The worldwide water crisis has set water research and technology on a journey towards providing clean drinking water in a way that can be translated from the lab to society. Before pollution and consequences of climate change took to effect, clean water was accessible in almost all human habitats, even though freshwater amounts to only 2% of the total water worldwide.
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Presently, access to clean water is a major issue for millions of people. Under the dire scenario of global water-stress, even sea water is treated to make clean water available. Graphene is used as a sieve to filter sea water, capitalizing on two of its key advantages over other materials: ‘permeability and selectivity.’ Graphene has the potential to deliver clean water from the sea by desalination and removal of pollutants.
Graphene and its Properties
Graphene is a carbon-based, two-dimensional material with the thickness of a single atom. It is a new class of ultra-thin membrane with atomically defined nanopores that are comparable in size to hydrated ions. A pristine single layer of graphene is impermeable to standard gases. Advances in graphene synthesis has enabled researchers to produce atomically thin permeable films for water purification by etching pores and nanoscale apertures in the graphene film that allow water to filter out. Graphene-based membranes are also attractive for desalination purposes due to their chemical and physical stability, concentration polarization and fouling.
Removal of Water Pollutants Using Graphene
When trying to remove pollutants from water, most filtration or purification technologies do not cover a wide spectrum of water-pollutants, presenting a challenge for water treatment. In a paper published in Nature communications, researchers have demonstrated water desalination through membrane distillation using graphene membranes. These graphene membranes exhibit high salt rejection rates and superior anti-fouling capability and have the capacity to remove various contaminants such as salts, oils and surfactants. They have tested processing sea water through these graphene nanochannels which “serve as an effective water permeation route.”
Scientists from the University of Manchester published their reports in Nature Nanotechnology where they created a new functionalized graphene-based sieve to filter sea-water. Graphene oxide is another popular material used for filtering sea water; however, graphene oxide swells allowing ions to pass through. This is stopped by using a protective epoxy membrane or other such chemical modifications (polydopamine, reduction, etc.) to arrest the swelling. Nanoporous graphene (NPG) and graphene oxide (GO) membranes exhibit exceptional anti-fouling properties as well.
Conclusion
Water contamination is a ubiquitous problem and using graphene-based materials for the removal of pollutants is more effective than other water treatment methods such as reverse osmosis. The challenges scientists now face involve scaling up graphene production, improving technology performance and making the system less resource-intensive and affordable. However, graphene remains one of the most promising materials for the ongoing battle to meet the demand for clean water worldwide.
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