The new invention consists of a coating that produces a hydrophilic, oil-repellent film on the surface of the filter. These metal oxide molecules seize any loose water atoms while resisting oil. For scientists, these dual properties are called hydrophilic and oleophobic.

“One of the best ways to clean oily water is to use a membrane,” says Seth Darling, director of the Argonne Institute of Molecular Engineering. "The problem is that the oil sticks to the membrane and blocks the pores until the membrane stops working. Today, if people have oily membranes, either they change it or they try to wash it with irritating chemicals to wash off the oil."

Scientists have used a method called atomic layer deposition that uses chemical vapor to deposit a very thin layer of metal oxide on the surface of all filters. They tried to use different metal oxides on off-the-shelf commercial polymer films to find out which works best. The team announced the results on the ACS Nano on August 14 .

Darling said that the atomic layer deposition itself is not new, but this method has never been used to modify the film.

"This is a frontier," Darling said. “The coating thickness is only a few nanometers. If the coating is thicker than this, it will close the pores. What you want is a small change in the pore structure, but you want to change the pores of the chemical properties of the material.”

In order to create this layer in the past, attempts have been made to attach nanoparticles to the film by flowing the nanoparticles through the film or growing on the film. But when water flows through these systems, the particles tend to be ripped off. Atomic layer deposition is different because in this case, the metal oxide film forms a strong chemical bond with the polymer to which it is attached. During atomic layer deposition, the membrane is exposed to a series of vapors that bind the molecules together and form covalent bonds with the polymer.

“Some polymers are easier to bond than others, some will repel oil and some will not,” Darling talks about his group's use of various metal oxides. “At this point, we know very well what work and why.”

Tin oxide and titanium oxide form the closest bond with water molecules, trap them and layer them on the surface.

“When the oil comes into contact with the membrane, it will remain separate as it will flow through the water layer,” said Yang Haocheng, a postdoctoral researcher in charge of the project.

For the oil and gas industry, fouling membranes can be a costly problem. For example, when oil companies replace clogged filters during hydraulic fracturing, they must turn off their equipment to make changes. John Harvey, head of business development for Argonne, said that oil-resistant membranes like this can significantly reduce the need to replace filters and the downtime.

“Just from my understanding of the oil and gas industry, if the performance of the membranes we can produce is even a small part of what we see in laboratory testing, then it will be significantly higher than the available products now. Representing huge savings," Harvey said.

Another problem in this industry relates to water used for fracturing, which typically returns to the ground from the presence of oil, salt and other contaminants. If contaminated water poses a threat to the aquifer, it cannot be returned to the ground, so the industry usually has to find another treatment.

The membranes used today can remove other contaminants, but they can be contaminated with oil. The atomic layer deposition process prevents membrane clogging, thereby better filtering the water passing through them.

"With this technology, they can continue to use this water," Harvey said. “This may be a direct replacement for the filtration devices they use today.”

This method can also help with oil spill cleanup work. In an oil spill emergency, diesel fuel is used as a cleaning agent on pipes and vessels, which leaves a waste of diesel fuel mixed with oil and dirt. But Darling pointed out that the pipes and containers treated with oxides can be cleaned.

Dear, who invented the Oleo sponge, the material that can soak out the oil at sea, said that he believes that these two techniques can be used in the concert for future cleaning and also things that he and his scientists may have A host has not thought of it.

“One thing I learned from Oleo Sponge is that you can't imagine all possible applications at the beginning,” he said. “We are looking forward to the interest of oil companies , but we have also heard of the cosmetics industry and sporting goods manufacturers. So I suspect that once this happens, people will also come up with applications that we have never imagined.”

Further exploration: Researchers report two-sided Janus film applications

More information: Yang-Cheng Yang and others. Atomic Layer Deposition of Oil Repellent Film: Oxide Interface Engineering, ACS Nano (2018). DOI: 10.1021 / acsnano.8b04632