What is sol-gel technology in filtration membrane modification process

The sol-gel process for filter membrane modification is a technology in surface coating. It mainly uses sol (colloidal suspension of solid particles in a liquid) through chemical reactions such as hydrolysis and condensation at a specific temperature and Under humidity conditions, a gel coating is formed on the surface of the membrane, thereby changing the properties of the membrane, such as hydrophilicity, pore size, chemical resistance, etc.

The sol-gel process can be summarized as follows:

1. Sol preparation, select appropriate precursor molecules according to the required membrane properties, usually metal alkoxides or organosilanes, because these substances can undergo hydrolysis and condensation reactions to form a network structure, commonly used precursors in filter membrane coating Sols, including tetraethyl orthosilicate (TEOS) and other organosilanes, are prepared by dissolving the precursor in a suitable solvent.

2. Hydrolysis. After water is added to the sol, the metal or silicon alkoxide is hydrolyzed. The precursor molecules react with water molecules under the action of the catalyst, and the alkoxide group (OR) is replaced with a hydroxyl group (OH). The hydrolysis process can be expressed as for:

M(OR)_n + H₂O → M(OH)_n + nROH

Where M represents a metal or silicon atom. This reaction results in the formation of hydroxyl groups on the precursor molecules. During the hydrolysis reaction, the process can be controlled by adjusting the pH, temperature and reaction duration. After the hydrolysis reaction occurs, the precursor molecules will be converted into hydroxyl groups. Capped substances.

3. After condensation and hydrolysis, a condensation reaction occurs between the hydroxyl groups on the precursor molecules to form covalent bonds, metal-oxygen-metal (M-O-M) or silicon-oxygen-silicon (Si-O-Si) bonds, at the same time here Water or alcohol is released during the process.

2 M(OH)_n → M-O-M + H₂O

After the condensation reaction, a three-dimensional network structure connecting metal or silicon atoms is formed in the sol. Similarly, the condensation reaction can also be initiated and controlled by adjusting the pH value and temperature or by using a catalyst. The condensation process continues until a condensation is formed. Colloidal structure.

4. Gelation. After the condensation reaction, the viscosity of the solution increases. When the network of interconnected particles or oligomers becomes dense enough to form a solid-like structure, gelation occurs. At this time, the sol is transformed into A porous gel with an interconnected pore structure is created. This gelation process will be affected by factors such as precursor molecule concentration, solvent composition, and reaction conditions, but the porosity and density of the gel network can be controlled by the reaction conditions.

5. Aging and drying. After gelation, the gel is subjected to aging treatment. The purpose is to further strengthen and stabilize the molecular microstructure. The gel is aged for a specific time under controlled temperature and humidity. During this process, the molecular structure Rearrangements and bond formation can continue to enhance the mechanical properties and pore structure of the gel. After aging, the gel is dried to remove the solvent and form a solid film.

6. Heat treatment. Depending on the specific membrane performance requirements, some processes will add a heat treatment process, also called calcination or sintering. The purpose is to further solidify the gel to increase its mechanical strength, pore size control and filtration performance, such as heating at high temperatures. membrane to promote densification, crystallization or removal of residual organic components, etc.

A solid material produced through a complete set of sol-gel processes forms a thin and durable coating on the surface of the filter membrane. This coating can change the hydrophilicity, chemical resistance, pore size or other characteristics of the membrane. Through the above several It can be seen from the description of the points that the membrane surface modified by the sol-gel process and the precursor-sol used in the process are crucial.