Evelyn Wang grew up in the arid West, so she’s personally familiar with water and how precious this natural resource can be. In fact, she says, over half of the world’s population is affected by severe water shortages. Now Wang — the Esther and Harold E. Edgerton Assistant Professor of Mechanical Engineering — is working to help ensure that future generations have access to clean drinking water by taking advantage of a largely untapped source: seawater.
First, however, the salts dissolved in seawater must be removed, and current technological processes for doing so are expensive, energy-intensive, and involve large-scale facilities. This limits them to richer countries like Saudi Arabia and the United States.
“We’d love to create cheaper, more efficient systems that could also be used in third-world countries. Perhaps these systems could even be handheld, and therefore portable,” says Wang, who notes that a portable device could also be useful to soldiers.
Today there are two primary ways to desalinate water. One involves pushing seawater through a membrane that separates the water from the salts. However, among other problems, this technique requires a fairly large amount of energy to force the water through. The membrane is also prone to clogging.
In one project related to desalination, Wang is working to develop a better membrane. She is doing so by exploring the problem at the nanoscale, or billionths of a meter. Specifically, she’s working with tiny crystals of zeolite, a ceramic material characterized by pores so tiny that water molecules can flow through, but larger salt ions cannot.
Although zeolites are well known as good “molecular sieves” for the separation of different gases, their potential application to desalination is relatively new. As a result, says Wang, “there’s not a clear understanding of exactly what’s going on,” or how they separate water from salts. “We believe it’s related to pore size, but zeolites are also electrically charged,” and that charge could also be key to the separation process. So Wang and her team have focused first on “really understanding these transport mechanisms.”
To that end, her team became the first at MIT to make the crystals on campus. “That was a very big step for us,” Wang explains. “We’re not materials scientists, so we’re crossing boundaries here with our work.”
Now her team is studying the crystals with custom-made test devices. “It’s obviously very challenging because things are very small here,” says Wang, who is also director of MIT’s Device Research Laboratory, which focuses on materials and transport processes at the micro- and nanoscale. Ultimately, she says, “if we find that zeolites actually are ideal materials for water desalination, we’ll work toward integrating them into membranes.”
Wang notes that the project is still new and quite challenging. But the payoff could be large, and not just for desalination. “As we move more towards the nanoscopic scale, a fundamental understanding at this level will open up opportunities for other applications, maybe even innovations that we haven’t yet thought about.”