Core-shell structured, mixed cellulose ester-alumina composite membranes for air filters with improved environmental resistance

In this study, a composite membrane was developed by conformally coating an ultrathin Al2O3 layer through low-temperature (90 degrees C) atomic layer deposition (ALD) on a hydrophilic mixed cellulose ester (MCE) membrane with a 3D networked microporous structure. The thickness of the deposited Al2O3 layer, without clogging the pores of the membrane, was precisely controlled by varying the number of ALD cycles from 100 to 300. The ultrathin (similar to 33 nm) Al2O3 layer greatly enhanced the resistance to various environmental stimuli and contributed to the improved removal efficiency of airborne particulate matter (PM), owing to the reduced pore size. The resulting composite membrane installed on an insect screen exhibited excellent removal efficiency (>99%) for PM of various sizes (PM1.0, PM2.5, and PM10) at a controlled flow rate of 1 L/min. In particular, unlike polypropylene-based commercial PM filters that strongly rely on electrostatic adsorption for PM filtration, the reduction in the PM removal efficiency caused by water or ethanol was negligible in the developed composite membrane, enabling long-term use even in extreme environments.

Automated summary

In this study, a composite membrane with a 3D networked microporous structure was developed by coating an ultrathin Al2O3 layer on a hydrophilic mixed cellulose ester (MCE) membrane through low-temperature atomic layer deposition (ALD). The thickness of the deposited Al2O3 layer was precisely controlled without clogging the pores of the membrane. The ultrathin Al2O3 layer greatly enhanced resistance to environmental stimuli and improved the removal efficiency of airborne particulate matter (PM) due to the reduced pore size.