solution. Depending upon applied current and time, different particle-sized carbon
quantum dots are synthesized which is further confirmed by various spectroscopic
techniques.
Deng et al. (2014) prepared carbon nanodots by one-pot electrochemical carbonization of alcohol under basic condition. Uniform carbon dots were prepared using
low molecular weight alcohol. Herein, a three-electrode system is used where two
platinum sheets were used as working and counter electrodes placed 3 cm apart, and
calomel electrode was used as reference electrode. After electrolysis, the obtained
mixture was evaporated at 800
C until a yellow-colored powder was obtained
followed by dialysis using dialysis membrane. Shinde and Pillai (2012) prepared
uniform size graphene quantum dots from multi-walled carbon nanotube in
nonaqueous solvent via electrochemical method. Due to high photostability,
non-toxicity, and biocompatibility, graphene quantum dots are a promising candidate for various applications in nano-electronics and as biomarkers and chemosensors. The uniform-sized carbon dots can be further prepared from the bundle of
carbon fiber using three-electrode system at constant potential (Bao et al. 2011).
Here, carbon fiber was used as the working electrode, Pt sheet as the counter
electrode, and Ag wire as the quasi-reference electrode, respectively. Among these
methods, electrochemical method is a green method with large yield, less timeconsuming, and operated at low temperature.
Further, zero-dimensional graphene quantum dots with sizes ranging from 3 to
5 nm were synthesized via electrochemical method (Li et al. 2011b). Firstly, the
graphene film was prepared by direct filtration (pore size 220 nm) of colloidal
suspension of reduced graphene oxide. Then, dried graphene was mechanically
peeled to obtain graphene film, which is further treated with oxygen plasma for
just 10 s to increase hydrophilicity. In the electrochemical preparation, three electrodes were used: a graphene film (working electrode), Pt wire (counter electrode),
and Ag/AgCl (reference electrode). The mono-dispersed graphene quantum dots are
much smaller in size (3–5 nm) as compared to graphene quantum dots (10 nm)
synthesized by hydrothermal method (Li et al. 2008).
Other than carbon quantum dots, simple metal oxide or metal sulfide quantum
dots were also synthesized by electrochemical method. Gopalakrishnan et al. synthesize MoS 2 luminescent quantum dots of sizes ranging from 2.5 to 6 nm from bulk
solution using aqueous ionic liquid (Gopalakrishnan et al. 2015). Similarly, Valappil
et al. (2017) synthesize transition metal dichalcogenides quantum dots WS 2 via
electrochemical method with a wide application in optoelectronic devices. Earlier,
various methods for the synthesis of quantum dots are available. Synthesis of
potassium intercalation followed by ultrasonication is quite complicated and laborious; thus, it needs further purification for the removal of potassium ion (Lin et al.
2013). Another way is simple ultrasonication of WS 2 nanosheets but the size of the
product cannot be determined easily.
90
P. Shandilya et al.
quantum dots are synthesized which is further confirmed by various spectroscopic
techniques.
Deng et al. (2014) prepared carbon nanodots by one-pot electrochemical carbonization of alcohol under basic condition. Uniform carbon dots were prepared using
low molecular weight alcohol. Herein, a three-electrode system is used where two
platinum sheets were used as working and counter electrodes placed 3 cm apart, and
calomel electrode was used as reference electrode. After electrolysis, the obtained
mixture was evaporated at 800
C until a yellow-colored powder was obtained
followed by dialysis using dialysis membrane. Shinde and Pillai (2012) prepared
uniform size graphene quantum dots from multi-walled carbon nanotube in
nonaqueous solvent via electrochemical method. Due to high photostability,
non-toxicity, and biocompatibility, graphene quantum dots are a promising candidate for various applications in nano-electronics and as biomarkers and chemosensors. The uniform-sized carbon dots can be further prepared from the bundle of
carbon fiber using three-electrode system at constant potential (Bao et al. 2011).
Here, carbon fiber was used as the working electrode, Pt sheet as the counter
electrode, and Ag wire as the quasi-reference electrode, respectively. Among these
methods, electrochemical method is a green method with large yield, less timeconsuming, and operated at low temperature.
Further, zero-dimensional graphene quantum dots with sizes ranging from 3 to
5 nm were synthesized via electrochemical method (Li et al. 2011b). Firstly, the
graphene film was prepared by direct filtration (pore size 220 nm) of colloidal
suspension of reduced graphene oxide. Then, dried graphene was mechanically
peeled to obtain graphene film, which is further treated with oxygen plasma for
just 10 s to increase hydrophilicity. In the electrochemical preparation, three electrodes were used: a graphene film (working electrode), Pt wire (counter electrode),
and Ag/AgCl (reference electrode). The mono-dispersed graphene quantum dots are
much smaller in size (3–5 nm) as compared to graphene quantum dots (10 nm)
synthesized by hydrothermal method (Li et al. 2008).
Other than carbon quantum dots, simple metal oxide or metal sulfide quantum
dots were also synthesized by electrochemical method. Gopalakrishnan et al. synthesize MoS 2 luminescent quantum dots of sizes ranging from 2.5 to 6 nm from bulk
solution using aqueous ionic liquid (Gopalakrishnan et al. 2015). Similarly, Valappil
et al. (2017) synthesize transition metal dichalcogenides quantum dots WS 2 via
electrochemical method with a wide application in optoelectronic devices. Earlier,
various methods for the synthesis of quantum dots are available. Synthesis of
potassium intercalation followed by ultrasonication is quite complicated and laborious; thus, it needs further purification for the removal of potassium ion (Lin et al.
2013). Another way is simple ultrasonication of WS 2 nanosheets but the size of the
product cannot be determined easily.
90
P. Shandilya et al.