DESALINATION
Desalinating water with sunlight An international research team, led by Monash University, has developed a method that can successfully desalinate water using sunlight.
D
esalination has been used globally to address escalating water shortages, but is considered too costly in many areas due to its high energy and chemical requirements. Now, a global research team has successfully transformed brackish water and seawater into safe drinking water in less than 30 minutes using metal-organic frameworks (MOFs) and sunlight. MOFs are a class of compounds consisting of metal ions that form a crystalline material with the largest surface area of any known material. The research team created a dedicated MOF called PSP-MIL-53, which was synthesised by introducing poly(spiropyran acrylate) (PSP) into the pores of MIL-53 – a specialised MOF well known for its breathing effects and transitions upon the adsorption of molecules such as water and carbon dioxide. Desalinating 2 233 parts per million (ppm) of water sourced from a river, lake or aquifer, the team demonstrated that PSP-MIL-53 was able to yield 139.5 ℓ of fresh water per kilogram of MOF per day, with a low energy consumption. The process also filters out harmful particles and could provide potable water for millions of people across the world. The World Health Organization suggests good-quality drinking water
20
JAN/F E B 2021
should have a total dissolved solids (TDS) of <600 ppm. Researchers were able to achieve a TDS of <500 ppm. According to lead author Professor Huanting Wang, from the Department of Chemical Engineering at Monash University in Australia, this highlights the durability and sustainability of using this MOF for future clean water solutions.
Sustainable solution
“Sunlight is the most abundant and renewable source of energy on earth. Our development of a new adsorbentbased desalination process through the use of sunlight for regeneration provides an energy-efficient and environmentally sustainable solution for desalination,” says Wang. The PSP-MIL-53 MOF can adsorb salts from brackish water and seawater, and provide clean drinking water in less than 30 minutes. The entire desalination process is energy efficient, low cost and sustainable. In addition, the MOF can be regenerated for reuse within four minutes when the MOF crystals are exposed to sunlight. “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,” says Wang.
“These sunlight-responsive MOFs can potentially be further functionalised for low-energy and environmentally friendly means of extracting minerals for sustainable mining and other related applications.” The research was published in the prestigious journal Nature Sustainability and is available here: www.nature.com/ articles/s41893-020-0590-x.
