Nanomaterials

Nanometer material has great potential for growth. Because of the small size effect of nanomaterials, the self-organization caused by strong coherence has greatly changed its properties. In addition, the dimension of nanomaterials is close to the wavelength of light, and due to its special surface effect, its characteristics, such as thermal conductivity, melting point, electrical conductivity, magnetism, optics,etc., are often different from the properties of the substance in its macrostate (The same composition, but the particle size is not nanometer size).

Applications:

Two important properties of nanomaterials are high-concentration grain boundaries (the cause of grain boundary effect) and nano-crystal grains (the cause of small-size quantum effect). These two effects have greatly changed the mechanical, superconductivity, magnetic, dielectric, optical, and thermodynamic properties of nanomaterials. Materials scientists mainly focus on the plasticity of nano-ceramics, the electrical conductivity of nano-crystals and the large elasticity, high strength and diffusivity of nano-metals.

Figure 1. Application of nanomaterials

• Nano-catalyst: Nanometer catalyst has high activity, good stability, large surface area, etc. Compared with ordinary catalysts, nano-catalysts can greatly improve the reaction efficiency, control the reaction speed, and even allow the reactions that were not possible to proceed. Compared with ordinary catalyst, nanometer catalyst improves the response speed of 10 - 15 times.
• Nano-magnetic material: Because the characteristic physical length of nanometer magnetic material is at the nanometer scale, compared with the traditional magnetic material, the property has changed. Due to its small size, single magnetic domain structure and high coercivity, the magnetic recording material made of it has good sound quality, image and signal-to-noise ratio. Therefore, nano-magnetic materials can be widely used in information recording, magnetic induction, biomedicine and other fields. Especially, superparamagnetic ferromagnetic nanoparticles can also be made into magnetic fluids, which are widely used in fields such as electroacoustic devices and damping devices.
• Nano-ceramic material: Compared with traditional ceramic materials, the atoms of nano-ceramic materials are easy to migrate under the condition of external force deformation, so they have good toughness and certain ductility. Nano-ceramic material is a new super-structural ceramic material developed in the past 20 years. It is widely used in protective materials, high temperature materials, artificial organ manufacture, clinical application and electrical properties, etc.
• Carbon nanotube: Carbon nanotubes, also known as bucky tubes, are one-dimensional quantum materials with special structures. Carbon nanotubes have light weight and hollow structure, and can be used as excellent containers for storing hydrogen. In addition, carbon nanotubes can also be used as molds, and their centers can be filled with metals, oxides and other substances to prepare nanoscale wires.
• Others: In addition to the above important applications, in terms of detection technology, nanomaterials can be used as semiconductors and sensors; in biomedicine, they can be used as diagnostic chips for cell chips and gene chips; in optical, they can make excellent luminous substances.

Production Processes:

There are many methods for preparing nanomaterials, which can be classified into solid phase method, gas phase method and liquid phase method according to the material state.

• Solid phase method: This method includes thermal decomposition of solid phase materials and physical pulverization. Thermal decomposition of solid materials usually uses thermal decomposition of metal compounds to produce ultrafine particles. The physical grinding method uses ultrafine grinding to prepare ultrafine particles.
• Evaporation-condensation method: This method uses vacuum evaporation, laser, electron beam irradiation and other methods to vaporize or form plasma, and then quench it in the medium to condense it. It has the advantages of high purity, good crystal structure, and controllable particle size, but it requires sophisticated technical equipment.
• Chemical vapor method: This method uses the gas chemical reaction of volatile metal compounds to synthesize the required powder, a typical gas phase method whose advantages are high product purity, controllable particle size, uniform and small particle size distribution, and no agglomeration. The disadvantages are large equipment investment, high energy consumption and high cost.
• Chemical precipitation method: In this method, a precipitation agent is added to the metal salt solution to form a precipitate, which is then filtered, dried, and calcined to prepare a nano-sized powder. How to control the uniformity of the powder components and prevent the formation of hard lumps is the key issue of this method.
• Hydrothermal method: This method uses a high-temperature and high-pressure aqueous solution to react insoluble or water-insoluble substances to produce a product, and reaches a certain degree of supersaturation to precipitate into a composite powder. Its greatest advantage is that it avoids the calcination process of the precursor, so the powder does not contain hard agglomeration and the obtained powder has excellent sintering property.
• Sol-gel method: The method takes metal compounds which are easy to hydrolyze as raw materials, makes them react with water in a certain solvent, gradually gelatinizes through hydrolysis and polycondensation processes, and then dries and calcines to the required oxide nano powder. Because from sol to gel to powder, the uniformity and dispersibility of the components are basically maintained, and the calcination temperature is low, the particle size of the obtained powder is generally tens of nanometers.
• Solvent evaporation method: In this method, the solvent is directly evaporated by heating, and then the solute is supersaturated and separated from the solvent. However, this is only suitable for drying single component solution. For multi-component systems, due to the difference of solubility of each component in the solution, the order of precipitation of each solute evaporated is different, which will lead to the separation of components and the loss of chemical uniformity of the system.

References:

1. Hu Xiaoge, Dong Shaojun. Metal nanomaterials and carbon nanotubes—synthesis, functionalization and potential applications towards electrochemistry[J]. J. Mater. Chem., 2008, 18, 1279-1295.
2. Hulteen J. C., Martin C. R., A general template-based method for the preparation of nanomaterials[J]. J. Mater. Chem., 1997, 7(7), 1075-1087.
3. Rao C. N. R., Kanishka Biswasa, S. R. C., Govindaraj A., Synthesis of inorganic nanomaterials[J]. Dalton Trans., 2007, 3728-3749.