Tip and Inner Wall Modification of 4.9 nm Diameter Multi-Walled Carbon Nanotubes and Its Nanocomposite Polyamide...

The tip and inner surface of large diameter multi-walled carbon nanotubes (MWCNTs) (4.9 nm diameter) were functionalized on the tip and inner surface to improve the rate of desalination and maintain high water flux. The modified MWCNTs-doped reverse osmosis membranes were fabricated by interfacial polymerization using trimesoyl chloride (TMC) solution in n-hexane and aqueous solutions of m-phenylenediamine (MPD) containing functionalized MWCNTs. The functionalized MWCNTs were analyzed by X-ray photoelectron spectroscopy (XPS), thermal gravity analysis (TGA), high resolution transmission electron microscopy (HRTEM), UV-Vis spectroscopy and other techniques. The obtained results showed that changes occurred in the structure of the carbon nanotubes with the inner diameter becoming smaller, and the dispersibility and stability were improved. Carboxyl, acyl chloride, amide and amino groups were successfully grafted on the tip and interior of MWCNTs. The surface characteristics of the prepared membranes were studied by scanning electron microscopy (SEM) and contact angle analysis. The desalination performance of the membranes was investigated in terms of water flux and salt rejection. The experimental results revealed that the incorporation of the modified MWCNTs (especially containing hydrophilic groups such as carboxyl groups) into the polyamide layer of RO membranes led to a significantly increase of the water flux and salt rejection.