Nanocomposite membranes matrices

CS-based mixed matrix membranes and nanocomposite membranes are much useful in heavy metal removal. Salehi et al. [82] synthesized amine functionalized multiwalled carbon nanotubes (F-MWCNTs) and utilized to prepare novel CS/polyvinyl alcohol (PVA) thin adsorptive membranes for copper ion removal from water. Copper ion adsorption on the membranes was more favorable at higher CNT contents as well as increased temperatures. The adsorption capacity of the membrane containing 2 wt.% CNTs (20.1 mg/g at 40°C) was almost twice as large as that of the plain membrane (11.1 mg/g). Salehi et al. [83] used PE glycol and amino-modified MWCNTs to modify CS/PVA thin adsorptive membranes for copper ion adsorption. Adsorption capacity of CS/PVA membrane was increased from 11 to 30 mg/g by the addition of 5 wt.% PEG to the blend. Addition of CNTs,... 

Recently, in our group, we evaluated the potentiality of a poly(iniide) (PI)/ organically-modified montmorillonite (O-MMT) nanocomposite membrane for the use in alkaline fuel cells [73]. Both X-ray diffraction and scanning electron microscopy revealed a good dispersion of O-MMT into the PI matrix and preservation of the O-MMT layered structure. When compared to the pure PI, the addition of O-MMT improved thermal stability and markedly increased the capability of absorbing electrolyte and ionic conductivity of the composite. Based on these results, the PI/ O-MMT nanocomposite is a promising candidate for alkaline fuel cell appUcations. 

Nanocomposite membranes, also known as mixed matrix membranes, and FTMs are two distinguished and promising generations of gas separation membranes. 

Commercial membranes for CO2 removal are polymer based, and the materials of choice are cellulose acetate, polyimides, polyamides, polysulfone, polycarbonates, and polyeth-erimide [12]. The most tested and used material is cellulose acetate, although polyimide has also some potential in certain CO2 removal applications. The properties of polyimides and other polymers can be modified to enhance the performance of the membrane. For instance, polyimide membranes were initially used for hydrogen recovery, but they were then modified for CO2 removal [13]. Cellulose acetate membranes were initially developed for reverse osmosis [14], and now they are the most popular CO2 removal membrane. To overcome state-of-the-art membranes for CO2 separation, new polymers, copolymers, block copolymers, blends and nanocomposites (mixed matrix membranes) have been developed [15-22]. However, many of them have failed during application because of different reasons (expensive materials, weak mechanical and chemical stability, etc.). 

An important event of recent years in membrane science was the discovery of a new phenomena observed when nano-particles are added into (mainly high permeability) polymer matrix references to these pioneer works can be found in chapters of Section II Nanocomposite (Mixed Matrix) Membranes. So it is not surprising that several presentations at ICOM2008 dealt with such systems. Golename et al. (Chapter 6) investigated the Systran that contained perfiuorinated polymers and surface-fiuorinated zeolites as nano-additives. Perfiuorinated polymer AF2400 with nano-additives was also the object... 

Depending on the nature of the particles embedded in the polymeric matrix, polymer-inorganic hybrid membranes can be divided into two nonexclusive groups mixed matrix membranes (MMMs) and nanocomposite membranes (NCMs). 

V. Vatanpour, S.S. Madaeni, A.R. Khataee, E. Salehi, S. Zinadini, H.A. Monfared, Ti02 embedded mixed matrix PES nanocomposite membranes influence of different sizes and types of nanoparticles on antifouling and performance. Desalination 292 (2012) 19-29. 

S. Takahashi, D.R. Paul, Gas permeation in poly (ether imide) nanocomposite membranes based on surface-treated silica. Part 1 without chemical coupling to matrix. Polymer 47 (2006) 7519-7534. 

Fig. 7.33 Schematic representation of the proton-conductive nanocomposite membranes composed of ionomer (matrix) and sulfopropylated polysilsesquioxane (SiOPS) (Reprinted from [97] with permission from Wiley Interscience)...

SiOPS. These results suggest that well-dispersed nanocomposite membranes were formed. Nanocomposite membranes thus obtained showed much higher proton conductivity (up to 30 times) than that of the original membranes and accordingly less dependence of the conductivity upon the humidity. The ionomer properties such as thermal, hydrolytic and oxidative stability, and gas permeability were rather unaffected by the SiOPS. The methodology seems to be versatile as confirmed by the two different series of polymer electrolytes, although the miscibility with SiOPS depended on the matrix polymer. 

To overcome these problems, a number of synthetic IPs have been proposed. Among these alternative IPs, sulfonated hydrocarbon polymers have received sig-niflcant attention, owing to their eost effectiveness, ease of fabrication, tunable stiffness, and good ion-transport properties, whieh result from their controllable monomer composition, especially via the manipulation of the block copolymers. Naturally abundant functional biopolymers such as cellulose derivatives and chitosan have been considered for their high ionic conductivity, environmental friendliness, low cost, and ability to form uniform films. Another solution is to embed functional nanoparticles in a polymer matrix to fabricate a high-performance nanocomposite membrane (Jo et al. 2013). 

Fig. 8.4 CNT nanocomposite membrane process, (a) Schematic membrane fabrication process. Step h The functionalized CNTs are dispersed in THF solution. Step 2 The CNTs/THF solution is filtered through 0.2 pm pore size hydrophobic polytetrafluoroethylene (PTFE) membrane filter. Step 3 The CNTs/PTFE membrane is spin coated with a dilute PS solution. Some nanotube tips are embedded in polymer matrix, (b) Side-view SEM image of CNTs standing vertically on a membrane filter, (c) Side-view SEM image of aligned nanotube/PS nanocomposite membrane after spin-coating. Polymer coating is so thin that some CNT tips are exposed on top of the surface, (d) Side-view SEM image of aligned nanotube/PS/PDMS composite membrane with a protective PDMS coating of 4 pm. (From [8])...

Stability. The nanocomposite membrane showed low methanol permeability (1.9-1.3 X10 cm s ) and slow water dehydration. APTMS and imidazole gly-cidoxypropyl trimethoxysilane precursors are utilized to generate (RSiOi.5) in a SPEEK matrix by a sol-gel process by Karthikeyan et al. [69]. 

Nanocomposite mixed-matrix membranes have been investigated for close to a decade. Ti02-poly(amide-imide) membranes showed selectivity improvement but suffered loss of productivity when TiOa was added. Nonporous, nanoscale, fumed silica was embedded in a glassy, amorphous polymer, poly(4-methyl-2-pentyne), which resulted in enhancements in both permeability and selectivity for the mixed-matrix membrane. These membranes were discovered to be reverse selective, so the membrane is selective for the larger penetrant. This phenomenon is attributed to increased free volume in the bulk polymer from chain packing disruption, which occurs when the filler is added. ... 

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