organic Radical-Assisted Electrochemical Exfoliation for the Scalable Production of High-Quality Graphene
Despite the intensive research efforts
devoted to graphene fabrication
over the past decade, the production of high-quality graphene on a
large scale, at an affordable cost, and in a reproducible manner still
represents a great challenge. Here, we report a novel method based
on the controlled electrochemical exfoliation of graphite in aqueous
ammonium sulfate electrolyte to produce graphene in large quantities
and with outstanding quality. Because the radicals (e.g., HO<sup>ā¢</sup>) generated from water electrolysis are responsible for defect formation
on graphene during electrochemical exfoliation, a series of reducing
agents as additives (e.g., (2,2,6,6-tetramethylpiperidin-1-yl)Āoxyl
(TEMPO), ascorbic acid, and sodium borohydride) have been investigated
to eliminate these radicals and thus control the exfoliation process.
Remarkably, TEMPO-assisted exfoliation results in large graphene sheets
(5ā10 Ī¼m on average), which exhibit outstanding hole
mobilities (ā¼405 cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup>), very low Raman <i>I</i><sub>D</sub>/<i>I</i><sub>G</sub> ratios (below 0.1), and extremely high carbon
to oxygen (C/O) ratios (ā¼25.3). Moreover, the graphene ink
prepared in dimethylformamide can exhibit concentrations as high as
6 mg mL<sup>ā1</sup>, thus qualifying this material for intriguing
applications such as transparent conductive films and flexible supercapacitors.
In general, this robust method for electrochemical exfoliation of
graphite offers great promise for the preparation of graphene that
can be utilized in industrial applications to create integrated nanocomposites,
conductive or mechanical additives, as well as energy storage and
conversion devices
Modifying the Size of Ultrasound-Induced Liquid-Phase Exfoliated Graphene: From Nanosheets to Nanodots
Ultrasound-induced
liquid-phase exfoliation (UILPE) is an established
method to produce single- (SLG) and few-layer (FLG) graphene nanosheets
starting from graphite as a precursor. In this paper we investigate
the effect of the ultrasonication power in the UILPE process carried
out in either <i>N</i>-methyl-2-pyrrolidone (NMP) or <i>ortho</i>-dichlorobenzene (<i>o</i>-DCB). Our experimental
results reveal that while the SLGs/FLGs concentration of the NMP dispersions
is independent of the power of the ultrasonic bath during the UILPE
process, in <i>o</i>-DCB it decreases as the ultrasonication
power increases. Moreover, the ultrasonication power has a strong
influence on the lateral size of the exfoliated SLGs/FLGs nanosheets
in <i>o</i>-DCB. In particular, when UILPE is carried out
at ā¼600 W, we obtain dispersions composed of graphene nanosheets
with a lateral size of 180 nm, whereas at higher power (ā¼1000
W) we produce graphene nanodots (GNDs) with an average diameter of
ā¼17 nm. The latter nanostructures exhibit a strong and almost
excitation-independent photoluminescence emission in the UV/deep-blue
region of the electromagnetic spectrum arising from the GNDsā
intrinsic states and a less intense (and strongly excitation wavelength
dependent) emission in the green/red region attributed to defect states.
Notably, we also observe visible emission with near-infrared excitation
at 850 and 900 nm, a fingerprint of the presence of up-conversion
processes. Overall, our results highlight the crucial importance of
the solvent choice for the UILPE process, which under controlled experimental
conditions allows the fine-tuning of the morphological properties,
such as lateral size and thickness, of the graphene nanosheets toward
the realization of luminescent GNDs