Fast mass transport through sub-2-nanometer carbon nanotubes

Area of Science:

• Materials Science
• Nanotechnology
• Fluid Dynamics

Background:

• Microfabricated membranes with precisely controlled pore sizes are crucial for filtration and mass transport studies.
• Existing models often struggle to accurately predict fluid behavior at the nanoscale, particularly within confined geometries.

Purpose of the Study:

• To investigate gas and water transport through membranes utilizing aligned carbon nanotubes as nanopores.
• To compare experimental flow rates with predictions from established diffusion and hydrodynamics models.
• To evaluate the potential of carbon nanotube membranes for high-performance filtration applications.

Main Methods:

• Fabrication of microfluidic devices incorporating aligned carbon nanotubes (CNTs) with sub-2-nanometer diameters as selective pores.
• Experimental measurement of gas and water flow rates through the CNT membranes.
• Comparison of experimental data with predictions from the Knudsen diffusion model for gases and continuum hydrodynamics for water.
• Extrapolation of flow rates from molecular dynamics simulations for water transport.

Main Results:

• Gas flow through CNT membranes exceeded Knudsen diffusion predictions by over an order of magnitude.
• Water flow surpassed continuum hydrodynamics calculations by more than three orders of magnitude.
• Water flow rates were comparable to those predicted by molecular dynamics simulations.
• CNT membranes demonstrated gas and water permeabilities several orders of magnitude higher than commercial polycarbonate membranes, despite smaller pore sizes.

Conclusions:

• Aligned carbon nanotubes serve as highly efficient nanopores for mass transport.
• Current theoretical models inadequately describe fluid flow in sub-2-nm confined environments.
• CNT-based membranes offer superior performance for nanoscale filtration, enabling more energy-efficient processes.