Optimization of amine functionalization of MCM-41 for its covalent decoration in nanofiltration membranes for purification of saline- and micropollutant-contaminated feeds

The recovery of valuable water from industrial wastewater, seawater and brackish water resources is an attractive alternative to the dwindling conventional freshwater resources. A nanofiltration membrane was fabricated by covalently decorating MCM-41 in the active layer of the membrane. Three different versions of MCM-41 were synthesized by using in situ and post-synthetic methods leading to M Zeolite (unmodified MCM-41), ISM Zeolite (in situ modified MCM-41) and PSM Zeolite (post-synthesis modified MCM-41). The functionalization was carried out by using N¹-(3-trimethoxysilylpropyl)diethylenetriamine (TMSPTA). All of the versions of MCM-41 were covalently decorated in the active layer of the nanofiltration membrane through interfacial polymerization. The three variants of MCM-41 and the resultant membranes were characterized by SEM analysis, water contact angle (WCA), AFM, ATR-FTIR spectroscopy, EDX analysis and elemental mapping. The membranes' nanofiltration performance was evaluated by using feeds of salt solutions and pharmaceutical drugs. Out of all of the synthesized variants of MCM-41, the ISM Zeolite derivative proved to be the best material for membrane fabrication. The ISM@PS/PET (in situ modified MCM-41 in an active layer on polysulfone/PET support) rejected the salts in the following order: MgCl₂ ≈ CaCl₂ (97%) > MgSO₄ (90%) > Na₂SO₄ (87%). However, in the case of monovalent NaCl, the rejection was 65%. The rejection of the drugs by ISM@PS/PET followed the following order: sulfamethoxazole HCl (93%) > amitriptyline (90%) > loperamide (82%) > caffeine (80%). The flux of the ISM@PS/PET reached 38 L m⁻² h⁻¹ (LMH).