(115d) Water Treatment Opportunities Utilizing the Dramatic Nano-Fluidic Properties of Carbon Nanotube Membranes

Carbon nanotubes have three key attributes that make them of great interest for novel membrane applications   1) atomically flat graphite surface allows for ideal fluid slip boundary conditions   2) the plasma cutting process to open CNTs inherently places functional chemistry at CNT core entrance and  3) CNT are electrically conductive allowing for electrochemical reactions and application of electric fields gradients at CNT tips.  In general, the transport mechanisms through CNT membrane are a) ionic diffusion is near bulk expectation with no enhancement from CNT  b) gas flow is enhanced by ~1-2 order of magnitude due to specular reflection off of flat graphitic surface  c) and pressure driven flux of a variety of solvents are 4-5 ORDERS OF MAGNITUDE FASTER than conventional Newtonian flow due to atomically flat graphite planes inducing nearly ideal slip conditions.  Facilitated transport, electrocatalytic defouling and electroosmotic pumping through CNTs are observed.  For water treatment applications such, as RO desalination, a 2 wt% CNT polymer has the potential to result in a 100 fold reduction in membrane area.  However one of the key difficulties is that to impart membrane chemical selectivity, chemical functionalization of CNT surfaces ruin the slip boundary condition and dramatically reduce flow enhancements.  Efforts in the field generally rely on placing high charge density at CNT tips to reject ions or to precisely control CNT diameter to allow only single file columns of water.