Fabrication And Performance Of Multi-Walled Carbon Nanotube (MWCNT)/Polyacrylonitrile (PAN) Nanocomposite Ultrafiltration Membrane

Polyacrylonitrile (PAN) exhibits high glass-transition temperature, good thermal and chemical stability, resistance to most organic solvents. It is always applied in fabrication of reverse osmosis (RO) substrates, ultrafiltration membranes, and protein filtration, due to its good hydrophilicity over other materials. However, the mechanical properties are relatively weak because the cyano group (-CN) in the repeating unit of the PAN restricts the mobility of the bond.Carbon nanotubes (CNTs) possess extraordinary mechanical properties and large specific surface area, which make the CNTs excellent candidates for the development of CNT-reinforced polymer nanocomposites. However, rarely reports have covered the fabrication of the CNT/polymer nanocomposite membranes. In this paper, the MWCNT/PAN nanocomposite ultrafiltration membranes were fabricated via immersion precipitation method (IP) to improve the mechanical properties of the PAN membranes. Other performances such as water separation and anti-fouling properties were also investigated.Firstly, the effect of the solvents, PAN concentration, sonication time, thickness of the membranes on the membranes performance were investigated. It was found that the tensile strength and Young’s modulus of the membranes prepared by DMF were higher than prepared by DMAc. The elongation of the membranes prepared by DMAc was higher than prepared by DMF. The thicker the membranes, the lower the mechanical properties, while the larger the porosity was. Therefore, the concentration of PAN was set at15wt%, the sonication time was fixed at3h with the100±20um thickness.The temperature of functionalizing the MWCNT was investigated. It was found that the higher the temperature, the higher concentration of the hydrophilic groups anchored on the MWCNT. While with the increased temperature, the yield decreased due to the cutting and shorting by acidification.The pristine MWCNT/PAN nanocomposite membranes were fabricated via IP. It was found the water separation performance of the membranes was better than the PAN membranes. Water permeability and BSA rejection of the nanocomposite membranes reached the maximum at the lwt%and4wt%of the MWCNT loading respectively. The mechanical properties of the membrane showed no significant improvement. The tensile strength reached the maximum2.39MPa then decreased sharply with the increased MWCNT. The elongation decreased with the increased MWCNT. The hydrophilicity enhanced, which can be confirmed by the decreased contact angle. The flux recovery ratio increased from35%to70%.In order to further improve the mechanical properties of the membranes, the functionalized MWCNT/PAN nanocomposite membranes were fabricated via IP. Compared with the pristine MWCNT/PAN membranes, the tensile strength of the functionalized MWCNT/PAN membranes was slightly higher, the elongation of the functionalized MWCNT/PAN membranes increased with the increased MWCNT. The tensile strength of the membranes in both wet and dry state increased with the increased MWCNT loading. The elongation of the membranes in wet state enhanced with the MWCNT. The water separation performance improved remarkblely. The water permeability increased from56L/m2h to417L/m2h by7folds. The BSA rejection remained the same. Due to the enhanced hydrophilicity, the flux recovery ratio increased from37%to70.1%.