Role of alkane-α,ω-diamine in the nanostructure of carboxylic functionalized multiwalled carbon nanotubes grafted on amino-enriched nylon fabric toward metal ion absorption

Through a direct two-step functionalization reaction with alkane-α,ω-diamine (H2N(CH2)nNH2, n = 2, 4, 6, 8) and carboxylic functionalized multi-walled carbon nanotubes (MWCNT-COOH), the membrane labeled as C@(A[n]-nylon), is made up of nylon 6 fabric and intermediate amino-enriched nylon (A[n]-nylon) fabric. FTIR and Raman spectra confirm the efficient formation of amide bonds between the two amino heads of the alkane-α,ω-diamine, both with hydrolyzed nylon 6 and MWCNT-COOH. As a result, MWNCT-COOH were grafted to the nylon fiber side wall without causing damage to the nylon backbone. The SEM images confirm the plexus of MWCNT covering the amino-enriched nylon fibers. The long carbon chain of alkane-α,ω-diamine as an arm help amino groups reach beyond the surface of polyamide fiber, making it easier for -COOH groups of MWCNT-COOH to form amide bonds instead of being ejected when approaching CO groups on the polyamide surface. As-prepared C@(A8-nylon) membranes have metal ion rejection of more than 10% in vacuum filtration test with solution of M(CH3COO)2 (M = Ca, Co, Pb). Such membrane is long lasting for about 20 cycles, showing potential of turning polyamide fabrics with large pore sizes into highly efficient nanofiltration of reverse osmosis (RO) membranes. This unique structure opens up new possibilities for nanocomposite membranes and mass production by the proposed simple method.