Rapid industrialization has resulted in the contamination of water bodies with potentially toxic heavy metals, such as copper, arsenic, and lead. It has become a serious concern because the contaminated water, if consumed, leads to several diseases, particularly organ disorders [Briffa
et al. Heliyon 6.9 (2020) e04691]. Therefore, there is a need to treat the heavy metals-polluted water sources using advanced water treatment technologies. There are various methods, e.g., coagulation and flocculation, ion exchange, photocatalysis, adsorption, and membrane filtration, to remove potentially toxic heavy metals from the water system. In recent years, membrane separation has gained immense popularity. In particular, the one-step adsorption-ultrafiltration membrane separation process is presently the preferred water purification method. Because it offers high removal efficiency, cost-efficiency, high water flux, less prone to fouling, low-pressure operation, and scalability. In this process, the polluted water is passed through the adsorptive ultrafiltration membranes, which perform the adsorption and filtration in a single-step [Huang
et al. J. Appl. Polym. Sci. 137 (2020) 48579]. Several nanomaterials, such as metal/metal oxide nanoparticles, carbon nanotubes, and zeolites, have been used as adsorbents to prepare adsorptive membranes to remove heavy metals from the contaminated water systems. Recently, metal organic frameworks, particularly zeolitic imidazole frameworks (ZIFs), have gained tremendous attention due to their exceptional physicochemical properties, e.g., high surface area to volume ratio, tunable pore size, and ease of synthesis and functionalization [Nasir
et al. Chemosphere 232 (2019) 96-112, Adam
et al. Membrane Separation Principles and Applications. Elsevier (2019) 361-400]. However, upon their addition to the polymer matrix, they agglomerate, which can be mitigated by preparing them in a graphene oxide environment [Wang
et al. ACS Appl. Mater. Interfaces 8.38 (2016) 25508-25519].
Based on the above considerations, in the present study, novel ZIF-67/GO nanohybrid incorporated polyethersulfone hollow fiber adsorptive membranes (HFMs) were prepared. The ZIF-67/GO-PES HFMs showed favorable surface morphology, functionalization with oxygen-enriched surface groups, improved hydrophilicity, and a negatively charged surface. The prepared adsorptive membranes showed remarkably high pure water flux (346.4 ± 11.2 L/m2/h) and flux recovery (95.7%) for the HFMs embedded with 0.5 wt.% ZIF-67/GO nanohybrid. The adsorption capacity of these HFMs was found to be 66.4 ± 3.2 mg/g and 86.4 ± 4.3 mg/g for Cu2+ and Pb2+, respectively. Upon testing these membranes with the simulated naturally contaminated water, significantly high removal of Cu2+ (94.5 ± 1.2%) and Pb2+ (97.8 ± 1.1%) was measured. These novel adsorptive HFMs were regenerated for 5 filtration cycles, and they maintained their separation performance. These adsorptive HFMs showed preferential removal (>50 %) of these heavy metal ions from the mixture of different major competing ions found in the naturally contaminated water. Thus, from these results, it was inferred that ZIF-67/GO nanohybrid embedded polyethersulfone hollow fiber adsorptive membranes are potential candidates for the efficient removal of potentially toxic heavy metals from water bodies.
