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Materials Science, Coatings & Films
Nanomaterials have the advantage of having a large surface area, making it easier to express more efficient properties, and they have been widely applied recently in various fields. When designing new materials for specific applications, it is often important to control the shape, size distribution, surface properties, dispersion, and agglomeration stability of synthetic nanoparticles, as well as the elemental and nanocrystalline compositions of the materials. Nanomaterials have infinite potential.
- nanowire
- morphological characteristics
- nanograin
- nanoplate
- chemosensors
1. Introduction
In recent years, the importance of nanotechnology has become prominent in this era, where cutting-edge technologies, such as secondary batteries, batteries, and artificial intelligence, are in the spotlight. Nanotechnology, in particular, is a state-of-the-art ultrafine processing technology that requires a level of precision of one billionth of a meter. This has created new technology areas by horizontally connecting existing material fields, inducing synergy between existing academic fields and human resources, and contributing to minimization and performance improvements. In addition, it enables the exploration of the ultrafine world, which has been unknown thus far, and enables the manufacture of new materials, such as those needed for the cloning of animals and plants, using DNA structures and steel fibers. In the field of electronic engineering, the precision of nanometers is required, and, if this is realized, manufacturing technologies such as large-scale integrated circuits (LSIs) are expected to improve dramatically. Many nanomaterials are dispersed in the form of nanoparticles. However, other materials can also use nanostructures within them. For example, metal–organic skeletons can incorporate nanovoids into crystal structures and become host carriers for high concentrations of other molecules. These include active pharmaceutical components. When metal–organic skeletons are dispersed as nanoparticles in biocompatible fluids, they can access cells through surface changes and then release a variety of active and targeted drugs directly, where needed, in the body. Nanomaterials that have recently been in the spotlight include TiO2, metal nanowires (Cu, Ag, etc.), graphene, SWCNTs, DWCNTs, and MWCNTs, along with various other nanomaterials that are being studied [1,2,3,4,5,6,7,8,9,10,11,12,13]. Nanomaterials are already used in the form of synthetic nanoparticles in various consumer products, such as textiles, paints, sunscreen, and other medical products.
2. Nanomaterials
2.1. Nanoparticles
Nanoparticle refers to ultrafine particles whose unit of size is one billionth of a meter. Nanoparticles are a type of particle, belonging to the domain of nanotechnology, that manipulate molecules or atoms to create new materials, structures, machines, equipment, and devices; further, there have been studies conducted on their structures. Research materials related to nanoparticles include polymer nanoparticles, silica particles, large-pore mesoporous silica nanoparticles, sulfur compounds, etc. [21,22,23,24,25,26]. Nanoparticles, unlike linear nanowires, have a relatively round circular shape. Due to their large surface area, they exhibit stronger efficacy than microparticles in terms of antimicrobial properties and strength. There are cases in which nanoparticles are used to study the application of nanomaterials in drug delivery, photolysis, tensile strength improvement, regenerative treatment, oxidation catalysts, supercapacitors, energy storage devices, etc.
Polymer, metal, silica, carbon, and hybrid nanoparticles are different types of nanomaterials and are currently used in disease treatment, as well as in many other applications. Nanoparticles are often able to provide suitable features for providing nanoformulations with improved performance, including good drug dynamic profiles and processing efficiency in custom applications. The study can be applied to cancer therapy, chemosensors, biomedical applications, etc. [27]. In a prior study, a high yield strength (~396 MPa) and ultimate tensile strength (~451 MPa) were obtained after high-temperature extrusion and aging, which was achieved by designing a Mg-10Gd-4Dy-1.5Ag-1Zn-0.5Zr alloy via the multielement composite addition method. The potential and fine particles introduced by the extrusion process accelerated the precipitation rate of nanostructures, improving aging curing efficiency, as well as promoting the formation of more uniform and finer nanoconditions. Accordingly, prior research has suggested that introducing nanodeposit networks into fine structures is an effective strategy for developing high-strength Mg alloys.
2.2. Nanowire
Nanowire is one of the top 10 new technologies that will change the world and is currently considered one of the most efficient fields in nanotechnology. Nanowires refer to wire structures with a nanometer size. In the microworld, the influence of quantum mechanical effects is dominant, so these wire structures are sometimes called quantum wires. The term generally refers to nanowires with diameters of less than 10 nm to hundreds of nanometers. There is no particular limitation in the length direction of a nanowire. Nanowires are used in various fields, such as lasers, chemical sensors, transistors, and memory. The materials used include semiconductor silicon (silicon), chemically sensitive tin oxide, and gallium nitride (which is a light-emitting semiconductor). Research materials related to nanowires include nanowire Ni−Pd mixed-metal complexes, GaAs nanowires, Ta/InAs nanowires, Cu nanowires, silver nanowires, Ag-Doped CuV2O6 nanowires, etc. [33,34,35,36,37,38].
Yalcin et al. used cryogenic electron microscopy with multimodal functional images and a series of electrical, biochemical, and physiological studies. They also found that nanowires consist of cytochrome OmcZ and OmcS, which transmit electrons through a smooth stacking of hems across micrometers. The study can be applied to bioenergy, biofuels, sensing, synthesis, bioelectronics, and energy production [39].
In addition, atomic-resolution scanning tunneling microscopic images represent electronic state modulation in heterojunction regions with a length of five metal atoms (~2.5 nm). It was argued that the study was the first to show the heterojunction of 1D chains experimentally and investigate them on a macroscopic and atomic scale [41].
2.3. Nanoplates
Nanoplates are plate-shaped nanostructures. Graphene has a large surface area due to its wide plate shape. Studies related to nanoplates include graphene, an Au nanoplate, a polypyrrole-modified NH4NiPO4·H2O nanoplate, a LiMnPO4 nanoplate, Bi2Te3, Bi2Se3 nanoplates and etc. [49,50,51,52].
Meng Zhao et al. reported that solution-synthesized hexagonal Bi2Te3 nanoplates without lattice configurations can exhibit multiple plasmon modes in transmission electron microscope-based electron energy-loss spectroscopy and cathode emission spectroscopy. Theoretical calculations show that the observed plasmon in the visible range is mainly due to the strong spin–orbit coupling that induces the metal surface state of Bi2Te3. The research shows advancement in the field of plasmonics, with strong spin−orbit coupling-induced metallic surface states of Bi2Te3 [53]. Bin-Bin et al. reported polarized femtosecond laser light-mediated growth and the programmable assembly of silver nanoparticles reduced to triple-layer fine patterns.
Zijie Yan et al. explained that synthesized Au nanoplates have the potential to serve as micrometer-sized mirrors that enhance electrodynamic interactions. In other words, the Au nanoplates improve the brightness of light scattered from Ag nanoparticles near the nanoplate surface measured by a dark-field microscope due to their plasmonic properties. In addition, the improvement in the interparticle force constant was found to be more than 20 times higher than expected for the increase in intensity due to steady-wave interference. They showed that additional stability for optical coupling occurs in the limited heat storage motion of nanoparticles, which binds to fluctuations in the lateral plane and decreases [56].
Nanoplates have various advantages due to their structure and are applied in various fields. Nanoplates are expected to be used in various fields, such as electrically conductive materials, nonflammable foam, and solar energy industries. As mentioned above, nanoplates are expected to be applicable in metal nanoplate-based sensors, thermoelectric sensors, optical biosensing, environmental sensing, electrochemical sensors, semiconducting nanoplate-based sensors, capacitive pressure sensors, etc.
2.4. Nanorolls
2.4.1. SWCNTs and Their Composites
Single-walled carbon nanotubes (SWCNTs) consist of a two-dimensional hexagonal lattice of carbon atoms and have their own mechanical, electrical, optical, and thermal properties. Research related to SWCNTs includes aerogels, in situ electropolymerization, hybrid films, transistors, sensing, gas sensor, etc. [74,75,76,77,78,79].
SWCNTs may be synthesized with various chiral indices to determine specific properties. This work theoretically investigates the electron transport that occurs in different directions along SWCNTs. The electrons studied in the work of Charoenpakdee et al. move in quantum dots that can move right or left in SWCNTs with different probabilities, depending on the valley. These results show the existence of valley polarization currents. The valleys in the left and right directions have a configuration of valley degrees of freedom in which the components K and K′ are not the same. These results can be theoretically tracked by certain effects. The performance and effectiveness of nanoscale devices, including artificial antennas, transistors, quantum computers, solar cells, and nano electronic circuits, must be improved in order to achieve a variety of benefits [80].
2.4.2. DWCNTs and Their Composites
DWCNT (double-walled carbon nanotube)-related studies include energy transfer, neuronal network engineering, optimal heat capacity, high-conductivity flexible electrodes, etc.
Benjamin et al. prepared a silica gel that was doped with double-walled carbon nanotubes (DWCNTs), which was achieved by using an aqueous sol–gel pathway under mild conditions. And they studied these two conduction paths, which are dominant in different characteristic time scales. The ion conduction of silica networks was independent of the DWCNT doping rate. The DWCNT networks were found to occur above the critical concentrations (0.175 wt%) corresponding to the nanotube penetration threshold. These materials can be useful in the design of sensors, including sensors that integrate biological species or electrical active chemical properties [94].
The sample combined DWCNT absorption, wavelength-dependent infrared fluorescence excitation (PLE), and wavelength-dependent resonance Raman scattering (RRS) spectroscopy. It was obtained by a refined DWCNT ultrasonic treatment or by careful solubilization that strictly avoids electronic classification, both of which eliminate unwanted SWCNTs that can be obscured by density-gradient ultracentrifugation [95]. Lionel et al. considered semiconductor oligomers, i.e., 2,7-bis-(3,3‴-didodecyl-[2,2′,5′,2″;5″,2‴]quaterthiophen-, and applied them as photocell components as a double-walled carbon nanotube (DWCNT) bulk heterojunction. The three-way system (QTF12-DWCNT and PCBM) showed an open voltage (Voc) = 0.53 V and a power conversion efficiency of 0.43%. The research can be applied in the fabrication of solar cells, etc. [96].
2.4.3. MWCNTs and Their Composites
Multi-walled carbon nanotubes (MWCNTs) are carbon nanotubes with two or more walls. They have good heat or electricity transfer properties, a long extension, are hard, have a similar electricity and thermal conductivity to copper and diamond, and have a strength of approximately 100 times that of steel. Although their physical properties are lower than those of single-walled carbon nanotubes (SWCNTs), they have excellent mechanical properties, thereby facilitating mass synthesis. Research related to MWCNTs includes electrochemical performance, sensors, thin films, electrocatalysts, batteries, etc. [100,101,102,103,104,105].
Yang et al. produced a Pt2CeO2 heterojunction nanocluster for multi-walled carbon nanotubes in a deep eutectic solvent, a special form of ionic liquid. And the catalyst was heat-treated at 400 °C with N2. The Pt2CeO2/CNTs-400 catalyst significantly improved the electrocatalyst performance in the methanol oxidation reaction (MOR) direction when compared to the heat-treated Pt2CeO2/CNTs-500 (60.3 mAmgPt−1), Pt2CeO2/CNTs-300 (45.9.2 M MgPt−1), and M2C6Cnt-1 (64S). The study demonstrates a new method for constructing high-performance Pt-CeO2 catalysts for direct methanol fuel cells (DMFCs). The research can be applied to direct methanol fuel cells, etc. [106]. Zhu et al. grew multi-walled carbon nanotubes (MWCNTs) on top of polydimethylsiloxane (PDMS) films, which were further transformed into polyaniline (PANI) by using chemical oxidation synthesis. The excellent flexibility of the PANI-MWCNT/PDMS films showed stable initial resistance values even under bending conditions. Flexible sensors showed excellent flexible NH3 detection performance, including low detection limits (10 ppb) at room temperature. The above results show the applicability of PANI-MWCNT/PDMS sensors to monitor NH3 in human respiration and food [107].
3. Summary
Currently, research and introduction cases on nanomaterials are increasing exponentially. Nanomaterials can be used in various fields, such as in body drugs, electrically conductive materials, and flexible displays. The representative materials of nanoparticles include TiO2, PDEN, Mo/Fe, Bi2MoO6, etc. In addition, the representative materials of nanowires include CuNW, AgNW, and GaAsP single nanowires. Moreover, nanoroll-type materials include SWCNTs, DWCNTs, and MWCNTs.
In the case of nanomaterials, there is a controversy over their harmfulness. In particular, in the case of certain nanomaterials, there has been a controversy over their harmfulness in Europe, resulting in restrictions being put on their exports. An example of a disorder is that, in 2003, NASA’s Johnson Space Center research team injected CNT into mice’s lungs as a solution, resulting in lung tissue damage. Nanomaterials increase the chances of causing stress at the cell level. They can also affect cardiovascular disease. Therefore, when coating or applying nanomaterials to other objects, it is necessary to select binders well to prevent nanomaterials from escaping. In addition, it is essential to wear protective wear, such as special masks, when processing nanomaterials.
As the demand for convergence chemosensor materials increases, more eco-friendly and high-value-added multifunctional nanomaterials are expected to be introduced in the future. In particular, their applications in substances, drug delivery systems, and coating sheets, which maximize functional expression due to their large surface area, is expected to increase.
This entry is adapted from the peer-reviewed paper 10.3390/chemosensors11100537
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