| Amidoxime group is a good functional group for uranyl ion adsorption due to itshigh activity and selectivity of uranyl ions chelating. Meanwhile amidoximemodificated polymer fibrous adsorbent are the hot candidate absorbents for uraniumextraction research because of its strong mechanical property and high adsorptionselectivity, which are promising to be used to field extraction of uranium from actualseawater. Generally speaking, the specific surface area of fibrous adsorbents can beeffectively increased by reducing the diameter of fibers, and the enlarged specificsurface will improve the adsorption capacity of adsorbents. Therefore, the nanoscalefibrous adsorbents which have good mechanical properties and large specific surfaceare our major research. In this study, new nanofibrous adsorbents were prepared byelectrospinning. What‘s more, bifunctional system was built to increase the adsorptionperformance. The main research focused on the mechanical property and adsorptionperformance of nanofibrous adsorbent, as well as the synergistic effect of bifunctionaladsorbent.Polyamidoxime (PAO)/polyethylene glycol diacrylate (PGDA) nanofibrous matwas prepared by electrospinning PAO and PGDA mixture. Whereafter, a facileapproach to improve the mechical properties of this electrospun fibrous mat wasdeveloped by using γ-ray irradiation induced crosslinking. BET measurements andadsorption testing indicated that both the specific surface area adsorption capacity ofPAO-PGDA electrospun mat were much larger than those of trantional AO-basedpolyethylene (PE) nonwovens. These proved that the nanofibrous adsorbent withhigher specific surface area, which can promote the increasement of adsorptionperformance, could be successfully prepared by electrospinning.Studies showed that although the mechanical properties of electrospunnanofibrous adsorbent could be enhanced by γ-ray irradiation induced crosslinking,the effect was limited. And the poor compatibility with other polymer of PAO limitedthe using of miscibility method. On this basis, PVDF was introduced by a two-nozzleelectrospinning process to further improve the mechanical strength of electrospun fibrous adsorbent and PAO/PVDF composite electrospun fibrous mats weresuccessfully prepared. Porosity test results showed that the porosities of theseelectrospun mats were greater than50%, and increased with the increasement ofPVDF content. On the contrary, the improvement of PVDF content resulted in thereduction of hydrophilic. Adsorption experiment showed that under the condition ofgood hydrophilicity, increasing the porosity could effectively improve the utilizationof amidoxime group. However, adsorbends with bad hydrophilicity would lead to lowutilization of amidoxime groups. So increasing both the porosity and hydrophilicity ofadsorbent is an effective method for improving the utilization of functional groups.In order to improve the adsorption performance of electrospun nanofibrousadsorbents, γ-ray irradiation graft polymerization technique was used to introducePAAc or PVP grafting chain. PVDF-g-PAAc/PAO and PVDF-g-PVP/AO nanofibrousmats were achieved by two-nozzle electrospinning. Adsorption experiment showedthat compared with PAO nanofibrous mat, the adsorption capacity increased2.1timesand2.4times respectively after introducing PAAc and PVP. This illustrated thatcarboxylic acid group and pyrrolidone group had synergistic effect with amidoximegroup. Furthermore, the adsorption performance of PVDF-g-PAAc/PAO compositenanofibrous adsorbent was assessed in simulated seawater with uranium concentrationof3.3ppb. The result showed that the adsorption capacity was2.86mg U g-1abs. in30days. It proved that this composite nanofibrous mat with bifunctional group couldextract uranyl ions in very low concentration, and was expected to be used in the realseawater. |
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