Fabrication of high-performance and high-fouling resistance reverse osmosis membrane by a natural deep eutectic solvent (NDES) as a new generation of co-solvents

Here, we modify the RO membrane employing thymol:acetic acid (Th:AA) natural deep eutectic solvent (NDES) as a new generation of the co-solvent. The Th:AA NDES was synthesized with the heating method. The co-creation of the NDES synthesis was confirmed by FTIR and NMR spectroscopy. For the impact assessment of Th:AA in the CAIP process, the dosage of the NDES as a co-solvent in the organic phase was initially optimized. Then, in the second step, the effect of the AA molar ratio on the membrane performance was investigated. Alteration changes in the morphology of PA/NDES membranes were investigated by SEM, AFM, ATR-FTIR, zeta potential, and water contact angle analyses. PA/NDES membranes have thinner selective layers, smoother surfaces, and a more hydrophilic nature without changes in the chemical structure. The performance of different types of PA/NDES RO membranes was assessed by the pure water flux and NaCl rejection experiments. The results indicated that at the optimum amount and molar ratio of the Th:AA NDES, the permeability reached 5.35 LMH/bar while the rejection didn't reduce and was constant at 98%. Also, the antifouling performance was explored by the NaCl/HA solution with the 2000/10 mg/L concentration. The outcomes of this experiment showed the PA/NDES13 membrane with a 1.5% flux decline had the best antifouling features. Moreover, the long-term test indicated the PA/NDES13 membrane has long-time stability. Also, the chlorine resistance of this membrane was much better than unmodified PA and commercial membranes. In the end, it was found that using Th:AA NDES as a co-solvent in the CAIP process produced a RO membrane with high permeability and high fouling resistance features along with better features than a commercial BWRO membrane, making it an excellent candidate for industrial application due to the ease of NDES synthesis and membrane fabrication.