Design And Preparation Of Multi-Walled Carbon Nanotubes (MWNTs) Incorporating Polyamide Thin Film Nanocomposite Reverse Osmosis Membrane

With the growing water problem, reverse osmosis technology has been more and more widely used in the field of water treatment application, there are needed significant innovations in RO membrane for desalination with increased water permeability for energy savings, improved selectivity in membrane separation, and more fouling resistant surfaces. Aiming at above-mentioned objective, in this work, pristine Multi-Walled Carbon Nanotubes (MWNTs) were firstly modified. Then the functionalized MWNTs introduced into the interfacial polymerization process for preparing MWNT-polyamide nanocomposite membranes, and used for desalination and organic aqueous solution separation. Mainly research of the thesis includes the following four aspects:(1) The modification of MWNTs. The functionalized MWNTs are obtained by the treatment of pristine MWNTs with the mixed acid of H2SO4 and HNO3 (3:1 v/v) and SOCl2, respectively. The analysis results show that the acidified MWNTs disperse more evenly in the aqueous solution. Compared to the pristine MWNTs, the acidified MWNTs yield some carboxyl groups and hydroxy groups, and the acyl cholride MWNTs have been grafted on some acyl chloride groups.(2) Study on preparation and performance of the acidified MWNT-polyamide thin film nanocomposite membranes. The results of transmission electron microscopy (TEM) and Fourier transform infrared spectrometry (FTIR) demonstrate that the functionalized MWNTs penetrated through the polyamide layer. Compared with the bare polyamide membrane, the water flux of MWNT-polyamide membranes is improved dramatically. While hydrated ion rejection decreases obviously, meanwhile, PTA rejection is all higher than 98%. For 20000 ppm 1-butanol solution was tested at 25℃and 1.6 MPa, the water flux of acidified MWNT-polyamide membranes with 0.1% acidified MWNTs (w/v) in the MPD-Water solution achieved 53.13 L/m2·h, which is almost 2.43 times that of pure polyamide membrane, while 1-butanol rejection decrease slightly. The acidified MWNT-polyamide membranes have more acid and organic solution resistant than the pure polyamide membrane. (3) Study on preparation and performance of acyl cholride MWNT-polyamide thin film nanocomposite membranes. When the 2000 ppm NaCl solution was tested as feed at 25℃and 1.6 MPa, with increased MWNTs content, water permeation of the acyl cholride MWNT-polyamide membranes were improved dramatically. The water flux of thin film nanocomposite membrane with 0.2% (m/v) MWNT-COCl was almost 2.0 times that of pure polyamide membrane. While observed NaCl rejections of MWNT-polyamide membranes decreased significantly. The acyl cholride MWNT-polyamide membranes have high rejection for negatively charged organic compounds with molecular weight larger than 100.(4) Preliminary study on aligned carbon nanotubes. The MWNTs disperse in ethanol, and then the suspension is filtered through 0.2-μm-pore hydrophilic nylon filter paper. Because the nylon filter is hydrophilic and the MWNTs are hydrophobic, the MWNTs stand up on the filter and self-assemble into an oriented film.