The special effects of nanoparticles due to their surface effects and bulk effects make the materials composed of nanoparticles, ceramics or catalysts exhibit superior properties different from bulk materials in terms of fracture toughness, strain rate, superplasticity, sintering performance, and catalytic activity. Therefore, the preparation technology of various nanometer powders has been developed rapidly.
Figure 1. Some applications of nanoparticles.
- Biomedicine: Magnetic nanoparticles have good magnetic permeability, biocompatibility and biodegradability, and can combine a variety of biological functional molecules (enzymes, DNA, proteins, etc.). It can be used for DNA separation and purification, magnetic targeting drug guidance, medical detection and diagnosis, cell separation and immunoassay, adsorption and immobilization of protease, etc.
- Water treatment agent: Compared with traditional water treatment materials, nanoparticles have good dispersibility in water, better biocompatibility, and an adjustable outer shell. Nanoparticles have a large specific surface area and small size effect, so they have strong adsorption capacity and can quickly reach adsorption equilibrium. In particular, magnetic nanomaterials have strong magnetic properties that allow them to be quickly separated from water in an external magnetic field. Therefore, magnetic nanoparticles have strong advantages in the field of water treatment.
- Catalyst: Catalysts can be simply divided into homogeneous and heterogeneous catalysts, each with its own advantages and disadvantages. The dosage of homogeneous catalyst is small and its selectivity is high, but it has the disadvantages of complex preparation method, high cost and difficulty in recovery. Although heterogeneous catalyst is easy to be recovered, its catalytic efficiency is low. In order to improve the efficiency of heterogeneous catalyst, the catalyst is made into nanometer size to increase its surface area and improve its catalytic efficiency.
- Gas phase method: This method enables the direct use of gas or various means to turn a substance into a gas, causing it to undergo physical or chemical changes in the gas state, and condense and grow to form nanoparticles during cooling process. According to needs, different heating sources can be used to obtain nanoparticles with the required particle size, wide selectivity, simple preparation and controllable particle size.
- Liquid phase method: This method refers to the separation of the solute from the solvent in a homogeneous solution by various ways. And the solute is formed into particles of a certain shape and size to obtain the precursor of the desired powder, and nanoparticles are obtained after pyrolysis.
- Solid-phase method: This method includes thermal decomposition of solid-phase materials and physical crushing method. The solid-phase material thermal decomposition method uses the thermal decomposition of a metal compound to prepare ultrafine particles, but its powder is easy to consolidate and needs to be crushed again, and the cost is high. The principle of physical crushing is to make the medium and material to grind and impact each other to obtain ultrafine particles.
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