Carbon Nanotubes give Graphene-Based Water Filter Strength Part 1

Nanotechnology scientists are closing in on a practical use for graphene as a desalination membrane. By applying a mesh of carbon nanotubes to strengthen and block holes in the graphene, the researchers have taken a step towards converting sea water into fresh water with low energy inputs – a massive leap in solving a global issue.

At present, the world needs better desalination technologies. Drought is a major issue for not only millions of poverty-stricken people in coastal areas, but also in industrialised countries where climate change and agricultural expansion has put extreme pressure on natural fresh-water resources.

In Israel, diverting the Jordan river for agricultural use may mean that the Dead Sea dries up completely. In Californian many farmers faced ruin following a 7 year-long drought. In Western Australia, the wine-making industry is nearing collapse as climate change is causing the naturally sparse annual rains to fall out at sea, not on the vineyards. While in South Africa, water rationing in 2018 resulted in Cape Town residents queueing in the streets for water handouts and capturing shower water in buckets for later use in flushing toilets. Harsh fines for being in excess of metered household water limits are still in place.

While a wetter year and a massive public campaign to reduce household water consumption has solved much of Cape Town’s water shortage, the city also installed a number of desalination plants to avert the crisis.

Removing the salt from sea water can easily be achieved with evaporation – an energy intensive process. While the most common desalination technology uses reverse osmosis through a polymer membrane. However these polymer membranes still have their faults, as the journal Technology Review notes, “Reverse osmosis is expensive because it requires a great deal of electricity to push water through a filter. It’s also costly to treat the water to kill microbes and to replace the filters. Researchers are hoping that improved membrane materials could make this process cheaper, leading the industry to look for better membranes.”

Today, Cape Town is experiencing a period of major power shortages, in part caused by the electricity needed to fuel the desalination plants. The sustained lack of essentials such as power and water can take both a physical and psychological toll, as Claudia Smargiasso, a digital marketing strategist who lives in a Cape Town suburb told the German news agency, DW, “Capetonians are just exhausted. We're tired of being in crisis mode. From having no water to this energy crisis. It's just exhausting to always have to be prepared for something.”

The good news for Claudia and the rest of the planet, is that both of these problems are now closer than ever to being solved.

Graphene has long been touted as a potential chemical or desalination membrane. As a strong, porous sheet, just a single atom thick, graphene seems ideal for use as a separation tool. Much like pouring water through a sheet of muslin or similarly thin cloth, impurities (including salt) can be filtered out without the need for expensive evaporation or powerful pumps.

Nanoporous two-dimensional materials are already possible for ionic and molecular nanofiltration but are until now have been limited by insufficient mechanical strength over large areas.

Earlier studies had already proven this to be possible. As far back as 2017, the BBC reportedhow a team from Manchester University had, “… created a graphene-based sieve capable of removing salt from seawater.”

By puncturing a layer of graphene with holes large enough for water molecules to pass through (yet small enough to stop the larger salt molecules), nanotechnology specialists hoped to provide a practical alternative to desalination.

However, designs for graphene-based water filters consistently hit two major problems.

To discover what those problems are and how carbon nanotubes can solve them, follow this link to read the second half of this article.

Photo credit: WuhanUniversity, Science, Physicsworld, BBC, Farm1, Ocregister & Worldfinance