Spectrum of Emerging Sciences, 2 (1) 2022, 66-77
Spectrum of Emerging
Journal homepage: https://esciencesspectrum.com
Carbon Quantum Dot and Application: A Review
Bhupendra Kande1, Prachi
1Shri Shankaracharya Professional
University, Bhilai 490020 Chhattisgarh, India.
E-mail Address: firstname.lastname@example.org
available online at: https://esciencesspectrum.com/AbstractView.aspx?PID=2022-1-2-3
25 June 2022
20 July 2022
Carbon quantum dots, fluorescence, surface Passivation,
doping, sensing, bioimaging, nanomedicine, photocatalysis, electrocatalysis.
carbon nanoparticles or carbon quantum dots or carbon dots, a brand new
category of carbon material, had high interest due to its optical and
fluorescence properties with advantages of eco-friendly, low coast and simple
way of synthesis. Their physical – chemical properties also depend to on functionalization
and surface passivation. From the discovery of non – toxic caron nano
materials, CQDs had numerous applications in different areas like sensing,
biological sensing, vivo and vitro imaging, nano drug, drug carrier, drug
delivery, energy, food industry, agriculture, photocatalysis and
electrocatalysis etc. Here, we described here, the methods of synthesis and functionalization
of carbon quantum dots, properties and applications with future prospects.
nanomaterials had extensive studied and received great attention since the
discovery of Buckminster fullerene . Carbon
dots (CDs) consist, graphene, carbon quantum dots (CQDs), carbon nanotubes
(CNTs), carbon nano onions (CNOs) and now it’s a new, important fluorescent
carbon nanomaterial with below than 10 nm in size. These carbon nano materials
had strong luminescent property and highly soluble in aqueous medium . An
experiment designed to understand the procedure of the preparation of long
chain carbon moieties interstellar space, took the place of fullerene. The
characterization of carbon nanotubes (CNTs) was made after this . After a year of the discovery of
CNT, another member of carbon family, carbon nano onion (CNO) or carbon quantum
dot (CQD) was discovered , an ideal member of the carbon
allotropes, which made up of concentric graphitic shells . It was first synthesized and
obtained by Iijima in 1980 , in vacuum deposited amorphous
carbon films by high resolution TEM (Fig. 1). After discovery CNO, Ugarte
observed a transformation of CNT to CNO . CNO had a quasi-spherical onion
like structure composed of concentric graphitic layers with an inner core,
which either hollow or encapsulated with metal. Because of the ideal structure,
potential applications of CNO for lubricants [7, 8], magnetic storage materials , devices  and electrochemical capacitors . Carbon
quantum dots (CQDs) had amorphous sp2-conjugated nanocrystalline
core with sp2/sp3 hybridization and consist highly
abundant oxygen groups (like carboxyl, hydroxyl, aldehyde etc) on the surface , which consider those nano materials as water soluble
CQDs (Fig. 2). They had wonderful electron donor-acceptor induced
photoluminescence and fluorescence properties. Due to photoluminescence
property, critical to re-size and change the surface chemical groups of carbon
dots . Doping with other elements also used to increase
their properties . Carbon quantum dots or carbon dots, consider as next
generation material in nanomaterial technology which had unique optical and
In comparison of other quantum dot semiconductors,
organic agents, and other fluorescent sensors, carbon quantum dots (CQD) had
very interesting properties like unique emissions with various fluorescence
excitation, chemical compositions, cheap and simple synthesis,
functionalization of surface and modification, photo-chemical stability , which proved CQDs or CDs could be apply in different
technical, medical applications. Carbon dots easily played favourable roles in
applications due to their simple and cheap synthesis, easily water soluble and
biocompatible [15-18]. Those fluorescent carbon nano materials attract the interest of
researchers due to their wide variety of applications like bioimaging,
bioanalysis, sensor, drug delivery, photocatalysis, optoelectronics, electrocatalysis,
fuel cell and many more .
Many fluorescent quantum dots like graphene quantum
dots (GQDs) [20-24], polymer dots (PDs) [25, 26], carbon nanotube (CNT) dots [27, 28], nano diamonds (NDs) [29-33], and CQDs synthesised previously. According to
density of states (DOS), quantum dots had distinct materials with compact atoms.
When the size of QD particles decreased upto below the size, bandgap energy
increased. Because of electron-hole radiative recombination, effect of quantum-confinement
did not relevant to carbon dots. Carbon quantum dots consist small size with high
surface defects. Size-dependent optical properties because of various surface
defect and surface to volume ratio .
Here, we described the synthesis, characterization and properties of carbon
quantum dots with their application in various areas.
Fig.1. Spherical particles of graphitic carbon nano-onions found in the
amorphous carbon films, (a – d). (scale bar 2 nm) 
Fig.2. Structure of carbon quantum dots (CQDs) .
2. Synthesis of nano carbon quantum dots (CQDs):
quantum dots (CQDs), serendipitously determined in the process of single wall carbon nano tubes
(SWCNTs) purification .
Suspension of SWCNTs on gel electrophoresis, differentiated into three
important classes of materials, included a fast moving band of high fluorescent
material which showed size dependent
fluorescent properties. It was first
discovery of carbon nanoparticles or carbon dots. CDs contain contained lower
amount of carbon with high oxygenated groups, also called carbogenic nanodots .
Baker et al. described different synthesis process and properties of
carbon nanoparticles. Synthesis
of CDs divided into two classes of methods; top-down and bottom-up. Top down
method included synthesis of nanoparticles from large carbon structure. And other
hand, in bottom-up method CDs prepared by molecular precursor.
fluorescence nano materials CDs stable graphene sheets, carbon fibres, CNTs,
CNOs, carbon soots etc, classified as following methods:
method: Bottini et al. 
used electric arc technology to synthesized luminescence CDs through pristine
CNTs and oxidized (with nitric acid) CNTs.
Laser ablation method: Sun's et al. 
synthesized CDs via Q-switched Nd : YAG laser ablation at 900 °C and 75 kPa, by
graphite and cement mixture hot pressing. Carbon dot’s surface were passivated
via diamine-terminated oligomeric PEG1500N with passing acid; which
attached with organic moieties on the surface of CDs obtained (Fig. 3a).
Hydrothermal cutting method: Pan et al. 
synthesized CDs via hydrothermal method,
in it cutting graphene sheets into 10 nm sized functionalized graphene quantum
dots. These functionalized GQDs exhibited blue fluorescence which induced
through edge effect.
Chemical oxidation method: Zhou et al. 
reported that carboxylic group attached onto carbon nano materials or GQDs
surface, synthesized through oxidation reaction under UV irradiation, in between
graphene oxide (GO) and Fenton reagent (Fe2+/Fe3+/H2O2).
Electrochemical oxidation method: Zhou et al.
synthesis of CD through multiwall carbon
nanotubes which fabricated by electrochemical oxidation method (Fig. 3b).
Fig.3. Schematic view of synthesis of (a) fluorescent
carbon nano dots (CDs) via laser ablation and attached with PEG on the surface ;
(b) GCDs synthesized by exfoliation in ionic liquid