Water Purification Using Sunlight Technology

Clean water is the ultimate goal. These new floating mats could help purify industrial pollutants using only sunlight. (fizkes/Shutterstock)

In a nutshell

Researchers developed copper-doped titanium dioxide nanofiber mats that float on water and use natural sunlight, not UV lamps, to break down pollutants.
These “floating blankets” outperform commercial photocatalysts like P25 by degrading over 90% of contaminants under visible light, without requiring complex filtration afterward.
The mats are lightweight, reusable, and made using scalable manufacturing methods, offering a promising low-cost solution for water purification in resource-limited settings.

COLUMBUS, Ohio — Researchers have developed what they’re calling “nanofibrous blankets” that float on contaminated water and use ordinary sunlight to break down pollutants. These lightweight, self-supporting mats could revolutionize water treatment by eliminating the need for expensive ultraviolet lamps while solving one of the biggest headaches in water purification: how to remove tiny particles after they’ve done their job.

A technique called photocatalytic water treatment relies on titanium dioxide (TiO2) nanoparticles that need UV light to work, but these particles create their own problem. Once they’ve cleaned the water, you have to fish them out, which is costly and complicated. According to a study published in Advanced Science, scientists at Ohio State University have engineered a solution that sidesteps both issues entirely.

Their breakthrough centers on copper-infused TiO2 nanofibers woven into mat-like structures that can be shaped into various forms. Unlike conventional photocatalysts that require UV light to activate, these mats work under visible light, meaning they can harness natural sunlight for water purification. The mats float on water surfaces and can be easily removed once the cleaning process is complete.

“There hasn’t been an easy way to create something like a blanket that you can lay on water and start creating energy,” says lead author Pelagia-Iren Gouma from Ohio State University, in a statement. “But we are the only ones who have made these structures and the only ones to demonstrate that they actually work.”

Why Is This An Upgrade?

a,b) Cu-doped TiO2 heat-treated nanofiber blankets, c) SEM im age of the nanofiber. (Credit: Advanced Science)

The researchers modified TiO2, a compound commonly used in sunscreen and self-cleaning surfaces. Pure TiO2 only responds to UV light, which makes up less than 5% of sunlight. Adding copper changed the material so it could absorb visible light from the sun, instead of just ultraviolet.

Copper also helped create a rare crystal form called brookite. This structure helps the material clean water more effectively by stopping the energy from fading too fast during the reaction.

The team used electrospinning to create nanofibers with diameters about 1,000 times thinner than human hair. These fibers form interconnected mats that the researchers describe as having a texture similar to potato chips. The result is a porous, lightweight material that maximizes surface area while remaining sturdy enough to use.

Testing the Floating Cleaners

Researchers compared the copper-infused mats against pure TiO2 and P25 Degussa, a commercial photocatalyst considered the gold standard in the field. They used methylene blue, a common industrial dye, as their test pollutant in controlled laboratory conditions.

When tested under regular light (with UV rays blocked), the copper-treated mats worked far better than the other materials. While the standard P25 cleaner barely made a dent, the new mats broke down over 90% of the test pollutant in just four hours.

Tests showed that the copper-doped mats produced a noticeable electric signal under visible light, something the regular TiO₂ didn’t. This signal means the mats successfully created and separated the energy particles needed to power the cleaning process.

In another test using dye-filled Petri dishes and light with the UV filtered out, the copper-enhanced mats broke down all of the dye. The older P25 material, by comparison, had very little effect, showing how well the new mats work with just visible light.

Tests showed that the copper was successfully built into the structure of the material, rather than forming unwanted byproducts. It took the place of some titanium atoms and created tiny gaps that help the material clean more effectively.

When sunlight hits the material, it produces tiny energy particles. Some of these particles react with water to create powerful cleaning agents called hydroxyl radicals. Others (called electrons) react with oxygen to create more of these cleaning agents. Together, they break down pollutants into harmless carbon dioxide and water.

“These nanomats can be used as a power generator, or as water remediation tools,” says Gouma. “In both ways, you have a catalyst with the highest efficiency reported to date.”

The brookite crystal structure plays a key role by holding onto these energy particles just long enough to boost the cleaning reaction, instead of letting them cancel each other out too quickly.

Could This Become a New Method for Water Purification?

These mats solve a major problem with earlier water-cleaning materials: they’re easy to use and remove. Since they float and hold their shape, costly equipment is not needed to fish them out after treatment.

They also turn yellow instead of white, which is a sign that the copper was added correctly and that the mats can absorb sunlight, not just UV light.

When tested under full sunlight (including both UV and visible light), the copper-enhanced mats still outperformed the leading commercial material. This shows how powerful the mats are at using regular sunlight to clean water.

Electrospinning, the method used to create these mats, could be scaled up for commercial use. The researchers mixed the ingredients with a temporary ‘carrier’ material that burned away during heating, leaving behind pure, copper-treated fibers.

Advanced imaging showed that copper was spread evenly throughout each fiber, which is important for making sure the mats work consistently. Tests also confirmed that the titanium, oxygen, and copper were evenly mixed with no clumping or unwanted side reactions.

“It’s a safe material, it won’t hurt anything, and it’s as clean as it can be,” says Gouma.

Environmental and Economic Implications

Current water treatment technologies often require energy-intensive UV lamps or complex particle recovery systems that increase operational costs and environmental impact. By harnessing natural sunlight and eliminating particle separation requirements, these floating photocatalyst mats could significantly reduce the energy footprint of water purification.

The material requires no external energy input beyond ambient sunlight, making it particularly attractive for remote or resource-limited treatment. It is also economically friendly because it can be retrieved and potentially reused.

“We have the tools to make them in large quantities and translate them to various industries,” says Gouma. “The only limitation is that it needs someone to take advantage of these abundant resources.”

These mats could be especially useful for industries that deal with dye pollution, like textile, paper, or chemical factories. Because they float, the mats can be placed directly into treatment ponds or tanks and get to work without the need for fancy equipment or complicated setups.

By creating self-supported structures that work under natural sunlight, these floating blankets could make advanced water treatment accessible where it’s needed most, transforming how we approach cleaning our most precious resource.

Paper Summary

Methodology

Researchers used electrospinning to create copper-doped titanium dioxide (TiO2) nanofibers. They dissolved titanium precursors and copper acetate in a polymer solution, then used electrical forces to spin this mixture into ultrathin fibers 60-190 nanometers in diameter. After heat treatment at 500°C to remove organic components, they obtained interconnected mats of pure copper-doped TiO2 nanofibers. The team characterized these materials using X-ray diffraction, electron microscopy, UV-visible spectroscopy, and X-ray photoelectron spectroscopy to understand their structure and properties.

Results

The copper-doped mats successfully absorbed visible light due to a reduced bandgap (2.62 eV compared to 3.1 eV for pure TiO2) and contained both anatase and brookite crystal phases. Under visible light testing, these mats achieved over 90% degradation of methylene blue dye within 240 minutes, significantly outperforming commercial P25 photocatalyst and pure TiO2. Electrochemical measurements confirmed photocurrent generation under visible light (180 nA) compared to negligible current from undoped samples. The mats floated on water and could be easily retrieved after treatment.

Limitations

The study used only methylene blue as a model pollutant in controlled laboratory conditions. Real-world performance with complex pollutant mixtures, long-term durability, and regeneration capabilities were not evaluated. The optimal copper doping concentration and detailed mechanistic understanding require further investigation. Scalability from laboratory synthesis to commercial production has not been demonstrated.

Funding and Disclosures

This research was supported by the National Science Foundation through grant SNM1833345. The authors declared no conflicts of interest.

Publication Information

The paper “3D Self-Supported Visible Light Photochemical Nanocatalysts” was authored by Mikaeili, F., Rahaman, M.M., and Gouma, P.-I. It was published in Advanced Science (vol. 12, article 2502981) on March 24, 2025.