Ultrafine nanoparticles generally refer to tiny nanoparticles with a particle size between 1 and 100 nm. In the industrial field, a large number of nano-gold particles and nano-silver particles are used as catalysts. Because of the advantages of strong oxidation resistance, good biocompatibility, and high density, nano-gold particles are widely used in the biomedical industry. Other than being employed as a catalyst, nano-silver particles have a broad application of electroplating, new energy as well as modern medicine, for its unique high-efficiency sterilization properties. Other common nano-SiO₂, nano-ZnO, nano-SiO₂ composite powder materials are also largely used in textile and other fields.
 
The more extensive the application of ultrafine nanoparticles becomes, the more mature the preparation methods and technologies of ultrafine nanoparticles become. These days, the main preparation methods are physical preparation methods and chemical preparation methods. There are three physical preparation methods, in general, mechanical crushing method, cooling drying method and ion sputtering method. There are three chemical preparation methods as well, including the gas phase method, the solid phase method and the liquid phase method, among which the liquid phase method is the most common one in industrial field.
 
When preparing ultrafine nanoparticles by liquid phase method, several difficulties may occur, like difficulty in collection due to tiny particles, uneven particle sizes and other impurities in the nanoparticle solution, not to mention the high cost of equipment for collecting nanoparticles. In this way, an economical and reliable separation and purification system is needed to collect the nanoparticles in the preparation solution and simultaneously remove impurity components.
 
Based on years of experience, Guochu Technology (Xiamen) Co., Ltd. has applied advanced membrane technology to the purification of ultrafine nanoparticles. With this new membrane technology, ultrafine nanoparticles can be effectively purified and uniform particle size and high purity nanoparticles can be efficiently collected.
 
A membrane is a selective barrier between two sides. Technically, a membrane is a polymer material that can selectively separate the feed liquid through pressure difference. The whole isolation process is called membrane separation. It differs from traditional filters in that the membrane can function within the molecular range, and this process is a physical process, without the need for phase changes and additives. The thickness of the membrane is generally micron-sized. According to the pore size, the membrane can be categorized into microfiltration membrane, ultrafiltration membrane, nanofiltration membrane and reverse osmosis membrane. In the cross-flow membrane process, the separation and retention performance of various membranes is distinguished by the pore size and molecular weight cut-off of the membrane. The following figure roughly illustrates four different membrane separation processes: (turn arrows indicate that the substance cannot pass through the membrane and is retained):


The main process of membrane technology in the preparation of high-purity nanoparticles:
 

 
 

Using the new membrane separation technology of Guochu Technology can accomplish the particle size classification and impurity removal of ultra-fine nanoparticles to obtain high-purity nanoparticles. In the meantime of purification, the ultrafine nanoparticles can be productively concentrated to reduce the subsequent processing investment. The uniquely designed membrane system adopted by Guochu Technology is competent to avoid the wear of ultrafine nanoparticles on the system seal and effectually prolong the service life of the membrane system. Now one can get mature preparation of nano-gold and nano-silver particles from Guochu Technology Ltd..
 
Guochu Technology (Xiamen) Ltd. is a high-tech enterprise with membrane separation technology as the core and dedicated to the promotion of new separation technology. With rich experience in the application of special membranes in the pharmaceutical, chemical, food, beverage, petroleum, petrochemical, nuclear energy and other industries, Guochu Technology has the ability to research and develop membrane products and types of equipment, according to customer needs.