Robert L. McGinnis

Energy-efficient water purification made possible by Yale engineers

In the US, researchers based at Yale University are developing an energy-efficient system for water purification. Using a new twist on old technology, the engineers are employing ‘forward osmosis’, which exploits the natural diffusion of water through a semi-permeable membrane.

Large-scale polymeric carbon nanotube membranes with sub–1.27-nm pores

We report the first study of large-scale polymer membranes with <1.27-nm-diameter aligned carbon nanotubes. We report the first characterization study of commercial prototype carbon nanotube (CNT) membranes consisting of sub–1.27-nm-diameter CNTs traversing a large-area nonporous polysulfone film. The membranes show rejection of NaCl and MgSO4 at higher ionic strengths than have previously been reported in CNT membranes, and specific size selectivity for analytes with diameters below 1.24 nm. The CNTs used in the membranes were arc discharge nanotubes with inner diameters of 0.67 to 1.27 nm. Water flow through the membranes was 1000 times higher than predicted by Hagen-Poiseuille flow, in agreement with previous CNT membrane studies. Ideal gas selectivity was found to deviate significantly from that predicted by both viscous and Knudsen flow, suggesting that surface diffusion effects may begin to dominate gas selectivity at this size scale.