Fouling reduction and retention increment of polyethersulfone nanofiltration membranes embedded by amine-functionalized multi-walled carbon nanotubes

Flat sheet asymmetric amine-functionalized multiwalled carbon nanotubes (NH₂-MWCNTs)/polyethersulfone (PES) nanocomposite nanofiltration membranes with different nanofiller contents were prepared by the phase inversion method. The characteristics of the mixed matrix membranes were analyzed by SEM, AFM, contact angle and zeta potential measurements. The performance of the membranes was evaluated in terms of pure water flux (PWF), static protein adsorption and bovine serum albumin (BSA) filtration. Results showed that the hydrophilicity and PWF of the nanocomposite membranes were enhanced with increase of NH₂-MWCNTs dosages. Increasing the nanotube dosages from 0wt% to 0.045wt% led to increase of PWF from 13.6 to 23.7L/m²h. The SEM images illustrated that the fabricated membranes possessed a typical asymmetric finger-like structure. The salt rejection experiments and zeta potential measurements evidenced that the surface charge of the NH₂-MWCNT embedded membranes was negative and the retention mechanism of the solutes was mainly the Donnan exclusion mechanism. The salt retention sequence for 0.045wt% NH₂-MWCNT was Na₂SO₄ (65%)>MgSO₄ (45%)>NaCl (20%) after 180min filtration. The increase of the salt solution pH caused more negative surface charge and higher retention. The addition of the modified MWCNTs, in BSA filtration analysis, led to significant improvement of the fouling recovery ratio (FRR) due to lower roughness, more negatively charged surface and higher hydrophilicity of the membrane surface.