(351ap) Ultra-Permeable Wafer-Scale SWCNT Membranes for Efficient Dye/Salt Fractionation

Enhanced fluid transport in single-walled carbon nanotubes (SWCNT) promises to enable major advancements in many membrane applications, from efficient water purification to advanced protective garments. So far, practical realization of these promises has been hampered by the difficulty of fabricating large-area, defect-free membranes with a high density of open, small diameter SWCNT pores. To simultaneously increase permeability, selectivity, and membrane area, we fabricated membranes from wafer-scale (100 mm) SWCNT forests optimized for high CNT number density (2 x 10¹² tubes/cm²) and narrow diameters (average < 2 nm) and ensured complete opening of all conducting nanotubes in the composite. Opening all the nanotubes enabled us to quantify pressure-driven transport enhancement for gases and liquids more accurately than previous experimental reports. Measured gas permeances exceed Knudsen diffusion by more than 100-fold, whereas water transport rates surpass the no-slip Hagen-Poiseuille prediction by 6200 times. In addition, we demonstrate the ability to scale up membrane area 60 times without loss of performance. Fabricated CNT membranes at both small- and large-scale display water permeances in excess of 200 L/m²hbar, significantly larger than those of commercial loose nanofiltration/tight ultrafiltration membranes of similar pore size and reject nanometer-sized molecules while simultaneously permitting the complete passage of concentrated salt solutions (NaCl and Na₂SO₄). Taken together with their excellent chemical resistance, these membranes offer opportunities for energy-efficient nanofiltration/ultrafiltration processes in chemically demanding environments.