Tag Archives: Ke Liu

Osmotic power: electricity generated with water, salt and a 3-atoms-thick membrane


EPFL researchers have developed a system that generates electricity from osmosis with unparalleled efficiency. Their work, featured in “Nature”, uses seawater, fresh water, and a new type of membrane just three atoms thick.

A July 13, 2016 news item on Nanowerk highlights  research on osmotic power at École polytechnique fédérale de Lausanne (EPFL; Switzerland),

Proponents of clean energy will soon have a new source to add to their existing array of solar, wind, and hydropower: osmotic power. Or more specifically, energy generated by a natural phenomenon occurring when fresh water comes into contact with seawater through a membrane.

Researchers at EPFL’s Laboratory of Nanoscale Biology have developed an osmotic power generation system that delivers never-before-seen yields. Their innovation lies in a three atoms thick membrane used to separate the two fluids. …

A July 14, 2016 EPFL press release (also on EurekAlert but published July 13, 2016), which originated the news item, describes the research,

The concept is fairly simple. A semipermeable membrane separates two fluids with different salt concentrations. Salt ions travel through the membrane until the salt concentrations in the two fluids reach equilibrium. That phenomenon is precisely osmosis.

If the system is used with seawater and fresh water, salt ions in the seawater pass through the membrane into the fresh water until both fluids have the same salt concentration. And since an ion is simply an atom with an electrical charge, the movement of the salt ions can be harnessed to generate electricity.

A 3 atoms thick, selective membrane that does the job

EPFL’s system consists of two liquid-filled compartments separated by a thin membrane made of molybdenum disulfide. The membrane has a tiny hole, or nanopore, through which seawater ions pass into the fresh water until the two fluids’ salt concentrations are equal. As the ions pass through the nanopore, their electrons are transferred to an electrode – which is what is used to generate an electric current.

Thanks to its properties the membrane allows positively-charged ions to pass through, while pushing away most of the negatively-charged ones. That creates voltage between the two liquids as one builds up a positive charge and the other a negative charge. This voltage is what causes the current generated by the transfer of ions to flow.

“We had to first fabricate and then investigate the optimal size of the nanopore. If it’s too big, negative ions can pass through and the resulting voltage would be too low. If it’s too small, not enough ions can pass through and the current would be too weak,” said Jiandong Feng, lead author of the research.

What sets EPFL’s system apart is its membrane. In these types of systems, the current increases with a thinner membrane. And EPFL’s membrane is just a few atoms thick. The material it is made of – molybdenum disulfide – is ideal for generating an osmotic current. “This is the first time a two-dimensional material has been used for this type of application,” said Aleksandra Radenovic, head of the laboratory of Nanoscale Biology

Powering 50’000 energy-saving light bulbs with 1m2 membrane

The potential of the new system is huge. According to their calculations, a 1m2 membrane with 30% of its surface covered by nanopores should be able to produce 1MW of electricity – or enough to power 50,000 standard energy-saving light bulbs. And since molybdenum disulfide (MoS2) is easily found in nature or can be grown by chemical vapor deposition, the system could feasibly be ramped up for large-scale power generation. The major challenge in scaling-up this process is finding out how to make relatively uniform pores.

Until now, researchers have worked on a membrane with a single nanopore, in order to understand precisely what was going on. ” From an engineering perspective, single nanopore system is ideal to further our fundamental understanding of 8=-based processes and provide useful information for industry-level commercialization”, said Jiandong Feng.

The researchers were able to run a nanotransistor from the current generated by a single nanopore and thus demonstrated a self-powered nanosystem. Low-power single-layer MoS2 transistors were fabricated in collaboration with Andras Kis’ team at at EPFL, while molecular dynamics simulations were performed by collaborators at University of Illinois at Urbana–Champaign

Harnessing the potential of estuaries

EPFL’s research is part of a growing trend. For the past several years, scientists around the world have been developing systems that leverage osmotic power to create electricity. Pilot projects have sprung up in places such as Norway, the Netherlands, Japan, and the United States to generate energy at estuaries, where rivers flow into the sea. For now, the membranes used in most systems are organic and fragile, and deliver low yields. Some systems use the movement of water, rather than ions, to power turbines that in turn produce electricity.

Once the systems become more robust, osmotic power could play a major role in the generation of renewable energy. While solar panels require adequate sunlight and wind turbines adequate wind, osmotic energy can be produced just about any time of day or night – provided there’s an estuary nearby.

Here’s a link to and a citation for the paper,

Single-layer MoS2 nanopores as nanopower generators by Jiandong Feng, Michael Graf, Ke Liu, Dmitry Ovchinnikov, Dumitru Dumcenco, Mohammad Heiranian, Vishal Nandigana, Narayana R. Aluru, Andras Kis, & Aleksandra Radenovic. Nature (2016)  doi:10.1038/nature18593 Published online 13 July 2016

This paper is behind a paywall.

Storing isotopes in nanocontainers for safer radiation therapy

While it can be effective, radiation therapy is known to be destructive  for cancerous cells and healthy cells. Researchers at Kansas State University and their colleagues in other institutions have devised a new technique that contains the isotopes so they reach the cancerous cells only. From an April 2, 2014 news item in ScienceDaily,

Researchers have discovered that microscopic “bubbles” developed at Kansas State University are safe and effective storage lockers for harmful isotopes that emit ionizing radiation for treating tumors.

The findings can benefit patient health and advance radiation therapy used to treat cancer and other diseases, said John M. Tomich, a professor of biochemistry and molecular biophysics who is affiliated with the university’s Johnson Cancer Research Center.

Tomich conducted the study with Ekaterina Dadachova, a radiochemistry specialist at Albert Einstein College of Medicine in New York, along with researchers from his group at Kansas State University, the University of Kansas, Jikei University School of Medicine in Japan and the Institute for Transuranium Elements in Germany. They recently published their findings in the study “Branched Amphiphilic Peptide Capsules: Cellular Uptake and Retention of Encapsulated Solutes,” which appears in the scientific journal Biochimica et Biophysica Acta.

The study looks at the ability of nontoxic molecules to store and deliver potentially harmful alpha emitting radioisotopes — one of the most effective forms of radiation therapy.

An April 2, 2014 Kansas State University news release (also on EurekAlert), which originated the news item, provides more details about this research that in some ways dates from 2012,

The study looks at the ability of nontoxic molecules to store and deliver potentially harmful alpha emitting radioisotopes — one of the most effective forms of radiation therapy.

In 2012, Tomich and his research lab team combined two related sequences of amino acids to form a very small, hollow nanocapsule similar to a bubble.

“We found that the two sequences come together to form a thin membrane that assembled into little spheres, which we call capsules,” Tomich said. “While other vesicles have been created from lipids, most are much less stable and break down. Ours are like stones, though. They’re incredibly stable and are not destroyed by cells in the body.”

The ability of the capsules to stay intact with the isotope inside and remain undetected by the body’s clearance systems prompted Tomich to investigate using the capsules as unbreakable storage containers that can be used for biomedical research, particularly in radiation therapies.

“The problem with current alpha-particle radiation therapies used to treat cancer is that they lead to the release of nontargeted radioactive daughter ions into the body,” Tomich said. “Radioactive atoms break down to form new atoms, called daughter ions, with the release of some form of energy or energetic particles. Alpha emitters give off an energetic particle that comes off at nearly the speed of light.”

These particles are like a car careening on ice, Tomich said. They are very powerful but can only travel a short distance. On collision, the alpha particle destroys DNA and whatever vital cellular components are in its path. Similarly, the daughter ions recoil with high energy on ejection of the alpha particle — similar to how a gun recoils as it is fired. The daughter ions have enough energy to escape the targeting and containment molecules that currently are in use.

“Once freed, the daughter isotopes can end up in places you don’t want them, like bone marrow, which can then lead to leukemia and new challenges,” Tomich said. “We don’t want any stray isotopes because they can harm the body. The trick is to get the radioactive isotopes into and contained in just diseases cells where they can work their magic.”

The radioactive compound that the team works with is 225Actinium, which on decay releases four alpha particles and numerous daughter ions.

Tomich and Dadachova tested the retention and biodistribution of alpha-emitting particles trapped inside the peptide capsules in cells. The capsules readily enter cells. Once inside, they migrate to a position alongside the nucleus, where the DNA is.

Tomich and Dadachova found that as the alpha particle-emitting isotopes decayed, the recoiled daughter ion collides with the capsule walls and essentially bounces off them and remains trapped inside the capsule. This completely blocked the release of the daughter ions, which prevented uptake in certain nontarget tissues and protected the subject from harmful radiation that would have otherwise have been releases into the body.

Tomich said that more studies are needed to add target molecules to the surface of the capsules. He anticipates that this new approach will provide a safer option for treating tumors with radiation therapy by reducing the amount of radioisotope required for killing the cancer cells and reducing the side effects caused by off-target accumulation of the radioisotopes.

“These capsules are easy to make and easy to work with,” Tomich said. “I think we’re just scratching the surface of what we can do with them to improve human health and nanomaterials.”

I hope this new technique proves effective and travels soon from the laboratory to clinical practice in the foreseeable future.

In the meantime, here’s a link to and a citation for the paper,

Branched amphiphilic peptide capsules: Cellular uptake and retention of encapsulated solutes by Pinakin Sukthankar, L. Adriana Avila, Susan K. Whitaker, Takeo Iwamoto, Alfred Morgenstern, Christos Apostolidis, Ke Liu, Robert P. Hanzlik, Ekaterina Dadachova, and John M. Tomich. Biochimica et Biophysica Acta (BBA) – Biomembranes (Biochim Biophys Acta) 2014 Feb 22. pii: S0005-2736(14)00069-8. doi: 10.1016/j.bbamem.2014.02.005. Available online 22 February 2014

This paper is behind a paywall.