Heterogeneous polyamide composite membranes based on aromatic poly (amidoamine) dendrimer for molecular sieving

Membrane separation technologies featuring environmentally friendly and highly efficient processes have been widely adopted for sustainable development. Non-linear macromolecules, represented by aromatic poly(amidoamine) dendrimers (ArPD), have good potential for increasing the porosity of the active layer in thin-film composite (TFC) membranes. However, they are often difficult to use as the sole monomer in interfacial polymerization to prepare membranes with high separation accuracy. Herein, the DMF/H2O system was determined to resolve the problem of ArPD dissolution, and the behavioral differences of ArPD for different generations in film-forming were then elucidated. For G4 (the fourth generation of ArPD) -TMC (trimesoyl chloride) membranes, the good sieving performance is attributed to the relatively dense polyamide networks from interfacial polymerization, and the continuous pore channels from the tightly packed macromolecules. Therefore, the final polyamide layer shows significant heterogeneity. Moreover, a "patching" strategy was employed to further improve the separation performance. The ArPD-based membranes exhibit about 3 times higher permeance than MPD (m-phenylenediamine)-based membranes under the comparable NaCl rejection. For the repaired membrane, the water permeance reaches 3.2 L m- 2 h-1 bar- 1 with the NaCl rejection of about 94.9%, which is advantageous compared with reported macromolecule-based membranes. The repaired membrane also shows excellent performance in the removal of small organics in organic solvent system. For example, the methanol permeance achieves 1.5 L m-2 h-1 bar- 1 with the rejection to potassium cinnamate (186.25 g mol-1) about 90.3%. This work provides a typical paradigm for the application of macromolecules in the preparation of TFC membranes.