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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5416_Библиотеки_им_академика_М_И_Перельмана
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Figure 2.2: Procedures in changes of fluorescence properties of CDs: solvent, size, functional groups, and surface effects [2].
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18 Omar Dagdag et al.
Chapter 2 Main properties and characteristics of carbon dots 19
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confirmed by fluorescence and XPS spectral data. The size of CDs is the next significant
factor to identify stability by limiting the change in the fluorescence wavelength. For
example, Fan et al. [16] have specially installed CDs with multi-coloured narrow bandwidth emissions. Transmission electron microscopic images show triangular CDs and QY
CDs of about 54–72%. Symmetric phloroglucinol was selected for this research work. The
active functional groups of amino and hydroxyl are mainly responsible for the formation
of CDs. The blue, green, yellow, and red colours appeared on 1.9, 2.4, 3.0, and 3.9 nm, respectively (Figure 2.2c). The distance between the bonds decreases with increasing size,
leading to constant friction [17].
2.2.3 Phosphorescence
In recent years, researchers developed CDs with higher RTP (room-temperature phosphorescent) content and longer shelf life [2]. Deng and his colleagues reported another
RTP phenomenon by dispersing PVA (polyvinyl alcohol). CD was prepared by pyrolysis
of ethylenediaminetetraacetic acid disodium salt at 400 °C under N
when CDs were coated with a PVA matrix, fluorescence was observed under the influence of UV light at room temperature. When comparing the sample images with CDPVA and CD with H
O, a peak at 220 nm and bandwidth between 300 nm were observed
2
due to the change in the n–π* binding and π–π* transitions of C=O bonds, respectively.
In the phosphorus band, strong binding at 260–340 nm was observed for C = O and another band at 500 nm, suggesting that phosphorescence may be induced by carbon dioxide, which binds to C = O. The obtained results suggested that the phosphorescence of
CD is caused by the three phases of the gaseous carbonyl component and that the PVA
molecule activates these products by adding hydrogen. The energy of vibration or rotation was importantly depleted by the presence of hydrogen [18].
Furthermore, Li et al. [19] suggested that the C = N interaction affects the RTP performance on CD. The C = N bonds of this system were mainly responsible for phosphorescence effects. It constructed the CD RTP complex by treating urea and nitrogen-doped
CD (NCD) with the heat method. Because the doubling of the recrystallized urea and the
hydrogen bonding between the burette and the NCD reduces the triple trigger distribution, the CD system has a longer lifetime than the single device in Figure 2.3a. Figure 2.3b
anddillustratestheopticalpropertiesandimpactsofhydrogenpresenceinH-NCDcompounds. H-NCDs were formed by hydrogen bonding. The optical properties of H-NCDs
were changed by the protonation processes. In Figure 2.3d, the green colour of
H-NCDs was altered to blue by protonation. As observed from the obtained data that
H-NCD had a longer lifetime and higher RTP utilization than the three CD types, it is
confirmed that the third group was involved in the hydrogen bonding between H-NCD
and the biuret.
. It is indicated that
2
20 Omar Dagdag et al.
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Figure 2.3: Pictorial representation of RTP and impacts [2].
2.2.4 Dispersibility and biocompatibility
Most CDs have good hydrophilicity and dispersion, so they form O-products in the
first step of the process. Additionally, changes in the hydrophilicity and hydrophobicity of CD can be achieved by adjusting the surface coefficients. Hsu et al. [20] reported
that hydrothermal deposition of hydrophilic CD has been described in boilers. It has
been suggested that these groups play an important role in determining the hydrophilicity of CD deri vatives. In addition, Mitra et al. [21] prod uced hydrophobic CDs obtained by microwave pyrolysis of co-polymer Pluronic F-68.
Chapter 2 Main properties and characteristics of carbon dots 21
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2.3 Conclusions
CDs are a new generation of carbon-based nanomaterials. Currently, CDs are mostly
used in pharmacology, medicine, nanotechnologies, surface, drug determination, wastewater treatments, and removal processes from heavy metals. Many CDs have recently
been tested for composition, material, and base. In this section, we introduce some of
the important aspects of CDs discussed earlier, such as their biocompatibility, dispersibility, and optical properties.
Abbreviations
RTP room-temperature phosphorescent
PCDs Polymer CDs
PVA Polyvinyl alcohol
References
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[2] Li Z, Wang L, Li Y, Feng Y, Feng W. Frontiers in carbon dots: Design, properties and applications.
Mater Chem Front. 2019, 3, 2571–2601.
[3] Thompson BC, Fréchet JM. Polymer–fullerene composite solar cells. Angew Chem Int Ed. 2008,
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[4] DRESSELHAUS, M. S. D. G.; Eklund, PC; Rao, AM, The Physics of Fullerene-Based and Fullerene-Related
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[5] Feng W, Long P, Feng Y, Li Y. Two‐dimensional fluorinated graphene: Synthesis, structures,
properties and applications. Adv Sci. 2016, 3, 1500413.
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Lett. 2004, 4, 11–18.
[7] Kaur M, Kaur M, Sharma VK. Nitrogen-doped graphene and graphene quantum dots: A review on
synthesis and applications in energy, sensors and environment. Adv Coll Interf Sci. 2018, 259, 44–64.
[8] Essner JB, Baker GA. The emerging roles of carbon dots in solar photovoltaics: A critical review.
Environ Sci Nano. 2017, 4, 1216–1263.
[9] Tang L, Ji R, Cao X, Lin J, Jiang H, Li X, et al. Deep ultraviolet photoluminescence of water-soluble
self-passivated graphene quantum dots. ACS Nano. 2012, 6, 5102–5110.
[10] Li D, Jing P, Sun L, An Y, Shan X, Lu X, et al. Near‐infrared excitation/emission and multiphoton‐
induced fluorescence of carbon dots. Adv Mater. 2018, 30, 1705913.
[11] Ding H, Yu S-B, Wei J-S, Xiong H-M. Full-color light-emitting carbon dots with a surface-state-
controlled luminescence mechanism. ACS Nano. 2016, 10, 484–491.
[12] Hu S, Trinchi A, Atkin P, Cole I. Tunable photoluminescence across the entire visible spectrum from
carbon dots excited by white light. Angew Chem Int Ed. 2015, 54, 2970–2974.
[13] Bao L, Liu C, Zhang ZL, Pang DW. Photoluminescence‐tunable carbon nanodots: Surface‐state
energy‐gap tuning. Adv Mater. 2015, 27, 1663–1667.
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[14] Han L, Liu SG, Dong JX, Liang JY, Li LJ, Li NB, et al. Facile synthesis of multicolor photoluminescent
polymer carbon dots with surface-state energy gap-controlled emission. J Mater Chem C. 2017,
5, 10785–10793.
[15] Zhu J, Bai X, Bai J, Pan G, Zhu Y, Zhai Y, et al. Emitting color tunable carbon dots by adjusting solvent
towards light-emitting devices. Nanotechnology. 2018, 29, 085705.
[16] Yuan F, Yuan T, Sui L, Wang Z, Xi Z, Li Y, et al. Engineering triangular carbon quantum dots with
unprecedented narrow bandwidth emission for multicolored LEDs. Nat Commun. 2018, 9, 1–11.
[17] Qu S, Zhou D, Li D, Ji W, Jing P, Han D, et al. Toward efficient orange emissive carbon nanodots
through conjugated sp2‐domain controlling and surface charges engineering. Adv Mater. 2016,
28, 3516–3521.
[18] Deng Y, Zhao D, Chen X, Wang F, Song H, Shen D. Long lifetime pure organic phosphorescence
based on water soluble carbon dots. Chem Comm. 2013, 49, 5751–5753.
[19] Li Q, Zhou M, Yang Q, Wu Q, Shi J, Gong A, et al. Efficient room-temperature phosphorescence from
nitrogen-doped carbon dots in composite matrices. Chem Mater. 2016, 28, 8221–8227.
[20] Hsu P-C, Chang H-T. Synthesis of high-quality carbon nanodots from hydrophilic compounds: Role
of functional groups. Chem Comm. 2012, 48, 3984–3986.
[21] Mitra S, Chandra S, Kundu T, Banerjee R, Pramanik P, Goswami A. Rapid microwave synthesis
of fluorescent hydrophobic carbon dots. RSC Adv. 2012, 2, 12129–12131.
Vinayak Sahu
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Chapter 3
Synthetic strategies of carbon dots
Abstract: Sinceitsdiscoveryin2004,carbondots(CDs),anaffluentialinthefieldof
carbon nanomaterials, have gotten a lot of attention. Many ways to synthesizing CDs
have been explored to date, and many efforts have been made to leverage simple,
cost-effective, and sizable-scale synthesis passage. Simultaneously, CD photoluminescence (PL) mechanisms have been extensively studied, with the primary causes
being molecule state, surface state, carbon core state, and their synergistic e ffect.
CDs have been widely used in catalysis, biomedicine, optoele ctronic devices, lubrication, sensing, and other fields due to their advantageous properties such as brilliant
optical, tremendous biocompatibility, good catalytic activity, tiny size, less virulent,
and ecological. This chapter provides a comprehensive overview of the development
of CD synthesis strategies. The potential and challenges for CD research are examined in depth based on the synopsis. The goal of this study is to motivate associated
researchers to overcome different technical hur dles, fill in the gaps in conventional
research, and fully use the prospects of CDs.
3.1 Introduction
Conventional quantum dots (QDs), which include heavy metals like Cd and Pb, have
excellent ocular proper ties and vast a pplicability potential; nevertheless they lack
biocompatibility and environmental friendliness due to their known high lethality
and harmful for environm ent and severely restrict their applicability, particularly
applications in the field of biology [1–3]. As a result, developing a new form of environmentally friendly QDs is critical. Luckily, carbon dots (CDs), a new class of zerodimensional fluorescent carbon nanomaterial, were introduced by Xu et al. [4] in 2004
while purifying single-walled carbon nanotubes (CNTs). CDs, in contrast to semiconductor Q Ds, have reduced lethality, greater biocompatibility, and superior photostability, indicating that they have a strong prospect to be a safe and less-virulent
alternative. CDs are nanoparticles of carbon with a diameter below 10 nm and hav ing fluorescent properties [5, 6]. A single CD structure contains a core of carbon and
heteroatomslikeN,S,O,andfunctionalgroupslike–OH, –COOH, and –NH
with varied morphologies have non-uniform names due to their complex structure
Vinayak Sahu, National Institute of Technology Raipur, Chhattisgarh 492010, India;
Governmental Model College Raipur, Chhattisgarh 492099, India, e-mail: vinayaksahu2208@gmail.com
https://doi.org/10.1515/9783110799958-003
[7]. CDs
2
24 Vinayak Sahu
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and countless variants. Yang’s group [6] classified CDs into three categories based
on their cores of carbon and chemical states of the surface:carbon nanodots (CNDs),
graphene quantum dots (GQDs), and polymer dots (PDs). Anisotropic GQDs have
quantum confinement and single/multiple films of graphene, crystalline also has lateral dimensions, whereas CNDs have a spherical morphology, resulting heights
equal to lateral dimensions roughly, andCNDshavetwosubcategoriesintoamorphous carbon nanoparticles (CNPs) and cross-linked CNDs with PDs with and polymeric creatures, quantum confinement effect not shown by polyme rizing small
molecule/polymer precursors. The distinction between carbon sources of synthetic
and synthetic techniques is largely responsible for the diversity of CDs. CNTs, carbon
nano-onions (CNOs), nano-diamond, graphene, fullerene, and their derivatives have
many advantages: (1) Optical qualities that are favourable PL is rarely visible in
pure CNOs, nano-diamond, CNTs, graphene, and fullerene due to the Dirac c one’s
zero optical bandgap. CDs, on the other hand, have controllable emission of PL and
great resistant to photobleaching as well as high, near 100% PL quantum yields
(PLQYs) [8] and (2) synthesis is simple and cost-effectiv e. Various synthetic preparation methods for the above carbon nanomaterials have been developed, such as for
CNTs, graphene, and nano-diamond chemicalvapourdeposition,forCNOhightemperature annealing, and for fullerene arc discharge, numerous shortcomings
such as expensive, poor yields, tedious proces ses, and a large amount of raw material requirements must still to overcome. The vast majority of c arbonaceous materials, including glucose, graphene oxide (GO),citricacid,CNTs,hair,coal,leaves,
graphite, grass, durian, and even garbage of household, have been used as CD precursors [9–19]. In addition, a wide range of synthetic techniques, including hydrothermal synthesis, chemical oxidation, microwave treatment method, pyrolysis
method, and others, have been used to create CDs. Consequently, getting CDs at inexpensivepricesissimpler;(3)excellentstability and solubility. T he aforementioned
CDs have poor solubility and stability in aqueous or other solvents due to their restricted surface groups and chemical inertness. Although it is frequently expensive
and ineffective, surface modification is meant to increase their solubility. Due to the
large number of surface groups in CDs, they exhibit good long-term solubility and
stability in aqueous solvent. Importantly, the polarity of CDs can be easily altered by
utilizing the right precursors, making them amenable to dispersion in a wider range
of solvents. Additionally, CDs have appealing catalytic activity due to their distinct
electronic structures and energies. As a result, CDs are receiving more and more attention. Many attempts are being made right now to take advantage of simple, economical,
and extensive preparation. Chen and co-workers [23] have recently developed a hyperthermia magnetic technique to quickly and easily produce multi-colour luminous CDs
on a large scale. The specifics mechanism of the PL of CDs is still up for discussion despite the fact that the synthesis of CDs has advanced significantly. Carbon core state,
surface state, molecule state, and their synergistic effect are currently the main perspectives for the PL genesis of CDs. In addition, their benefits include favourable optical
Chapter 3 Synthetic strategies of carbon dots 25
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properties, attractive catalytic performance, chemical inertness, tiny size, ecological, as
well as ease of synthesis [20–31].
Numerous outstanding reviews on PL mechanisms and synthetic methods or the
possible applicabilities of CDs have been recently described. For instance, Tan’s group
[32] both offered information on the development of CDs in light-emitting diodes (LEDs)
and nanomedicine from the year 2020. In a different review, Lu’s group described the
mechanisms of PL of CDs, which included crosslink-enhanced emission, internal factors
dominated emission, and external factors dominated emission. Additionally, Yang’ s
group [33] and Ding’s group [34] outlined developments in chiral CDs and solid-state
CDs, respectively, by the year 2020. However, CDs continue to make amazing strides forward every day. More significantly, a thorough study that methodically presents synthesis procedures, PL roots, and prospective CD applications is currently lacking. As it is
known, prospective CD applications, mechanisms of PL, and synthetic techniques interact and support one another rather than existing alone. For instance, the ability to prepare multi-colour-emitting CDs at controlled temperatures encourages the application
in bioimaging and optoelectronic devices. In addition, the creation of CDs with clearly
defined structures using the right precursors and reaction circumstances makes it easier to understand how their PL mechanism works. Meanwhile, the discovery of the
mechanism of PL will direct the synthesis of CDs with controlled PL, for biomedicine
applications need a preparation method to obtain CDs with stable PL, good PLQYs, and
low lethality. Additionally, a deeper comprehension of the origin of PL of CDs should
make it easier to build applications (such as sensing and bioimaging) that depend on PL
alterations.
In order to carefully explain the synthetic processes, the source of fluorescence,
and the prospective uses of CDs, a thorough examination is absolutely necessary. Due
to this, this study focu ses on thoroughly documenting the development of common
preparation procedures, the most widely recognized theories for PL mechanisms, and
prospective CD applications. The many procedures used to create CDs, such as electrochemical, pyrolysis reaction, chemical oxidation, microwave treatment, laser ablation,
hydrothermal synthesis, and other methods, are described in depth.
3.2 Synthetic strategies
The synthesis processes for CDs are of two types: bottom-up and top-down route. Both
routes are briefly described in Figure 3.1.
26 Vinayak Sahu
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Figure 3.1: Synthetic strategies of CDs.
Chapter 3 Synthetic strategies of carbon dots 27
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3.2.1 Chemical oxidation
Chemical oxidation involves oxidizing the reactants to produce CDs using strong acidic
solutions like conc. HNO
was used to the modification of CDs with the various functional groups; as a result, the
CDs are become water soluble and effective for the bio-imaging. Xu et al. [4] in 2004 separated the suspension using gel electrophoresis after oxidizing arc-discharge soot with
strong HNO
. Finally, CDs that emit blue, orange, yellow, and green light were unin-
3
tentionally acquired [4]. Even though the CDs highest PLQY was just 1.6% this groundbreaking breakthrough created a fascinating new area of research in carbon nanomaterials. Later, Mao and colleagues [28] used candle soot instead of arc-discharge soot to
synthesize CDs while concentrated HNO
3% PLQY and have good water solubility, and an average diameter of particles 2–6nm
may be used as a cell-imaging probe, then, by refluxing in conc. HNO
and carbon black [36] also served as carbon sources to synthesize CDs, but all of the
resulting CDs had a low PLQY of less than 5%. Sun’s group [37] published a two-step
approach in 2010 to create CDs with a high PLQY of close to 60% utilizing PEG1500N as
a functionalizing agent, based on the observation that surface modification was one of
the most successful strategies to upgrade PLQYs. First, HNO
soot, which served as the carbon source, to create the precursor CNPs. In order to create
PEG-passivated CDs with good PLQY, the starting material was first mixed with SOCl
and then subjected to a reaction with PEG1500N [37], which held tremendous promise
for bioimaging. Similar to this, Li and colleagues [38] and Huo and colleagues [39]
merged surface passivation and chemical oxidation to create CDs with high PLQY using
GO and activated carbon, conc. HNO
compounds as surface functionalizing agents. This method is cheap and easy but produces CDs with poor yield and non-tuneable PL. Then, group of Zhu [40] and group of
Zhang [41] used carbon fibres (CFs) as carbon sources to synthesize CDs by oxidative
cutting. CDs were an efficient fluorescent sensor for the selective detection of Cu
Based on the optical properties, it is possible that a significant number of tiny sp
bon by chemical oxidation, crystallites present in coal have been easily terminated and
surface-passivated, which is the method by which coal-based CDs were formed [42–44].
The production method of CDs created using chemical oxidation utilizing powder of
carbon as precursor carbon source was also attributed by Leblanc’s group to the breaking off of particles of graphite buried in the huge carbon skeleton, which resulted in the
creation of tiny particles with oxidized surfaces. Strong acids were utilized in all of the
aforementioned literatures to create CDs, restricting the usage of chemical oxidation.
was used to effectively peel off GQDs from black carbon/GO or without side prod-
H
2O2
ucts in order to reduce the environmental risks associated with strong acids. However,
this method needed auxiliary catalysts or high temperatures [45–47]. More importantly,
bulk carbon compounds that were used as precursors had poor yields and low PLQYs.
These limitations were anticipated to be alleviated by t he tin y compounds used as
+ conc. H2SO4or oxidants like H2O2and FeCl3. This method
3
was refluxed for 12 h. The produced CDs have
3
,carbonsoot[35],
3
wasusedtorefluxcarbon
3
as oxidizing agent, and amino group containing
3
2+
2
ions.
car-
2
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