The most densified vertically-aligned carbon nanotube membranes and their normalized water permeability and high pressure durability

• The highest pore density of a vertically aligned carbon nanotube membrane was fabricated.
• The membrane was fabricated by combining vaporization of ethanol and mold pressing.
• Urethane monomer was effectively filled between the carbon nanotubes.
• The membrane showed the highest water permeability and low compaction index.
• The pore size of VA CNTs mainly contributed to the enhancement of water permeability.

Vertically aligned (VA) carbon nanotubes (CNTs) could be a promising material for membrane filtration due to their ultrahigh water permeability. However, VA CNT based membranes showed three challenging issues: low pore density, poor mechanical strength, and a complex fabrication process. In this study, the highest pore density 3.0×1012 pore/cm2 was achieved by combining volatile ethanol addition and subsequent mold pressing. Urethane monomer was infiltrated between CNTs through an ethanol stream. Polymerized urethane provided mechanical strength to the VA CNT membrane. Membrane pore size distribution was analyzed based on the polyethylene oxide rejection. Pore size distribution ranged from 3.0 to 5.5 nm and the average pore size was 4.1 nm. The pressure durability representing mechanical strength was analyzed based on the compaction index (CI). The VA CNT membrane showed 4 times higher CI than that of the commercial ultrafiltration (UF) membrane due to its reinforcement. The VA CNT membrane showed 938 times higher water permeability than the UF membrane. Water permeabilities of all VA CNT membranes studied until now were compared using normalized forms based on the membrane pore structural parameters in the Hagen–Poiseuille (HP) equation. The results demonstrated that the VA CNT membrane fabricated in this study showed the highest water permeability enhancement and membrane pore size showed the highest deviation from HP theory among three structural parameters.

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