IISc researchers produce a superior water filter

• A membrane capable of producing safe drinking water by filtering out objects at the nanoscale level and killing the commonly found pathogenic bacteria E. coli has been developed by a team led by Dr. Suryasarathi Bose, Assistant Professor, Department of Materials Engineering, IISc, Bengaluru.

• The membrane is produced by mixing two polymers — poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) — that become miscible at about 220 degree C. While PVDF crystallises during cooling, PMMA does not and separates out; the PMMA is removed using a solvent. This property of selective crystallisation and separation is taken advantage of to produce a nano-porous membrane.
• As the membrane is about 1 mm thick, a combination of fine pores and channels are produced when the PMMA is removed. The average pore size is 50 nm.The nano-sized porous structure can prevent bacteria from passing through the pores as bacteria are typically micron-sized.
• However, the bacteria can form a biofilm on the structure. As a result, the filter’s efficiency will be reduced within a short period.
• To prevent this and to kill the bacteria, they mixed silver, titanium dioxide and carbon nanotubes to the PVDF-PMMA mixture. Due to polarity and specific interaction with PVDF, all the three added materials got embedded only on the PVDF.
• Titanium dioxide also kills the bacteria. Though its antibacterial property is best in the presence of UV light, the present study did not use UV light.
• Carbon nanotubes kill the bacteria through direct physical contact — the roughness of the nanotubes kills the bacteria.
• A combination of all the three nanoparticles was superior in killing the pathogenic bacteria E. coli.

• Source: The Hindu