Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education, China), School of Environmental Science and Technology , Dalian University of Technology , Dalian 116024 , China.
School of Civil and Environmental Engineering , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States.
Environ Sci Technol. 2019 Jan 15;53(2):868-877. doi: 10.1021/acs.est.8b04268. Epub 2018 Dec 27.
Nanofiltration (NF) is considered a promising candidate for brackish and seawater desalination. NF exhibits high multivalent ion rejection, but the rejection rate for monovalent ions is relatively low. Besides, great challenges remain for conventional NF membranes to achieve high ion rejection without sacrificing water flux. This work presents an effective strategy for improving the ion rejection of conductive NF membrane without decreasing the permeability through electrically assisted enhancement of surface charge density. When external voltage is increased from 0 to 2.5 V, the surface charge density of the membrane increases from 11.9 to 73.0 mC m, which is 6.1× higher than that without external voltage. Correspondingly, the rejection rate for NaSO increases from 81.6 to 93.0% and that for NaCl improves from 53.9 to 82.4%; meanwhile, the membrane retains high permeabilities of 14.0 L m h bar for NaSO filtration and 14.5 L m h bar for NaCl filtration. The Donnan steric pore model analysis suggests that the Donnan potential difference between the membrane and bulk solution is increased under electrical assistance, leading to increased ion transfer resistance for improved ion rejection. This work provides new insight into the development of advanced NF technologies for desalination and water treatment.
纳滤（NF）被认为是一种有前途的咸水和海水淡化候选技术。NF 表现出对高价离子的高排斥率，但对单价离子的排斥率相对较低。此外，对于传统的 NF 膜来说，在不牺牲水通量的情况下实现高离子排斥率仍然存在巨大挑战。本工作提出了一种通过电辅助增强表面电荷密度来提高导电 NF 膜离子排斥率而不降低渗透性的有效策略。当外加电压从 0 增加到 2.5 V 时，膜的表面电荷密度从 11.9 增加到 73.0 mC m，比没有外加电压时增加了 6.1 倍。相应地，NaSO 的截留率从 81.6%提高到 93.0%，NaCl 的截留率从 53.9%提高到 82.4%；同时，膜对 NaSO 的过滤保持了 14.0 L m h bar 的高渗透性，对 NaCl 的过滤保持了 14.5 L m h bar 的高渗透性。Donnan 位阻孔模型分析表明，在外加电场的作用下，膜与体相溶液之间的 Donnan 电位差增大，导致离子传递阻力增大，从而提高离子排斥率。本工作为海水淡化和水处理领域先进 NF 技术的发展提供了新的见解。
