Aligned Multiwalled Carbon Nanotube Membranes

TLDR

The authors fabricated a polymer‑embedded membrane of aligned carbon nanotubes whose lengths were tuned by selective electrochemical oxidation and whose carboxylate‑terminated ends were functionalized, yielding a well‑ordered nanoporous structure. Electron microscopy, electrical, gas, and ionic transport measurements confirmed the aligned CNT membrane, showing nitrogen permeance matching Knudsen diffusion and Ru(NH₃)₆³⁺ transport through the cores, with biotin‑functionalized tips reducing Ru(NH₃)₆³⁺ flux fifteenfold upon streptavidin binding, illustrating gated transport for separations and sensing.

Abstract

An array of aligned carbon nanotubes (CNTs) was incorporated across a polymer film to form a well-ordered nanoporous membrane structure. This membrane structure was confirmed by electron microscopy, anisotropic electrical conductivity, gas flow, and ionic transport studies. The measured nitrogen permeance was consistent with the flux calculated by Knudsen diffusion through nanometer-scale tubes of the observed microstructure. Data on Ru(NH 3 ) 6 3+ transport across the membrane in aqueous solution also indicated transport through aligned CNT cores of the observed microstructure. The lengths of the nanotubes within the polymer film were reduced by selective electrochemical oxidation, allowing for tunable pore lengths. Oxidative trimming processes resulted in carboxylate end groups that were readily functionalized at the entrance to each CNT inner core. Membranes with CNT tips that were functionalized with biotin showed a reduction in Ru(NH 3 ) 6 3+ flux by a factor of 15 when bound with streptavidin, thereby demonstrating the ability to gate molecular transport through CNT cores for potential applications in chemical separations and sensing.