Thin-film composite mixed-matrix

The geometries for asymmetric mixed-matrix membranes include flat sheets, hollow fibers and thin-fihn composites. The flat sheet asymmetric mixed-matrix membranes are formed into spirally wound modules and the hollow fiber asymmetric mixed-matrix membranes are formed into hollow fiber modules. The thin-film composite mixed-matrix membranes can be fabricated into either spirally wound or hollow fiber modules. The thin-film composite geometry of mixed-matrix membranes enables selection of different membrane materials for the support layer and low-cost production of asymmetric mixed-matrix membranes utilizing a relatively high-cost zeolite/polymer separating layer on the support layer. 

Thin-Film Composite Mixed-Matrix Membranes... 

Thin-film composite mixed-matrix membranes can be made by a coating method or by a dual-layer co-extrusion technology, as discussed in Section 11.5.2.2. 

Jia and coworkers prepared thin-film composite zeolite-filled silicone rubber membranes by a dip-coating method [82]. The membranes have a thin silicalite-1/ silicone rubber mixed-matrix selective layer on top of a porous polyetherimide support. 

The new concept of using mixed-matrix membranes with commercially attractive thin-film composite geometry for desalination of water has been demonstrated by Jeong and coworkers [83]. 

Cross-section structure. An anisotropic membrane (also called asymmetric ) has a thin porous or nonporous selective barrier, supported mechanically by a much thicker porous substructure. This type of morphology reduces the effective thickness of the selective barrier, and the permeate flux can be enhanced without changes in selectivity. Isotropic ( symmetric ) membrane cross-sections can be found for self-supported nonporous membranes (mainly ion-exchange) and macroporous microfiltration (MF) membranes (also often used in membrane contactors [1]). The only example for an established isotropic porous membrane for molecular separations is the case of track-etched polymer films with pore diameters down to about 10 run. All the above-mentioned membranes can in principle be made from one material. In contrast to such an integrally anisotropic membrane (homogeneous with respect to composition), a thin-film composite (TFC) membrane consists of different materials for the thin selective barrier layer and the support structure. In composite membranes in general, a combination of two (or more) materials with different characteristics is used with the aim to achieve synergetic properties. Other examples besides thin-film are pore-filled or pore surface-coated composite membranes or mixed-matrix membranes [3]. 

S., Khadivi, M. A., and Rostami, E. 2013. Novel thin film composite membrane fabricated by mixed matrix nanoclay/ chitosan on PVDF microfiltration support Preparation, characterization and performance in dye removal. J. Membr. Sci. 436 97-108. 

Recently, interesting results have been obtained in this field by combining the plasma polymerization and sputtering methods. For instance, the synthesis of composite thin films made of platinum nanoclusters (3-7 nm) embedded in a porous hydrocarbon matrix was carried out by simultaneous PECVD of pp-ethylene and sputtering of a platinum target. The metal content in the films could be controlled over a wide range of atomic percentages (5-80%) (Dilonardo et al., 2011). Aniline mixed with functionalized platinum nanoparticles as a precursor of PECVD was, in turn, used to prepare a typical 3D-catalyst. The plasma deposition was performed under atmospheric pressure conditions. Plasma polymerized aniline (pp-aniline), which is characterized by both electronic and ionic conductivity, associated with the Pt catalyst in a 3D porous network, without doubt lead to the development of the three-phase boundary (Michel et al., 2010). 

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