Metal-phenol coordination is a widely used method to prepare nanofiltration membrane. However, the facile, controllable and scaled fabrication remains a great challenge. Herein, a novel strategy was developed to fabricate a loose nanofiltration membrane via integrating blending and interfacial coordination strategy. Specifically, iron acetylacetonate was firstly blended in Polyether sulfone (PES) substrate via non-solvent induced phase separation (NIPS), and then the loose selective layer was formed on the membrane surface with tannic acid (TA) crosslinking reaction with Fe3+. The surface properties, morphologies, permeability and selectivity of the membranes were carefully investigated. The introduction of TA improved the surface hydrophilicity and negative charge. Moreover, the thickness of top layer increased about from ~30 nm to 119 nm with the increase of TA assembly time. Under the optimum preparation condition, the membrane with assembly 3 h (PES/Fe-TA3h) showed pure water flux of 175.8 L·m−2·h−1, dye rejections of 97.7%, 97.1% and 95.0% for Congo red (CR), Methyl blue (MB) and Eriochrome Black T (EBT), along with a salt penetration rate of 93.8%, 95.1%, 97.4% and 98.1% for Na2SO4, MgSO4, NaCl and MgCl2 at 0.2 MPa, respectively. Both static adhesion tests and dynamic fouling experiments implied that the TA modified membranes showed significantly reduced adsorption and high FRR for the dye solutions separation. The PES/Fe-TA3h membrane exhibited high FRR of 90.3%, 87.5% and 81.6% for CR, EBT and MB in the fouling test, stable CR rejection (>97.2%) and NaCl permeation (>94.6%) in 24 h continuous filtration test. The combination of blending and interfacial coordination assembly method could be expected to be a universal way to fabricate the loose nanofiltration membrane for effective fractionation of dyes and salts in the saline textile wastewater.

Excellent perm-selectivity and fouling resistance are highly desirable for membrane separation in water treatment. Electrically conductive membranes have been recognized as an effective means for overcoming the permeability−selectivity trade off and enhancing the antifouling capability. However, the facile and controllable fabrication of conductive membranes with good flexibility, high conductivity, and stable separation performance remains a challenge. Herein, a novel conductive poly(vinylidene fluoride) (PVDF) ultrafiltration (UF) membrane with a thin silver nanoparticle (Ag NP) coating layer was developed via nonsolvent phase separation and green in situ reduction methods. Especially, the tannic acid/Fe 3+ (TA/Fe) complex and carbon nanotube (CNT) were first blended into a PVDF UF membrane. The thin Ag NP coating layer was then in situ formed and firmly fixed on the membrane with TA to produce a conductive PVDF/TA-Ag composite membrane. The introduced Ag NP coating layer not only narrowed the pore size but also increased the electrical conductivity of the PVDF/TA membrane, which resulted in an enhanced electrostatic repulsion and remarkable humic acid (HA) rejection. The optimal membrane (i.e., PVDF/TA-Ag12) achieved an improved HA solution flux of 265 LMH/bar and an HA rejection of 97% under −2 V applied voltage, which are 2 times and 1.7 times higher than those of the uncharged membrane, respectively. Moreover, the PVDF/TA-Ag12 membrane exhibited a superior antifouling performance under an external electrical field. Meanwhile, the electrochemical reduction of Ag + to Ag 0 on the membrane matrix can effectually avoid the Ag NP leaching, keeping the stability of the separation performance. These findings provide an alternative and cost-effective method for the development of polymer conductive membranes to enhance pollutant rejection and mitigate membrane fouling.

The effective separation of dyes and inorganic salts is highly desirable for recycling inorganic salts and water resource in printing and dyeing wastewater treatment. In this work, tannic acid (TA) and polyethyleneimine (PEI) were grafted on the PES/Fe ultrafiltration membrane via the coordination assembly and Michael addition strategy to fabricated a loose nanofiltration membrane (LNM). The effect of PEI concentration on membrane morphologies and properties was systematically investigated. The membrane surface becomes more hydrophilic and transforms into positive charge after the PEI grafting. The optimized PES/Fe-TA-PEI membrane possesses high pure water flux (124.6 L·m−2·h−1) and excellent dye rejections (98.5%, 99.8%, 98.4%, and 86.4% for Congo red, Eriochrome black T, Alcian blue 8GX, and Bromophenol blue, respectively) under 2 bar operation pressure. Meanwhile, the LNM showed a high Alcian blue 8GX rejection (>98.4%) and low NaCl rejection (<5.3%) for the dye/salt mixed solutions separation. Moreover, the PES/Fe-TA-PEI LNM exhibited good antifouling performance and long-term performance stability. These results reveal that such LNM shows great potential for effective fractionation of dyes and salts and recycling of textile wastewater.