Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong SAR 999077, China.
Department of Mechanical Engineering, The University of Hong Kong, Pokfulam, Hong Kong SAR 999077, China.
Environ Sci Technol. 2022 Jul 19;56(14):10279-10288. doi: 10.1021/acs.est.1c08691. Epub 2022 Jul 8.
The permeance and selectivity of a reverse osmosis (RO) membrane are governed by its ultrathin polyamide film, yet the growth of this critical film during interfacial polymerization (IP) has not been fully understood. This study investigates the evolution of a polyamide nanofilm at the aqueous/organic interface over time. Despite its thickness remaining largely constant (∼15 nm) for the IP reaction time ranging from 0.5 to 60 min, the density of the polyamide nanofilm increased from 1.25 to 1.36 g cm due to the continued reaction between diffused -phenylenediamine and dangling acyl chloride groups within the formed polyamide film. This continued growth of the polyamide nanofilm led to a simultaneous increase in its crosslinking degree (from 50.1 to 94.3%) and the healing of nanosized defects, resulting in a greatly enhanced rejection of 99.2% for NaCl without sacrificing water permeance. Using humic acid as a molecular probe for sealing membrane defects, the relative contributions of the increased crosslinking and reduced defects toward better membrane selectivity were resolved, which supports our conceptual model involving both enhanced size exclusion and healed defects. The fundamental insights into the growth mechanisms and the structure-property relationship of the polyamide nanofilm provide crucial guidance for the further development and optimization of high-performance RO membranes.
反渗透（RO）膜的渗透性和选择性由其超薄聚酰胺薄膜决定，但界面聚合（IP）过程中该关键薄膜的生长尚未被充分理解。本研究调查了聚酰胺纳米薄膜在水/有机界面随时间的演变。尽管在 0.5 至 60 分钟的 IP 反应时间内，其厚度基本保持不变（约 15nm），但由于在形成的聚酰胺薄膜内扩散的 - 苯二胺和悬空酰氯基团之间的持续反应，聚酰胺纳米薄膜的密度从 1.25 增加到 1.36gcm。聚酰胺纳米薄膜的持续生长导致其交联度（从 50.1%增加到 94.3%）和纳米级缺陷的愈合同时增加，从而在不牺牲水渗透性的情况下，对 NaCl 的截留率大大提高到 99.2%。使用腐殖酸作为密封膜缺陷的分子探针，解决了增加的交联和减少的缺陷对更好的膜选择性的相对贡献，这支持了我们涉及增强尺寸排除和修复缺陷的概念模型。对聚酰胺纳米薄膜生长机制和结构-性能关系的深入了解为高性能 RO 膜的进一步开发和优化提供了关键指导。
