Why can't microporous membranes be used to separate ions and small molecules

Microporous membranes cannot be used to separate ions and small molecules. Due to the following main reasons, here is a summary and sharing:

1. Membrane pore size: Because the size exclusion of the membrane is limited, although the microporous membrane diameter is also very small, it can effectively screen larger molecules and particles, however, they cannot effectively separate ions and very small molecules. Since the pore size of the microporous membrane is usually micrometer or nanometer, the size alone cannot provide sufficient selectivity to separate ions and small molecules.
2. Membrane charge interaction: Lack of selectivity, microporous membranes do not have the necessary charge selectivity, it is impossible to effectively separate ions according to the charge characteristics of ions, because ions are small charged particles that can interact with the membrane surface, which will result in very limited selectivity of ions in the separation process.
3. Diffusion: Here we are talking about the diffusion of small molecules. Since the size of small molecules is relatively small, they can diffuse through the micropores of the membrane even if the pores are very small. This diffusion will limit the ability of the membrane to effectively retain small molecules during the separation process.

4. Ion permeability: During ion transport, ions can permeate microporous membranes due to their small size and charge characteristics. For ions in solution, it is difficult for microporous membranes to achieve selective separation because ions can pass through the membrane with other molecules.
5. Selective permeability: It will use the selectivity of the membrane to become limited. Microporous membranes lack the selectivity required to separate specific ions or small molecules from complex mixtures. Selective separation usually requires membranes with customized properties, such as ion exchange functions or specific pore structures designed for molecular exclusion.
6. Membrane fouling: Blockage and scaling will occur during filtration. During the separation of ions and small molecules, microporous membranes are easily blocked and scaled by particles or substances in the feed solution, which will undoubtedly further hinder the separation efficiency and effectiveness of the membrane.

From the above analysis, it can be seen that although microporous membranes can effectively separate according to particle size and are often used in applications such as filtration and gas separation, they should not be ideal for separating ions and small molecules. For applications that require selective separation of ions and small molecules, other types of membranes (such as ion exchange membranes or nanofiltration membranes) should be given priority.