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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5882_Библиотеки_им_академика_М_И_Перельмана.pdf
Carbon-Based Nanostructured Materials: Designing … 45
3.2 Hydrothermal and Solvothermal Techniques
This synthesis method involves crystallizing a material under low temperatures and
high pressure. Several reactions take place during this process that occurs in an
aqueous or non-aqueous media. Typically, this technique uses a stainless-steel autoclave that can produce relatively low temperatures (above room temperature) and
high pressures, allowing those insoluble compounds to form complexes in the used
solution. Commonly, solvents are employed, and the combination of some parameters like temperature, pressure, synthesis time, type of solvent, pH, surfactant, and
type of material (organic or inorganic) can directly affect the properties of the final
product, such type of nanocrystal, surface area, purity, agglomeration, and particle
size, among others [12, 13].
The solvothermal technique is a one-step procedure that allows the formation
of nanomaterials with high production yields with low requirements. The method
permits a uniformly heated material and low reaction conditions, which allows the
manipulation of the particle diameter and shape. As in hydrothermal methods, in
solvothermal synthesis, low temperatures and high pressures are required. Also, the
solvothermalmethod uses some organic solvents that, in combination with the control
of parameters such as temperature, pressure, and solvent type, can produce materials
with different characteristics such as crystallinity, purity, particle size, and surface
area [12–15]. The produced materials with these synthesis methods can be used
for environmental applications as a photocatalyst [12], supercapacitor, or electronic
applications [13–16], depolymerization of hardly degradable wastes such as plastics
[15], energy storage, medicine or pharmaceutical, and solid-state light emission [14].
3.3 Microwave-Assisted Technique
This synthesis method was developed as an eco-friendly and rapid technique
to produce various nanomaterials. It is reported that the microwave assisted is
commonly used to synthesize organic and inorganic nanomaterials. The primary
distinction between traditional methods is that this technique employs microwave
radiation to heat the solution along with all the reactants. The method is based on
the facility of a material to gain energy and transform it into calorific energy, a few
compounds and elements have this property. Jiang [17] describes three paths in which
this can occur: (a) By a pretreatment of some organic precursors with microwaves,
allowing the absorption of the energy by the reactants. (b) By avoiding the use of
precursors with metals on them. (c) Finally, by using water or polar molecules since
these polar molecules have an electric dipole moment and can generate heat by
this. The microwaves are electromagnetic radiations that have low energy and can
heat uniformly by increasing the collision between all the molecules in the mixture,
which reduces synthesis times [18–20]. The main advantages of this method are fast
crystallization, faster nucleation, nanomaterials with reduced diameter, low reaction
46 V. Esparza-Cordero et al.
times, uniform heating, high purity, and higher yields compared with other synthesis
methods [17].
3.4 Chemical Oxidation Synthesis
This method consists of the mixing of a high oxidant with a precursor material. This
method is commonly used because of r apid reaction times and facile escalation. This
method is based on that the precursor material is oxidized by the oxidant when the
solution is heated, producing precursor oxides. The diffusion and oxidation reactions
occur in the solid–liquid phase of the oxidant solution and the precursor. The size
of the final nanomaterial will be a function of the stirring speed. Newly developed
methods use ultrasonic mixing. Ultrasonic waves cause a collision between the solid
phase; the liquid is thinned, generating tiny bubbles allowing an expansion and rapid
collapse, generating strong waves that increase contact surface area, promoting the
mass transfer in the interface of the two phases [21, 22].
As shown in Table 1, several carbon-based nanohybrid materials have been used
for numerous applications, such as energy storage and the development of new electronic devices [13, 23–25]. The synthesis methods can be based on graphite, activated carbon, or graphene, but also some organic compounds are reported, like urea,
melamine, or chitosan. Some of the applied synthesis methods require high temperatures of up to 700 °C for about six hours [26]; these high temperatures can raise the
cost of the final products. However, because of the novel materials’ multi-proposal
capabilities or their performance, the synthesis costs of these materials are worth
it. Most of the synthesized materials were employed for environmental applications
such as the photocatalytic removal of synthetic pollutants like rhodamine or synthetic
dyes, which can act as endocrine disruptors or modify some natural processes in
natural streams. The novel photocatalytic pollutants have enhanced optical properties and can be activated by using artificial sources of light; however, some of these
can remove the pollutants mentioned above under visible light, this property can
make them feasible for future environmental applications [25, 27–29].
4 Properties of Carbon-Based Nanostructured Materials
As mentioned previously, combining the different states of carbon with other
atoms in synthesizing nanomaterials can create a new material with different structures and properties. This section describes carbon materials’ thermal, mechanical, optoelectronic, antimicrobial, and biological properties. This section describes
the thermal, mechanical, optoelectronic, antimicrobial, and biological properties of
carbon materials.
Ta bl e 1 Synthesis methods of carbon-based nanohybrids and their applications
Nanomaterial Precursors Synthesis method Applications References
Graphitic carbon
nitride-strontium oxide
Urea (CH4N2O), strontium nitrate (Sr
(NO
), and activated carbon
3)2
Green microwave-assisted approach Energy storage and
environmental applications
[25]
(photocatalytic applications)
Polyaniline grafted
graphene oxide
Graphite powder and vinyltriethoxysilane
aniline
Modified Marcano method Electronic applications [24]
nanohybrid
Carbon
nanotube-bridged
MoS
/ZnO nanohybrids
2
Sodium dihydromyldimolate
(Na
MoO4·2H2O), the L-cysteine
2
(C
((CH
S), zinc acetate dihydrate
3H7NO2
COO)2Zn·2H2O), and commercial
3
Hydrothermal method Photocatalytic removal of
synthetic pollutants and
disinfection of aqueous
matrix
[27]
carbon nanotubes
Mn2O3-TiO2decorated
graphene
Graphite-based
nanohybrid material
WO3-rGO nanohybrids Graphene oxide powder, sodium tungstate
Carbon nanotubes with
inorganic compounds
nanohybrids
Chitosan-coated iron
oxide/graphene
quantum dots
Graphene powder, titanium isopropoxide,
and manganese acetate
Calcium chloride (CaCl2), melamine, and
ammonium sulfate
(Na
2WO4
)
Cr(NO3)2.9H2O, Fe(NO3)2.9H2Oand
pristine multi-walled carbon nanotubes
FeCl3·6H2O, graphite powder, and
chitosan
Sol–gel method Selective dopamine sensing [30]
Simple pyrolysis method Detection of dopamine [26]
Hydrothermal method (modified
Hummers’ method)
A two-step synthesis method by
co-precipitation and
Detection of NO2at low
temperatures
Anode materials for
lithium–ion batteries
[31]
[32]
ultra-sonication-assisted route
A reported method that uses an
in situ catalytic
Diagnosis and cancer
treatment
[33]
phosphate polymerization reaction
(continued)
Carbon-Based Nanostructured Materials: Designing … 47
Ta bl e 1 (continued)
Nanomaterial Precursors Synthesis method Applications References
Fe3O4@SiO2@alginate/
FeCl3·6H2O, FeCl2·4H2O, and citric acid Co-precipitation method Drug delivery [34]
carbon
Quantum dots
nanohybrid
Te-doped black-P
nanoflakes/aramid
Kevlar, 1-methyl-2-pyrrolidone, and
carbonyl iron powder
Vacuum extraction and freezing
drying method
Ultra-broadband microwave
absorption
[35]
nanofibers/carbonyl-Fe
nanopowder aerogel
rGO-based Fe2O3/CuO/
PANI
Graphite powder, Fe (NO3)3.(H2O)9,and
Cu(NO
3)2
·3H2O
Hydrothermal method (modified
Hummers’ method)
Energy storage [36]
quaternary nanohybrid
SrO-mpg-CN/TiO
nanocomposite
Guanidine hydrochloride, Ludox HS40
2
colloidal silica, titanium chloride, and
strontium hydroxide octahydrate, and
Thermal condensation of an organic
compound in the presence of silica
nanoparticles
Photocatalytic removal of
synthetic pollutants
[37]
cuprous chloride
Carbon dots with ceria Taurine, ammonium ceric nitrate, sodium
molybdate
Molybdenum sulfide/
graphitic carbon nitride
(Na2MoO40.2 H2O), and thiourea
(H
NCSNH2)
2
Thermal decomposition method Photocatalytic removal of
[29]
synthetic pollutants
Sono-chemical method Substrate for solar cells [23]
nanohybrid
Dy2O3/graphitic carbon
nitride
Dysprosium (III) nitrate hydrate (Dy
(NO
.6 H2O), and melamine
3)3
Hydro-thermal process Photocatalytic removal of
synthetic pollutants
[28]
Nanohybrid
48 V. Esparza-Cordero et al.
Carbon-Based Nanostructured Materials: Designing … 49
4.1 Thermal Properties
Carbon materials also have high thermal resistivity, so their performance under
elevated t emperatures is better than that of other materials. Carbon materials are
porous and can adsorb solid impurities and even separate gases. Another thermal
property is weldability since carbon materials have excellent heat conduction and
catalysis performance due to their high stability and ability to combine with various
atoms.
4.2 Mechanical Properties
The main mechanical property of carbon-based materials is the resistance in
their different structures due to covalent bonds, which prevents deformation. The
maximum tensile strength of carbon is 15 MPa for graphite and 3500 MPa for carbon
fibers. The Young’s modulus of carbon ranges from 4.1 GPa for graphite to 228 GPa
for carbon fibers. Due to the hexagonal crystalline structure in carbon-based materials and the strength of the chemical bonds that cause this cell repetition, properties
such as ductility, hardness, and resistance are attributed to it [1, 38].
4.3 Optoelectronic Properties
Recently, carbon-based materials have been increasingly used in new applications, such as solar cells, advanced oxidation processes, and biosensor design.
However, carbon-based materials are synthesized in nanometric sizes such as
quantum dots, carbon nanotubes, or hybrid nanomaterials with inorganic semiconductors to generate greater quantum efficiency. Graphene is a zero band gap semiconductor material with a Dirac cone. Additionally, mobility is a vital factor for the
electrical properties of semiconductor materials and for determining their potential
electronic applications. Carbon materials with highly anisotropic transport properties can conduct electricity. Furthermore, doping the carbon material with other
compounds can enhance its electronic properties [1, 39, 40].
4.4 Antimicrobial Properties
Carbon-based nanomaterials have an antimicrobial property, and this characteristic is
mainly related to their size, compassion, and the chemical modifications that they can
present on their surfaces. Likewise, these nanocomposites reduce the surface/volume
ratio, which is essential. Since this causes the destruction of the cell wall, generating
50 V. Esparza-Cordero et al.
Fig. 5 General mechanism of action of CNMs as antimicrobials
an inhibitory effect [2, 41, 42]. The general mechanism of action presented by the
CNMs is destruction. This organelle provides the bacteria with morphology, supports
it in addition to osmotic regulation, and protection against mechanics to stress and
resistance; when destroyed, this component can cause its dysfunction and leakage
of cytoplasmic components, which generates structural damage in addition to the
physical isolation of the cell from its entire biological environment. In turn, due to
the size of the nanomaterials, these can penetrate the microbial cells and generate
oxygen-based radicals, which are non-selective reactive species. The inactivation of
bacteria can take place in an indirect way, where the nanomaterials are functionalized
with metals; these nanomaterials provoke an electron transfer to the membrane cell,
damaging it, which generates oxidative stress and damages structures such as DNA
and microorganisms’ micro-biotic mitochondria and therefore inhibit their growth
and survival, as well as prevent cell division, Fig. 5 [43–47].
Each CNM has specific properties that trigger antimicrobial action mechanisms,
such as carbon quantum (CD); their chemical structure is directly related to the central
nanomaterial and the activated groups of the nanomaterial that can react on the surface
of the CD. In addition, the system of CDs will depend strictly on the materials used
for the synthesis and the controlled parameters during the synthesis. It has been
shown that positively charged CDs have electrostatic interactions with the cell wall,
promoting the internalization of these substances and causing the death of the cell
[3]. These electrostatic interactions occur with the following groups: −OH, −COOH,
and −NH
, causing electrostatic interactions with the opposite charge group of the
2
bacterial membrane [42]. It has been demonstrated that CD has excellent photoactivity, which promotes the production of reactive species that oxidate the bacteria
cell wall, causing the depletion of the bacteria population. This property is based on
its ability to absorb light and transfer energy to the oxygen molecules present in its
Carbon-Based Nanostructured Materials: Designing … 51
environment. When the CDs are illuminated with adequate light, the electrons are
excited and can transfer energy to nearby oxygen molecules, thus generating super-
−
oxide (O
) and hydroxyl radicals (·OH), which, as mentioned above, can damage
2
the cellular structures of microorganisms and inhibit their growth and survival [47].
Carbon nanotubes (CNT) interact directly with cell walls and membranes, generating
cellular damage. The diameter of CNT is an important property for the correct inhibition of pathogen microorganisms with higher disinfection rates at smaller diameters
(≈1.5 nm), which produces a higher contact surface area with the cell wall, acting
as needles crossing the Diane cell while larger diameter ones only cross through the
lateral membrane (≈15–30 nm), which is also harmful to the cell [48].
The performance of graphene oxide (GO) as an antimicrobial agent will depend on
the purity of the precursor materials, the size of the synthesized nanosheet, the final
concentration of GO in the final nanomaterial, and the experimental time used. The
general mechanism of action is given by (i) oxidative stress, derived from the penetration of the nanocomposites, which, when internalized, generates reactive oxygen
species (ROS) such as intracellular superoxide, which oxidizes cellular components;
(ii) the presence of nanosheets and their sharp edges, these are capable of generating damage to bacterial structures such as the wall cell and the plasma membrane,
causing the escape of the internal components of the cell and therefore the death of
the microorganism, an effect known as nanoblade; and (iii) Wrapping or Trapping
(WT), the capture mechanism, where the bacteria is biologically isolated from its
external environment, generating metabolic deterioration, stopping cell propagation,
and avoiding cell feeding; this is a typical mechanism observed in a nanocomposite
in solution [49–52].
The antibacterial mechanism of fullerenes occurs in different ways in both types
of bacteria. In Gram-positive bacteria, cell wall deterioration occurs caused by the
generated reactive species, which cause a modification in the composition of the
phospholipids present in the cell wall and increase the permeability of the cell
membrane. Gram-negative cells change the portions of the cell wall components,
causing cyclopropane fatty acids to increase while unsaturated fatty acids decrease.
The electrostatic force of the fullerene is essential in the inhibition of microbial
activity; these forces will depend on the type of fullerene (C
and C
–NH2); in turn, it has been observed that oxygen can significantly increase
60
–OH, C60–COOH,
60,C60
the generated ROS and, thus, lead to a higher depletion of the bacteria population
[2]. Also, conductivity is a desired property in the newly synthesized carbon-based
nanomaterials, which can promote higher production of ROS and, as a result, higher
bacteria inactivation compared to those materials with lower conductivity values,
such as graphite oxide and GO. The specific surface area is another property that
gives antibacterial activity to graphene materials. It has been shown that GO with
a higher surface level provides more antibacterial activity for all types of bacteria
[53]. Carbon-based nanomaterials are excellent antimicrobial candidates, presenting
themselves as an alternative for microbial control; this characteristic was derived
from the different properties offered, the nanomaterials’ typology, and the microorganism’s very nature. However, research is still needed to understand the precise
mechanisms of action.
52 V. Esparza-Cordero et al.
4.5 Biological Properties
The diversity of carbon-based nanomaterials (CNMs) is given by the structural
conformation of carbon atoms, which forms a variety of carbon allotropes. These
nanomaterials own biological properties that make them of huge attention for research
and applications in biomedicine. Carbon nanocomposites present carbon atoms with
2
hybridization, such as the case of fullerenes, carbon nanotubes (CNT), and
sp
graphene and its derivatives; however, nanodiamonds (ND) present a sp
conformation, and carbon dots (CD) and graphene quantum dots (GQD) are made
2
up of carbon atoms with a mixture of sp
and sp3hybridization. This characteristic
determines that CNMs have different dimensions (1–100 nm), which is an essential characteristic due to their small and adjustable size distribution, comparable to
essential biomolecules like DNA and proteins [54]. This property makes them good
candidates for serving as carriers for the cellular uptake of therapeutic payloads,
Fig. 6.
All CNMs have the functionalization capacity; this characteristic is achieved from
covalent and non-covalent methods, where modifications are generated in the electrical hydrophilic character, as well as in mechanical and optical properties. Within
non-covalent methods, it is achieved through π–π stacking, van der Waals forces,
and electrostatic forces. The functionalization by the covalent method is carried out
3
atomic
Fig. 6 General scheme of the biological properties of CNMs
Carbon-Based Nanostructured Materials: Designing … 53
through simple oxidation, which is why all compounds with oxygen are excellent
for reacting with some functional groups or polymers. These chemical modifications
allow for the enhancement and control of the properties of carbon nanomaterials,
making them useful in a wide range of applications [55].
Regarding the biocompatibility that CNMs may exhibit, it is determined by size,
dose, exposure time, cell type, and surface chemistry; the present materials influence
this feature. Some studies have shown that specific carbon nanomaterials can have
cytotoxic effects and generate inflammatory responses in cells and tissues. However,
research has also demonstrated the biocompatibility and potential benefits of these
materials. Carbon nanomaterials have a three-dimensional structure with a large
surface area, giving them a high surface-to-volume ratio. This property allows a more
significant interaction with biological molecules and a higher capacity for carrying
molecules, making them excellent candidates for controlled drug release. Among the
various materials, graphene quantum dots (GQDs) have shown in several studies that
they are biocompatible with cells and non-toxic to them. These nanomaterials have
a size that ranges between 20 and 60 nm, allowing them to penetrate cell membranes
readily. GQD suspensions are stable in the presence of electrolytes and lower pH.
They also exhibit luminescence and fluorescence, which allows the use of these
nanomaterials in biological studies, including biosensing and bioimaging [42, 47].
Similarly, carbon dots (CDs) exhibit excellent biocompatibility, allowing the
biological activity even at high concentrations. Also, the surface of CDs has good
−
stability and solubility due to their hydrophilic groups such COOH
−
. They also possess photoluminescence (PL) properties, including fluorescence
OH
,NH2, and
and phosphorescence, which are influenced by factors such as emission from the
central and surface states. Their photostability benefits long-term cell imaging [46].
Diverse physicochemical properties characterize graphene and its derivative GO. GO
−
is hydrophilic and has a high specific surface area. It can have OH
, epoxide, ketone,
and R − COOH groups on its surface, which significantly modify its properties and
enable biochemical reactions and bioconjugation on the basal plane and edges of
GO. Additionally, GO has mechanical strength and behaves as a semiconductor due
to its low oxidation rate. Graphene oxide is considered a candidate to be used as a
scaffold in tissue engineering for the proliferation of muscle tissue due to its property
of being an excellent conductive biomaterial.
GO can absorb proteins, and this characteristic can avoid proteolysis. Protein
binding depends on the type of protein and the polypeptide, as they can be adsorbed
on the GO surface through electrostatic and hydrophobic interactions, H-bonds, and
van der Waals forces. GO can also be conjugated with antibodies and is an excellent
catalyst support [6]. Carbon nanohorns (CNH) were discovered by Iijima in 1998.
These present a tuba-shaped structure made from a single sheet of graphene. One
characteristic of SWCNHs is their broad surface area and numerous horn interstices,
allowing for the adsorption of large quantities of molecules and providing suitable
sites for incorporating and protecting drugs. SWCNHs can spread throughout the
body and cross the plasma membrane of epithelial cells through transcytosis, a characteristic given by its bioadhesive properties. It has been observed that SWCNHs
have low toxicity; however, it has been shown that these compounds can accumulate
54 V. Esparza-Cordero et al.
in various tissues after administration in animals, especially in macrophage cells of
the mononuclear phagocytic system. At the same time, it has been observed that
the oxidation of these components generates excellent biocompatibility and better
elimination. One way to regulate the stability and solubility of SWCNH is functionalization in various solvents because they have an extremely hydrophobic surface
[56].
Carbon nanotubes (CNTs) are carbon allotropes discovered in 1991 by Iijima.
One parameter to determine the properties of nanotubes is the number of concentric walls that make up a CNT. Usually, a single nanotube has a diameter from 1 to
2 nm, while the diameter of multi-walled carbon nanotubes (MWCNT) can reach
approximately 100 nm. The chemical composition of the nanoparticle’s crystalline
structure provides the nanomaterials with several properties, such as hydrophobicity
or hydrophobicity, charge, dissolution, photocatalytic activity, etc. These characteristics will drive nanoparticle interactions with their environment, especially protein
adsorption (corona). Alternatively, the surface functionalization of CNTs is achieved
by covalent oxidation or in combination, which results in the union of functional
groups that contain oxygen on the external wall surface, as well as the opening
of the CNT. Nevertheless, functionalization can occur by assimilating molecules
such as DNA, polymers, carbohydrates, or other derivatives. The properties of these
nanocomposites determine their application in the biological field as biosensors since
they have been used on electrode surfaces, where a rapid electron transfer is generated
with greater sensitivity for electrochemical detection. They also possess fluorescence
properties for image detection. CNTs provide an appropriate surface for cell growth
and can help improve neural signaling. CNTs could also enter cells, regardless of the
external functional groups, allowing the exchange of substances inside and outside
the cell, gene transfer, and protein delivery. This property can be used to develop
gene silencing therapy due to the brief delivery of small interfering RNA (siRNA)
to the cytoplasm. Leveraging the photothermal properties of CNTs with NIR laser
stimulation has been considered to treat cancer directly [57].
Carbon nano-onions (CNOs) due to their hydrophobic carbonaceous composition are almost non-soluble in water and in some organic solvents. On the other
hand, they present a variety of properties for biological applications, such as cellular
internalization, diffusion in tissues due to interaction with the cell membrane,
generated by the almost spherical structure, as well as the functionalization of its
surfaces by biomolecules, which gives it the ability to be a candidate to be used in
obtaining cellular images [58]. For their part, fullerenes can be used as antimicrobial antiviral agents or for eliminating contaminants when illuminated in the visible
1
region (535 nm) and generating singlet oxygen (
O2) with a high quantum yield of
0.96. Singlet oxygen, in comparison with other oxidant species, has a longer lifetime
(τ) of 2–4 μs compared to 1 ns for hydroxyl (˙OH), in addition to being a selective
oxidant due to its low reduction potential [ 59]. Carbon nanomaterials are candidates
for use in the field of biology. Synthesis methods, including concentration, size, and
functionalization, guarantee that these materials are harmless and, in combination
with enzymes, antibodies, drugs, or metallic-based nanomaterials, can be applied in
various areas of biomedicine (shown in Fig. 6)[60].