Semi permeable membrane is of quite much importance in today’s time for the purification techniques. This membranes are used for the purification techniques by means of reverse-osmosis process. This symmetrical membrane prevents higher flow rate for the fluid as it permits blocking of the fluid containing particles.
Asymmetrical Membrane: Effective in water purification
For coping up with the same, IISc researchers have developed an asymmetrical membrane, the pores has made it quite difficult for passing off the bacteria and other contaminants. This membrane is also permitting for the higher flow rate across the same and will be killing off 99 percent of the E. Coli.
Going a step further, IISc researchers from the IISc Bangalore has improved water purification membrane which they have developed in 2014. This membrane has also allowed for the higher flow rate across the same and is killing nearly 99 percent of the E. Coli being present in water. Results of the same is published recently in the Journal Nanoscale.
Thinking creatively, instead of creating a membrane consisting of sub-micro pore size, a team of researchers which is led by Prof. Suryasarathi Bose, the corresponding author of the paper from the Department of Materials Engineering, has developed a more permeable structure by means of creating pores which are bigger in size and more interconnected.
Equal mixing of polymers
The pores were bigger and more tortuous which were produced by means of mixing equal amounts of two polymers – polyethylene (PE) and polyethylene oxide (PEO). As PEO is one of the soluble material in water unlike PE, whose pores tends to be forming when the membrane containing PEO is dipped in water.
Earlier, the researchers has used tiny amount of PEO and sheared it at quite high speed for forming tiny droplets of PEO for creating smaller pores. Prof. Bose commenting over the same says, “We took equal amounts of PE and PEO so we get more tortuous pores upon removal of PEO. This is not possible if we take tiny amounts of PEO.”
Besides being tortuous, pores were quite asymmetrical – pore dimensions were being quite uniform throughout. At some of the places the pores were getting so narrow which were tending to be small as the micro holes which team has produced two years ago.
- While explaining the logic behind the asymmetrical pores he added, “If the pores are asymmetrical then bacteria and other contaminants will have a tougher path to pass through, so they will get trapped. To prevent this and control the morphology we added maleated polyethylene. The maleated polyethylene does not allow the droplets to get bigger. Maleated polyethylene basically interacts with PE (polyethylene) on the one hand and reacts with PEO on the other hand. So it is a kind of interfacial stabilising agent and doesn’t allow the morphology to coarsen.”
- Pores were even well connected and thereby increasing the ability for the water for passing through the membrane. This two of the polymers gets mixed with each other and are subjected for post processing application which includes applications like hot pressing the initial PEO droplets which are tending to become bigger. This bigger droplets of PEO are tending to leave bigger pores.
- Over the initial attempt, for rendering the membrane antibacterial, graphene oxide was mixed with two polymers and it was made functional with the help of amine groups. Adding to the same he says, “Earlier the antibacterial effect was not significant as graphene oxide was embedded inside the membrane. But now we have made it more effective by anchoring graphene oxide on the surface of the membrane.”
Generation of reactive oxygen species
Antibacterial studies by means of direct contact with the E. Coli with the graphene oxide has resulted in 100 fold reduction over the E. Coli colony. It occurs while forming the units at the end of 12 hours of the contact with the membrane. According to him, graphene oxide is having a very sharp edge and will be helping in piercing and destroying the cell wall of the bacteria.
Even the amine group of the graphene is interacting with the phosphate group of the lipids being present in the cell and is generating the reactive oxygen species which eventually destroys the cell membrane. Since polyethylene is inert while researchers had to render suitable surface modifications for anchoring graphene oxide over it, which otherwise would have been very difficult.
Lab studies has even revealed that there is unimpeded permeation of the water across the membrane while suggesting that anchoring the graphene oxide over the surface would not be clogging the surface.