Nanotechnology Reduces Pore Size in Materials
Porous materials have holes that water or other liquids can seep through. Materials containing nano-sized holes — called nanopores — offer some intriguing possibilities for the way in which pores can be used.
Many substances are porous. For example, porous underground rock (called an aquifer) contains voids that absorb water. However, a significant portion of the volume of the porous rock is solid, limiting the amount of water that it can contain.
By making porous material of nanoparticles, the percentage of the material that is solid can be reduced, which allows the nanoporous material to store a gas or liquid within a much higher percentage of its volume.
If a solid substance is riddled with nanopores, you can store a large volume of gas in the solid. A good example is aerogels. Aerogels are made up of nanoparticles separated by nanopores that are filled with air. Because the bulk of the aerogel material is air, the material makes a very good insulator.
Another use of reduced pore size using nano is in designing nanoporous materials to maximize the internal surface area and customize the size of the openings. Researchers have created materials called metal-organic frameworks (MOFs). MOFs are being developed, for example, to store gases to capture carbon dioxide or to store hydrogen for fuel cell use.
Having a nanoparticle riddled with nanopores with increased surface area available for contact with gases or liquids can also improve the effectiveness of catalysts. A catalyst disassembles molecules involved in a reaction into atoms. These atoms can then react with the other type of molecule involved in the reaction to form the desired result, an entirely different chemical substance.
When a catalyst is nanoporous, the atoms that are to be disassembled can land on the inside surface of the nanopores, providing more surface area for the catalyst to disassemble the molecules and move the reaction along. These improved catalysts have a better capability to break down air pollutants, as well as to improve electrodes used in batteries, resulting in increased charging rate and storage capacity of the battery.
A few more applications of nanopores you can check out elsewhere in this book include the following:
Membranes containing nanopores are used for water filtration to reduce the energy required to separate water from salts in desalinization of seawater. When the pores are formed with carbon nanotubes, water molecules flow very easily through them, but the larger salt molecules can’t pass through.
You can use nanopores to transport protons (hydrogen ions) in fuel cells. Researchers are developing membranes that include nanopores containing an acidic solution, which makes it easier for the hydrogen ions to pass through the membrane.
Nanopores can be used to quickly analyze the structure of DNA. When a DNA molecule passes through a nanopore that has a voltage applied across it, researchers can determine the structure of the DNA by the changes in electrical current.