Efficient removal of nickel(II) from high salinity wastewater by a novel PAA/ZIF-8/PVDF hybrid ultrafiltration membrane.

Enhanced removal of trace toxic metals (ppm level) from high-salinity wastewater is crucial to ensure water safety but still a challenging task. In this study, we fabricated a new hybrid ultrafiltration membrane (PAA/ZIF-8/PVDF) by immobilizing zeolitic imidazolate framework-8 (ZIF-8) particles onto the surface of trimesoyl chloride (TMC)-modified polyvinylidene fluoride (PVDF) membrane under protection of polyacrylic acid (PAA) layer. The resultant PAA/ZIF-8/PVDF membrane exhibited relatively high water flux of 460 L·m-2 h-1 and outstanding nickel ion (Ni(II)) capacity (219.09 mg/g) from a synthetic high-salinity ([Na+] = 15000 mg/L) wastewater. X-ray photoelectron spectroscopic studies revealed that preferable Ni(II) uptake was mainly attributed to the specific interaction between Ni(II) and hydroxyl groups on ZIF-8 frameworks and carboxyl groups in PAA layer as well. Compared to PAA, ZIF-8 could selectively bind Ni(II) with negligible effect exerted by concentrated sodium ion. The filtration study showed that the 12.56-cm2 membrane could effectively treat 5.76 L high-salinity wastewater ([Ni(II)0 = 2 mg/L, [Na+]0 = 15000 mg/L) to conspicuously reduce Ni(II) below the maximum contaminant level of China, 0.1 mg/L. Moreover, the hybrid membrane could be regenerated by HCl-NaCl solution (pH = 5.5) for repeated use under direct current electric field. Generally speaking, the newly developed ZIF-8 hybrid ultrafiltration membrane showed a very promising potential in enhanced removal of toxic metals from high-salinity wastewater treatment.