Graphene Filtration | A revolution in Desalination technology!

recently a group of manchester institute of science and technology researchers made a major breakthrough in the graphene-based desalination process they were able to remove 97 percent of common salts in an energy efficient way the current reverse osmosis desalination technology is energy intensive and desalination plants capital costs are high by the year 2025 14 of the world's population will experience water scarcity which makes this discovery very important moreover graphene-based filtration technology could come to your kitchen very soon however before getting into graphene-based desalination technology let's see how the current ro desalination works consider this interesting experiment salty water and pure water is divided with a semi-permeable membrane a semi-permeable membrane won't allow the transfer of salt ions but it will allow water molecules through nature always has an urge to balance molecular concentration therefore if you wait a few minutes you'll notice that the salt water level will increase naturally here the water molecules from the right side migrate to the left side in an attempt to balance the salt level concentration this naturally occurring process is called osmosis we definitely don't want this result what we need is the exact reverse of this process water molecules from the left side should migrate to the right side so what can we do to get pure water we can apply good pressure on the salt water side the increased pressure will force the water molecules in the salty side to migrate to the clean water side obviously the semi-permeable membrane blocks migration of salt ions this method is known as reverse osmosis however pumps require enormous amounts of energy to apply pressure on water and the equipment costs make it difficult to build more desalination plants the quantity of pure water is smaller as well now we'll introduce to you graphene graphene is a wonder material with a lot of miraculous properties let's see how we can use it for the desalination process a graphene sheet with a lot of small pores is an excellent candidate for the desalination process ion bombardment and selective etching processes can fabricate desired pores in a graphene sheet these holes allow water molecules to pass easily while blocking salt ions on an industrial scale however the position of the holes cannot be precisely predicted thus it is impractical to use graphene as a filtration membrane for large-scale manufacturing a good alternative for graphene is graphene oxide which is formed by oxidizing graphite later these layers are exfoliated to get graphene oxide graphene oxide sheets are cheap and are easily mass produced one fascinating property of graphene oxide which makes it ideal for desalination is its hydrophilic nature which means that water flows through it quickly however making pores on geo sheets via ion bombardment is not a practical solution another way to create pores is by stacking geo sheets together and tuning the distance between them let's test this newly made geo membrane for our desalination purpose the water passes through the membrane automatically via capillary action the observed result shows no salt permeation detectable for the 6.4 angstrom pore size because salt atoms have a larger diameter than water atoms salts are blocked salt is present in seawater in an ionic state as na plus and cl minus when these salt ions are in water they hydrate put simply as the ions are charged they attract water surrounding them in concentric shells thus increasing the salt ions diameter so the pore size of graphene oxide membranes is designed accordingly to block these hydrated ions the salt to water molecules are bonded in covalent bonds which are stronger than water-to-water hydrogen bonds this difference in strength is why water-to-water molecules can break and permeate easily whereas salt to water bonds are tougher to break and hardly permeate through a geo membrane geo membranes are easy to fabricate on a larger scale compared to graphene membranes here's how geo membranes are fabricated the design of a geo filtration mechanism is not over yet if we use this geo stack for desalination we won't get good results because graphene oxide has higher affinity to water when the stack of geo sheets is immersed in water two to three layers of water molecules intercalate between pores causing it to swell this swelling increases the pore size which can then permeate the salt atoms too to overcome this problem graphene oxide laminates are physically constrained from swelling by using stycast epoxy graphene oxide laminate and stycast epoxy are alternated in layers to form filtrating membranes a typical ro membrane can remove up to 90 to 95 percent of salts whereas the graphene oxide based membranes can remove up to 97 percent of salts graphene oxide membranes due to their high tensile strength and higher affinity to water are perfect candidates for desalination in ro plants we need to reverse a naturally occurring process using external energy therefore electrical energy required for the pumps accounts for approximately 44 of an ro plant's total cost the graphene oxide method on the other hand is a naturally occurring filtration process another improvement which can make manufacturing easier is using graphene sheets combined with graphene oxide membranes this way the graphene sheets replace the epoxy the geo membrane discovery will definitely save a lot of power let's hope that this promising technology will soon penetrate not only the market but our households thank you for watching the video

Channel: Lesics

Views: 596,829

Keywords: graphene, graphene filtration, osmosis, reverse osmosis

Id: tAN0QNQFDbg

Length: 6min 15sec (375 seconds)

Published: Thu Jul 23 2020