An aerogel-based light-driven knudsen pump approaching complete passive capturing of airborne particles in wide size ranges

Abstract

Aerosol sampling stands as an essential step in air quality monitoring and characterization. Active sampling provides accurate aerosol determination, while passive sampling offers cost-effective and power supply-free design. However, passive sampling is subject to sampling conditions and brings about uncertainties concerning particle sizes and flow rates, and collection efficiencies, which requires calibration assisted by active samplings. In this work, we presented a polyimide (PI) aerogel-based passive sampler operating in a flow-through and active-sampling mode without artificial power supply, generating a gas flow rate in the range of mL min^-1 cm^-2 (volume flow rate/surface area of PI aerogel) or cm min^-1, induced by light-driven thermal transpiration effects. It demonstrated a remarkably high collection efficiency of airborne particles approaching 100% in the particle range of 10 nm–10 µm, enabling the calibration-free sampling of airborne particles without requiring an additional power supply. We explored the effects of light intensity and pore size on the sampling performance, establishing a relationship between temperature gradient and flow rate. An analysis of the distribution and penetration of NaCl particles and real-world particles was conducted at the micrometer level, which exhibits a main penetration depth of < 100 µm. With further modifications and scaling-up of the PI aerogel passive sampler for ambient applications, it holds great potential to function independently for sampling and analysis of water-soluble airborne compounds (e.g. Mg and Fe) and promote the extensive and cost-effective air quality monitoring and control.