| Microorganisms and some of their metabolite still remain a great threat to human health.Currently,chlorine disinfection is among the most commonly used techniques to control microbial pollution,though generation of disinfection by-products(DBPs)and regrowth of bacteria have raised public concern.Phosphorus is an essential nutrient for bacteria growth,thus an extremely low concentration of phosphate(<20μg-P/L)will allow nutrient starvation-killing of bacteria without generation of DBPs.Nowadays,phosphate starvation-killing antibacteria is mainly based on hybrid membrane containing La(Ⅲ)oxide nanoparticles(NPs),and their application is intensively hindered by relatively high cost,hard to regenerate after adsorption,and tendency to cause fouling during filtration due to the generation of La(Ⅲ)phosphate crystals.Low-cost Fe(Ⅲ)oxide NPs exhibit specific adsorption toward phosphate.Given very short contact time between contaminant and NPs in membrane filtration,high content loading of Fe(Ⅲ)oxide NPs is essential to deep treatment of phosphate contaminated water,which inevitably results in NPs aggregation and severe membrane pore blockage.In this paper,we confined iron oxide NPs inside inert silicates(MPS)of varying pore size(3.0,5.7 and 15.7 nm)and obtained three nanocomposite adsorbents.Effect of NPs size on As(V)adsorption by the resultant nanocomposite adsorbents were particularly concerned.The maximum As(V)adsorption capacity of the iron oxide NPs was negatively correlative with their size.Based on in situ Gran plots of the nanocomposites,decreasing NPs size resulted in higher surface hydroxyl density.More interestingly,the reactivity of the hydroxyl groups binding smaller NPs was significantly enhanced over the larger one,as indicated by the higher molar ratio of the adsorbed As to the hydroxyl groups.Effect of pH and competitive anions on As(V)adsorption was also involved to further examine the role of NPs size on the properties of the resultant composites.Afterwards,we prepared mesoporous nano-Fe2O3@polyacrylonitrile membrane(Fe2O3@PAN)via flash freezing of the blend of PAN solution and monodispersed 3 nm Fe2O3NPs.The loading content of iron element could reach as high as 30 wt%,exerting negligible effect on mesoporous structure of the resultant nanocomposite membrane,as confirmed by nitrogen adsorption desorption test.SEM-EDS and TEM tests suggested that the embedded Fe2O3 NPs were well-dispersed and uniformly distributed inside the polystyrene matrix.Batch adsorption experiments indicated that Fe2O3 NPs embedded inside the polystyrene matrix exhibited higher preference than unloaded Fe2O3 NPs toward phosphate removal.Besides,accessible site density of Fe2O3@PAN calculated based on in situ Gran plots method remained constant with NPs loading increase from 10 wt%to 30 wt%(in mass of Fe element),higher than un-supported NPs.As suggested by XPS Ols analysis,the embedded Fe2O3 NPs possessed higher proportion of Fe-OH,the most reactive groups responsible for phosphate adsorption,than the un-supported NPs.Simulated wastewater containing phosphate(0.2 mg-P/L)and E.coli(105 CFU/L)was filtrated by Fe2O3@PAN membrane,and negligible E.coli(<1 CFU/mL)as well as phosphate(<20μg-P/L)was detected in the effulent.Besides,the nanocomposite membrane with higher NPs loading was capable of producing more amount of purified water,e.g.,the purification capacity of Fe2O3@PAN(30 wt%in mass of Fe)reached 660 L/m2.During filtration,flux of Fe2O3@PAN membrane remained constant,implying ignorable fouling of membrane occurred.This paper provided an example of novel NPs-loading hybrid membrane of high mesoporosity as well as an example of phosphate starvation-killing antibacterial application. |
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