Centre for Advanced 2D Materials, National University of Singapore , Singapore 117542.
Department of Physics, National University of Singapore , Singapore 117551.
Nano Lett. 2017 Feb 8;17(2):728-732. doi: 10.1021/acs.nanolett.6b03837. Epub 2017 Jan 19.
Nanostructured graphene-oxide (GO) laminate membranes, exhibiting ultrahigh water flux, are excellent candidates for next generation nanofiltration and desalination membranes, provided the ionic rejection could be further increased without compromising the water flux. Using microscopic drift-diffusion experiments, we demonstrated the ultrahigh charge selectivity for GO membranes, with more than order of magnitude difference in the permeabilities of cationic and anionic species of equivalent hydration radii. Measuring diffusion of a wide range of ions of different size and charge, we were able to clearly disentangle different physical mechanisms contributing to the ionic sieving in GO membranes: electrostatic repulsion between ions and charged chemical groups; and the compression of the ionic hydration shell within the membrane's nanochannels, following the activated behavior. The charge-selectivity allows us to rationally design membranes with increased ionic rejection and opens up the field of ion exchange and electrodialysis to the GO membranes.
具有超高水通量的纳米结构氧化石墨烯（GO）层状膜是下一代纳滤和反渗透膜的优秀候选材料，只要在不牺牲水通量的情况下，离子截留率能够进一步提高。通过微观漂移扩散实验，我们证明了 GO 膜具有超高的电荷选择性，对于具有相同水合半径的阳离子和阴离子物种，其渗透率相差一个数量级以上。通过测量不同尺寸和电荷的多种离子的扩散，我们能够清楚地区分导致 GO 膜离子筛分的不同物理机制：离子与带电化学基团之间的静电排斥；以及膜纳米通道内离子水合壳的压缩，遵循激活行为。这种电荷选择性使我们能够合理地设计具有更高离子截留率的膜，并将离子交换和电渗析领域扩展到 GO 膜。
