Centre for Membrane Separation and Water Science & Technology, Department of Chemical Engineering, Zhejiang University of Technology, Hangzhou, 310014, P. R. China.
Collaborative Innovation Center of Membrane Separation and Water Treatment of Zhejiang Province, Hangzhou 310014, China.
Environ Sci Technol. 2020 Mar 17;54(6):3559-3569. doi: 10.1021/acs.est.9b05892. Epub 2020 Mar 5.
Transport of water, solutes, and contaminants through a thin film composite (TFC) membrane is governed by the intrinsic structure of its polyamide separation layer. In this work, we systematically characterized the nanoscale polyamide structure of four commercial TFC membranes to reveal the underlying structure-property relationship. For all the membranes, their polyamide layers have an intrinsic thickness in the range of 10-20 nm, which is an order of magnitude smaller than the more frequently reported apparent thickness of the roughness protuberances due to the ubiquitous presence of nanovoids within the rejection layers. Tracer filtration tests confirmed that these nanovoids are well connected to the pores in the substrates via the honeycomb-like opening of the backside of the polyamide layers such that the actual separation takes place at the frontside of the polyamide layer. Compared to SW30HR and BW30, loose membranes XLE and NF90 have thinner intrinsic thickness and greater effective filtration area (e.g., by the creation of secondary roughness features) for their polyamide layers, which correlates well to their significantly higher water permeability and lower salt rejection. With the aid of scanning electron microscopy, transmission electron microscopy, and tracer tests, the current study reveals the presence of nanosized defects in a polyamide film, which is possibly promoted by excessive interfacial degassing. The presence of such defects not only impairs the salt rejection but also has major implications for the removal of pathogens and micropollutants.
水、溶质和污染物通过薄膜复合（TFC）膜的传输受其聚酰胺分离层的固有结构控制。在这项工作中，我们系统地表征了四种商业 TFC 膜的纳米级聚酰胺结构，以揭示潜在的结构-性能关系。对于所有的膜，它们的聚酰胺层具有 10-20nm 的固有厚度，这比由于在排斥层中普遍存在纳米空隙而导致的更频繁报道的粗糙度突起的表观厚度小一个数量级。示踪过滤测试证实，这些纳米空隙通过聚酰胺层背面的蜂窝状开口与基底中的孔很好地连接，使得实际的分离发生在聚酰胺层的前侧。与 SW30HR 和 BW30 相比，疏松膜 XLE 和 NF90 的聚酰胺层具有更薄的固有厚度和更大的有效过滤面积（例如，通过形成二次粗糙度特征），这与其更高的水透过率和更低的盐截留率相关。借助扫描电子显微镜、透射电子显微镜和示踪剂测试，本研究揭示了聚酰胺膜中存在纳米尺寸的缺陷，这可能是由过度的界面脱气引起的。这些缺陷的存在不仅会降低盐的截留率，而且对病原体和微污染物的去除也有重大影响。
