Electrically Conductive PVDF Ultrafiltration Membrane with In Situ Formation of a Ag NP Coating Layer for Perm-Selectivity Enhancement and Fouling Mitigation

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/Fe3+ (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 Ag0 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.