Recyclable nanoscale zerovalent iron (nZVI)-immobilized electrospun nanofiber composites with improved mechanical strength for groundwater remediation

Nanoscale zero-valent iron (nZVI), as a promising material, has been widely used in groundwater remediation. Membrane-supported nZVI can both avoid nZVI agglomeration for better reactivity and recycle nZVI/contaminants to lower the risk of secondary pollution. However, membrane mechanical strength is a critical property for long-term operation and the regeneration of nZVI membranes. This study tried to use a high molecular weight dual-crosslinking method to improve the mechanical strength of polymeric electrospun nanofiber membranes. Specifically, high molecular weight polyacrylic acid (PAA, Mw = 450,000) was dual-crosslinked by adding polyvinyl alcohol (PVA) as covalent cross-linker (named as M450k) and Fe(II) or Fe(III) as the ionic cross-linker (named as M450k-II and M450k-III). The results indicated that the M450k had better thermal resistance against membrane shrinkage, thus having larger surface areas and more COOH groups to immobilize more nZVI particles. Besides, M450k-III had the highest tensile strength at 8.5 MPa, 5 times the figure for the mono-crosslinked low molecular weight membrane (M2k). In terms of nZVI immobilization and filtration performance, the Fe(II)crosslinked membrane had better nZVI immobilization with the highest removal capacity at 463 mg/g while Fe (III)-crosslinked membrane had overwhelming mechanical strength with decent and stable removal capacity under multiple nZVI regenerations over 15 filtration cycles. Generally, the high molecular weight Fe(III)crosslinked PAA-PVA electrospun nZVI showed better potential for long-term filtration process.