Monash University technology has been used to purify brackish water and seawater in less than 30 minutes, using metal-organic frameworks (MOFs) and sunlight.

In a discovery that could provide potable water for millions of people across the world, researchers say they were not only able to filter harmful particles from water and generate 139.5L of clean water per kilogram of MOF per day, but also perform this task in a more energy-efficient manner than current desalination practices.

Monash University’s Professor Huanting Wang says the work opens up a new direction for designing stimuli-responsive materials for energy-efficient and sustainable desalination and water purification.

“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 says.

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

“Sunlight is the most abundant and renewable source of energy on Earth. 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.”

Metal-organic frameworks are a class of compounds consisting of metal ions that form a crystalline material with the largest surface area of any material known.

The research team created a dedicated MOF called PSP-MIL-53. This 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.

Researchers demonstrated that PSP-MIL-53 was able to yield 139.5L of fresh water per kilogram of MOF per day, with a low energy consumption.

This was from desalinating 2,233 ppm water sourced from a river, lake or aquifer.

Professor Wang said this highlights 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,” Professor 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.”

The study is accessible here.