Researchers from the Institute of Industrial Science at the University of Tokyo — recognizing that masks used during the COVID-19 pandemic featured mesh sizes small enough to capture viruses (usually around 100 nm in size) also restricted air flow — have designed a filter capable of capturing nanoparticles such as viruses without significantly restricting air flow.

To accomplish this, the team concentrated on the pore structure of the filter, which is comprised of nanosheets featuring an ordered mesh made up of porphyrins, which are flat, ring-shaped molecules with a central hole. The tiny holes in the porphyrin molecules are appropriately sized to encourage the passage of small gas molecules in the air while preventing the passage of larger particles, like viruses. These nanosheets are supported on a fabric modified with nanofibers that contain pores of several hundred nanometers to create the filter.

Source: Institute of Industrial Science, The University of Tokyo

"The porphyrin-based nanosheets are constructed through interfacial reactions that are driven by the movement of reactants caused by the gradient of surface tension at the air–solvent interface, known as the Marangoni effect," the researchers noted. "The nanosheets are then compressed and coated on nanofiber-modified fabric using a stamp method."

During particle filtration tests, the filter effectively trapped particles that were as small as viruses, achieving a particle filtration efficiency of 96%, which reportedly exceeds the 95% requirement for an N95 face mask.

"Our porphyrin-based filter collected nanoparticles with a diameter as small as one hundred nanometers," the researchers concluded. "Importantly, the filter also showed minimal decrease of differential pressure in gas flow measurements. This indicates that the filter is capable of trapping particles as small as viruses, while barely restricting air flow."

The article detailing the team's findings, “Hybridization of Nanofiber-modified Fabrics with Porphyrin-based Nanosheets for Nanoparticle Capture,” appears in the journal Materials Advances.