Ultrasonic Spray Coating Prepares BTESE Membranes

Ultrasonic spraying technology creates novel organosilicon nanofiltration membranes, facilitating efficient separation of organic solvents.

In the production processes of chemical and pharmaceutical industries, it is often necessary to separate and purify small molecules in organic solvents. Traditional distillation processes rely on high temperatures for component separation, which is not only energy-intensive but also prone to causing deterioration of heat-sensitive substances. Organic solvent nanofiltration, as a pressure-driven, room-temperature membrane separation technology, has gradually become the preferred solution for industrial purification due to its low energy consumption, mild operation, and high separation accuracy. Developing high-performance, easy-to-prepare nanofiltration membranes has become a research hotspot in the field of membrane separation.

Currently, most mainstream nanofiltration membranes on the market are made of polyamide, produced through interfacial polymerization. However, these membranes are prone to side reactions during preparation, leading to structural defects within the membrane. When dealing with molecules with molecular weights below 300 Daltons, their separation effect is not ideal. Meanwhile, while novel porous materials such as graphene oxide and metal-organic frameworks exhibit excellent separation performance, they generally suffer from weak solvent swelling resistance and complex synthesis processes, making large-scale industrial production difficult.

Organic-bridged silica is a promising new type of membrane material. It introduces covalently linked organic structures into the silica framework, forming a unique three-dimensional network system. This system possesses excellent resistance to organic solvent swelling and allows for flexible control of pore size, perfectly meeting the requirements of organic solvent nanofiltration. However, traditional preparation methods have significant drawbacks: commonly used processes such as dip coating, spin coating, and blade coating are cumbersome, requiring complex substrate pretreatment, additional intermediate transition layers, and precise control of membrane thickness, resulting in poor stability and repeatability of the finished product. Meanwhile, vapor-phase preparation methods such as chemical vapor deposition rely on high-vacuum environments and expensive equipment, making large-scale production extremely difficult.

To overcome this industry challenge, researchers have introduced ultrasonic spraying technology into the preparation of organic-bridged silica membranes, exploring a simple and efficient new film formation scheme.

Ultrasonic spraying differs fundamentally from ordinary spraying. It utilizes high-frequency ultrasonic vibration to atomize the precursor solution into extremely small, uniform microdroplets. These ultrafine droplets are uniformly transported to the heated porous substrate surface, where the solvent evaporates rapidly under high temperature. Since the evaporation rate is much higher than the rate at which the liquid permeates into the substrate pores, the solution is prevented from seeping into the support layer at the source, eliminating the need for an intermediate layer and allowing for the direct formation of a complete separation membrane on the substrate surface.

The research team systematically optimized key parameters such as solvent type, spraying distance, and solution delivery rate. Experiments revealed that solution viscosity is the core factor affecting atomization; lower viscosity solutions more easily form uniformly sized microdroplets, which is fundamental for preparing high-quality films. Meanwhile, the surface tension of the solvent affects the droplet spreading pattern on the substrate surface, thus altering the smoothness of the membrane. Through the control of multiple parameters, the researchers successfully achieved flexible adjustment of the membrane thickness within the range of 150–400 nanometers. The final separation membrane is continuous and intact, with a surface roughness of less than 2 nanometers, and structural defects are significantly reduced.

Performance testing results show that this novel organic-bridged silica nanofiltration membrane exhibits outstanding overall performance. With an effective molecular weight cutoff of 270 Daltons, it is specifically designed for the separation of small organic molecules in the 200-300 Dalton range. Tests using common dye molecules as the separation target and ethanol as the solvent showed that the membrane achieved a retention rate of 97.4% for the target small molecules while maintaining stable solvent permeation efficiency. This balances high separation precision and flow performance, effectively overcoming the shortcomings of traditional polyamide membranes in retaining small molecules.

From an application perspective, the ultrasonic spraying process is simple, offers strong parameter controllability, and is highly adaptable to equipment, overcoming the limitations of traditional processes with multiple steps and high barriers to entry, and possesses strong potential for large-scale production. This research fully demonstrates that ultrasonic spraying is an excellent technical route for preparing high-performance organic-bridged silica separation membranes and provides a new direction for the development of organic solvent nanofiltration.

In the future, with continuous process optimization and material system expansion, this type of novel membrane is expected to be applied to more complex industrial separation scenarios, playing a greater role in fine chemicals, pharmaceutical purification, solvent recovery, and other fields, and promoting the further popularization of green and energy-saving membrane separation technologies.

About Cheersonic

Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.

Our coating solutions are environmentally-friendly, efficient and highly reliable, and enable dramatic reductions in overspray, savings in raw material, water and energy usage and provide improved process repeatability, transfer efficiency, high uniformity and reduced emissions.

Chinese Website: Cheersonic Provides Professional Coating Solutions