Exploring Single-File Diffusion in One-Dimensional Nanochannels by Laser-Polarized 129Xe NMR Spectroscopy

Single-file diffusion behavior is expected for atoms and mols. in 1-dimensional gas phases of nanochannels with transverse dimensions that do not allow for the particles to bypass each other. Although single-file diffusion may play an important role in a wide range of industrial catalytic, geol., and biol. processes, exptl. evidence is scarce despite the fact that the dynamics differ substantially from ordinary diffusion. The authors demonstrate the application of continuous-flow laser-polarized 129Xe NMR spectroscopy for the study of gas transport into the effectively 1-dimensional channels of a microporous material. The novel methodol. makes it possible to monitor diffusion over a time scale of tens of seconds, often inaccessible by conventional NMR expts. The technique can also be applied to systems with very small mobility factors or diffusion consts. that are difficult to det. by currently available methods for diffusion measurement. Expts. using xenon in nanochannel systems can distinguish between unidirectional diffusion and single-file diffusion. The exptl. observations indicate that single-file behavior for xenon in an org. nanochannel is persistent even at long diffusion times of over tens of seconds. Finally, using continuous-flow laser-polarized 129Xe NMR spectroscopy, the authors describe an intriguing correlation between the obsd. NMR line shape of xenon within the nanochannels and the gas transport into these channels