Scientists have developed new technology that can convert seawater into clean drinking water in less than 30 minutes.
Researchers based in Australia used a metal-organic frame (MOF), a type of roasted crystal, to desalinate water.
The hollow frame of pores separates the salt solute into the brackish water or even saltier seawater, in a process known as molecular seeding.
Under dark conditions, the frame absorbs salt and other impurities in the water in 30 minutes. The MOF itself is then regenerated in just four minutes, using sunlight to remove the adsorbed salts.
The light-responsive MOF was used to filter harmful particles out of water and generate 139.5 liters of clean water per kilogram of MOF per day.
Scientists say their technology is more energy efficient than current desalination practices, including reverse osmosis, and could supply drinking water to millions worldwide.
An illustration of the proposed single column setting for desalination in the dark and again under light. Under dark conditions, the technology adsorbs ions in water in 30 minutes, and with sunlight it releases these adsorbed salts rapidly in four minutes.
Water scarcity is one of the biggest global risks in the coming years, according to the World Economic Forum (WEF).
Processes for thermal desalination by evaporation with solar energy are widely used to produce fresh water, but can be very energy intensive.
‘Sunlight is the most powerful and sustainable source of energy on earth,’ said Professor Huanting Wang of the Department of Chemical Engineering at Monash University in Australia.
‘Our development of a new adsorbent-based desalination process using sunlight for regeneration provides an energy-efficient and environmentally sustainable solution for desalination.’
Metal-organic frames are a class of compounds consisting of metal ions that form a crystalline material with the largest surface of any known material
Desalination – the process of undrinkable salt as well as salt water in potable water – has been used to address the escalating water shortage worldwide.
“Because of the availability of brackish water and seawater, and because desalination process is reliable, treated water can be integrated into existing aquatic systems with minimal health risks,” said Professor Wang.
The World Health Organization suggests that good quality drinking water should have a total dissolved solids (TDS) of less than 600 parts per million (ppm).
Monash researchers were able to reach a TDS of less than 500 ppm in just 30 minutes and regenerate the MOF for reuse in four minutes under sunlight by rapidly releasing the adsorbed salts.
MOFs were discovered in the 1990s and could have potential for use in hydrogen storage, solar energy and even the emission of toxic gases from the air.
They are a class of compounds consisting of metal ions that form a crystalline material with the largest surface area of any known material.
They are so porous that they can fit the entire surface of a football field in a teaspoon.
The research team created a dedicated MOF called PSP-MIL-53, which is photoreversible, which means that the functions can be changed from one to the other by the light.
PSP-MIL-53 was synthesized by introducing poly (spiropyran acrylate) (PSP) into the pores of MIL-53 – a specialized MOF known for its respiratory effects and transitions on the adsorption of molecules such as water and carbon dioxide.
PSP-MIL-53 could produce 139.5 liters of fresh water per kilogram of MOF per day, with a low energy consumption, generated from a river but or an aquifer.
“This study has successfully shown that photoresponsive MOFs are a promising, energy-efficient and sustainable adsorbent for desalination,” said Professor Wang.
Spectrum of spectra of SP and MC activated below different pH levels in 10,000 ppm sodium chloride solution
‘Our work provides an exciting new route for the design of functional materials for the use of solar energy to reduce energy demand and improve the sustainability of water desalination.
‘These sunlight-responsive MOFs could potentially continue to operate for low-energy and environmentally friendly means of extracting minerals for sustainable mining and other related applications.’
Processes for thermal desalination by evaporation are usually energy intensive, while other technologies such as reverse osmosis have some disadvantages.
Brackish water has more salt extraction than fresh water, but not as much as seawater. Desalination was increasingly used to address the escalating water shortage, due to the wide availability of brackish water and seawater.
In reverse osmosis, water, with dissolved salt molecules, is forced through a semi-permeable membrane filter.
Larger salt molecules do not pass through the membrane cavities, but the smaller water molecules do.
Reverse osmosis is an effective means of desalinating salt water, but it is more expensive than other methods and has high energy consumption.
The study was published in the journal Nature Sustainability.
.
