Polyethersulfone-ZnO mixed matrix hollow fiber membrane with antifouling properties for humic acid removal

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Date
2015-11-01
Authors
Abdullah Adnan Abdulkarim
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Abstract
A new technique was proposed to synthesize mixed matrix (MM) hollow fiber (HF) membrane from pre-determined MM flat sheet membrane formulation. To achieve this goal, different MM flat sheet membranes were synthesized from dope solution containing polyethersulfone (PES), ZnO nanoparticles (ZnO-NPs), polyvinylpyrrolidone (PVP), and dimethylacetamide (DMAc) solvent using phase separation technique. It was shown that the ZnO-NPs increased both membrane hydrophilicity and surface roughness of flat sheet membrane. Upon the addition of ZnO-NPs, the permeability, humic acid (HA) rejection, and anti-fouling property of membrane were also enhanced. The addition of hydrophilic ZnO-NPs to PES can alleviate the humic acid fouling provided the NPs are well dispersed inside the polymeric matrix. Flat sheet membrane results further indicated that the ZnO-NPs to PVP ratio should be equal to or more than unity to ensure good dispersion of ZnONPs inside PES matrix. Hollow fiber (HF) membrane inner contour could be varied by both spinning conditions as well as during the spinning time. The optimum formulation obtained was used in the development of MM HF membrane with fully controlled inner contour. Structural stability study of HF membrane was performed based on the residence time in the air gap region (Rtm). The regularity of the inner contour was proved to be fully circular with increasing Rtm. This might be due to enhancement in the internal mass transfer, polymer relaxation, molecular orientation, and stress release. It was shown that the critical Rtm that produced fully circular inner contour was 0.67 s. Subsequently, MM HF membrane was synthesized at Rtm equal to 0.82 s and tested for synthetic HA solution. The MM HF membrane showed enhancement in hydrophilicity, permeability, and anti-fouling property during HA filtration. However, the membrane antifouling properties were lower than the pristine PES due to the presence of CaCl2. The rejection performance of MM HF membranes during filtration of river water indicated that incorporation of 0.5 wt.% of ZnO-NPs was able to remove 26.15 % of the TOC compared to only 6.92 % for pristine PES. During long hours of river water filtration, ultimate flux recovery ratio (FRR) of 96.8 % was obtained at 0.5 wt.% of ZnO-NPs compared with only 75.55 % of FRR for the pristine PES. This showed that the modified MM HF membranes had been successfully developed for humic acid removal.
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