(1) The chemical reduction method is a method in which the metal salt aqueous solution is directly reduced with a strong reducing agent. Commonly used reducing agents include potassium borohydride and sodium borohydride.
(2) The chemical precipitation method is a method of preparing fine powders using the characteristics of metal organic alkoxides that are soluble in organic solvents and may undergo hydrolysis to form hydroxides or oxide precipitation.
(3) Hydrothermal method Hydrothermal reaction is a general term for the chemical reaction in water (aqueous solution) or steam and other fluids under high temperature and high pressure. At present, there are many examples of preparing nanoparticles by hydrothermal method.
(4) The sol-gel method (Sol-Gel) hydrolyzes the metal alkoxide or inorganic salt directly into a sol or decoagulates to form a sol, then polymerizes the solute to gel, and then the gel is dried and roasted to remove organic components , And finally get inorganic materials. This method has the advantages of good product chemical uniformity, high purity, fine particles, insoluble components or non-precipitating components, etc., but also has the disadvantages of low sintering temperature, poor sintering between gel particles, and large shrinkage during drying.
(5) Microemulsion method Microemulsion is a thermodynamically stable, isotropic, transparent or translucent dispersive system with a particle size of 1-100nm, formed by two immiscible solutions under the action of surfactants, called microemulsion . Correspondingly, the technology of preparing microemulsions is called microemulsification technology (MET). When MET is used in the preparation of nanoparticles, it includes two technologies: Microreactor or nanoreactor and microemulsion polymerization. In the microemulsion system, the nanoreactor usually refers to the W/O type system, which is generally composed of organic solvents and aqueous solutions. It consists of four components: active agent and co-surfactant. Commonly used organic solvents are mostly C6-C8 linear hydrocarbons or cycloalkanes; surfactants generally include AOT [2-ethylhexyl] sodium sulfosuccinate]. AOS, SDS (sodium dodecyl sulfate), SDBS (sodium cetyl sulfonate) anionic surfactant; CTAB (hexadecyl trimethyl ammonium bromide) cationic surfactant; TritonX (polyoxyethylene Ethers) non-ionic surfactants, etc. The co-surfactant is generally a fatty acid with a medium carbon chain of C5 to C8. Microemulsion is a thermodynamically stable system, so its formation is spontaneous and does not require external energy. Because of the low technical requirements for the formation of microemulsions, controllable droplet size, simple experimental equipment and easy operation, the microemulsion reactor has been more researched and applied as a new method for preparing ultrafine particles.