Osmosis plays a central role in many chemical separation processes. Among various biological and artificial channels, carbon nanotubes (CNTs) stand out due to their exceptional water transport efficiency and variability of pore-size, down to molecular dimensions, thereby approaching ideal semipermeability. We report osmotically driven water and salt transport across a membrane of vertically aligned CNTs in a titania matrix whose surface is functionalized with a self-assembled monolayer of octadecylphosphonic acid. The increased steric hindrance and hydrophobicity at the pore entrance of CNTs improved salt rejection while maintaining enhanced osmotic water transport, thanks to an atomically smooth surface of the nanotubes. In addition to the experimental demonstration of osmosis, we observed a net negative osmotic water flow at lower salt concentration gradient and non-Fickian behavior of the reverse salt flux. This observation is attributable to the interface-driven fluidic phenomenon known as diffusio-osmosis that drives water flow in the direction opposite to osmotic flow. The ion–CNT interactions are responsible for the simultaneous occurrence of the two osmotic transport mechanisms and the salt-specific osmotic transport characteristics.

中文翻译：

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跨表面功能化碳纳米管膜的渗透运输。

渗透在许多化学分离过程中起着核心作用。在各种生物和人工渠道中，碳纳米管（CNTs）因其出色的水传输效率和低至分子尺寸的孔径变化而脱颖而出，从而接近理想的半渗透性。我们报道了渗透驱动的水和盐在二氧化钛基质中垂直排列的碳纳米管的膜上的迁移，其表面被十八烷基膦酸的自组装单层功能化。由于纳米管的原子光滑表面，CNT孔入口处增加的空间位阻和疏水性改善了除盐率，同时保持了增强的渗透水传输。除了渗透的实验证明之外，我们观察到较低盐浓度梯度下的净负渗透水流量和反向盐通量的非Fickian行为。该观察结果归因于被称为扩散渗透的界面驱动流体现象，该现象驱动水沿与渗透流相反的方向流动。离子-CNT相互作用负责同时发生两种渗透转运机制和盐特异性渗透转运特性。