Why are mesopores better than micropores? Is this statement correct?

A common saying is that mesopores in microporous filtration membranes are better than micropores? To solve this problem, we need to start with the difference between the two and analyze:

First of all, it is certain that both mesoporous and microporous structures belong to through-holes in microporous membranes. Micropores are smaller pores in filtration membranes. Their diameters are usually less than 2 nanometers (nm) and are responsible for the main filtration function in filtration. The micropores of the membrane act as a physical barrier in filtration, selectively allowing smaller molecules or particles to pass through while blocking larger molecules or particles. Therefore, the pore size of the micropores determines the size of the particles retained by the membrane. Mesopores are mesopores, which are larger pores in microporous filtration membranes, with diameters usually between 2 and 50 nanometers. On the surface, mesopores are not that important for microporous filtration, but they can enhance the overall performance and function of the membrane because mesopores can increase the flux rate, help the permeability and porosity of the filtration membrane, and affect the overall filtration efficiency and capacity.

The differences between micropores and mesopores include the following aspects:

1. Pore size. The main difference between mesopores and micropores is their size range. As mentioned above, the diameter of micropores is less than 2 nanometers (nm), while the diameter of mesopores is usually between 2 and 50 nm. The difference in size determines their unique filtration properties and the types of substances that can be selectively allowed or blocked. In the case of larger pores, it is more suitable to accommodate larger molecules, such as proteins or enzymes, which may not be suitable or unable to function optimally in the smaller pores of microporous materials. Therefore, some mesoporous structures are widely used in biotechnology, bioengineering and biomedicine.

2. Different arrangement. Micropores are closely packed and orderly arranged in the filter membrane to form a dense network of small pores, which provides a tortuous path for molecules or particles passing through the membrane. In contrast, mesopores are usually less dense and have an irregular arrangement, which is used to form larger interconnected gaps or channels in the membrane, providing channels for fluid flow and promoting faster mass transfer. In practical applications, mesoporous materials have greater flexibility in synthesis and pore size control. The pore size can be adjusted within its own size range and can be customized according to specific applications. This adjustability is more conducive to designing materials with desired properties, such as filtering some specific adsorbents or catalysts.

3. Difference in surface area of micropores. Compared with micropores, mesopores have a larger surface area. In theory, the larger the pore size and the more open the structure, the higher the accessibility of the membrane surface, and the easier it is for molecules to approach and enter the internal structure of the material to interact with it, which is more conducive to applications such as adsorption or catalysis.

4. Transport characteristics. Micropores affect the size filtration characteristics of the membrane, which can be screened according to the size of the particles; while mesopores enhance the transport characteristics of the membrane, providing a larger surface area and volume available for adsorption or storage of molecules in the case of larger size. Compared with microporous materials, it has a higher load capacity, which is more conducive to faster diffusion and flow of fluids, improves permeability and reduces filtration resistance. For example, in the drug delivery system of the pharmaceutical industry, this higher drug loading capacity can increase the drug dosage and prolong the drug release time.

5. Functionality. Micropores are essential for achieving precise size separation because they can retain or pass particles based on their size relative to the micropore diameter; while mesopores, while less important for size-based filtration, contribute to the overall functionality and performance of the membrane, such as enhancing permeability, increasing the surface area for interaction, and promoting adsorption or molecular sieving, among other advantages.

In short, the choice between mesoporous and microporous materials depends on the specific application and the required properties. Simply judging that mesoporous is better than microporous is also a relatively objective judgment. Although mesoporous materials have advantages in mass transfer, load capacity, and accessibility, microporous materials may also have advantages in certain needs, such as selective filtration and exclusion based on size separation. Therefore, each porous material has its own advantages and limitations. How to choose them should be based on the intended application and specific requirements to draw a reasonable conclusion.