Performance of TFN nanofiltration membranes through embedding internally modified titanate nanotubes

Abstract

High toxicity of water resources by heavy metal ions is common and membrane filtration is one the solutions to this problem. Titanate nanotubes (TNT) are generally used due to their unique characteristics such as meso-porous structure, and high specific surface area. In this study, the internal surface of TNT was coated through a novel in-situ polymerization method with various polymers to alter the property and size of inner surface of the nanotubes, and then was embedded in the polyamide layer of the nanofiltration membrane. The modified nanotubes were supposed to act as the channels for water transport and reject the multivalent/monovalent ions; this phenomenon was more pronounced in the modified nanotubes because of the reduction in inner diameter. Fourier transform infrared spectroscopy, X-ray diffraction and Brunauer-Emmett-Teller analysis were used to characterize the unmodified/modified nanotubes. Furthermore, the membranes were synthesized by in-situ interfacial polymerization of trimesoyl chloride and m-phenylenediamine containing 0.05 wt% nanotubes; the performance of the fabricated membranes in terms of pure water flux (PWF), contact angle, feed flux and Na+ and Cu2+ rejections was studied. Generally, incorporation of the modified nanotubes improved the trade-off between the permeation and rejection. Among the fabricated membranes, the maximum PWF was 26.13 L m−2 h−1 for the membrane containing 0.05 wt% polystyrene modified TNT, 71.23% more than neat thin film membrane and without any significant change in the rejection; that can be related to the hydrophilicity of the nanotube and the formation of small cavities on the membrane surface.