ABSTRACT
The polyamide layer in a thin film composite membrane typically exhibits an irregular and compact structure, often presenting uneven ridge-and-valley patterns or nodular formations. Examination and measurement of this structure are commonly conducted using electron microscopy techniques. However, microscopic examinations do not provide a comprehensive understanding of the inherent attributes of the polyamide layer. Thus, Tan et al. [91] conducted membrane filtration tests by filtrating gold nanoparticles with a concentration of 1.0×1012 ppm at 4.8 bar for 10 min. Subsequently, they employed microscopic characterization to visually inspect the spatial distribution of water permeability sites within the Turing-structured membranes. It was revealed from transmission electron microscopy micrographs that the deposition of gold nanoparticles was not uniformly distributed on the polyamide surface. Two Turing-structured membranes were investigated in this study, with TS-1 and TS-II denoting membranes with nanoscale spots and stripes, respectively. The TS-II membrane exhibited higher water flux of 125 L/m2.h, which was approximately two times higher than that of the TS-I membrane of 64 L/m2.h, while maintaining similar Na2SO4 rejections (>99%) under the same testing conditions (measured at 4.8 bar, 2000 ppm Na2SO4). This finding exhibited a strong correlation with the surplus surface area ratio of the membranes. This correspondence suggests that the Turing structures exert a significant influence on the water flux. Thus, it was concluded that certain distinct regions within the Turing structures gave relatively heightened water permeability, which contribute to the membranes exhibiting improved water transport characteristics.
