Construction of hollow fiber nanofiltration separation layer with bridging network structure by polymer-anchored co-deposition for high-concentration heavy metal ion removal

In this work, a positively charged hollow fiber nanofiltration (NF) membrane with a bridging network structure was prepared by applying the polymer-anchored co-deposition method. The microstructural regularity of the bridging network structure during the formation and evolution process were interpreted. The acquired results indicated that both tannic acid (TA) and ferric ion (Fe3+) can be rapidly deposited and then anchored on the membrane surface by the chemical bridging with polyethyleneimine (PEI), which effectively filled the pores and significantly improved the positive charge of the membrane surface. Interestingly, the proposed membrane showed an excellent removal efficiency of high-concentration heavy metal ion (4000 mg L−1, Fe3+ (95.7%), Cu2+ (94.1%), Mn2+ (92.9%), Zn2+ (91.1%)), while keeping a high pure water permeance (23.18 L m−2 h−1 bar−1). By combining the relationship between the hydrated diameter about the heavy metal ions, the molecular weight cut-off (MWCO) of NF membrane and the surface charge of membrane, the underlying mechanism of high-concentration heavy metal ion removal was expounded. In addition, the membrane exhibited excellent ability to resist acid/base, anti-fouling capacity and long-term stability. Our work provides a new method for the fabrication of hollow fiber NF membrane with high separation performance to high-concentration heavy metal ions.