Nucleophilic-functionalized β-cyclodextrin-polyethersulfone structures from facile lamination process as nanoporous membrane active layers for wastewater post-treatment: Molecular implications

Nanocomposite membranes consisting of functionalized beta-cyclodextrin (f beta-CD) and polyethersulfone (PES) were fabricated, characterized, and used for low-pressure wastewater post-treatment. The impact of nucleophilic functionalization of beta-CD on the performance of these membranes was evaluated via three substitution routes: Crosslinking with nucleophilic dicarboxyl groups (M1) in maleic acid; co-polymerization with excess amino group (M2) in hyperbranched polyethyleneimine (HPEI); and nucleophilic modification with amino and hydroxyl groups (M3) in chitosan. All f beta-CD-incorporated membranes were hydrophilic as a result of the highly populated -OH groups at the exterior of beta-CD. Although there are higher-energy intermolecular C-O bonds in M1 membrane, less degree of nucleophilic crosslinking restricted kinetic hindrance and led to an increase in the mean pore size of M1 membrane to 52 nm. A dense structure, the lowest mean pore size of 22 nm, and the highest porosity of 45% was imparted to M2 membrane by the flexible C-N linkages provided by HPEI. Nucleophilic attack by the abundant N-H groups in HPEI also improved the tensile strength of M2 membrane reaching 20 MPa. Consequently, the water permeability of M2 membrane was significantly enhanced via beta-CD's solution-diffusion property. M1, M2, and M3 membrane water permeability were 61, 239, and 167 LMH bar(-1), respectively. M3 membrane showed the highest removal efficiencies for heavy metal ions (92% of Cr6+, 90% of Zn2+, 82% of Fe2+, and 87% of Cd2+) since it is the most hydrophilic membrane with abundant -OH groups in chitosan. However, M2 membrane displayed the highest removal efficiencies for residual organics, i.e. 67% chemical oxygen demand (COD) and 84% bacteria due to the hydrophobic interior of its dense f beta-CD.