Anonym / Monday, November 2, 2015

Researchers discover a remarkably easy way to make filters at the nano scale

From your average spaghetti strainer to the screen on your windows, filters are a part of our every-day life. In their simplest form, they keep debris out of air and water. Yet as filter technology advances, so does the level of precision around what we can keep out.
Today, it’s possible to create membranes that filter a range of substances on a nano (microscopic) scale, and a QNRF, NPRP grant-funded project has made significant progress in doing just that. A member of the team and advanced research fellow in experimental physics in the Biological and Soft Sciences Department at the University of Cambridge, Dr. Easan Sivaniah, explained:
"A membrane is rather like a barrier through which things pass. Depending on the application, it can even filter gases. Gas separation is important, for example, environmentally. If you have oxygen and nitrogen, that’s air, but then typically the things that come out of a power station are nitrogen and carbon dioxide because you’ve burnt all the oxygen up. You’d like to be able to separate the carbon dioxide and capture it, so you don’t emit carbon dioxide."
The process of putting microscopic holes in membranes is complicated, but scientists have found that certain materials would make great nano-filters.
“The development of such nano-porous materials depends mainly on exploring the behavior of polymers [i.e., materials comprising chemical compounds arranged in a repeated pattern],” said Dr. Shaheen Al-Muhtaseb, Associate Professor in chemical engineering at Qatar University and investigator on the study. “Polymers are used as starting materials for the final, developed membranes. Based on the types of pores created, and their structures, we can then produce the required materials for a given purpose, like filtering gases and microscopic particles.”
The question then arises—how do you make such tiny holes? Drs. Al-Muhtaseb and Sivaniah—along with researchers from Lawrence Berkeley National Lab, Berkeley, California, and the Instituto de Ciencia de Materiales de Sevilla, Seville, Spain—recently put their various skillsets together to develop a simple approach. What they found was featured in Nature Materials as a breakthrough that holds promise for the future of membrane technology.
“If your assumption is you have a material made of two components, and you need to take out one of the components,” said Dr. Sivaniah, “in principle you need to be able to access that component. It would be for example like taking a cork out of a wine bottle. You actually have to put the corkscrew into the cork to pull the cork out.
“But what we were able to show was that you don’t necessarily have to have the access to the cork. If you build enough pressure inside the wine bottle it will push the cork out, effectively. So you generate pressure inside these components and they will actually explode at a nano-scale and deform the material in a way that creates nano-scale pores.”
The pressure created in the team’s experiment resulted from techniques involving a basic chemical law called osmosis, which is based on particles and how they naturally seek a balance in liquid environments.

“The idea of osmotic pressure is that it’s really like swelling,” Dr. Sivaniah explained. So if you have a plastic bag that contains salt and water, and you suspend it in fresh water, the water from the outside would actually like to go in and dissolve the salt since the salt inside the bag can’t get out. So you get a kind of build-up of pressure in the bag. It gets larger and larger and eventually it could explode.”
In the case of polymers, Dr. Sivaniah said that the molecules are arranged according to their surface energy effect, in a pattern that is seemingly impossible to penetrate, but this osmotic effect can bypass this arrangement.
“Materials, where even minor components are entirely encapsulated in a matrix with no apparent way out, can be made porous or nano-porous,” he said. “In our experiments, we essentially show osmosis works in materials with these trapped minor components, leading to a series of bursts that connect together and to the outside, releasing the trapped components and leaving an open porous material.”
Dr. Al-Muhtaseb explained that the laboratories of the Department of Chemical Engineering and the Central Laboratory Unit at Qatar University contain a range of high-tech facilities used to test nano-porous materials.* He is working with membranes that both filter and absorb substances. For researching nanoporous materials, he said that the facilities at Cambridge and the expertise have proven essential, saying that there is a “benefit from their facilities and also knowledge transfer that is relevant to membrane technologies.”
The team plans to further develop the membrane technology for application in gas and liquid separation throughout a range of sectors, including fuel production and desalination.
“Qatar hosts substantial natural gas processing and petrochemical industries,” said Dr. Al-Muhtaseb. “Such industries rely on purification and filtration for optimum performances. Furthermore, knowing that such industries produce various gas and liquid waste streams, which contain harmful substances that need to be controlled, the efficient removal (separation) of these substances is essential for environment protection.”
Dr. Sivaniah said he is quite excited about Qatar, for the country itself. “Qatar, as I look at it from the outside, it’s open, it has funds, it has the opportunity to grow, and you really see that this place could be a Singapore.”
As he mentioned a recently-awarded NPRP grant related to desalination, Dr. Sivaniah said he is impressed with QNRF, and its regulations, which help shape the development of the research culture in Qatar:
“For how young they are, they’ve done a remarkable job of pulling people in from around the world. I totally support the idea that they put the money mainly into Qatar. I think you have to set these limitations, that at least 65 percent of the money has to stay in the country, because that forces people to keep a focus on Qatar.”
Dr. Al-Mahtaseb echoed these sentiments, saying that “Qatar is heading progressively toward becoming a regional leader in producing advanced knowledge. This can be seen clearly through the remarkable support provided by Qatar Foundation for various promising initiatives that advance research. The development of these novel and important nano-porous materials is just one example.”
*These facilities include high resolution transmission electron microscope (TEM) and nano-level scanning electron microscope (SEM), energy dispersive X-ray analysis system (EDX), two Micromeritics ASAP-2420 surface area and porosimetry analyzers (one for nanoporous materials with enhanced micropore option, and another for meso- and macro- porous materials), Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analyzer (TGA), differential scanning calorimetry (DSC) and others

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