New technology uses sunlight to turn seawater into drinking water in 30 minutes

It provides an energy-efficient and environmentally-sustainable solution for desalination.

Clean drinking water is essential to sustain human life and is of paramount importance to human health. Fortunately, the planet has enough freshwater for every inhabitant. However, billions of people across the world are deprived of access to clean, safe drinking water.

Now, in a groundbreaking study led by Monash University, researchers have succeeded in transforming brackish water and seawater into safe, clean drinking water. Instead of heat or electricity, the new technology harnesses the power of sunlight to desalinate and purify water in less than 30 minutes. This breakthrough has generated a hope to solve the scarcity of clean and safe drinking water in areas that may not have access to a reliable electric grid necessary for other methods of desalination.

The study has used a combination of metal-organic frameworks (MOF) and sunlight to filter harmful particles from water. Each kilogram of MOF can generate large amounts of clean water per day. In addition, the technology performs this task in a more energy-efficient and environmentally friendly manner than other desalination methods.

MOFs are so porous with the largest surface area of any material known – they can fit the entire surface of a football field in a teaspoon. This characteristic makes it really effective at sucking up salt from water. In their study, the team created a dedicated MOF called PSP-MIL-53 – a poly (spiropyran acrylate) (PSP) functionalized metal-organic framework (MOF), which was able to yield 139.5L of fresh drinking water per kilogram of the material per day, with low energy consumption.

The system was tested using water with a TDS of 2,233 parts per million (ppm). The researchers found that their system is capable of achieving a TDS of less than 500 ppm – exceeding the standards set by the World Health Organisation (WHO) for good quality drinking water. The WHO suggests that good quality drinking water should have a total dissolved solid (TDS) of no greater than 600 ppm.

Once the absorption is done, the MOF is ready to be reused after four minutes of exposure to sunlight, which causes the material to release its collected salt.

The research opens up a new direction for designing stimuli-responsive materials for energy-efficient and sustainable desalination and water purification.

This study has successfully demonstrated that the photoresponsive MOFs are a promising, energy-efficient, and sustainable adsorbent for desalination,” said lead author Professor Huanting Wang from the Department of Chemical Engineering at Monash University in Australia. “Our work provides an exciting new route for the design of functional materials for using solar energy to reduce the energy demand and improve the sustainability of water desalination.”

These sunlight-responsive MOFs can potentially be further functionalized for low-energy and environmentally-friendly means of extracting minerals for sustainable mining and other related applications.”

Journal Reference:
  1. A sunlight-responsive metal–organic framework system for sustainable water desalination. DOI: 10.1038/s41893-020-0590-x

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