Fabrication of composite nanofiltration membranes by dopamine-assisted poly(ethylene imine) deposition and cross-linking

Abstract

Positively charged composite nanofiltration (NF) membranes with good stability were prepared by dopamine (DA) assisted poly(ethylene imine) (PEI) deposition on a polysulfone ultrafiltration (UF) substrate followed by a cross-linking step. Attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electronic microscopy, and atom force microscopy were employed to characterize the surface chemistry and morphology of the obtained composite membranes. The DA and PEI co-deposition conditions were optimized based on knowledge of the co-deposition mechanism. The effects of the cross-linker concentration, cross-linking time, and reaction temperature on the permeation and separation properties of the prepared composite membranes were investigated in detail. Under optimized conditions, the MgCl₂ rejection and permeation flux of the composite membrane reached 80.4% and 19.6 L/(m²·h), respectively (the feed was 0.01 mol/L of MgCl₂ solution under a test pressure of 0.4 MPa). The rejection of various salts followed the order MgCl₂≈CaCl₂>MgSO₄>NaCl>Na₂SO₄, suggesting the membranes were positively charged. The composite membranes showed good durability under alkaline aqueous conditions. This study provided new insights into the fabrication of mussel-inspired thin-film composite nanofiltration membranes.

摘要

目的

利用多巴胺改性构建一种简单制备荷正电复合纳 滤膜,解决多巴胺类改性材料耐碱性差的问题。

创新点

1. 利用共沉积技术与交联反应成功制备了荷正电 复合纳滤膜;相较于传统多巴胺改性膜,该复合 膜的稳定性大大提高。2. 经过测试表征,制备得 到的纳滤膜的分离尺寸属于疏松纳滤膜范围,可 用于相应尺度的分离领域。

方法

1. 通过多巴胺与聚乙烯亚胺共沉积,首先实现二 者的表面沉积,随后通过交联剂交联制备复合膜 (图1);2. 对改性膜前后表面理化性质进行相应 表征(表2 和图3~6);3. 通过测试通量和截留等 性能及分析相关纳滤模型,表征该复合膜分离性 能(图7 和8,公式(5)和(7));4. 通过长期 分离测试及碱性溶液清洗,测试复合膜的稳定性 和耐碱性。

结论

1. 成功制备了具有荷正电性的复合纳滤膜;2. 通 过通量和截留数据拟合分析得出该膜截留尺寸 在1.5 nm 和2 nm 之间,属于疏松纳滤膜,可用 于相应尺度分离;3. 该复合膜具有良好的稳定性 及耐碱性,应用范围更广。