A mesoporous material has openings within its structure that are between 2 and 50 nanometers (nm) in diameter. In terms of porousness, it is in between microporous material, which has openings less than 2 nm, and macroporous material, which has openings greater than 50 nm. One of the chief materials in this class is silica, and the majority of its scientific uses stem from filling the pores with a secondary material. Since the openings are so small, the mesoporous material will cause different responses within systems than the secondary material alone.
In physical science, a pore is a measurement of empty space. A porous object has a large amount of emptiness in it when compared to its size while a solid or dense object does not. In most cases, the importance of pores within a mesoporous material is based on surface and accessible pores. Any completely closed off voids are typically not viable for use.
Meso is a prefix that means ‘middle.’ In this case, mesoporous material gets its name from the fact that it has bigger pores than the class under it but smaller than the class above. The reason this particular size is important is simply its intermediate nature. In some ways, it acts like a bigger small material and in other ways it acts like a small big material, allowing it to do things the other classes can’t.
While a majority of mesoporous materials are silica-based, there are several other types as well. Several metals or their initial bases, such as tin, titanium or alumina, are mesoporous. These metals are often transitional, meaning that they are actively, or have the possibility to, turn into something else. As a result, the much more stable and plentiful silica materials are used instead.
Most of the uses for a mesoporous material stem from two factors. First, the pores are small enough that they make up a comparatively small portion of the entire substance. Therefore, when a system interacts with the material, it typically responds as though it was pure even if there are secondary substances carried along with it. Second, the relative surface area of the substance is much greater than its size would indicate. This allows larger amounts of material to move within the same physical size when compared to microporous material.
The main jobs of a common mesoporous material fall into two categories: transport and filtration. For transport jobs, the material’s pores are filled with a secondary substance and released. These materials will interact with their environment as the main material and the secondary material will simply ride along. For filtration, the process works in reverse: the pure material is released into a system where secondary materials enter the pores. This creates a simple method of removing specific materials from a standing mixture.