In a laboratory at Oregon State University, researchers have harnessed the power of ultrafast lasers to watch molecules break apart in real time—and in doing so, they've discovered a simple, cheap way to clean up a stubborn water pollutant that plagues communities near highways and chemical plants. Chong Fang, a chemistry professor at OSU, and his team used what they call "molecular movie" technology to observe how ultraviolet light and zinc—a plentiful, inexpensive metal—work together to dismantle nitrophenols, toxic compounds that cling to water and resist natural degradation.
Nitrophenols are a persistent environmental threat. They leak into surface water and air from vehicle emissions, pesticides, wildfires, and industrial waste, and once there, they linger. Unlike many pollutants that break down on their own, nitrophenols stubbornly remain in the environment, serving as precursors to other air and water contaminants like nitrous acid. For people exposed to these compounds—whether through contaminated drinking water or air—the effects are tangible: headaches, nausea, breathing problems, eye and skin irritation. Communities near busy roads and older treatment facilities report higher concentrations of nitrophenols in their water systems, making this not merely an abstract environmental problem but a public health one.
What makes Fang's work groundbreaking is the technology itself. The "molecular movie" technology, which Fang unveiled in 2014, uses short-pulse lasers to observe chemical and biological reactions as they unfold at the femtosecond scale—one-millionth of one-billionth of a second. To grasp the scale, a femtosecond is to a second roughly as a second is to 32 million years. By slowing down the observation of these impossibly fast chemical processes, researchers can understand the exact sequences of reactions and, critically, identify the weak points in pollutant molecules.
Working with postdoctoral researcher Taylor Krueger, graduate students Seth Johnson and Chieh-Hsi Kuan, and research associate Cheng Chen, Fang trained the technology on nitrophenols in water exposed to ultraviolet radiation. What they observed was elegant: when UV light hits a nitrophenol molecule, it triggers excited-state intramolecular proton transfer—a positively charged hydrogen ion leaps from one location within the molecule to another, creating a temporary, unstable intermediate form called an aci-nitro intermediate. This intermediate is the key. Because it absorbs longer wavelengths of light than the original molecule, it becomes far easier to break down, even under ordinary visible sunlight. And through additional spectroscopic techniques that measure molecular vibrations, the team discovered that water molecules themselves play an active role in this breakdown process.
"Knowing about this proton transfer step lets us understand where and how the molecule is vulnerable, which is critical information environmental engineers need for designing cleanup methods," Fang said. The role of zinc is equally important: zinc ions accelerate the transformation and help semi-stabilize the intermediate form, creating an opening to attack and degrade the pollutant. The discovery points toward practical, affordable remediation strategies that could be deployed in water treatment facilities and contaminated sites, offering real hope to the communities where nitrophenols have accumulated.