A team of UConn chemists has discovered a new way of making a class of porous materials that allows for greater manufacturing controls and has significantly broader applications than the longtime industry standard.
The process, more than three years in the making, has resulted in the creation of more than 60 new families of materials so far, with the potential for many more. The key catalyst in the process is recyclable, making it a 'green' technology.
"This is definitely the most exciting project I've been involved in over the past 30 years," says Board of Trustees Distinguished Professor Steven L. Suib, the project's principal investigator.
The research team's novel process creates monomodal mesoporous metal oxides using transition metals such as manganese, cobalt, and iron. The mesopores are between 2 and 50 nanometers in diameter and are evenly distributed across the material's surface.
UConn's scientists used nitric oxide chemistry to change the diameter of the pores. This unique approach helped contain chemical reactions and provided unprecedented control and flexibility.
Having materials with uniform microscopic pores allows targeted molecules of a particular size to flow into and out of the material, which is important in such applications as adsorption, sensors, optics, magnetic, and energy products such as the catalysts found in fuel cells.
"When people think about these materials, they think about lock-and-key systems," says Suib. "With certain enzymes, you have to have pores of a certain size and shape. With this process, you can now make a receptacle for specific proteins or enzymes so that they can enter the pores and specifically bind and react. That's the hope, to be able to make a pore that will allow such materials to fit, to be able to make a pore that a scientist needs."
UConn's chemists replaced a long-standing water-based process with one employing a synthetic chemical surfactant to create the mesopores. By reducing the use of water, adding the surfactant, then subjecting the resulting nanoparticles to heat, the research team found that it could generate thermally-controlled, thermally-stable, uniform mesoporous materials with very strong crystalline walls. The mesopores, Suib says, are created by the gaps that are formed between the organized nanoparticles when they cluster together. The team found that the size of those gaps or pores could be tailored – increased or decreased – by adjusting the nanostructure's exposure to heat, a major advancement in the synthesis process.
"Such control of pore-size distribution, enhanced pore volumes, and thermal stabilities is unprecedented …," the team wrote in its report.
The UConn team found that the process could be successfully applied to a wide variety of elements of the periodic table. Also, the surfactant used in the synthesis is recyclable and can be reused after it is extracted with no harm to the final product.
"We developed more than 60 families of materials," says Suib. "For every single material we made, you can make dozens of others like it. You can dope them by adding small amounts of impurities. You can alter their properties. You can make sulfides in addition to oxides. There is a lot more research that needs to be done."