Department of Civil Engineering , The University of Hong Kong , Pokfulam, Hong Kong SAR , China.
College of Chemical and Biological Engineering , Zhejiang University , Hangzhou , 310027 , China.
Environ Sci Technol. 2019 Aug 20;53(16):9764-9770. doi: 10.1021/acs.est.9b03210. Epub 2019 Aug 7.
Surface roughness and the associated nanosized voids inside the roughness structures have great influence on the separation performance of thin film composite polyamide reverse osmosis (RO) membranes. Inspired by the recent findings that these voids are formed due to the degassing of CO nanobubbles during interfacial polymerization, we systematically investigated the role of carbonate chemistry, particularly the solubility of CO, in the aqueous -phenylenediamine (MPD) solution for the first time. "Ridge-and-valley" roughness features were obtained when the pH of the MPD solution was between the two acidity constants of the carbonate system (i.e., 6.3 ≤ pH ≤ 10.3), under which condition HCO dominates over the other carbonate species. Increasing pH over this range led to both increased water permeability and better rejection of various solutes, thanks to the simultaneously enhanced effective filtration area and cross-linking degree of the polyamide layer. Further increase of pH to 12.5 resulted in more disparate rejection results due to membrane hydrolysis: rejection of neural solutes (B and As(III)) was compromised whereas that of charged solutes (NaCl and As(V)) was maintained. The mechanistic insights gained in the current study reveal the critical need to design RO membranes directly for end applications based on first principles.
表面粗糙度及其内部的纳米级空隙结构对薄膜复合聚酰胺反渗透（RO）膜的分离性能有很大的影响。受最近的研究发现的启发，这些空隙是由于界面聚合过程中 CO 纳米气泡脱气形成的，我们首次系统地研究了碳酸盐化学的作用，特别是 CO 的溶解度，在水相-苯二胺（MPD）溶液中的作用。当 MPD 溶液的 pH 值在碳酸盐体系的两个酸度常数之间（即 6.3≤pH≤10.3）时，得到“脊谷”粗糙度特征，在此条件下，HCO3- 比其他碳酸盐物种占主导地位。在此范围内增加 pH 值，由于聚酰胺层的有效过滤面积和交联度同时增强，不仅提高了水的渗透率，而且提高了对各种溶质的截留率。进一步将 pH 值提高到 12.5 会导致由于膜水解而产生更不一致的截留结果：中性溶质（B 和 As(III))的截留率受到影响，而带电溶质（NaCl 和 As(V))的截留率则保持不变。当前研究中获得的机理见解揭示了根据第一性原理直接为最终应用设计 RO 膜的关键需求。
