Toward tailoring nanofiltration performance of thin-film composite membranes: Novel insights into the role of poly(vinyl alcohol) coating positions

Nanofiltration (NF)-based purification technology has been considered as an efficient approach for providing freshwater due to its excellent feasibility and selectivity for treating saline water. However, the preparation of high-performance NF membranes with simultaneously high water permeance and fouling resistance still remains a bottleneck in the practical fabrication process. To provide new insights into the fabrication of highly permeable and fouling resistant TFC membranes, two NF membranes were fabricated via a gutter- and coating layer-assisted strategy using poly(vinyl alcohol) (PVA). The surface morphologies, chemical structures, and filtration performances were systematically evaluated. The PVA gutter-layered NF membrane (PA-TFC-I) showed a much rougher and higher negatively charged surface, reaching an outstanding water permeability of 28.2 ± 0.3 L m−2 h−1 bar−1 with excellent rejection to Na2SO4 (99.8 ± 0.1%). In contrast, superior antifouling performance was observed for the PVA-coated membrane (PA-TFC-P), presenting an ≥ 80.0% flux recovery ratio after each physical cleaning process during three cycles filtration of humic acid. Compared to the control NF membrane, the PVA coating rendered the PA-TFC-P membrane with excellent antifouling performance without sacrificing its rejection performance, while the PVA gutter-layered strategy endowed the PA-TFC-I membrane with ultrahigh water permeance and enhanced salt rejections. Therefore, a double modification strategy integrating the PVA-coating and guttering may be a hopeful avenue for developing highly-efficient NF membranes with both high water flux and outstanding antifouling properties.