Introduction to Nanomaterials and Their Related Applications
Release time:
2023-06-08
Nanostructured materials, often referred to as nanomaterials, are materials whose structural units have dimensions ranging from 1 nanometer to 100 nanometers. Because their size is already comparable to the coherence length of electrons, their properties undergo significant changes due to self-organization brought about by strong quantum coherence. Moreover, given that their scale is close to the wavelength of light and considering their unique surface effects arising from their large surface area, the characteristics they exhibit—such as melting point, magnetism, optical properties, thermal conductivity, and electrical conductivity—are often quite different from those exhibited by the same material in its bulk state.
I. Definition and Introduction to Nanomaterials
Nanostructured materials, often referred to as nanomaterials, are materials whose structural units have dimensions ranging from 1 nanometer to 100 nanometers.
Because its size is already close to the coherence length of electrons, its properties undergo significant changes due to self-organization brought about by strong coherence. Moreover, given that its scale is comparable to the wavelength of light and considering its unique surface effects, the characteristics it exhibits—such as melting point, magnetism, optical properties, thermal conductivity, and electrical conductivity—are often quite different from those exhibited by the same material in its bulk state.
II. Classification of Nanomaterials
1. Classified by chemical composition:
Nano-metals, nano-crystals, nano-ceramics, nano-glasses, nano-polymers, and nano-composites.
2. Classified by material properties:
Nano-semiconductors, nano-magnetic materials, nano-linear optical materials, nano-ferroelectrics, nano-superconducting materials, nano-thermoelectric materials, and others.
3. Classified by application:
Nano-electronic materials, nano-optoelectronic materials, nano-biomedical materials, nano-sensing materials, nano-energy-storage materials, and others.
III. The Five Major Effects of Nanomaterials
1. Volume effect
When the size of nanoparticles becomes comparable to or smaller than the de Broglie wavelength of conduction electrons, the periodic boundary conditions are disrupted. As a result, properties such as magnetism, internal pressure, light absorption, thermal resistance, chemical reactivity, catalytic activity, and melting point undergo significant changes compared to those of conventional particles. This phenomenon is known as the size effect in nanoparticles.
2. Surface effect
The surface effect refers to the changes in properties that arise when the ratio of surface atoms to total atoms in nanoparticles increases dramatically as particle size decreases. As particle size diminishes, the number of surface atoms rises rapidly. Moreover, as particle size shrinks, both the surface area and surface energy of nanoparticles increase rapidly. This is primarily because the smaller the particle size, the greater the proportion of atoms located on the surface. The crystal-field environment and binding energy of surface atoms differ from those of bulk atoms. Surrounding surface atoms lack neighboring atoms, leaving many unsaturated bonds with dangling bonds, which confer an inherently unsaturated nature. Consequently, these surface atoms readily form chemical bonds with other atoms to achieve stability, thereby exhibiting high chemical and catalytic activity.
3. Quantum size
When the particle size decreases to a certain value, the phenomenon in which electron energy levels close to the Fermi level transition from quasi-continuous levels to discrete levels is known as the quantum size effect. In semiconductor nanoparticles, the electronic states evolve from the continuous energy bands characteristic of bulk materials—as the particle size shrinks—toward discrete energy levels with a well-defined structure. This manifests itself in the absorption spectrum as a transition from a broad absorption band lacking any discernible structure to an absorption feature endowed with a distinct spectral pattern. The wave nature of electrons occupying discrete, quantized energy levels in nanoparticles gives rise to a host of unique properties, such as high optical nonlinearity and distinctive catalytic and photocatalytic behaviors.
4. Quantum tunneling
The ability of microscopic particles to penetrate potential barriers is known as the tunneling effect. It has been discovered that certain macroscopic quantities—such as the magnetization of tiny particles, magnetic flux in quantum coherent devices, and electric charge—also exhibit tunneling effects. These quantities can cross potential barriers in macroscopic systems and undergo changes, which is why this phenomenon is referred to as macroscopic quantum tunneling. This concept can qualitatively explain phenomena such as the persistence of superparamagnetism in ultrafine nickel particles at low temperatures.
5. Dielectric Confinement
The dielectric confinement effect of nanoparticles has received relatively little attention. In real samples, nanoparticles are surrounded by media such as air, polymers, glass, and solvents—media whose refractive indices are typically lower than that of inorganic semiconductors. When illuminated by light, the difference in refractive indices gives rise to interfaces, leading to a significant enhancement of the electric field strength in regions adjacent to the nanoparticle surface, on the nanoparticle surface itself, and even within the nanoparticle interior, compared to the intensity of the incident light. This localized field enhancement directly influences the photophysical and nonlinear optical properties of semiconductor nanoparticles. For inorganic-organic hybrid materials and photocatalytic materials used in multiphase reaction systems, the dielectric confinement effect exerts a crucial impact on reaction processes and kinetics.
IV. Three New Nanomaterials with Huge Potential
1. Graphene
Graphene (rphene) is a two-dimensional carbon nanomaterial composed of carbon atoms arranged in a hexagonal lattice with sp² hybridized orbitals, forming a honeycomb-like crystal structure. Graphene exhibits outstanding optical, electrical, and mechanical properties, and holds great promise for applications in materials science, micro- and nano-fabrication, energy, biomedicine, and drug delivery. It is widely regarded as a revolutionary material of the future. In 2010, Andre Geim and Konstantin Novoselov, physicists at the University of Manchester in the UK, successfully isolated graphene from graphite using the micromechanical exfoliation method, for which they jointly received the Nobel Prize in Physics. Common methods for producing graphene powders include mechanical exfoliation, redox methods, and SiC epitaxial growth; while the most prevalent method for producing graphene films is chemical vapor deposition (CVD).
Development trend:
The 2010 Nobel Prize in Physics has made graphene a hot topic in recent years, both in technology and the capital market. Over the next five years, graphene is poised for explosive growth in fields including optoelectronic displays, semiconductors, touch screens, electronic devices, energy storage batteries, displays, sensors, aerospace, military industry, composite materials, and biomedicine.
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Introduction to Nanomaterials and Their Related Applications
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