Porous metal foams have been one of the most sought-after materials owing to their combination of bulk metallic characteristics (e.g., thermal/electrical conductivity and ductility) and nanometric size-effect properties (e.g., catalytic reactivity, plasmonic behavior, and high surface area). Traditional sol-gel approaches, though one of the most frequently used method to produce mesoporous metal foams, were hindered for scalable production and wide applications because of its tedious multistep procedure, time-consuming gelation time, and polydisperse pore sizes. Herein, by depositing biological nanofibrils (chitin, cellulose, and silk) on commercial filtration membranes, we report a facile approach to sieve and recycle sub-6 nm nanoparticles of noble metals (Au and Pt) via nonclogging filtration into three-dimensional (3D) networks with interconnected mesopores. The porous networks could withstand air-drying, in contrast to freezing/supercritical drying conventionally used for mesoporous foams preparation. This approach was also applicable to both mesoporous monometallic (Au, Pt) and bimetallic (Au-Pt) foams. Moreover, the resultant mesoporous metallic foams show high porosity up to 90%, homogeneous mesoporous structure, and metallic conductivity up to 104 S/cm. Thus, this rapid and scalable sieving procedure not only offers a possibility of sieving noncloggingly for efficient recovery of metal nanoparticles but also starts a pathway to produce conductive and flexible mesoporous foams applicable in broad fields such as continuous flow catalysis and smart actuating.
Keywords: biological nanofibrils; conductive mesoporous foams; electrical actuators; noble metal nanoparticles; noncloggingly sieving.