Microstructure manipulation in PVDF/SMA/MWCNTs ultrafiltration membranes: Effects of hydrogen bonding and crystallization during the membrane formation

Amphiphilic copolymers and functionalized nanoparticles have been severally used to modify polymeric membranes to enhance their antifouling properties. However, their synergistic effects on the membrane microstructure and performance have been rarely reported. Herein, sodium styrene-maleic anhydride copolymer (SMANa) and functionalized multi-walled carbon nanotubes with carboxyl groups (MWCNT-COOH), amino groups (MWCNT-NH) and hydroxyl groups (MWCNT-OH) were utilized to blend with poly (vinylidene fluoride) (PVDF) to fabricate the composite membrane by phase inversion. The hydrogen bonding between functional groups and SMANa, and the nucleation of MWCNTs were systematically investigated during the membrane formation. The hydrogen bonding strength followed the tendency of MWCNT-COOH > MWCNT-NH > MWCNT-OH. For MWCNT-NH, weak hydrogen bonding resulted in its aggregation in the dope solution and some large pores on the membrane surface. The α-nucleation of MWCNT-OH mainly dominated the membrane microstructure instead of hydrogen bonding, leading to a dense surface skin layer. In contrast, uniform and suitable pore structures were constructed on the MWCNT-COOH modified membrane thanks to the strong hydrogen bonding. Correspondingly, the resultant membrane simultaneously exhibited a better permeate flux (1266.50 L/m 2 ·h·bar) and rejections to BSA (98.60%), Congo red (62.85%) and methyl blue (29.19%), and the highest flux recovery ratio (88.5%), indicating excellent antifouling properties.