Membrane-based electrospun poly-cyclodextrin nanofibers coated with ZnO nanograins by ALD: Ultrafiltration blended photocatalysis for degradation of organic micropollutants

Membranes with simultaneous selective adsorption functionality and excellent photocatalytic response have been proposed for water remediation, especially for treating textile and industrial wastewater. However, state-of-the-art membranes are easily fouled by pollutant adsorption that impacts their reusability. Here we report the development of a crosslinked electrospun poly-cyclodextrin (Poly-CD) nanofiber (NF) membrane coated by atomic layer deposition (ALD) with ZnO nanograins for the removal of pollutants from wastewater. The inherent high affinity of poly-CD NFs favored the selective adsorption of cationic impurities, and the reactive oxygen species produced by photoirradiation of the ZnO surface effectively degraded adsorbed contaminants. The NFMs has signifies that, even under the dark, they have a removal efficiency of around 80% which may be due to the high adsorption nature. Further, these NFM are highly reusable while decorating the ZnO nanograins on the NFM, which degraded the adsorbed pollutant and opened up the active site to further adsorb the dye molecule on the poly-CD surface. Under the static mode, the ZnO(100)@poly-CD NFM achieved the highest MB removal efficiency of 94.3%, followed by ZnO(25)@poly-CD, ZnO(200)@poly-CD, and poly-CD, which had removal rates of 91.3%, 87.7%, and 83.1%, respectively in 120 min of photoirradiation. Modulating the photocatalytic reaction in a flow channel, ZnO(100)@poly-CD nanofibrous membranes (NFMs) achieved 2.19-fold higher removal efficiencies (98.6% in 60 min) in a flow-through filtration system than under static conditions (a non-filtration method). Furthermore, the flow-through mode promoted the mass transfer of pollutants through NFMs, which increased reactive oxygen species production by inhibiting electron-hole recombination. Furthermore, the inherent self-cleaning function conferred by the photocatalytic activity of surface ZnO increased membrane structural stability and provided a faster removal rate.