A polyamide membrane with tubular crumples incorporating carboxylated single-walled carbon nanotubes for high water flux

Abstract

Membranes having excellent water permeability and high salt rejection are needed for developing nanofiltration technology. In the present work, a modified interfacial polymerization involving low-concentration monomers was utilized to synthesize an ultrathin polyamide (PA) layer. Carboxylated single-walled carbon nanotubes (COOH-SWCNT) were embedded into the ultrathin PA layer. The resultant additional molecular transportation pathways could reduce the trade-off effect. Besides, the morphology of ultrathin PA layer was sensitive to the presence of nanofillers, and contributed to a rougher surface of the thin film nanocomposite (TFN) membrane. As a result, the permeable area was increased, which is beneficial for water permeation. At the optimized COOH-SWCNT dosage of 0.001 wt%, even tubular crumples appeared on the fabricated membranes. Thereby, the membrane achieved an ultrahigh water permeance of 22.67 L·m−2·h−1·bar−1 while maintain a high rejection for divalent salt. For example, the rejection of Na2SO4 and MgSO4 were 95.69% and 90.03%, respectively. These excellent results were achieved using low loadings of nanofillers and under relatively low pressure (3.5 bar). The current work provides a feasible method to adjust the morphologies of NF membrane for improving its performance. And this is a promising approach due to its simplicity, and low consumptions of materials and energy.