The rapidly increasing industrialization in many parts of the world comes with economic benefits, but also serious long-term health and environmental consequences. Stanford professor Yi Cui had become increasingly concerned about the air quality in Beijing during his frequent visits in recent years, so he set to work developing a potential solution. His materials science lab mostly deals with battery technology, but the team has succeeded in creating a new type of high-efficiency filter that removes harmful particulates from the air.
The starting point for Cui’s team was to find a material that would be able to attract the most dangerous microscopic particles in air pollution, those less than 2.5 micrometers. These so-called PM2.5 particles post the greatest risk to human health as they are able in infiltrate the lungs and cause respiratory distress. They’re also expensive to filter out of indoor environments. The researchers eventually settled on polyacrylonitrile (PAN), which is used to produce non-latex surgical gloves. PAN can attract these tiny particles and as a bonus, it’s extremely strong.A process called electrospinning was used to convert the liquid PAN into a bundle of solid fibers like a spiderweb. The individual fibers are about one thousandth the width of a human hair, but when integrated into a crisscrossing network with other fibers, it effectively filters particulate matter out of the air. The filters made from electrospun PAN are still 70% transparent to visible light, but can capture more than 99% of particles blown through it. Perhaps most importantly, they don’t impede air flow.
To test the new material, the team first set up two glass chambers separated by the filter (seen above). Incense was burned in one side of the system, but it didn’t make it through to the other despite good airflow. The 99% figure above is based not only on this lab test, but a field test conducted in Beijing. Cui estimates the PAN fibers making up these filters will be able to accumulate about 10-times their weight in pollution before they need to be replaced. That would give them a useful life of around a week in a highly polluted region like Eastern China.
Even with frequent filter swaps, the PAN fibers created by the Stanford team are cheap to make. They could be integrated into face masks for personal use, or in the existing ventilation system of buildings. The filters might even be added to windows — a gentle breeze is enough for the filters to do their work.
Attaching these filters to the source of pollution could be effective as well. Power plants, factories, and even cars could use these filters to prevent particulates from entering the atmosphere in the first place. These applications are a little further off because of the possibility other chemical agents in these environments could damage the fibers.
There’s still more testing to be done before polyacrylonitrile filters make it to consumers, so don’t breathe too deeply just yet.