Membranes are used for all sorts of important tasks, including desalination, industrial filtration and even kidney dialysis. But most membranes used today are not able to tackle emerging challenges. More advanced membranes, however, could open up all sorts of new technologies, from filtering PFAS and recovering precious minerals from wastewater to improving devices for cleaner energy, like fuel cells and batteries.
Rahul Sujanani, who joined the Department of Chemical and Biological Engineering as an assistant professor in August 2025, is working to realize these potentials by developing design rules for new polymer membranes.
“My research is really at the interface of polymer science, materials engineering and separations,” says Sujanani. “I want to understand how ions and other small molecules interact with and transport across polymers in order to design scalable membranes with more favorable properties. The goal for us is to address some of the sustainability crises related to water purification, critical mineral recovery, pollution, and clean energy.”
Sujanani completed his undergraduate degree in chemical engineering at Rensselaer Polytechnic Institute, where his father completed a PhD in chemical engineering. Sujanani then earned his PhD at The University of Texas at Austin, where he focused on ion and water transport in water-swollen membranes, largely working with off-the-shelf materials to better understand and model their fundamental properties. As a postdoctoral researcher at the University of California, Santa Barbara, he worked on the molecular-level physics of polymer membranes used for batteries and learned new methods for synthesizing novel membranes.
At UW-Madison, he hopes to bring it all together. “I am really excited to combine those unique experiences in a new group that can help us advance beyond the handful of current membrane chemistries so that we can achieve these emerging and critical separations,” he says. “We essentially want to connect molecular-level interactions in newly synthesized polymers with separation performance to enable rational design of next-generation membranes.”
One key area he hopes to tackle is critical mineral recovery. Current membrane technologies are not selective, meaning that when membranes filter water, they typically separate out all salts indiscriminately.
Sujanani, however, hopes to develop very selective membranes that can filter out specific critical minerals. “If we want to pick out just lithium ions from a wastewater source that has many similar ions, that’s a very different design paradigm than desalination,” he says. “That’s going to be a feature of my group in particular: trying to address the challenge of designing ion-specific selectivity in membranes.”
He also says his lab will work on membranes for electrochemical applications and will continue to investigate the fundamentals of water purification.
Though he has no direct links to the extensive UW-Madison chemical engineering academic “family tree,” Sujanani says he already feels a strong connection. That’s because of his admiration for Chemical Engineering Professors Robert Bird, Warren Stewart and Edwin Lightfoot, who wrote one of chemical engineering’s foundational texts, Transport Phenomena; and Professor Don Paul, one of his mentors at UT-Austin and a luminary in the membrane field who earned his PhD at UW-Madison.
“The way that I learned the foundational concepts of my field is shaped so much by UW-Madison,” says Sujanani. “The chance to come here and mentor and train the next generation and do cutting edge research alongside world-class faculty, staff, and students is just incredible.”