Environmental Engineering Research Centre, Department of Civil Engineering , The University of Hong Kong , Pokfulam , Hong Kong, China.
Shenzhen Environmental Science and New Energy Laboratory, Tsinghua-Berkeley Shenzhen Institute , Tsinghua University , Shenzhen 518055 , China.
Environ Sci Technol. 2019 Mar 5;53(5):2660-2669. doi: 10.1021/acs.est.8b05741. Epub 2019 Feb 14.
A novel noninvasive technique-microscopic laser-induced fluorescence (micro-LIF)-has been applied to achieve in situ visualization of concentration polarization (CP) of nanoparticles during cross-flow ultrafiltration at high resolutions. The reversible, highly dynamic nature of CP and its sensitive response to the filtration conditions were investigated and validated by direct visualization of the CP layer and the well depicted concentration profile near the membrane surface. Using micro-LIF, the formation of a CP layer during filtration and its back-diffusion after the filtration ceased can be directly observed. The dynamic variation of the CP layer with the cross-flow velocity and transmembrane pressure (TMP) change has also been demonstrated. The results showed that CP reached the steady state approximately 1 min after the filtration condition change. A higher cross-flow velocity and/or a lower TMP decrease the CP concentration and thickness. Further quantitative analysis of the filtration test results using the film theory model helps to obtain the particle concentration at the membrane surface and the thickness of the CP layer (30-50 μm). Accordingly, the nature of CP dynamics was characterized and the deficiency of the traditional CP model was explored.
一种新颖的非侵入性技术——微观激光诱导荧光（micro-LIF）已被应用于在高通量过滤过程中实现纳米粒子浓度极化（CP）的高分辨率原位可视化。CP 的可逆、高度动态特性及其对过滤条件的敏感响应通过 CP 层的直接可视化和膜表面附近的良好浓度分布进行了研究和验证。使用 micro-LIF，可以直接观察到过滤过程中 CP 层的形成以及过滤停止后的反向扩散。还展示了 CP 层随错流速度和跨膜压力（TMP）变化的动态变化。结果表明，在过滤条件变化后约 1 分钟 CP 达到稳定状态。较高的错流速度和/或较低的 TMP 会降低 CP 浓度和厚度。使用膜理论模型对过滤测试结果进行进一步的定量分析，有助于获得膜表面的颗粒浓度和 CP 层的厚度（30-50μm）。因此，对 CP 动力学的性质进行了表征，并探讨了传统 CP 模型的不足。
