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New Hydrogels Enable Purification of Water Using Direct Sunlight

The United Nations has declared that 30,000 people die every week from drinking unsafe water. Despite the fact that a huge majority of these deaths happen in developing nations, unexpected water shortages occur even in the United States, specifically following tropical storms, hurricanes, and other natural disasters that can interrupt the supply of water without any warning.

A research team headed by Guihua Yu, associate professor of materials science and mechanical engineering at The University of Texas at Austin, in UT Austin’s Cockrell School of Engineering, has devised a compact and cost-efficient technology with the help of combined gel-polymer hybrid materials.

These “hydrogels,” which are networks of polymer chains with high water absorbency, possess semiconducting (solar-adsorbing) and hydrophilic (attraction to water) properties, thereby enabling the production of safe and clean drinking water from any source, whether from contaminated supplies or the oceans. The outcomes of the study have been reported in the latest issue of the Nature Nanotechnology journal.

We have essentially rewritten the entire approach to conventional solar water evaporation,” stated Yu. The Texas Engineering scientists have created an innovative hydrogel-based solar vapor generator that uses ambient solar energy to power up the evaporation of water to perform effective desalination.

Prevalent solar steaming technologies employed to treat saltwater include a highly expensive process that is dependent on optical instruments to concentrate sunlight. The UT Austin researchers synthesized nanostructured gels that need very less energy—requiring only naturally existing levels of ambient sunlight to operate—and are capable of considerably increasing the volume of water that could be evaporated.

Water desalination through distillation is a common method for mass production of freshwater. However, current distillation technologies, such as multi-stage flash and multi-effect distillation, require significant infrastructures and are quite energy-intensive. Solar energy, as the most sustainable heat source to potentially power distillation, is widely considered to be a great alternative for water desalination.

Fei Zhao, Postdoctoral Researcher

The hydrogels enable the water vapor to be produced under direct sunlight and then pumped to a condenser for the delivery of freshwater. The desalinating characteristics of these hydrogels were also investigated on water samples from the salt-rich Dead Sea and overwhelmingly passed.

The UT engineers used samples of water from one of the saltiest water bodies on Earth - the Dead Sea - and were successful in considerably reducing its salinity after putting it through the hydrogel process. They were able to accomplish levels that satisfied the accepted drinking water standards as drafted by the U.S. Environmental Protection Agency and the World Health Organization.

Our outdoor tests showed daily distilled water production up to 25 liters per square meter, enough for household needs and even disaster areas. Better still, the hydrogels can easily be retrofitted to replace the core components in most existing solar desalination systems, thereby eliminating the need for a complete overhaul of desalinations systems already in use.

Guihua Yu, Associate Professor

Since salt is one of the most challenging substances to be segregated from water, scientists have also successfully shown the potential of the hydrogels in filtering out several other common contaminants found in water, which are deemed unsafe for consumption.

Yu is hopeful that the technology can be commercialized and has been organizing his group in anticipation of requests from industry to carry out scalability tests.The prospective influence of this technology could be far-reaching since the global requirement of clean, fresh water exceeds the prevalent natural supplies.

A patent application has been filed, and Yu has collaborated with the university’s Office of Technology Commercialization to support the commercialization and licensing of this innovative category of hydrogels.

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