**4. Conventional membrane material**

Almost all industrial membrane processes are carried by organic membranes made up of natural (wool, rubber (polyisoprene)) or synthetic (polyamide, polystyrene and poly-tetra-fluoro-ethylene (Teflon) polymers. (http://www.separationprocesses. com; [6]). Membranes can also be manufactured from other non-polymeric materials. Such membranes materials can be inorganic membranes (like metal, ceramic, carbon, and zeolites) and liquid membranes. But their application in water purification is not exhibited (http://www.separationprocesses.com).

For purification of water; currently the polymeric membrane governed the membrane market including real-world application and academic research due to its advantages of energy-efficiency, easy-operation, low-cost, and inherent simplicity. However, there are limitations related to the conventional membranes exhibited in most practical applications. Most of them tend to foul have low resistance to chlorine, strong acids/alkaline, high temperature and organic solvents, high contaminant permeation relative to stringent selectivity requirement and suffer from aperture shrinkage under high pressure [6]. The strong trade-off relation between membrane selectivity and permeability is a common challenge for all of polymeric membranes.

Because of the mentioned limitations the development of novel membrane materials is a major research thrust for academia, industry, and national laboratories. The desirable membrane properties, which are constantly searched by the researchers are good mechanical strength, superior chemical stability, thermal stability, water permeability, as well as high selectivity [6].
