Nanosheet Filters Capture Virus-Sized Particles Without Sacrificing Breathability
The novel material design achieves efficient filtration with minimal air resistance.
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While already a common sight in some countries, the need for personal protective masks has become a global focus since the COVID-19 pandemic.
In turn, this has led to increased attention on the challenge of designing filters that balance particle capture with good breathability. Traditional filtration materials capable of trapping virus-sized particles typically use a very small mesh size which significantly reduces airflow, making them uncomfortable to wear for extended periods.
Researchers from the Institute of Industrial Science at The University of Tokyo have developed a new filtering material that addresses this limitation.
Their work, published in Materials Advances, describes a hybrid fabric that combines porphyrin-based nanosheets with nanofiber-modified textiles to create a breathable and efficient filter.
Filtering with nanoscale control
Viruses typically range from about 20–400 nanometers in size, making them difficult to intercept using conventional textile filters.
The new filter design uses nanosheets consisting of an ordered mesh made from porphyrin molecules – flat, ring-shaped structures with nanoscale central pores – as the foundational building blocks. The holes in these nanosheets are selectively sized to allow air molecules to pass through while blocking larger airborne particles, such as viruses.
The nanosheets are supported by fabric substrates that have also been modified with nanofibers that contain pores measuring several hundred nanometers in diameter. This dual-scale pore structure improves filtration without significantly impeding airflow.
"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," said senior author Kazuyuki Ishii. "The nanosheets are then compressed and coated on nanofiber-modified fabric using a stamp method."
Marangoni effect
The Marangoni effect is a phenomenon in fluid dynamics where variations in surface tension cause fluid movement along an interface. It often occurs in liquid films and is exploited in material science for self-assembly processes.
This method of production allows for uniform deposition of the filtering material without disrupting the underlying nanofiber network. As a result, the final filter maintains its structural integrity and airflow characteristics.
Performance surpasses N95 standards
To evaluate the effectiveness of their filter, the research team used a standard particle filtration test that is typically applied to N95 masks.
In testing, the new filter demonstrated a filtration efficiency of 96%, which exceeds the 95% benchmark required for N95 certification. Scanning electron microscopy images of the fabrics post-test confirmed that the filters were able to capture particles less 100 nm in size. This is a relevant benchmark as virus such as COVID-19 and influenza A are similarly on the order of 100 nm in size.
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"Our porphyrin-based filter collected nanoparticles with a diameter as small as one hundred nanometers," explained senior author Kazuyuki Ishii. "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."
While the study was conducted using synthetic particles to simulate virus-sized contaminants, the results suggest the material could serve as a useful platform for future filter development. The dual-layer structure, combining molecular-level selectivity with supportive nanofiber scaffolding, offers a promising direction for next-generation filtration systems.
Reference: Kuramochi Y, Aoki Y, Enomoto K, et al. Hybridization of nanofiber-modified fabrics with porphyrin-based nanosheets for nanoparticle capture. Mater Adv. 2025. doi: 10.1039/D5MA00058K
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