In the present study, a novel thin-film nanocomposite (TFN) membrane was developed consisting of a crosslinkined nano-modified polyvinyl alcohol (PVA) selective layer on an organic acid-modified polyvinylidene fluoride (PVDF) support membrane. The nano-modification of the PVA selective layer was performed via incorporating different amounts of the amine-functionalized multi-walled carbon nanotubes (MWCNTs-NH2) into the PVA matrix (0 to 1.5 wt.%). The effect of citric acid (0-1 wt.%) on the chemical structure and morphology of the PVDF support was also investigated. The modified PVDF support, the thin-film composite (TFC), and the TFN membranes were characterized via the attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, field-emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), tensile test, and contact angle measurement. The performance of the resultant membranes in the nanofiltration (NF) of MgSO4 and acid yellow-17 aqueous solutions was also studied. The results indicated that the modification of the support with 0.5 wt.% of citric acid increased the water permeance from 1.59 LMH/bar for PVA/PVDF to 4.49 LMH/bar for the PVA/modified PVDF membrane. Furthermore, the optimum value of MWCNT-NH2 (0.6 wt.%) increased the permeance of the resultant TFN membrane to 4.94 LMH/bar while maintaining a high rejection rate. Interestingly, the incorporation of MWCNT-NH2 into the PVA selective layer and citric acid into the PVDF solution resulted in a double-modified TFN membrane with the highest permeance of 6 LMH/bar. It can be concluded that the high-performance TFN NF membranes can be developed through the employed double-modification method.

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