A team of Brown University researchers has found a way to orient the gaps that form between sheets of graphene that are stacked on top of each other. The tiny gaps, called nanochannels, are positioned by the team in a way that makes them more useful for filtering water and other liquids of nanoscale contaminants.

Structure and fabrication steps leading to vertically aligned Zr-GO/epoxy membranes. Image from article

In the last decade, a whole field has sprung up to study these spaces that form between 2D nanomaterials, said Robert Hurt, a professor in Brown’s School of Engineering and coauthor of the research. You can grow things in there, you can store things in there, and there’s this emerging field of nanofluidics where you’re using those channels to filter out some molecules while letting others go through.

Researchers led by Northwestern University engineers and Argonne National Laboratory scientists have reached new findings regarding the role of ionic interaction within graphene and water. Their insights could open the door to the design of new energy-efficient electrodes for batteries or provide the backbone ionic materials for neuromorphic computing applications.

"Every time you have interactions with ions in matter, the medium is very important. Water plays a vital role in mediating interactions between ions, molecules, and interfaces, which lead to a variety of natural and technological processes," said Monica Olvera de La Cruz, Lawyer Taylor Professor of Materials Science and Engineering, who led the research. "Yet, there is much we don't understand about how water-mediated interactions are influenced by nanoconfinement at the nanoscale."

Vanderbilt engineers recently designed a simple defect-sealing technique to correct variations in pore size in graphene membranes. The researchers reported a breakthrough in scalable fabrication of graphene membranes with a sealing technology that corrects variations in the pore size so they remain small enough to trap salt ions and small molecules but allow water to pass.

One of the most complex engineering challenges when making membranes so thin is to maintain integrity in the uniformity of the pores, which requires drilling atomically precise holes in a one-atom thick sheet of carbon atoms. A single large hole can cause high leakage and compromise membrane performance, said Piran Kidambi, assistant professor of chemical and biomolecular engineering.

Chinese researchers from AECC Beijing Institute of Aeronautical Materials (AECC BIAM) have developed a new type of face mask with graphene material on the key filter layer. The researchers have reportedly put a graphene-polypropylene material on the melt-blown fabric, which is the key filter layer of masks.

The graphene material is said to help the masks features stronger antibacterial properties, better air permeability and enhanced durability. The graphene face mask makes use of the nanoknife effect of the graphene material to destroy the cell wall of bacteria.

Researchers at NIST have used a graphene membrane to solve a long-standing problem affecting the understanding of both living cells and batteries. When a solid and an electrically-conducting liquid come into contact, a thin sheet of charge forms between them. Although this interface, known as the electrical double layer (EDL), is only a few atoms thick, it plays a central role in a wide range of systems, such as keeping living cells nourished and maintaining the operation of batteries, fuel cells, and certain types of capacitors.

For instance, the buildup of an EDL on a cell membrane creates a difference in voltage between the liquid environs outside the cell and the cell's interior. The voltage difference draws ions such as potassium from the liquid into the cell, a process essential for the cell's survival and ability to transmit electrical signals.

Graphenea has announced the launch of a new product highly flat monolayer graphene. The graphene is grown by CVD on copper thin film on a 2 sapphire substrate. With extremely low roughness that is less than 4 nm, this new product is targeted at applications in photonics, high-performance electronics, magnetic memory, and freestanding membranes.

The product aims to meet wafer-scale integration requirements to build uniform graphene devices in a fashion compatible with current industrial fabrication methods. The flat graphene product is ready to be transferred by electrochemical delamination or dry methods since the sapphire substrate is robust enough to withstand mechanical damage, preventing tearing and wrinkling of the thin Cu sheet. The total wafer thickness is 430 micrometers. Full product information can be found in Graphenea's online store.

A partnership between The University of Manchester and Khalifa University of Science and Technology in Abu Dhabi has yielded graphene-based membranes aimed at to taking salts out of water.

The most popular method for water desalination currently is a process called reverse osmosis, which requires large quantities of water to be forced through a membrane to remove the salts in the water. This method is particularly useful when there is a high salt content, however more efficient methods are required for bodies of water that have a lower salt content, known as brackish water. The team of researchers has developed new ion-selective membranes incorporating graphene oxide, for use in electromembrane desalination processes such as electrodialysis and membrane capacitive deionization.

Researchers at the University of Illinois examined how tiny defects in graphene membranes, formed during fabrication, could be used to improve molecule transport. They found that the defects make a big difference in how molecules move along a membrane surface. Instead of trying to fix these flaws, the team set out to use them to help direct molecules into the membrane pores.

Nanopore membranes have generated interest in biomedical research because they help researchers investigate individual molecules - atom by atom - by pulling them through pores for physical and chemical characterization. This technology could ultimately lead to devices that can quickly sequence DNA, RNA or proteins.

A way to cut CO₂ levels, produced from burning fossil fuels and released into the atmosphere, is through carbon capture, a chemical technique that removes CO₂ from emissions ("postcombustion"). The captured CO₂ can then be recycled or stored in gas or liquid form, a process known as sequestration.

CO2-selective polymeric chains anchored on graphene effectively pull CO2 from a flue gas mixture. Credit: KV Agrawal (EPFL)

Carbon capture can be done using high-performance membranes, which are polymer filters that can specifically pick out CO₂ from a mix of gases, such as those emitted from a factory's flue. These membranes are environmentally friendly, they don't generate waste, they can intensify chemical processes, and can be used in a decentralized fashion. They are now considered as one of the most energy-efficient routes for reducing CO₂ emissions. Now, scientists (led by Kumar Varoon Agrawal) at Ecole Polytechnique Federale de Lausanne (EPFL) have developed a new class of high-performance membranes that exceed post-combustion capture targets by a significant margin. The membranes are based on single-layer graphene with a selective layer thinner than 20 nm, and have highly tunable chemistry, meaning that they can pave the way for next-generation high-performance membranes for several critical separations.

KAUST researchers have tailored the structure of graphene-oxide layers to mimic the shape of biological channels, creating ultra-thin membranes to rapidly separate chemical mixtures. This may have the potential to inspire new materials to clean up chemical and pharmaceutical production.

"In making pharmaceuticals and other chemicals, separating mixtures of organic molecules is an essential and tedious task," says Shaofei Wang, postdoctoral researcher in Suzana Nuñes lab at KAUST. One option to make these chemical separations faster and more efficient is through selectively permeable membranes, which feature tailored nanoscale channels that separate molecules by size.