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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5936_Библиотеки_им_академика_М_И_Перельмана
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8 Elyor Berdimurodov et al.
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Figure 1.5: Synthesis of carbon dots from the waste biomass [36].
for metal detection in analytical chemistry. The host and guest interacted with each
other through hydrogen bonds, electrostatic forces, and variable intermolecular interactions including π–π. The supramolecular host contained the hydrophobic cavity, in
which the functional groups were on the surface of carbon dots. The host molecules
are attached to the surface of carbon dots; as a result, the surface characteristics are
changed to develop special performances. These modifications were widely used in
environmental remediation, metal extraction, drug delivery, and battery materials.
Chapter 1 Recent trends and developments in carbon dots 9
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Figure 1.6: Carbon dot modifications with the supramolecular hosts and applications [37].
10 Elyor Berdimurodov et al.
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Currently, the supramolecular host with carbon dots was successfully used in the
intramolecular charge transfer, internal filtration effect, Forster resonan ce energy
transfer, dynamic quenching, static quenching, and photoelectron transfer. For example, the calix[n]arenes contained 3D scaffolds with internal cavities, which interacted
with the surface of carbon dots. The amino functional groups are mainly attached to
the surface of carbon dots. The calix[n]arenes interacted with the amino function al
groups, which are attached on the surface (Figure 1.6). The fluorescent properties of carbon dots were enhanced with the calix[n]arene supramolecular complex with the carbon dots. The carbon dots have more active regions on the surface of carbon dots. The
calix[n]arenes are adsorbed on these active regions by the inner cavity. Consequently,
the fluorescence performance of carbon dots is enhanced. The free amino functional
groups of carbon dots were synthesized from ethylenediamine and glycerol by hydrothermal reactions. The zinc ions are adsorbed into a cavity of carbon dots; as a result,
the fluorescence intensity was increased at 418 nm. The sp
droxyl functional groups are mainly responsible for the adsorption of zinc ions’ inner
cavity of carbo n dots. Then, the electron-providing ability of these two groups was
blocked, which can promote the rise of fluorescence performance. High fluorescence is
very important in the determination of metal ions from the examples at low concentrations. The supramolecular complex with the carbon dots is a highly effective material
in the determination of metal ions [37].
2
nitrogen atoms and hy-
1.6 Recent trends in carbon dots/2D hybrid
materials
The carbon dots/2D hybrid materials are new materials in energy storage, optoelectronic, bioimaging, photocatalysis, and sensing applications. The reason for this is that
they are low toxicity, biocompatibility, photostability, photoluminescence, and small
size. The carbon dots interact with the nanomaterials through the functional groups attached to the surface of the carbon dots. The carbon dots are modified to follow the 2D
materials: layered double oxides (LDOs), layered double hydroxides (LDHs), layered
transition metal oxides (LTMOs), transition metal dichalcogenides (TMDCs), graphitic
carbon nitride (g-C
tropic physicochemical properties, show large surface-to-volume ratio, and are small in
size. These properties make the carbon dots more effective in various applications [38].
The g-C
3N4
dots, graphite quantum dots, and carbon quantum dots to enhance the unique properties in energy storage, photocatalysis, catalysis, optoelectronics, and sensing. The
nature of functional groups on the surface of carbon dots is a key factor in the electrochemical sensing of carbon dots. For example, the carboxyl functional groups on the
surface of carbon dots support copper detection (Figure 1.7). The metal ions effectively
), and graphene-based materials. These 2D materials have aniso-
3N4
effectively interacted with the carbon polymerized dots, carbon nano-
Chapter 1 Recent trends and developments in carbon dots 11
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Figure 1.7: Various carbon dots/2D hybrid materials [38].
interacted with the metal surface to form covalent bonds between the carboxyl functional groups and metal d-orbitals [38].
1.7 Conclusions
In this chapter, the recent trends and developments in carbon dots were discussed and
reviewed. At recent times, the carbon dots are synthesized by the top-down and bottomup methods. The electrochemical methods, ultrasonic treatment, laser ablation method,
and arc discharge method were mostly used in the top-down methods. These methods
used the following conditions: high energy, high potential, laser emission, and high acidity. The bottom-up methods have some advantages such as convenient methodology, precise control, easy instrumentation, cost-effectiveness, involvement of non-toxic precursor
molecules, practical applicability, and green materials. The carbon dots are synthesized
fromgreensourcessuchascarbohydrates,biomass, and bio-waste. The synthesis of carbon dots from environmentally friendly materials cannot require expensive methods and
hazardous chemicals. The carbon dots are modified with the supramolecular hosts to obtain unique carbon dots in the biometric elements, catalysts, and sensor applications. The
host–guest interactions can promote the fluorescence performance of carbon dots. The
carbon dots are modified to follow the 2D materials: LDOs, LDHs, LTMOs, TMDCs, g-C
and graphene-based materials. These 2D materials have anisotropic physicochemical
properties, show large surface-to-volume, ratio, and are small in size. These properties
make carbon dots more effective in various applications
3N4
,
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Omar Dagdag✶, Rajesh Haldhar, Seong-Cheol Kim,
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Elyor Berdimurodov
✶
, Ekemini D. Akpan and Eno E. Ebenso
✶
Chapter 2
Main properties and characteristics
of carbon dots
Abstract: Carbon dots (CDs) are new composites in nanomaterials. CDs are new types
of carbon allotropes such as carbon nanotubes, activated carbon, graphite, and many
other carbon nanotubes. Scientists have recently created new CDs and are exploring
their applications, including energy technology, optics, and biomedicine. This chapter
describes the different types and characteristics of CDs, including specificity, scalability, and biocompatibility.
Keywords: Carbon dots, functional nanomaterials, materials, optical, dispersibility,
biocompatibility properties
2.1 Introduction
Carbonated materials are used in many fields such as technology, chemistry, biomedicine, and other interdisciplinary fields [1]. There are many types of carbon compounds
in nature, and carbon compounds play an important tool in the innovation of carbonbased advanced materials. From conventional three-dimensional (3D) graphite [2] to develop carbon-based nanomaterials such as fullerenes [3], one-dimensional carbon nanotubes (CNTs) [4], and two-dimensional graphene [5], the simple exploration of new
carbon materials and their use is also an important topic in the fields of chemistry, materials, and physics. In recent years, there has been a search for graphene and CNTs
with optical, electrical, and biocompatible properties.
✶
Corresponding authors: Omar Dagdag, Centre for Materials Science, College of Science,
Engineering and Technology, University of South Africa, Johannesburg 1710, South Africa,
e-mail: dagdao@unisa.ac.za
✶
Corresponding authors: Eno E. Ebenso, Centre for Materials Science, College of Science,
Engineering and Technology, University of South Africa, Johannesburg 1710, South Africa,
e-mail: ebensee@unisa.ac.za
✶
Corresponding authors: Elyor Berdimurodov, Faculty of Chemistry, National University
of Uzbekistan, Tashkent 100034, Uzbekistan, e-mail: elyor170690@gmail.com
Ekemini D. Akpan, Centre for Materials Science, College of Science, Engineering and Technology,
University of South Africa, Johannesburg 1710, South Africa
Rajesh Haldhar, Seong-Cheol Kim, School of Chemical Engineering, Yeungnam University, Gyeongsan
38541, Republic of Korea
https://doi.org/10.1515/9783110799958-002
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Recently, much attention has been paid to new types of 3D models in luminous
carbon materials, such as carbon dots (CD), nanoparticles with non-spherical morphology, and nanometric energy (<10 nm).
Compared to quantum dots [2, 6], CDs are multifunctional, have low toxicity, have
high fluorescence, and are cost-effective, making them suitable for many applications
such as biomedicine and optoelectronics. In addition to this, during the synthesis of
new nanomaterials, CDs can be converted into solar cells due to their injection/fission
rate and stored as additional electrons (electron input/electron capture) [7, 8]. CD
training has significantly improved (Figure 2.1).
CDs have complex, crystalline microstructures of various sizes, so an important
relationship between CD structure and content needs to be explored. Many important
aspects of CD have been described, including fluorescence, UV absorption, scattering,
and biocompatibility. The following sections discuss about CD along with its contents.
Figure 2.1: Milestones in the development of CDs [2].
2.2 Main properties and characteristics
of carbon dots
2.2.1 UV–visible
Tang et al. [9] prepared microwave-generated graphe ne quantum dots (GQDs). This
GQD was detected by deep UV radiation and double wavelength UV radiation at 282
and 228 nm, respectively. Additionally, the growth in solubility and microwave effect of
Chapter 2 Main properties and characteristics of carbon dots 17
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GQD can be seen by comparing UV absorbance. For example, if the reaction increases,
the absorption edge turns red, but the maximum position does not change. The origin
of the top is due to the cross of the edge, which contains oxygen GQD. The π–π* interactions of the carbon–carbon bonds and n–π*interactionsofcarbon–oxygen bonds are
mainly responsible for the maximum UV absorbance at 228 and 282 nm, respectively. In
the research work of Li et al. [10], green preparation methods were performed to obtain
the photoluminescent CDs. Then, the formed CDs reacted with NaOH to form the solid
CDs1. Later, CDs1 reacted with the HCl acidic solution to form CDs2. It is indicated that
the maximum absorption depth of the UV–visible surface of CDs1 is 540 nm. CDs2 is
also a light source similar to CDs1, although it has a longer wavelength. It can be seen
that the absorption of UV radiation affects the working surface of the CD surface.
2.2.2 Fluorescence
The effect of other compounds on CD fluorescence has been studied in several recent
studies. Dean et al. [11] hydrothermally synthesized CDs with 35% quantum yield (QY),
which can be regulated by photoluminescence (PL) with locally available O atoms. The
atomic material of O plays an important role in regulating the coupling bandwidth between HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) [12]. Experimental results showed that when the oxygen concentration level
increased in the system, the bandwidth gradually decreased, and a red-shift of the emission peak appeared at 625 nm (Figure 2.2a). Bao et al. [13] also confirmed the discharge
mechanism of the surface condition made from carbon fibre concentrates oxidized by
.Thesize,shape,andmolecularpropertiesofCDdependonthesynthesismethodol-
HNO
3
ogy: temperature, time, and component concentrations. In the synthesis methodology,
the following main factors were observed: (1) the amount of oxidation on the surface
rose with the growth of synthesis time, which is responsible for the increase in the wavelength of the radiation; (2) higher acid concentrations and shorter reaction times lead to
longer discharge wavelengths. Han et al. [14] studied the fluorescence properties of CDs,
effects to these properties, and impacts of surface-state energy were studied. Self-healing
and disease are manifested by three types of polymer CD (PCD). It is clear from the obtained X-ray photoelectron spectroscopy (XPS) results that the nitrogen and carbon atoms
were accounted for 13.83% and 20.11%, respectively. The energy distinction between the
HOMO and LUMO regions decreased when the degree of surface oxidation rises. As a
result, the amorphous regions were decreased. The rise in the C = N content is responsible
for the rise in red-shift of PL bands. The energetic position of the PCD changed with the
rise in the C = N content, indicating that a large number of electrical changes were found,
and a red change was found in the PL band (Figure 2.2b). Zhu et al. [15] suggested that CD
fluorescence has a correlation effect between C = O and C = N. Three types of CDs were
prepared and installed with three different s olvents (H
ing to the hydrothermal application shown in Figure 2.2d. The obtained results were
O, C2H5OH, and DMF) accord-
2
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