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28 Vinayak Sahu
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precursors. Chen’s team still used HNO3as the oxidant while synthesizing PDs which
have 55.7% PLQY using o-phenylenediamine (o-PD) as the source of carbon [48]. Yu’s
team [43] was able to overcome this weakness. Low-temperature method using one pot
to create red-emissive PDs by oxidative polymerizing p-phenylenediamine (p-PD) at
80 °C using FeCl
boundaries, huge uniform dots, and monodispersed dots were all involved in the creation of
CDs. In addition to avoiding the need of strong acid, this innovation made it simple to make
long-wavelength-emissive CDs. One of the first methods for the synthesis of CDs, the chemical
oxidation approach, allows for the quick and efficient creation of multi-colour-emitting CDs
from soot, coal, GO, CFs, and so on. Centrifugation, neutralization, and dialysis are some of
the time-consuming steps and difficult post-treatments that are often required by the procedure. Moreover, to get CDs with high PLQYs, passivation of the surface is a crucial phase.
Furthermore, using acid oxidizing agents causes more environmental problems and falls
short of the desire for green preparation. Even while the use of simple nonacid oxidizing
agent and small precursor’s molecule can reduce environmental risks and produce CDs good
PLQY, it remains difficult to produce CDs with particular groups and intended emissions. As
a result, chemical oxidation cannot be broadly applied.
as the mild oxidant [49] and p-PD oligomer clusters, tiny dots with distinct
3
3.2.2 Laser-abscission method
The typical laser-abscission method uses a laser beam of high energy to attack a target
of carbon, which results in the exfoliation of nanoparticles of carbon that are then functionalized to create CDs. It is important to note that the laser-abscission method can directly create CDs without further passivation by carefully choosing the suitable carbon
target or its medium. Sun’s group [48] was the first to describe using a wavelength of
1,064 nm, Nd:YAG laser with a combination of cement and graphite powder as the carbon target to make CDs with 10% PLQY of in 2006 that emits various colours providing
a novel technique for making CDs and demonstrating the viability of CDs for bioimaging, but with evident flaws such preparation at high temperatures and low pressures
(900 °C and 75 kPa) and the requirement for organic species to passivate the CDs. Du’s
[51] team created single-step laser-abscission preparation of CDs by improving experimental settings, considerably streamlining the operations in order to skip the challenging preparation phases. In a nutshell, graphite powders dispersed in PEG200N were
exposed to a Nd:YAG laser for 2 h while being helped by ultrasound. This resulted in
combined preparation and passivation of CDs of 3.2 nm sizes and PLQY 5%. The pulsed
laser’s creation of a high-pressure, high-temperature in PEG200N solvent, which caused
graphite particles to heat up to plasma state, may be the cause of CD generation under
laser irradiation; pure CDs were created by the subsequent condensation of carbon
plasma; their surfaces were immediately oxidized by O atoms that had been broken
down; and subsequent reactions with PEG200N or its fragment molecules produced by
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the plasma ultimately led to the creation of CDs with carboxylate groups [49]. These
discoveries clarified the intricate phases of the laser ablation method, but the issues of
poor yields, low PLQYs, and non-tuneable morphology and PL of CDs persisted.
Yang’s [41] team created luminous CDs by laser-irradiating graphite flakes dispersed
in PEG1500N solution. They then adjusted the laser pulse width to affect nucleation and
growth,successfullycreatingCDswithaveragediametersof3,8,and13nm.Thiswork
was inspired by the findings shown earlier [50]. Similar to this, Li and colleagues [41, 42]
confirmed that the input of laser fluence could readily adjust the sizes and PL emissions
of CDs using a long-pulse-width laser conducive to research the link between optical performance and sizes of CDs. Instead of using bulk carbon materials, they used toluene as
a precursor for the carbon, eliminating the need for passivators like PEG. By using a
real-time detection system to track the PL changes of the solution, the formation process
of CDs was revealed, showing that, first, large pieces of graphene were formed as an
intermediate. As the irradiation continued, the graphene increased and superimposed to
form large multi-layer grapheme. Finally, the huge multi-layer graphene was laser ablated to produce CDs [51]. Kang’s group [52] also claimed that GQDs’ surface flaws were
more likely to become functionalized with shorter laser wavelengths, and that multiple
GQD surface states could be created by adjusting the laser’s wavelength. The discovery
of the link between the laser’s wavelength and the functionalization of CDs gave rise to a
fresh idea for modifying their shape and PL [52].
The discovery of the connection between the laser’s wavelength and the functionalization of CDs gave rise to a fresh idea for modifying their shape and PL. One of the
early approaches to creating CDs was the laser ablation process, which has the advantage of being easy to use.
3.2.3 Electrochemical synthesis
Good conductivity carbon materials are typically employed as working electrode and
sourcesofcarboninelectrochemicalsynthesis. Oxidation reaction occurs in the
anode once a certain voltage is applied, which involves the separation of CDs from
carbon precursors. Additionally, the electrolyte may implement bottom-up electrochemical synthesis of CDs by serving as a carbon source [53]. Sham and colleagues [56]
used the electrochemical method for the first time in 2007 to directly make emitting
blue light CDs that have 6.4% PLQY.
For the preparation of water-soluble and luminescent CDs, three electrode systems
were used: MWCNTs as carbon source covered carbon paper as the working electrode
and as a counter electrode Pt-wire used, as a reference electrode Ag/AgClO
nitrile solution-containing tetrabutylammonium perchlorate (TBAP) as the electrolyte.
According to one theory, CDs were exfoliated into the electrolyte solution when TBA
cations broke their structures near the flaws during electrochemical cycling after intercalating into the gap of MWCNTs [54]. This research introduced a novel strategy for the
,andaceto-
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direct synthesis of water-soluble CDs, although yields, PLQYs, and fluorescence tuneability of CDs needed to be improved. After that, CDs with a diameter of 2.0 nm on an average were prepared using graphite rod as the working electrode and phosphate buffer
solution as the electrolyte of a three electrode system, respectively [55]. A two-electrode
system using ammonia solution as the electrolyte and the prepared disc electrodes as
the working electrode and counter electrode was used to fabricate CDs in another instance, reducing the cost of production. In this case, petroleum coke was used to create
disc electrodes and this was a cost-effective solution. In addition to these, ionic liquids
(ILs) were employed as the electrolyte to complete the electrochemical synthesis of CDs,
and graphene sheet and screen-printed carbon electrodes were used as electrodes. The
hydroxylation or oxidation of graphite and subsequent release of CDs from the anode
might be the results of the production of oxygen and hydroxyl radicals by anodic oxidation of water [56]. Cell imaging and photovoltaics can use the produced CDs because of
their high degree of crystallinity, superior water solubility, and limited size distribution.
Despite the literatures mentioned above, the issues of poor yields, low PLQYs, monotonous CD fluorescence, and essential dialysis operation persisted. Li et al. [57] prepared
the GQDs were obtained by electrochemical oxidation method with NaOH aqueous solu-
3
¯
tion, saline solution of PO
buffer and aqueous solution of KCl as electrolyte. Alterna-
4
tively, Pang and colleagues [58] showed a controlled electrochemical approach for the
size-selective synthesis of monodisperse luminous CDs, although it was unable to significantly alter the PL emissions of CDs.
Fortunately, Kang’s team [59] was able to adjust the alkali-assisted electrochemical
system’s current intensity and produce a series of CQDs whose PL is size-dependent
that changed from brown to blue as diameters declined from 3.8 to 1.2 nm. Additionally,
utilizing acids as the electrolyte resulted in no CQD production, demonstrating that the
alkaline environment was the key element. In another instance, this group created various PL emissions and sizes of CQDs with photo increased catalytic activity by varying
the parallel spacing of graphite rods, utilizing two graphite rods as both anode and
cathode and ultrapure water as electrolyte [60]. However, the two aforementioned literatures produced little CQDs. Liu and colleagues [41, 44, 47] originally presented a simple
bottom-up production approach of CDs, finishing collection of solid-state CDs after becoming aware of the difficulties and needs for CDs synthesis. The creation mechanism
of CDs was hypothesized based on structural properties. Nitriles were polymerized and
carbonized to create CDs; at the same time, functional groups with positive charge produced by ILs passivated the surface of CDs. Importantly, the produced CDs with a PLQY
of more than 10% and exceptional solubility in water may be used for cell imaging and
ion detection. Although the PLQYs and CD yields were not much increased by this
study, it did offer a fresh notion for improving the electrochemical process.
The electrochemical method can produce CDs with water-solubility (mostly GQDs)
with high crystallinity and uniform size that are suitable for catalytic applications [59, 60]
and photovoltaic uses [55], and it is also environmentally benign. Importantly, by modifying the current density or potentials, CD diameters and PL hues may be altered. However,
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this technology has clear drawbacks, like poor PLQY, low yields, and a time-taking process, making it challenging to obtain CDs on large scale for a low cost.
3.2.4 Hydrothermal method
The main steps in the hydrothermal/solvothermal method are as follows: precursors
are dissolved in water or other solvents, and then they are put in a tightly sealed container that is where they go through carbonization and polymerization or exfoliated
to form CDs under relatively high pressure and temperature.
By slicing oxidized graphene sheets (GSs) into GQDs with a 5% PLQY, Wu’sgroup
[61] first revealed a hydrothermal method. The elimination of bridged oxygen atoms
from the epoxy lines caused by certain ultrafine GS particles that broke off during the
hydrothermal process might be the genesis mechanism for GQDs [61]. These results offered a new, simple method for producing GQDs, although poor PLQYs, non-uniform
GQD sizes, and pre-treatment of source materials needed to be addressed. Zhu et al. prepared amino-functionalized GQDs using ammonia solution as a solvent by the solvothermal method, giving GQDs, up to 29% of PLQY and a narrow size distribution. By
adjusting the temperature of the reaction, PL colours of GQDs were tailored from blue
to yellow, allowing GQDs to be used in multi-colour LEDs and bioimaging [62]. However,
this study continued to employ expensively oxidized GSs as the carbon source. In order
to get out of the situation, sustainable and replenishable leaves [22, 63] were used as
carbon sources to create CDs, greatly lowering the prices. Specifically, poplar leaves
were used as a carbon source to obtain CDs with a 10.64% of PLQY and a high throughput of 1.4975 kg by hydrothermal processing, providing an environmentally friendly
method for mass-producing CDs at a low cost. Notably, CDs were advantageous for electrocatalytic water splitting, sensing, and bioimaging due to their strong photostability
and minimal cytotoxicity. Additionally, taxus leaves were used to create deep red emissive PDs that shown significant promise in the fields of optoelectronics and biomedicine
because to their deep red PL, good PLQY of 31%, and narrow full width at half maximum [63]. Using a one-step solvothermal process, waste-expanded polystyrene was also
transformed into high-value CDs in addition to leaves [64]. However, the difficult postprocessing to eliminate unreacted by-products was essential for the top-down hydrothermal/solvothermal approach, greatly increasing preparation time and expense. Dai’s
team [19, 39, 67] created a productive hydrothermal approach to synthesis GQDs that
only uses starch as a precursor in order to overcome the drawback. In a nutshell, the
starch dispersed in deionized water was heated at 463 K for 2 h to obtain the products
only containing GQDs, water, and carbide precipitate. After centrifugation, the purified
GQDs were collected [65], discarding the time-consuming post-treatment and providing
a straightforward and affordable hydrothermal method to produce CDs. Small molecules as precursors have been shown to be more adaptable in altering the structural
and optical characteristics of CDs during hy drothermal/solvothermal processes than
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bulk materials. The tiny chemical L-ascorbic acid was initially used to create monodispersed blue-emitting CDs with a uniform size but a low PLQY of 6.79% by heating it to
180 °C for 4 h [66]. Fortunately, it was discovered that N-doped CDs obtained from chitosan and chitin had higher PLQYs and larger sizes than N-free CDs synthesized from glucose under the same hydrothermal synthetic conditions, indicating that molecular
precursors had a clear impact on the PLQYs and morphology of CDs. Yang’s team [67]
demonstrated that designi ng CDs with the usage of heteroatoms could change their
physicochemical properties very effectively and especially enhance PLQYs using citric
acid and ethylenediamine (EDA) as the respective carbon and nitrogen sources. To create N-doped CDs, anilines and their derivatives were often used as nitrogen sources [28,
68–73]. Using oPD, m-phenylenediamine (mPD), and pPD, respectively, with dithio salicylic acid in acetic acid via solvothermal reaction, red-, green-, and blue-emissive CDs
with aggregation-induced PL and an optimal PLQY of 20.77% were created. These CDs
were then applied to white LEDs (WLEDs) and fingerprint detection [69]. Additionally,
CDs with adjustable PL from blue to near-infrared [68, 70, 71, 73], even CDs with dualemission [28], have been created by modifying amine species, adding amide auxiliary
[68], carbon sources [28, 71, 72], additional nitrogen sources [73], or adjusting amine species. The effective synthesis of triple-emission [72] for bioimaging and WLEDs shows
how widely applicable the hydrothermal method is. In addition to aniline, other nitrogen sources used to create N-doped CDs included urea [74] and EDA [75, 76].
3.2.5 Pyrolysis route
The steps that make up the common pyrolysis method include carbonizing carbon
sources at high temperatures. CDs are gathered following purification and after treatment process such chromatographic separation, dialysis, centrifugation, and filtration. However, the separating process can be stopped by encapsulating CDs with a
suitable template to restrain their devel opment and shape during pyrolysis [77]. In
general, it is separated into liquid-phase and solid-phase pyrolysis depending on the
variousstatesofcarbonsources.Liu’s group [105, 110] developed a pyrolysis tech-
nique to create CDs which is soluble in oil using anhydro us citr ic acid and surface
functionalization agent 1-hexadecylamine and octadecane as solvent 300, inspired by
the synthesis of semi-conducto r and magnetic nanocrystals. The resultant CDs had
various optical and structural features depending on the duration of reaction or capping agent used to control the depolymerization, breakdown, and pyrolysis process
[78]. This study demonstrated that the optical characteristics of CDs may be changed
by only altering the pyrolysis parameters such as solvents, agents, or duration of pyrolysis. It also provided an easy approach to synthesize CDs having good PLQY. The
development of very blue luminous CDs with a PLQY of 31.6–40.6% was later accomplished by Wu’s group [79] using a one-step pyrolysis in solid phase. In this procedure,
the disodium salt of EDTA was just igniting at 400 °C for 2 h without the use of any
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solvent or agent [79] facilitating the pyrolysis route. Similar to this, GQDs could also
be made by citric acid through pyrolysis, and after increasing the period of pyrolysis,
the result was GO because of a greater extent of carbonization [80].
The CDs produced by pyrolysis had simple manipulation and desirable PLQYs, but
their application potential in catalysis was limited by their non-uniform size and propensity to aggregate [81]. Although it was time-consuming and expensive, separation by
chromatographic could be employed to produce CDs with uniform size. Zaitsev [79]
et al. coupled the pyrolysis process and templating method. To be more precise, CDs
made by pyrolyzing citric acid were created using silica gel-containing immobilized
aminopropyl groups as a template to control their form. The sizes and shapes of CDs
produced by pyrolysis were also controlled using metal-organic framework materials
as templates [81– 83]. However, collecting CDs from templates required alkaline solution etching of the support, which was bad for the environment. Some publications
have created N-CDs having excellent PLQYs by sensibly choosing surface passivation
agents or precursors in order to enhance the structural and PL characteristics of CDs
produced by pyrolysis [84–87]. For instance, GQDs with N-doping with 59.2% PLQY
were prepared by one-pot pyrolysis using tris(hydroxymethyl)aminomethane as a doping material and surface functionalizing agent and for carbon source citric acid was
utilized [88]. These GQDs also showed a strong detectability of 2,4,6-trinitrophenol.
Additionally, citric acid and EDA were pyrolyzed to enhance the N-CDs with PLQY
of 80% [86], preparation of CDs desirable for biological imaging process. In a different
instance, N-CDs were produced by pyrolyzing ammonium citrate and showed strong
corrosion inhibitive properties [85]. A high PLQY CD can be made by pyrolysis, which
has numerous advantages including easy operation, inexpensive sources of carbon,
and preparation on large scale. Additionally, the hydrophobic/hydrophilic characteristics and doping of atom, kinds of CDs can be altered employing various surface functionalizing agents or suitable starting materials. Although the approach is labourintensive, consumes a lot of energy, and is unable to avoid the tiresome purification
and after-treatment it is required to produce high quality CDs of a consistent size. The
preparation of long-wavelength CDs by pyrolysis is particularly challenging, severely
restricting the use of CDs in biomedicine and optoelectronics.
3.2.6 Microwave treatment
The quick production of CDs is made possible by microwave treatment. It just takes a
few minutes. Reactants with polar molecules have a tendency to absorb microwave energy during the therapy and then transform it internally. The internal energy provided
by the microwave approach, in contrast to the solvothermal/hydrothermal method. In
the year 2009, Yang’s group [21, 31] developed using PEG200N and glucose by microwave
treatment. CDs with high PLQYs and multi-colour emission were not formed. Doping with
nitrogen was thought to significantly raise PLQYs and alter PL hues. As a result, N-CDs
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with emission of red colour and have 15% PLQY were created by microwave irradiating
inexpensive urea and citric acid as the nitrogen and carbon, respectively. The PLQY
of N-doped CDs could be increased to 40.2% when EDA was used in place of urea as the
nitrogen source [89]. In order to create red-emitting N-CDs with a 15% PLQY, Wang
et al. [34, 39] microwave-treated pPD in a solution of ethanol and water. Because of the
red-colour PL and excellent PLQY, N-CDs can now be used as nanothermometers in living cells [90]. Magnetic-fluoroscent N-CDs, doped with Fe, were also prepared using citric acid and EDA with FeCl
. These CDs, due to their superparamagnetic and fluorescent
2
behaviours, showed promise in multi-modal cellular imaging [91]. The application of
the aforementioned literatures in optoelectronics was, however, constrained by their
inability to prepare multi-colour PL CDs. Liu et al. [41] created CDs using microwave
irradiation and poly(ethylenimine) solution with glutaraldehyde (GA) added to it to provide an answer. They were able to create multi-colour luminous CDs with an adjustable
wavelength ranging from 464 to 556 nm [92] by altering the GA and PEI ratio. CDs were
prepared by the microwave methods, as a result, the multi-colour CDs were prepared.
Additionally, it was demonstrated that the microwave approach contributed to prevent
direct pep contacts or transfer of excessive resonance energy in order to produce resistant to self-quenching CDs in solid-state PL in a matter of minutes [89, 93–95]. Numerous
studies have revealed that large-size d raw materials can also be used to create CDs
using the microwave method in addition to small molecules. For instance, the cleaving
generation mechanism of GQDs [61] has provided insight. GO as the source of carbon to
create greenish-yellow luminous GQDs having 11.7% PLQY, using the microwave technique in an acid environment [96], but this study needed a 3-h reaction time and employed strong acids as the solvent, restricting its widespread use. In order to address
these drawbacks, Wang’s group [97] used microwave technology to manufacture BGQDs having 21.1% PLQY, while avoiding the need of strong acids and cutting the
30 min of reaction time. However, it was still necessary to investigate low-cost sources
of carbon. Based on this, Wang’s team [98] developed a one-pot microwave process to
make N-doped CDs with a high PLQY of 46% utilizing silkworm chrysalis as the natural
carbon source, thus lowering the cost of sources of carbon. More recently, Zhang’steam
[26] produced narrow-dispersed CDs on a kilogramme scale at low cost without the
need of time-consuming fractionalization techniques and just utilizing cheap industrial
surfactants as carbon sources. The reaction media can be quickly and uniformly heated
using a microwave approach, which drastically reduces the reaction time and increases
product yields. The microwave way is more practical, cost-effective, and time-saving
than previous approaches, showing great promise for widespread industrialization.
Furthermore, it has been demonstrated that a vast array of carbon-containing
materials are readily available for use as carbo n sources in microwave synthesized
CDs. As a result, microwave processing enables the fabrication o f multi-colour and
high-PLQY CDs by choosing particular precursors. As a result, this method is frequently used to create CDs. microwave-derived CDs, in contrast to hydrothermal/
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solvothermal CDs, have wilder size distributions and lower PLQYs, which causes them
to perform badly in fields like optoelectronics and biomedicine.
3.2.7 Other chemical methods
In addition to the methods mentioned earlier, extensive research has been conducted
to examine additional chemical techniques for the quick and effective manufacture of
CDs. By employing inexpensive, natural eggs of chicken as the starting material and a
quick one-step plasma-induced technique, Chen’s group [99] was able to significantly
reduce the reaction time. Yan et al. [100] converted benzoic acid in GQDs with blueemitting light. The two aforementioned literatures introduced novel techniques for
quickly synthesizing CDs, but they had one thing in common: they called for expensive specialized equipment. The ultrasonic method is unique in that it benefits from
low-tech requirements, cheap equipment, and easy manipulation. A simple ultrasonic
approach to create CDs was given by Lee and colleagues [101], Meral and colleagues
[102], Liu and colleagues [103], Yan and colleagues [104], Leblanc and colleagues [7, 105].
They used a variety of carbon sources including food waste, graphene, blueberries, citric acid, application of the generated CDs to ion lubrication, detection, and bioimaging,
and additive ma nufacturing. Orange-emission N-doped CDs, for instance, were prepared by ultrasonication technique [105] employing solvent-deionized water, oPD, and
citric acid as nitrogen and carbon and sources, and acting as the fluorescent ink for 3D
printing by embedding in so dium polyacrylate. More significantly, waste food was
transformed into CDs with blue emission having uniform size and great photo stability
on a large scale utilizing ultrasound irradiation [101]. However, the long wave length
emission or adjustable PL of CDs could not be produced using the ultrasonic technique.
There have also been other straightforward met hods for making CDs. For instance,
Zhang and colleagues [106] and Nandi and colleagues [107] employed the photo-fenton
reaction and the sono-fenton reaction, respectively, to massively produce GQDs utilizing
GO as a carbon source. These methods were proven to be simple, but they did not successfully address flaws like a lack of available raw materials. This is due to the fact that
external irradiations like sonication and ultraviolet light enhanced the Fenton reaction.
On the other hand, Liu’s team [108] showed how to produce graphite-based GQDs with
a size of 8 nm using a magnetron sputtering technique.
Additionally, a number of environmentally friendly and sustainable synthesis
methods, such as the Schiff-base reaction [21, 109–111], self-exothermic synthesis [20, 24],
co-polymerization reaction base catalysis, and reduction methods [16], have attracted a
lot of interest due to their advantages, including energy conservation, ease of use, and
lack of specialized equipment. For instance, Huang’s group [20] report a large-scale onepot synthesis of highly PL CDs utilizing Schiff-base condensation by only storing a combination of triethylenetetramine and p-benzoquinone at ambient temperature for 20 h.
This group developed a method to prepare CDs in bulk scale by mixing hydroquinone
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with H2O2and further adding EDA at room temperature [20]. This method was based
onthefactthataself-exothermicreaction made the organic precursors (hydroquinone and EDA) carbonized to form the carbon c ores of CDs. However, the sustainable
synthesis technique is still in its infancy and requires further work to improve its effectiveness and decrease the use of hazardous materials in the production of CDs on a wide
scale. Recently, Chen’s group [23] introduced a new rapid magnetic hyperthermia strat-
egy to produce multi-fluorescence CDs using carbamide and citrate with three different
cations as precursors in order to achieve green, quick, and large-scale CD production.
This method, which preliminarily possessed the capacity for industrial production [23],
fully exploited the magnetocaloric effect to quickly and easily synthesize CDs with a
–1
yield of 60% and a production rate up to 85 g h
. However, there was still room for
further cost reduction and productivity enhancement. In conclusion, a lot of work has
been put into thoroughly researching the creation of CDs, and a lot of progress has
been accomplished. Numerous methods, including chemical oxidation, laser ablation,
electrochemistry, hydrothermal/solvothermal synthesis, pyrolysis reaction, and microwave treatment, have been used to create CDs. Regardless of the technique used, the
ability to alter the PL hues, PLQYs, sizes, hydrophilicity/hydrophobicity, and surface
groups of CDs makes them extremely promising in a number of fields, including biomedicine, sensing, and optoelectronics. The hydrothermal/solvothermal approach is regarded as the best preparation technique for efficiently fabricating CDs.
More significantly, it can easily prepare specifically made CDs with a high PLQY,
multi-colour emissions, and a consistent size, making it widely used. Other chemical techniques, such as gaseous detonation [100], magnetic hyperthermia [23], self-exothermic reaction [24], and the aldol condensation method [27], have also been developed and paved
the way for industrial preparation in order to achieve green, quick, one-pot, simple, and
large-scale production of CDs. The vast majority of carbon-containing substances,
such as glucose, citric acid, GO, CNTs, gr aphite, coal, leaves, grass, durian, hair, and
even household garbage, have manifested as precursors [5, 6, 9–18], laying the
groundwork for inexpensive CD preparation. However, there are still unavoidable
drawbacks including ill-defined o ptical qualities and CD sizes, undesirable purity,
and intermittent manufacture that must be overcome, substantially limiting the application potential of CDs. Therefore, it is imperative to improve the current processes
and continue to research new avenues for the quick, effective, environmentally friendly,
scaled-up, and manageable production of CDs. It is common knowledge that improved
knowledge of the PL genesis of CDs is anticipated to fundamentally direct and improve
their synthesis methods.
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