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This technology desalinates water using sunlight – in less than 30 minutes

Research using metal-organic frameworks (MOF) continues to deliver water purification solutions, with yet another successful application – this time to desalinate water with sunlight, in less than 30 minutes. 

Led by Monash University, a global research team has turned brackish water potable injecting MOF PSP-MIL-53: poly(spiropyran acrylate) 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. 

Not only does the new MOF absorb salts from water, but it can also regenerate for reuse within four minutes when the crystals are exposed to sunlight.

Monash University Professor Huanting Wang said the research had enabled a new direction for designing stimuli-responsive materials for energy-efficient and sustainable desalination and water purification.

“Desalination has been used to address escalating water shortages globally. Due to the availability of brackish water and seawater, and because desalination processes are reliable, treated water can be integrated within existing aquatic systems with minimal health risks,” Professor Wang said.

“But, thermal desalination processes by evaporation are energy-intensive, and other technologies, such as reverse osmosis, have a number of drawbacks, including high energy consumption and chemical usage in membrane cleaning and dechlorination.”

Desalination is energy intensive, but using sunlight as an energy source in the purification process drives down that cost, Wang said. 

“Sunlight is the most abundant and renewable source of energy on earth,” he said. 

“Our development of a new adsorbent-based desalination process through the use of sunlight for regeneration provides an energy-efficient and environmentally-sustainable solution for desalination.”

Professor Wang and his team have demonstrated that PSP-MIL-53 is able to yield 139.5 L of fresh water per kilogram of MOF per day, highlighting the durability and sustainability of using this MOF for future clean water solutions.

“This study has successfully demonstrated that the photoresponsive MOFs are a promising, energy-efficient, and sustainable adsorbent for desalination,” Wang said.

“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 functionalised for low-energy and environmentally-friendly means of extracting minerals for sustainable mining and other related applications.”

Progressing previous research

The development of MOF PSP-MIL-53 comes in the wake of similar MOF applications developed at Monash University, including a MOF designed to be compatible with specific anions, which can help with PFAS clean up. 

Monash University was also behind the development of MOF nanosheets that are permeable to water. 

Monash University's Professor Xiwang Zhang, who led the nanosheet study, said the membrane offered plenty of advantages as a water purification tool.

“Owing to the rich porosity and uniform pore size, [MOFs] offer significant advantages over other materials for the precise and fast membrane separation,” Professor Zhang said.

“In this world-first study, we were able to use these ultrathin Al-MOFs to create a membrane that is permeable to water, while achieving maximum porosity with nearly 100% rejection of ions.”

The latest research on MOFs was published in Nature Sustainability.