On the top floor of the University of Texas at Austin’s engineering building, students occasionally scribble notes as they quietly conduct experiments amid rows of cabinets packed with neatly labeled bottles. One table holds paper-thin slices of a white gel—with the appearance of a film—that has been cut into interlocking letters, a U and a T. The medium for this display of school spirit represents a major breakthrough in chemical engineering—a means of conjuring clean water out of thin air. It might even prove a lifesaver on a planet where two billion people lack access to safely managed drinking water.
The film—a water-absorbing, power-conducting hydrogel—is the most recent in a long line of discoveries to emerge from the Yu Research Group, a lab headed by Chinese-born chemist Guihua Yu. The hydrogel and other technology with potentially global implications have earned the 41-year-old Yu a reputation as a rising star in his field. His research in the emerging field of nanochemistry aims to create novel combinations of naturally occurring materials that are smaller than a standard microscope can perceive.
In awarding him a $100,000 prize early this year, the Houston-based Welch Foundation described Yu’s work as creating “functional polymer nanostructures with tunable chemical and physical interfaces and properties, with applications in energy and environmental science.” Yu told me there’s an easier way to understand what he does with simple, mostly inexpensive materials. “It’s like nanoscale Legos,” he said, an excited smile spreading across his face.
Take, for example, cellulose, the primary component of plant cells and fibers. If cellulose were a book, what you see under an optical microscope might be just the cover. Chemical engineers working in nanomaterials don’t—as the cliché goes—judge that book just by its cover. Employing powerful electron microscopes, they can “read” what’s inside the cellulose—the tiny building blocks from which it’s made. By removing those blocks and interlocking them with other, similarly tiny materials, engineers can create something new.
Yu and his students have done just that again and again. In 2018, using nanomaterials derived from polyvinyl alcohol (which is used in food packaging) and polypyrrole (a polymer that conducts electricity), they developed a gel that can distill contaminated water, using solar energy absorbed by the gel itself to do so. That technology, unveiled just months after Hurricane Harvey hit, was touted as something that could “help purify water during natural disasters.” In 2020, Yu’s team used the same sort of technology to develop self-watering soil, which draws power from the sun during the day to transform atmospheric moisture into water and irrigates the dirt at night. In 2021, they improved upon their water-purification gel with a version the size of an antacid tablet that can purify a liter of water in just one hour by neutralizing bacteria.
All of this earlier work paved the way for Yu’s hydrogel film that can capture water from the air. To make it, Yu and his researchers combine two types of cellulose with konjac gum, a thickening agent similar to cornstarch that’s found in many kitchens in Asia. You can make tasteless, gluten-free, keto-friendly noodles out of konjac gum and water because the gum binds with the water. In the same way, Yu’s hydrogel absorbs moisture in the atmosphere and then holds that water in place.
The hydrogel film has the consistency of a contact lens when it is first made. After being freeze-dried, it looks like a very thin sponge. Placed in a container outside, the sponge absorbs water from the atmosphere over the course of several hours. Then, with the sun’s heat (or a heating pad in a cold, dark environment) acting as a catalyst, the hydrogel wrings itself out, releasing the absorbed water into the container. In 24 hours, about two pounds of the gel film can produce more than six liters of water in arid environments where relative humidity is just 15 percent. If the humidity doubles, so too does the amount of water produced.
To create the hydrogel, Yu’s team snapped together various “nanoscale Legos” until they had built a porous material that attracts as much water as possible. “It’s got a hierarchical pore structure,” said Micah Green, a chemical engineering professor at Texas A&M University. “You can think of it as highways, and then side streets and then alleys and then driveways for water.” Into that water-absorbent structure, Yu’s team layered hydrophobic (water-resisting) cellulose that, once it’s heated, flushes the water out. “This technology is a really big breakthrough,” said Jodie Lutkenhaus, also a chemical engineer at A&M. “Not only can it absorb the water quickly, it can release it quickly, and this is a really big thing.”
Yu grew up in Putian, a coastal city in southeast China, where his father worked as a chemical engineer in a sugar plant. He earned degrees from the University of Science and Technology of China and from Harvard, and did postdoctoral research at Stanford. He believes his hydrogel film could be incorporated into a device anyone might buy at a hardware store and use while camping, or in the case of a boil-water notice. It could also, potentially, be scaled up into a system large enough to deliver water to entire communities—including those in arid climates.
Still, going from the lab to everyday use won’t be easy. Lutkenhaus said it would likely take a massive amount of space to create a hydrogel system that would serve an entire community. Green worries that it might not be practical to freeze-dry large quantities of the hydrogel film and wondered whether the material is durable enough to prove useful outside of a highly controlled lab setting.
But Yu’s team believes that there are ways to arrange the hydrogel material and its water trays to make them more compact. They also say the film can be reused for at least a month, potentially much longer. Yu is already in discussions with potential corporate partners about scaling up the product. Because the materials involved are relatively simple and easily accessible, Yu hopes a commercial product featuring the technology could be available within the next few years. And, at about $1 per pound to make the hydrogel film, it could be a relatively inexpensive source of clean drinking water compared with shipping in bottled water.
Yu’s hydrogel work has been funded by the Defense Advanced Research Projects Agency, an arm of the U.S. Department of Defense that underwrites scientific work that could benefit American soldiers. Though UT owns the hydrogel film technology, DARPA provided $3.2 million to fund Yu’s research because the product could serve as a water source for troops operating in remote, arid environments.
Yu came to UT-Austin to set up his lab in 2012 and has produced a staggering amount of work since. He has published more than 230 research papers, many in leading scientific journals. “It’s high-quality work,” said Donald Siegel, the chair of the department of mechanical engineering at UT. “And it’s high-quantity.” To produce all that work, Yu often lets his students take the lead on projects, and some of them have been key in the development of the lab’s inventions. “My philosophy,” he said, “is really to kind of learn and work with your students, and really focus on their passion.”
For instance, Youhong Guo, the lead author on a recent hydrogel paper published by Yu’s team, was a graduate student with an interest in solar energy when she came to study with Yu. “He really motivated students to do the work that we’re interested in,” she said. He also wanted them to know “that the material that we develop can be beneficial to society.” Along with other students, she was determined to use Yu’s past research on hydrogels to develop a product that could cheaply produce a significant amount of drinkable water. Now a postdoctoral researcher at MIT, Guo is using hydrogel technology to address climate change by attempting to pull carbon, instead of water, from the atmosphere.
Yu’s group, meanwhile, is also looking at potential new modes of energy storage. In one of their three lab rooms in UT’s engineering building, they have what amounts to a miniature battery factory. Yu is particularly intrigued by the possibility of improving upon flow batteries, which hold energy in liquid form. Electricity produced by solar panels and wind turbines could be dissolved into a liquid electrolyte, stored in tanks, then pumped back out through electrodes that convert the liquid back into electricity whenever it’s most needed. Yu said that if engineers can improve upon the chemical composition of flow batteries, that technology could help stabilize power grids by providing efficient storage of large amounts of electricity. One day, in fact, Yu hopes to be able to store such renewable energy in water—a safer and cleaner alternative.
And all of that work derives from those nanoscale building blocks. “If you are able to characterize them, to see them,” Yu said, “you will be able to do this magic chemistry.”
