Study On Preparation And Pervaporation Properties Of Functional Multi-Walled Carbon Nanotube/Polyurethane Hybrid Membranes

As a development and promising membrane separation technology, pervaporation has been widely studied. Because of the unique structure and performance, polyurethane(PU) has been widely used to separate organic matter by pervaporation. With high permeability and selectivity, multi-walled carbon nanotubes(MWCNT) are excellent as separation membrane materials. In this paper, MWCNT were modified through chemical method and doping, in order to prepare functional MWCNT such as oxidation, amine functionalization, diisocyanate functionalization, deped with Ag. These functional MWCNT were modified by in-situ polymerization to form a MWCNT/PU mixed matrix membrane. The MWCNT/PU hybrid membranes were used to separate benzene/cyclohexane mixtures by pervaporation. The relationship between membrane’s structure and pervaporation properties have been discussed. This paper has three parts followed: 1. The functionalization of carbon nanotubesPrimitive MWCNT were treated by HNO3/H2SO4mixture and H2O2to obtain oxidized MWCNT, which were grafted hexamethylenediamine, toluene diisocyanatethrough by chemical modification to botain MWCNT-NH2, MWCNT-NCO. Nano silver were doped into oxidized MWCNT to prepare MWCNT-Ag.The composition and structure of functional MWCNT were characterized by UV visible spectrophotometer (UV), Fourier transform infrared (FT-IR), Raman spectrum, Transmission electron microscope (TEM), Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The result shows that:①Primitive MWCNT have been successfully grafted oxygen-containing groups to its surface, with the higher degree of oxidation, MWCNT’s D and G peak intensity ratio (ID/IG) of Raman spectra was increased. Oxidation MWCNT’s oxidation degree has a great influence on its dispersibility in organic solvent, the higher oxidation degree, the better dispersibility.②There were amine compounds and isocyanate characteristic peak showed in infrared spectrum, which illustrate that amine compounds and isocyanate have been grafted to MWCNT. MWCNT-NH2and MWCNT-NCO dispersed better in organic solvent than oxidation MWCNT.③Using PEG as reductant to prepare MWCNT-Ag by hydrothermal synthesis, silver nano particles were loaded on MWCNT. When use PEG-400as reductant, the Ag nanoparticles doped on MWCNT more uniformly.2. The prepartion of MWCNT/PU mixed matrix membraneFunctional MWCNT were modified by in-situ polymerization with2,4-tolylene diisocyanate (TDI) and poly propylene glycol (PPG) to form a MWCNT/PU mixed matrix membrane. The composition and structure of functional MWCNT/PU were characterized by TEM. Using Contact angle meter (DSA) and Zeta potentiometer (Zeta) to analysis hybrid membrane’s surface charged property. Results indicated that the oxidation degree of oxidation MWCNT has a certain influence on its dispersibility in hybrid membrane, the higher oxidation degree of MWCNT, the higher Zeta potential value of the hybrid membrane, the better dispersibility of oxidation MWCNT in hybrid membrane. MWCNT-NH2, MWCNT-NCO and MWCNT-Ag, by contrast, had a better dispersion in hybrid membrane than the oxidation MWCNT. Zeta potential value of the hybrid membranes showed a trend of reducing the rise with the increment of functional MWCNT’s filling content. hybrid membrane which were filled MWCNT-NCO had a higher Zeta potential value and smaller values of the static contact Angle, so the polarity of the hybrid membrane is stronger. 3. Swelling properties and pervaporation performance of functional MWCNT/PU hybrid membrane in benzene/cyclohexaneIn this part, functional MWCNT/PU hybrid membrane’s swelling and pervaporation performance have been tested. Degree of oxidation, types of functional groups and filling content of functional MWCNT showed different properties and performance.①The results indicate that the higher oxidation that MWCNT/PU hybrid membrane had, the better swelling and pervaporation it performed in benzene/cyclohexane mixture. H-MWCNT/PU with3%H-MWCNT content, the membrane’s swelling and permeation selectivity in benzene/cyclohexane achived3.15and7.92.②MWCNT-NH2/PU, MWCNT-NCO/PU, MWCNT-Ag/PU, by contrast, showed a better performance than oxidation MWCNT/PU in separating benzene/cyclohexane mixture. MWCNT-NCO/PU with5.0wt%MWCNT-NCO content, the membrane’s swelling and permeation selectivity in benzene/cyclohexane achived3.36and16.7, membrane’s benzene permeate flux was878g/m2h and cyclohexane permeate flux was118g/m2·h③With the increasement of MWCNT filling content, hybrid membrane’s permeation selectivity showed a trend of decrease after first increasement, indicating that a moderate amount of filling MWCNT can significantly improve the MWCNT/PU hybrid membrane’s benzene permeability and benzene/cyclohexane permeation selectivity.