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10 Electrochemical Manufacturing Methods Based on Surface …
10.5.6 Exfoliation of Suspended Particles with Bipolar
Electrochemistry
Exfoliation methods included in the above chapters all referred to techniques in which
the material composed of covalently bonded atomic planes was used as an electrode
component. Hence, the electrode potential of the material to be exfoliated could
be known, just as the current passed through them. Unlike in the above discussed
methods, the bipolar electrochemical method applies a completely different electrochemical arrangement. As the first step of this method, a material composed of atomic
planes is used for microparticle synthesis, often applying a chemical intercalation
of lithium from t-butyllithium and then decomposition with water. The microparticles thus synthesized are suspended in an aqueous solution containing a supporting
electrolyte (which is most often Na 2 SO 4 in 0.1 M concentration). Two platinum electrodes are used for passing a current through the suspension. The cell voltage reported
is around 10 V with a 2-cm interelectrode separation. Although it can be inferred
from these experimental conditions that a vigorous hydrogen and oxygen evolution
takes place at the cathode and anode, respectively, the electrode reaction products are
neither of interest nor do they modify the chemical nature on the particles suspended.
Instead, the suspended particles are further fragmented, which is attributed to electrophoretic effect. Although it does not seem to be completely understood how a
relatively small voltage across the suspended micrometer-sized particles can lead to
intercalation and further exfoliation, the size reduction of the particles as a result of
the current passed through the solution is convincingly evidenced. The size reduction
of the suspended particles takes place as a result of the current over a period of less
than an hour. Therefore, an easy-to-implement, fast and scalable method is available
for even the mass production of nanoparticles.
The electrophoretic exfoliation was successfully applied to various semiconductor
particles such as black phosphorous [112], MoSe 2 [113], WS 2 [114] and MoS 2 [115].
In each case, the particle size could be reduced to below 100 nm, but the particles’
shape was not fully characterized in either of the above cited studies. Nothing is
known about the kinetics of the electrophoretic microparticle fragmentation since it
was not studied whether the reaction time selected resulted in a saturation particle
size. The particle size reduction was followed only with the absorption change of the
solution since the microparticle suspension was dark in each case, but the resulting
nanoparticle suspension was light or nearly transparent due to the reduction of the
absorption intensity with the particle size. The nanoparticles produced were tested
as components of various immunoassays.
Although the exfoliation mechanism was not completely understood for layered
semiconductor particles, it seemed to be reasonable that the current passing through
the solution can generate a potential difference across the particles, which induces a
redistribution of the charge carriers at their surface, hence leading to electrochemical
reactions. However, it is much unexpected that the bipolar exfoliation method was
found to work for a typical layered insulator, the hexagonal form of boron nitride
10 Electrochemical Manufacturing Methods Based on Surface …
10.5.6 Exfoliation of Suspended Particles with Bipolar
Electrochemistry
Exfoliation methods included in the above chapters all referred to techniques in which
the material composed of covalently bonded atomic planes was used as an electrode
component. Hence, the electrode potential of the material to be exfoliated could
be known, just as the current passed through them. Unlike in the above discussed
methods, the bipolar electrochemical method applies a completely different electrochemical arrangement. As the first step of this method, a material composed of atomic
planes is used for microparticle synthesis, often applying a chemical intercalation
of lithium from t-butyllithium and then decomposition with water. The microparticles thus synthesized are suspended in an aqueous solution containing a supporting
electrolyte (which is most often Na 2 SO 4 in 0.1 M concentration). Two platinum electrodes are used for passing a current through the suspension. The cell voltage reported
is around 10 V with a 2-cm interelectrode separation. Although it can be inferred
from these experimental conditions that a vigorous hydrogen and oxygen evolution
takes place at the cathode and anode, respectively, the electrode reaction products are
neither of interest nor do they modify the chemical nature on the particles suspended.
Instead, the suspended particles are further fragmented, which is attributed to electrophoretic effect. Although it does not seem to be completely understood how a
relatively small voltage across the suspended micrometer-sized particles can lead to
intercalation and further exfoliation, the size reduction of the particles as a result of
the current passed through the solution is convincingly evidenced. The size reduction
of the suspended particles takes place as a result of the current over a period of less
than an hour. Therefore, an easy-to-implement, fast and scalable method is available
for even the mass production of nanoparticles.
The electrophoretic exfoliation was successfully applied to various semiconductor
particles such as black phosphorous [112], MoSe 2 [113], WS 2 [114] and MoS 2 [115].
In each case, the particle size could be reduced to below 100 nm, but the particles’
shape was not fully characterized in either of the above cited studies. Nothing is
known about the kinetics of the electrophoretic microparticle fragmentation since it
was not studied whether the reaction time selected resulted in a saturation particle
size. The particle size reduction was followed only with the absorption change of the
solution since the microparticle suspension was dark in each case, but the resulting
nanoparticle suspension was light or nearly transparent due to the reduction of the
absorption intensity with the particle size. The nanoparticles produced were tested
as components of various immunoassays.
Although the exfoliation mechanism was not completely understood for layered
semiconductor particles, it seemed to be reasonable that the current passing through
the solution can generate a potential difference across the particles, which induces a
redistribution of the charge carriers at their surface, hence leading to electrochemical
reactions. However, it is much unexpected that the bipolar exfoliation method was
found to work for a typical layered insulator, the hexagonal form of boron nitride