Penn engineers develop filters that use nanoparticles to prevent slime build-up

November 01, 2017

Filtration membranes are, at their core, sponge-like materials that have micro- or nanoscopically small pores. Unwanted chemicals, bacteria and even viruses are physically blocked by the maze of mesh, but liquids like water can make it through.

The current standard for making these filters is relatively straightforward, but doesn't allow for much in the way of giving them additional functionality. This is a particular need when it comes to "biofouling." The biological material they are supposed to filter out -- including bacteria and viruses-- gets stuck on the surface of the mesh, blocking the pores with a slimy residue.

Beyond reducing the flow, such biofilms can potentially contaminate whatever liquid makes it through to the other side of the filter.

Researchers at the University of Pennsylvania's School of Engineering and Applied Science have a new way of making membranes that could address this problem. Their method allows them to add in a host of new abilities via functional nanoparticles that adhere to the surface of the mesh.

They have demonstrated this new process with membranes that block bacteria- and virus-sized contaminants without letting them stick, a property that would vastly increase the efficiency and lifespan of the filter.

The "antifouling" membranes they have tested would be immediately useful in relatively simple applications, like filtering drinking water, and could eventually be used on the oily compounds found in fracking wastewater and other heavy-duty pollutants.

The researchers' method, described in a paper recently published in the journal Nature Communications, allows for membranes made from a wide range of polymers and nanoparticles. Beyond antifouling abilities, future nanoparticles could catalyze reactions with the contaminants, destroying them or even converting them into something useful.

The study was led by Daeyeon Lee, a professor in Penn Engineering's Department of Chemical and Biomolecular Engineering, and Kathleen Stebe, Penn Engineering's Deputy Dean for Research and Richer & Elizabeth Goodwin Professor of Chemical and Biomolecular Engineering, along with Martin F. Haase, an assistant professor at Rowan University who developed the technology as a postdoctoral researcher in the labs of Stebe and Lee. Harim Jeon, Noah Hough, and Jong Hak Kim also contributed to the study.

The researchers' new membrane-making method relies on a specialized type of liquid mixture known as a "bicontinuous interfacially jammed emulsion gel," or "bijel." Unlike emulsions that consist of isolated droplets, both the oil and water phases of bijels consist of densely intertwined but fully connected networks. Nanoparticles introduced to the emulsion find their way to the interface between the oil and water networks.

Lee, Stebe and Haase previously devised a new way of making bijels that allows for a greater range of component materials, which they described in a 2015 Advanced Materials paper. Now, they have shown a way to make a solid filter using the same method.

"We knew this technology had promise," Stebe said. "Some of that promise is now being made real."

As with their earlier bijels, this filter begins as an intertwined network of water and oil, with a dense layer of nanoparticles separating the two. But by using an oil that can be polymerized with UV light -- crosslinking free-floating individual molecules into a solid, 3D mesh -- the researchers are now able to solidify the structure of the bijel.

Critically, this method leaves the dense layer of nanoparticles in place on the surface of the polymer after the water has been flowed away. Conventional ways of making polymer membranes don't allow for this.

"Polymers typically hate particles and will eject them, but interfaces love particles and will trap them," Stebe said. "The density of nanoparticles on the surface of our polymers is through the roof. They are jammed together like sand in a sandcastle."

The researchers imbued their filters with silica nanoparticles, and fashioned them into straw-like tubes. Silica nanoparticles can be modified with a wide range of chemicals with different functionalities, including the antifouling property the researchers tested. They demonstrated both their filtering and antifouling capabilities on water containing gold nanoparticles of various sizes.

"In our experiment, we were able to filter out very small gold nanoparticles, in sizes equivalent to viruses," said Lee. "The tube shape also works well in large-scale implementation of these filter membranes. Because they have large surface-area-to-volume ratios and don't get clogged, we can draw in fluid from the sides and suck it out from the end, allowing for continuous filtration."

"Membranes are typically passive materials that do not adapt their properties when environmental conditions change," said Haase. "An exciting aspect about our membranes is that they can be made to open and close their pores in response to a chemical signal. This unique feature enables the membrane to have controllable permeability, which is useful for the separation of different types of contaminants from water."

Lee is also a co-principal investigator at Penn Engineering's REACT, or Research and Education in Active Coatings Technologies for human habitat. This multidisciplinary program is aimed at improving shelters used in disaster relief, and as such, Lee has interacted with emergency responders and equipment providers, such as ShelterBox.

"When we spoke to people at ShelterBox, they said that more than a tent, what people need is clean water," Lee said. "REACT could potentially make these filters part of a system that does both."

With several ongoing refugee crises around the world and millions still without potable water after hurricane Maria struck Puerto Rico, the importance of this development is not lost on the researchers.

"There are really people right now who need this kind of technology so badly." said Stebe.
-end-
The research was primarily supported by National Science Foundation grant CBET-1449337 and partially supported through the German Research Foundation under the project number HA 7488/1-1.

University of Pennsylvania

Related Nanoparticles Articles from Brightsurf:

An ionic forcefield for nanoparticles
Nanoparticles are promising drug delivery tools but they struggle to get past the immune system's first line of defense: proteins in the blood serum that tag potential invaders.

Phytoplankton disturbed by nanoparticles
Products derived from nanotechnology are efficient and highly sought-after, yet their effects on the environment are still poorly understood.

How to get more cancer-fighting nanoparticles to where they are needed
University of Toronto Engineering researchers have discovered a dose threshold that greatly increases the delivery of cancer-fighting drugs into a tumour.

Nanoparticles: Acidic alert
Researchers of Ludwig-Maximilians-Universitaet (LMU) in Munich have synthesized nanoparticles that can be induced by a change in pH to release a deadly dose of ionized iron within cells.

3D reconstructions of individual nanoparticles
Want to find out how to design and build materials atom by atom?

Directing nanoparticles straight to tumors
Modern anticancer therapies aim to attack tumor cells while sparing healthy tissue.

Sweet nanoparticles trick kidney
Researchers engineer tiny particles with sugar molecules to prevent side effect in cancer therapy.

A megalibrary of nanoparticles
Using straightforward chemistry and a mix-and-match, modular strategy, researchers have developed a simple approach that could produce over 65,000 different types of complex nanoparticles.

Dialing up the heat on nanoparticles
Rapid progress in the field of metallic nanotechnology is sparking a science revolution that is likely to impact all areas of society, according to professor of physics Ventsislav Valev and his team at the University of Bath in the UK.

Illuminating the world of nanoparticles
Scientists at the Okinawa Institute of Science and Technology Graduate University (OIST) have developed a light-based device that can act as a biosensor, detecting biological substances in materials; for example, harmful pathogens in food samples.

Read More: Nanoparticles News and Nanoparticles Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.