Preparation And Property Of Organic/Inorganic Hybrid Membrane Incorporated Functionalized Multi-walled Carbon Nanotubes

Since the carbon nanotubes (CNTs) was first discovered in 1991, it has been of great interest in chemistry physics and materials science rapidly, and has a lot of potential applications in many fields, especially applying in preparation of new mixed matrix membranes (MMM), due to its peculiar mechanical, electronic, chemical properties. The constraints of separation performance of traditional membrane would be conquered by CNTs because of its unique one-dimensional and superhydrophobic tubal structure. However, how to fabricate a well-performance CNT mixed matrix membrane (CNTs-MMM) is really a tough task since the bad dispersibility of CNTs. If CNTs would be grafted by active group and thus create no void with polymers, the CNTs-MMM would exhibit more advantages than original polymer membrane. So the task of this thesis is first to exploit two different methods for functionalizing CNTs to improve its purity, stability and dispersion in polymers, and then mix the functionalized CNTs with polymers to fabricate three well-performance CNTs-MMMs which can be applied in ultrafiltration, pervaporation and reverse osmosis. The main contents include the following four parts:(1) The purification and functionalization of pristine multi-walled carbon nanotubes (MWNTs). First, the pristine MWNTs were treated by mixed acid in ultrasonic bath for purification. After that, according to the chemical structure of polymers, two different functionalized methods were used. One was acyl-chlorination (MWNTs-COC1). MWNTs were treated by 5-isocyanato-isophthaloyl chloride (ICIC) and acyl-chloride group was successful grafted on it. The second was carboxylation (MWNTs-COOH). MWNTs were treated by diisobutyryl peroxide and carboxyl group was successful grafted on it. After functionalziation, not only the dispersibility of MWNTs in water and organic solvents was remarkably improved, but also well dispersed in different polymer matrix.(2) Preparation and property of MWNTs/polysulfone (PSF) ultrafiltration hybrid membranes. Blends of polysulfone and different composition of MWNTs-COC1 to prepare a series of ultrafiltration membranes by phase-inversion method. According to the SEM and TEM, it was found that the content of functionalized MWNTs was an important factor influencing the morphology and permeation properties of the blend membranes. In addition, SEM images of the blend membrane surface and cross-section showed that the average pore size and pore structure of the blend membranes changed with the content of functionalized MWNTs up to 0.19%, then decreased. The static water contact angle of membrane surface showed that the hydrophilicity was improved with increasing content of functionalized MWNTs in blends. In separation experiments, pure water flux of the blend membranes increased from 40 L/m2·h to180 L/m2·h with the content of functionalized MWNTs, until up to 0.19%, and then gradually decreased. Finally, protein adsorption performance of membrane indicated that MWNTs content suppressed the adsorption of protein on membrane, and thus alleviated membrane fouling.(3) Preparation and property of MWNTs/chitosan pervaporation hybrid membranes. A series of MWNTs-COOH incorporated chitosan membranes were prepared by phase-inversion method. The morphology of surface and cross-section of membrane were observed by SEM and TEM. XRD and IR were employing to analyse chemical structure of membrane surface. In swelling experiment, the swelling degree of hybrid membranes in ethanol/water mixtures was 6 times than that of the pristine chitosan membrane. According to the Fick's law, the solubility and the diffusion coefficient of membranes in water, ethanol, and 90% ethanol/water mixtures were obtained. Compared with the calculated diffusion coefficient (D90), the measured diffusion coefficient (D90T) in 90% ethanol/water mixtures was higher, which indicated the functionalized MWNTs were more prone to increased water permeation when ethanol and water penetrated into the membrane simultaneously. In pervaporation experiment, the permeation flux of the membranes increased significantly with increasing functionalized MWNTs content in hybrid membrane in pervaporation. The effect of MWNTs content in the membrane matrix and operating temperature on pervaporation performance was investigated. After introducing functionalized MWNTs, the Arrhenius activation parameters for the total permeation decreased from 28.15 to 12.91 kJ/mol, which indicated that the carbon nanotubes filled membranes were easier to penetrate and exhibited higher flux performance than a pristine membrane.(4) Preparation and property of MWNTs/polyamide reverse osmosis composite membranes. Reverse osmosis composite membrane was prepared by interfacial polymerization of MPD with TMC on the surface of polysulfone support. The effects of monomers concentration, reaction time of IP, time and temperature of heat treatment on the separation performance of composite membranes were investigated. From the orthogonal experiment results, the optimum condition was obtained. In addition, the effects of phase-transfer catalyst and several alcohols as additions in water phase during IP on membrane performance were investigated, and the reason was also discussed. After that, MWNTs/polyamide reverse osmosis composite membranes were prepared by interfacial polymerization under the optimum condition. By comparing of structures, the surface of MWNTs/polyamide membrane was rougher than pure polyamide membrane, and some gaps occurred in polyamide layer because of micro-phase separation. Moreover, membrane surface became more hydrophilic and was decorated by more negative charges. In addition, after testing, the water flux of MWNTs/polyamide membrane was doubled than original polyamide membrane, and MWNTs/polyamide membrane could inhibit membrane fouling caused by organic or inorganic substances. The most important thing is the oxidation resistance of composite membrane has also been improved, the tolerance of active chlorine was up to 3000 ppm-h.In summary, the structure and performance of CNT mixed matrix membrane have more advantages than the original polymer membranes, and such hybrid membrane can break through the constraints of separation performance of traditional membrane, which provides an idea and method for the development of membrane technology.