Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: karthikaqpt on 05/04/2017 09:11:17

Title: How does graphene filter common salts from water to make it safe to drink?
Post by: karthikaqpt on 05/04/2017 09:11:17
A new research shows graphene can filter common salts from water to make it safe to drink.The new findings could lead to affordable desalination technology.

Graphene-oxide membranes have attracted considerable attention as promising candidates for new filtration technologies. Now the much sought-after development of making membranes capable of sieving common salts has been achieved.

New research demonstrates the real-world potential of providing clean drinking water for millions of people who struggle to access adequate clean water sources.

The new findings from a group of scientists at The University of Manchester were published in the journal Nature Nanotechnology. Previously graphene-oxide membranes have shown exciting potential for gas separation and water filtration.

Graphene-oxide membranes developed at the National Graphene Institute have already demonstrated the potential of filtering out small nanoparticles, organic molecules, and even large salts. Until now, however, they couldn’t be used for sieving common salts used in desalination technologies, which require even smaller sieves.

Previous research at The University of Manchester found that if immersed in water, graphene-oxide membranes become slightly swollen and smaller salts flow through the membrane along with water, but larger ions or molecules are blocked.

The Manchester-based group have now further developed these graphene membranes and found a strategy to avoid the swelling of the membrane when exposed to water. The pore size in the membrane can be precisely controlled which can sieve common salts out of salty water and make it safe to drink.

As the effects of climate change continue to reduce modern city’s water supplies, wealthy modern countries are also investing in desalination technologies. Following the severe floods in California major wealthy cities are also looking increasingly to alternative water solutions.

By 2025 the UN expects that 14% of the world’s population will encounter water scarcity. This technology has the potential to revolutionise water filtration across the world, in particular in countries which cannot afford large scale desalination plants.

It is hoped that graphene-oxide membrane systems can be built on smaller scales making this technology accessible to countries which do not have the financial infrastructure to fund large plants without compromising the yield of fresh water produced.

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Title: Re: How does graphene filter common salts from water to make it safe to drink?
Post by: puppypower on 05/04/2017 12:28:19
Graphene is impermeable to all gases as well as organic and ionic materials. However, it can be penetrated by water. This is what makes it a good filter for water.

If you look at the graphene matrix, it looks like a honey comb with six sided cells. If you notice, the carbon atoms show three covalent bonds, whereas carbon is expected to form four bonds. What this tells us is the three covalent bonds of the carbon in graphene, all have partial double bond character, allowing three bonds to add to the equivalent of four. What this does is allow resonance to form where electrons become delocalized as the partial double bonds shift.

This delocalization of electrons on the graphene matrix makes it harder for most materials to permeate the graphene. Polar and van der Walls interactions, from ions and organics, can't get a good bead on the moving charge, since the electron density is fluctuating. They tend to follow the surface.

Water is unique in that it forms hydrogen bonds, which have partial covalent bonding character. Water can participate in the electron delocalization of graphene. Water does not try to follow moving charge, but rather makes use of the moving electron charge to optimize itself.

The EM force or electromagnetic force is part electrostatic and part magnetic. Polar and van der Waals forces tend to be slanted toward the electrostatic side; charge attractions. A moving charge will create a magnetic field. The electron delocalization on graphene slants the surface toward the magnetic side of the EM force. Water can make use of this magnetic flux, due to moving electrons, via covalent aspect of its hydrogen bonding. The water can migrate through as though graphene is water.