Nanocomposite membranes

Abstract

Nanocomposites find their application in membrane technology to improve the performance of membrane material and enhance the membrane life. Membrane technology involves processes like microfiltration, ultrafiltration, nanofiltration, reverse osmosis, pervaporation, membrane distillation, dialysis, electrodialysis, gas separation, etc. The advantages of this technology over conventional separation methods are high removal capacity, flexibility of operation, and cost effectiveness. Since the past two decades, synthetic membranes are being researched and commercialized for industrial and domestic use. The membranes may be composed of organic substances (polymers) and inorganic substances (ceramics), though polymeric materials are widely studied due to mechanical strength, flexibility, and chemical stability. However, the main limitation to the greater use of membrane technology is membrane fouling. Fouling is the process of deposition or adsorption of colloids, particles, macromolecules (e.g. proteins, polysaccharides), salts, etc. on the membrane surface and/or inside pores and pore walls. This leads to decline in permeation flux, change in selectivity, and separability during filtration operation and reduces membrane life. When the fouling of membrane is caused by formation of biofilms of extracellular polymeric substances and microbial cells matrix, then it is called biofouling. It is concluded from various studies that intrinsic hydrophobicity of membrane materials is one of the main reasons for fouling. To overcome this drawback, various nanocomposite membranes are being tailored to impart properties such as hydrophilicity, anti-fouling, self-cleaning, photocatalytic, and photodegradation. Nanocomposite membranes are made by incorporating inorganic or organic nanoparticles (NPs) into polymeric membrane matrix. Some of the nanocomposite membranes reported include inorganic NPs viz. TiO₂, SiO₂, Al₂O₃, Si, Ag, ZnO, ZrO₂, Mg(OH)₂, CaCO₃, TiSiO₄, etc., organic NPs viz. graphene oxide (GO), carbon nanotubes, etc., and NP composites viz. GO-SiO₂, GO-TiO₂, SiO₂-TiO₂, Ag-SiO₂, etc. Detailed study is necessary in this area because improper selection of NPs and their composition might deteriorate the performances.

Keywords:

• Nanofiltration
• Nanocomposites
• Anti-fouling
• Hydrophilicity
• Membrane

Notes

Presented at Trombay Symposium on Desalination and Water Reuse, Mumbai, India, 22–23 January 2015