Porous Functional Membranes

Abstract

A membrane is an interphase between two adjacent phases acting as a selective barrier, regulating the transport of substances between the two compartments. The main advantages of membrane technology as compared with other unit operations in (bio)chemical engineering are related to this unique separation principle, i.e., the transport selectivity of the membrane (Ulbricht et al. 2006). With an annual market growth rate above 10 %, membranes now play a leading role in many industries including water treatment, energy, electronics, health care, and agrobusiness. The importance of membrane technology is emphasized by the fact that one of the major challenges of this century is the provision of safe drinking water for a growing population. The most promising solutions to this problem which are environmental and energy friendly could come from new filtration membranes tailored at nanoscale (Elimelech et al. 2011). In the past decade, membrane separations have gained high technical relevance in a wide range of applications, from water purification to medical applications. Membrane-based filtration processes, such as reverse osmosis and ultraor nanofiltration, are commonly used in desalination, waste-water treatment, and power generation. Major problems associated with membranebased separation processes include fouling (chemical and biological) and high pressure loss, which decrease the efficiency of the filtration, decrease membrane lifetime, and increase operation costs. Main challenges for the development of novel filtration membranes are a narrow and adjustable pore-size distribution and a thin barrier layer so that the trade-off between high selectivity and high flux could be overcome. Several polymeric materials are being studied in an effort to improve membrane performance. Generally, filtration membranes are derived from membrane-forming materials with better stability and durability such as polyamide, poly(ether sulfone), polyvinylidene fluoride, polyethylene terephthalate, polytetrafluoroethylene, etc. Membranes based on these polymeric materials are mainly prepared by either phase inversion process or track-etching process. The scanning electron microscopy image of tracketched and phase inversion membrane is given in Fig. 1. However, despite many benefits, these materials suffer with relatively high hydrophobic nature which is a considerable limitation in water filtration application because it does not allow water permeation at significant rate. Suitable functionalization and surface modification have been reported as material design strategies for increasing the hydrophilicity of these