Clean drinking water is one of the essences of life. However, safe drinking water is not a reality for more than 2 billion people worldwide. These individuals are at risk of potentially fatal waterborne diseases such as typhoid and polio.
This high-risk population is expected to grow over the next five years as the climate crisis creates more and more water-stressed areas, according to the World Health Organization (WHO).
Scientists have been working for decades to solve this problem, and although some solutions have found success in effective water purification, these energy-intensive solutions can be difficult to implement in communities without a stable electrical network.
Now, a team of scientists from Australia and China has proposed a sustainable solution that relies on sunlight to begin the filtration process instead of heat or electricity.
Using a super-porous material to absorb salt from brackish, salt water, researchers were able to almost create 40 gallons of clean drinking waterr per one kilogram of a metal material. Better yet, this drinking water was even cleaner than the official WHO guidelines.
This finding was published Monday in the journal Nature Sustainability.
“Sunlight is the most abundant and sustainable source of energy on Earth.”
The lead author of the study, Huanting Wang, a professor of chemical engineering at Monash University in Australia, says his team’s approach makes use of the planet’s most powerful source: sunlight. Their solar-powered method desalinates brackish, as stagnant, water more durable than previous methods.
“[T]”processes of hermal desalination by evaporation are energy intensive, and other technologies, such as reverse osmosis, have a number of disadvantages, including high energy consumption and chemical use in membrane cleaning and dechlorination,” says Wang. Sunlight is the brightest and most innovative source of energy on Earth. ”
Wang and his colleagues explain in the study that a sustainable energy source, such as sunlight, would be especially useful for communities that may not have access to a reliable electric grid needed for other methods of desalination.
How it works – Although sunlight is an important part of this process, another important player is the material the researchers chose to use. This material is a kind of metal composition consisting of metal ions configured in a crystalline pattern – not unlike the salt that it is intended to absorb.
Due to its unique crystal structure, this compound is incredibly porous, with so many angles and slits in it, that its total surface area is actually the largest per unit measurement of any known material.
So big in fact, that scientists estimate the entire area of a football field could fit within a single teaspoon of this material. A characteristic that makes it really effective at sucking salt out of water.
The researchers further improved the uptake of this material by adding other material to its pores, called PSP-MIL-53. This material is characterized by “having respiratory effects”, and is capable of promoting efficient absorption.
After testing this material on both natural saltwater and synthetic saltwater, they found that the compound could absorb enough water in 30 minutes to make nearly 40 gallons of sweet drinking water per single kilogram of the material.
In analyzing the resulting water, the researchers measured their total soluble solids (TDS) to be less than 500 parts per million – a standard even above that recommended by WHO, which categorizes clean drinking water as TDS no greater than 600 parts per million.
The initial uptake is done in the dark, but an exposure of four minutes to sunlight causes the material to release its collected salt and start the absorption process again for many more cycles.
“This study has successfully shown that it is photoresponsive [metal compounds] are a promising, energy-efficient and durable adsorbent for desalination, “said Wang. 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. “
What comes next – In addition to helping provide a sustainable solution for creating clean drinking water for communities with poor energy infrastructure, the researchers also say that this approach could be redesigned in the future to include other compounds and minerals, and creating a sustainable solution for mineral mining well. What needs to happen next is to determine how to get this tech out of the lab, and into the field.
Abstract: Light-responsive materials with high adsorption capacity and regenerability due to sunlight-triggered are highly desirable for their low and environmentally friendly processes for industrial separation. Here we report a poly (spiropyran acrylate) (PSP) functionalized metal – organic frame (MOF) as a sunlight-regenerable ion adsorbent for sustainable water desalination. Under dark conditions, the zwitterionic isomer rapidly adsorbs multiple cations and anions from water within 30 minutes, with high ion adsorption loads of up to 2.88 mmol g – 1 of NaCl. With sunlight, the neutral isomer releases this adsorbed salt rapidly within 4 minutes. One-column desalination experiments prove that PSP-MOF works efficiently for water desalination. A fresh water yield of 139.5 l kg – 1 d – 1 and a low energy consumption of 0.11 Wh l – 1 would be achieved for desalination of 2,233 ppm synthetic brackish water. Importantly, this adsorbent shows excellent stability and cycling performance. This work opens up a new direction for the design of stimulus-responsive materials for energy-efficient and sustainable desalination and water purification.
