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Abstract
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Surface modification of a commercial polyamide nanofiltration membrane was achieved by UV induced graft
polymerization of acrylic acid and incorporation of carboxylated-MWCNTs (COOH-MWCNTs). The grafting
process was done under different monomer concentrations and UV exposure times. The modified membranes
were characterized through scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle
and zeta-potential analysis, and cross-flow filtration experiments. Changes in the surface hydrophilicity, negative
charge and roughness of the modified membranes improved their permeability and fouling resistance significantly.
The membrane grafted with 50 g/L acrylic acid under 5 min UV exposure showed the best filtration
performance including pure water flux of 38.8 L/m
2
h, salt rejections of 97.43% (Na
2
SO
) and 93.4% (NaCl), and
flux recovery ratio (FRR) of 80.2% during bovine serum albumin (BSA) filtration. After optimizing grafting
condition, different amounts of COOH-MWCNTs were dispersed in the monomer solution for embedding in the
grafting layer. By adding 0.2 wt% COOH-MWCNTs to the grafting layer, a water flux improvement of around
30% was observed. But, excess loading of the COOH-MWCNTs led to compaction of the grafting layer and made
it inflexible and subsequently, reduced the hydrophilicity and permeability of the membrane. Fouling tests with
BSA aqueous solution showed that antifouling ability of the modified membranes was remarkably improved at
all concentrations of the COOH-MWCNTs. Furthermore, salt rejection results displayed that simultaneous surface
modification through grafting and COOH-MWCNTs embedding could effectively improve the nanofiltration
performance of the membranes in the term of permeability, desalination and fouling resistance.
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