Oil-stained waters can be filtered by sunlight, researchers suggest

A new method of water purification promises to use sunlight to clean even oil slicks, according to a study published in the scientific journal Nano Research and released last Tuesday (22).

According to the information released, the new method promises 90% greater energy efficiency than other similar processes, while avoiding bottlenecks inherent in their practice.

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Water purification method focuses sunlight on specific points, increasing vaporization and separating liquid from contaminating components such as oil (Image: Chinese National Academy of Sciences/Handout)

The proposal caught the attention of the United Nations (UN) Climate Committee precisely for this last part: according to the committee’s survey, about 4 billion people – almost half of the Earth’s population – do not have access to clean water to drink. .

Various methods for cleaning up polluted waters have been proposed, but almost all have some flaws: some are not large enough to have any practical positive effect, while others do not last long enough and would collapse after a few years.

This is where researchers from the Chinese Academy of Sciences and China’s Xiamen University enter: “There is tremendous demand for fresh water in households and industrial and agricultural applications, so various water purification technologies have been created to alleviate the shortage of this resource,” he said. Miao Wang of Xiamen and the study’s primary author. “Comparing to hand paths, solar purification of seawater or contaminated water, via interfacial evaporation, holds promise as a low-cost system.”

The very ingenious method of purification uses the heat of sunlight, which evaporates the contaminated water on the surface, separating the water-forming H2O molecules from their contaminants or salt. The water molecules escape in the form of steam to enter the natural condensation cycle – from where the rain comes out – in the form of clean water.

The problem: Attempts for systems of this type to be applied in real environments have been largely impeded by oil contamination, manufacturing processes, salt crystallization, or instability.

“To generate more purified water within the same amount of sunlight, how do we acquire more energy to heat the water locally to improve the rate of vaporization — without encountering the bottlenecks of other approaches?” asked Xu Hou, who co-authored the paper. “We answered that question in the study and developed an evaporation platform that can maintain an accelerated rate of evaporation while repelling oil and preventing contamination.”

The researchers combined two types of gel, generating a compound called organohydrogel, which can act in different states of matter, although it appears as something mostly liquid and endowed with several molecular webs. By dosing this gel with carbon nanotubes, the scientists created focal points where sunlight can focus, preventing heat from being dissipated.

In tests, the platform successfully evaporated about 2.4 kg of water per square meter every hour, and estimates say it could persist in operation for 240 uninterrupted hours – “even in conditions of extreme oil contamination”, said the researchers. experts.

“We have created an anti-oil contamination heating platform, with unique use of solar energy, which shows enormous potential for water purification through sunlight, even in highly polluted environments,” said Shutao Wang, another author. . “We hope that this cost-effective and sustainable solution will help to further alleviate the global shortage of fresh water.”

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