I love the video (wish the narrator had a more conversational style rather than the ‘read aloud’ style so many of us adopted in school),
Joel Goldberg’s April 28, 2021 news article (short read) in Science magazine online describes the research (Note: A link has been removed),
Behold the salt monsters. These twisted mineral crystals—formed from the buildup of slightly salty water in power plant pipes—come in many shapes and sizes. But the tiny monsters are a big problem: Each year, they cost the world’s power plants at least $100 billion because workers have to purge the pipes and scrub the crystals from filters.
Now, a solution may be at hand. Engineers can reduce the damage by coating the insides of the pipes with textured, water-repellant [hydrophobic] surfaces …
This paper is open access. As research papers go, this is quite readable, from the Introduction (Note: Links have been removed),
Many of the uses for water are intimately familiar to us. Drinking water, wash water, water for agriculture, and even water used for recreation have an omnipresent and essential impact on our lives. However, water’s impact and importance extend far beyond these everyday uses. In many developed countries, thermoelectric power production is one of the largest sources of water consumption (1), where it is used to cool reactors and transport heat. In 2015, 41% of all surface water withdrawals in the United States went toward cooling in thermoelectric power plants (2). Thermoelectric power accounts for 90% of all electricity generated within the United States and encompasses many forms of power production, including nuclear, coal, natural gas, and oil.
A January 26, 2021 news item on Nanowerk announces a promising discovery in ‘self-assembly research’ (Note: A link has been removed,
Self-assembly is ubiquitous in the natural world, serving as a route to form organized structures in every living organism. This phenomenon can be seen, for instance, when two strands of DNA — without any external prodding or guidance — join to form a double helix, or when large numbers of molecules combine to create membranes or other vital cellular structures. Everything goes to its rightful place without an unseen builder having to put all the pieces together, one at a time.
For the past couple of decades, scientists and engineers have been following nature’s lead, designing molecules that assemble themselves in water, with the goal of making nanostructures, primarily for biomedical applications such as drug delivery or tissue engineering.
“These small-molecule-based materials tend to degrade rather quickly,” explains Julia Ortony, assistant professor in [Massachusetts Institute of Technology] MIT’s Department of Materials Science and Engineering (DMSE), “and they’re chemically unstable, too. The whole structure falls apart when you remove the water, particularly when any kind of external force is applied.”
She and her team, however, have designed a new class of small molecules that spontaneously assemble into nanoribbons with unprecedented strength, retaining their structure outside of water. The results of this multi-year effort, which could inspire a broad range of applications, were described in Nature Nanotechnology (“Self-assembly of aramid amphiphiles into ultra-stable nanoribbons and aligned nanoribbon threads”) by Ortony and coauthors.
“This seminal work — which yielded anomalous mechanical properties through highly controlled self-assembly — should have a big impact on the field,” asserts Professor Tazuko Aida, deputy director for the RIKEN Center for Emergent Matter Science and professor of chemistry and biotechnology at the University of Tokyo, who was not involved in the research.
The material the MIT group constructed — or rather, allowed to construct itself — is modeled after a cell membrane. Its outer part is “hydrophilic,” which means it likes to be in water, whereas its inner part is “hydrophobic,” meaning it tries to avoid water. This configuration, Ortony comments, “provides a driving force for self-assembly,” as the molecules orient themselves to minimize interactions between the hydrophobic regions and water, consequently taking on a nanoscale shape.
The shape, in this case, is conferred by water, and ordinarily the whole structure would collapse when dried. But Ortony and her colleagues came up with a plan to keep that from happening. When molecules are loosely bound together, they move around quickly, analogous to a fluid; as the strength of intermolecular forces increases, motion slows and molecules assume a solid-like state. The idea, Ortony explains, “is to slow molecular motion through small modifications to the individual molecules, which can lead to a collective, and hopefully dramatic, change in the nanostructure’s properties.”
One way of slowing down molecules, notes Ty Christoff-Tempesta, a PhD student and first author of the paper, “is to have them cling to each other more strongly than in biological systems.” That can be accomplished when a dense network of strong hydrogen bonds join the molecules together. “That’s what gives a material like Kevlar — constructed of so-called ‘aramids’ — its chemical stability and strength,” states Christoff-Tempesta.
Ortony’s team incorporated that capability into their design of a molecule that has three main components: an outer portion that likes to interact with water, aramids in the middle for binding, and an inner part that has a strong aversion to water. The researchers tested dozens of molecules meeting these criteria before finding the design that led to long ribbons with nanometer-scale thickness. The authors then measured the nanoribbons’ strength and stiffness to understand the impact of including Kevlar-like interactions between molecules. They discovered that the nanoribbons were unexpectedly sturdy — stronger than steel, in fact.
This finding led the authors to wonder if the nanoribbons could be bundled to produce stable macroscopic materials. Ortony’s group devised a strategy whereby aligned nanoribbons were pulled into long threads that could be dried and handled. Notably, Ortony’s team showed that the threads could hold 200 times their own weight and have extraordinarily high surface areas — 200 square meters per gram of material. “This high surface-to-mass ratio offers promise for miniaturizing technologies by performing more chemistry with less material,” explains Christoff-Tempesta. To this end, they have already developed nanoribbons whose surfaces are coated with molecules that can pull heavy metals, like lead or arsenic, out of contaminated water. Other efforts in the research group are aimed at using bundled nanoribbons in electronic devices and batteries.
Ortony, for her part, is still amazed that they’ve been able to achieve their original research goal of “tuning the internal state of matter to create exceptionally strong molecular nanostructures.” Things could easily have gone the other way; these materials might have proved to be disorganized, or their structures fragile, like their predecessors, only holding up in water. But, she says, “we were excited to see that our modifications to the molecular structure were indeed amplified by the collective behavior of molecules, creating nanostructures with extremely robust mechanical properties. The next step, figuring out the most important applications, will be exciting.”
Both of these news bits are concerned with light for one reason or another.
Rice University (Texas, US) and breaking fluorocarbon bonds
The secret to breaking fluorocarbon bonds is light according to a June 22, 2020 news item on Nanowerk,
Rice University engineers have created a light-powered catalyst that can break the strong chemical bonds in fluorocarbons, a group of synthetic materials that includes persistent environmental pollutants.
In a study published this month in Nature Catalysis, Rice nanophotonics pioneer Naomi Halas and collaborators at the University of California, Santa Barbara (UCSB) and Princeton University showed that tiny spheres of aluminum dotted with specks of palladium could break carbon-fluorine (C-F) bonds via a catalytic process known as hydrodefluorination in which a fluorine atom is replaced by an atom of hydrogen.
The strength and stability of C-F bonds are behind some of the 20th century’s most recognizable chemical brands, including Teflon, Freon and Scotchgard. But the strength of those bonds can be problematic when fluorocarbons get into the air, soil and water. Chlorofluorocarbons, or CFCs, for example, were banned by international treaty in the 1980s after they were found to be destroying Earth’s protective ozone layer, and other fluorocarbons were on the list of “forever chemicals” targeted by a 2001 treaty.
“The hardest part about remediating any of the fluorine-containing compounds is breaking the C-F bond; it requires a lot of energy,” said Halas, an engineer and chemist whose Laboratory for Nanophotonics (LANP) specializes in creating and studying nanoparticles that interact with light.
Over the past five years, Halas and colleagues have pioneered methods for making “antenna-reactor” catalysts that spur or speed up chemical reactions. While catalysts are widely used in industry, they are typically used in energy-intensive processes that require high temperature, high pressure or both. For example, a mesh of catalytic material is inserted into a high-pressure vessel at a chemical plant, and natural gas or another fossil fuel is burned to heat the gas or liquid that’s flowed through the mesh. LANP’s antenna-reactors dramatically improve energy efficiency by capturing light energy and inserting it directly at the point of the catalytic reaction.
In the Nature Catalysis study, the energy-capturing antenna is an aluminum particle smaller than a living cell, and the reactors are islands of palladium scattered across the aluminum surface. The energy-saving feature of antenna-reactor catalysts is perhaps best illustrated by another of Halas’ previous successes: solar steam. In 2012, her team showed its energy-harvesting particles could instantly vaporize water molecules near their surface, meaning Halas and colleagues could make steam without boiling water. To drive home the point, they showed they could make steam from ice-cold water.
The antenna-reactor catalyst design allows Halas’ team to mix and match metals that are best suited for capturing light and catalyzing reactions in a particular context. The work is part of the green chemistry movement toward cleaner, more efficient chemical processes, and LANP has previously demonstrated catalysts for producing ethylene and syngas and for splitting ammonia to produce hydrogen fuel.
Study lead author Hossein Robatjazi, a Beckman Postdoctoral Fellow at UCSB who earned his Ph.D. from Rice in 2019, conducted the bulk of the research during his graduate studies in Halas’ lab. He said the project also shows the importance of interdisciplinary collaboration.
“I finished the experiments last year, but our experimental results had some interesting features, changes to the reaction kinetics under illumination, that raised an important but interesting question: What role does light play to promote the C-F breaking chemistry?” he said.
The answers came after Robatjazi arrived for his postdoctoral experience at UCSB. He was tasked with developing a microkinetics model, and a combination of insights from the model and from theoretical calculations performed by collaborators at Princeton helped explain the puzzling results.
“With this model, we used the perspective from surface science in traditional catalysis to uniquely link the experimental results to changes to the reaction pathway and reactivity under the light,” he said.
The demonstration experiments on fluoromethane could be just the beginning for the C-F breaking catalyst.
“This general reaction may be useful for remediating many other types of fluorinated molecules,” Halas said.
Caption: An artist’s illustration of the light-activated antenna-reactor catalyst Rice University engineers designed to break carbon-fluorine bonds in fluorocarbons. The aluminum portion of the particle (white and pink) captures energy from light (green), activating islands of palladium catalysts (red). In the inset, fluoromethane molecules (top) comprised of one carbon atom (black), three hydrogen atoms (grey) and one fluorine atom (light blue) react with deuterium (yellow) molecules near the palladium surface (black), cleaving the carbon-fluorine bond to produce deuterium fluoride (right) and monodeuterated methane (bottom). Credit: H. Robatjazi/Rice University
Called “robotic soft matter by the Northwestern team,” the materials move without complex hardware, hydraulics or electricity. The researchers believe the lifelike materials could carry out many tasks, with potential applications in energy, environmental remediation and advanced medicine.
“We live in an era in which increasingly smarter devices are constantly being developed to help us manage our everyday lives,” said Northwestern’s Samuel I. Stupp, who led the experimental studies. “The next frontier is in the development of new science that will bring inert materials to life for our benefit — by designing them to acquire capabilities of living creatures.”
The research will be published on June 22 [2020] in the journal Nature Materials.
Stupp is the Board of Trustees Professor of Materials Science and Engineering, Chemistry, Medicine and Biomedical Engineering at Northwestern and director of the Simpson Querrey Institute He has appointments in the McCormick School of Engineering, Weinberg College of Arts and Sciences and Feinberg School of Medicine. George Schatz, the Charles E. and Emma H. Morrison Professor of Chemistry in Weinberg, led computer simulations of the materials’ lifelike behaviors. Postdoctoral fellow Chuang Li and graduate student Aysenur Iscen, from the Stupp and Schatz laboratories, respectively, are co-first authors of the paper.
Although the moving material seems miraculous, sophisticated science is at play. Its structure comprises nanoscale peptide assemblies that drain water molecules out of the material. An expert in materials chemistry, Stupp linked the peptide arrays to polymer networks designed to be chemically responsive to blue light.
When light hits the material, the network chemically shifts from hydrophilic (attracts water) to hydrophobic (resists water). As the material expels the water through its peptide “pipes,” it contracts — and comes to life. When the light is turned off, water re-enters the material, which expands as it reverts to a hydrophilic structure.
This is reminiscent of the reversible contraction of muscles, which inspired Stupp and his team to design the new materials.
“From biological systems, we learned that the magic of muscles is based on the connection between assemblies of small proteins and giant protein polymers that expand and contract,” Stupp said. “Muscles do this using a chemical fuel rather than light to generate mechanical energy.”
For Northwestern’s bio-inspired material, localized light can trigger directional motion. In other words, bending can occur in different directions, depending on where the light is located. And changing the direction of the light also can force the object to turn as it crawls on a surface.
Stupp and his team believe there are endless possible applications for this new family of materials. With the ability to be designed in different shapes, the materials could play a role in a variety of tasks, ranging from environmental clean-up to brain surgery.
“These materials could augment the function of soft robots needed to pick up fragile objects and then release them in a precise location,” he said. “In medicine, for example, soft materials with ‘living’ characteristics could bend or change shape to retrieve blood clots in the brain after a stroke. They also could swim to clean water supplies and sea water or even undertake healing tasks to repair defects in batteries, membranes and chemical reactors.”
Fascinating, eh? No batteries, no power source, just light to power movement. For the curious, here’s a link to and a citation for the paper,
Supramolecular–covalent hybrid polymers for light-activated mechanical actuation by Chuang Li, Aysenur Iscen, Hiroaki Sai, Kohei Sato, Nicholas A. Sather, Stacey M. Chin, Zaida Álvarez, Liam C. Palmer, George C. Schatz & Samuel I. Stupp. Nature Materials (2020) DOI: https://doi.org/10.1038/s41563-020-0707-7 Published: 22 June 2020
All of the main points are made in the video but for those who like text, there’s a May 28, 2020 news item on phys.org describing this new smart sponge for cleaning up oil spills (Note: Links have been removed),
A Northwestern University-led [Chicago, Illinois, US] team has developed a highly porous smart sponge that selectively soaks up oil in water.
With an ability to absorb more than 30 times its weight in oil, the sponge could be used to inexpensively and efficiently clean up oil spills without harming marine life. After squeezing the oil out of the sponge, it can be reused many dozens of times without losing its effectiveness.
“Oil spills have devastating and immediate effects on the environment, human health and economy,” said Northwestern’s Vinayak Dravid, who led the research. “Although many spills are small and may not make the evening news, they are still profoundly invasive to the ecosystem and surrounding community. Our sponge can remediate these spills in a more economic, efficient and eco-friendly manner than any of the current state-of-the-art solutions.”
Oil spill clean-up is an expensive and complicated process that often harms marine life and further damages the environment. Currently used solutions include burning the oil, using chemical dispersants to breakdown oil into very small droplets, skimming oil floating on top of water and/or absorbing it with expensive, unrecyclable sorbents.
“Each approach has its own drawbacks and none are sustainable solutions,” Nandwana [Vikas Nandwana, a senior research associate in Dravid’s laboratory] said. “Burning increases carbon emissions and dispersants are terribly harmful for marine wildlife. Skimmers don’t work in rough waters or with thin layers of oil. And sorbents are not only expensive, but they generate a huge amount of physical waste — similar to the diaper landfill issue.”
The Northwestern solution bypasses these challenges by selectively absorbing oil and leaving clean water and unaffected marine life behind. The secret lies in a nanocomposite coating of magnetic nanostructures and a carbon-based substrate that is oleophilic (attracts oil), hydrophobic (resists water) and magnetic. The nanocomposite’s nanoporous 3D structure selectively interacts with and binds to the oil molecules, capturing and storing the oil until it is squeezed out. The magnetic nanostructures give the smart sponge two additional functionalities: controlled movement in the presence of an external magnetic field and desorption of adsorbed components, such as oil, in a simulated and remote manner.
The OHM (oleophilic hydrophobic magnetic) nanocomposite slurry can be used to coat any cheap, commercially available sponge. The researchers applied a thin coating of the slurry to the sponge, squeezed out the excess and let it dry. The sponge is quickly and easily converted into a smart sponge (or “OHM sponge”) with a selective affinity for oil.
Vinayak and his team tested the OHM sponge with many different types of crude oils of varying density and viscosity. The OHM sponge consistently absorbed up to 30 times its weight in oil, leaving the water behind. To mimic natural waves, researchers put the OHM sponge on a shaker submerged in water. Even after vigorous shaking, the sponge release less than 1% of its absorbed oil back into the water.
“Our sponge works effectively in diverse and extreme aquatic conditions that have different pH and salinity levels,” Dravid said. “We believe we can address a giga-ton problem with a nanoscale solution.”
“We are excited to introduce such smart sponges as an environmental remediation platform for selectively removing and recovering pollutants present in water, soil and air, such as excess nutrients, heavy metal contaminants, VOC/toxins and others,” Nandwana said. “The nanostructure coating can be tailored to selectively adsorb (and later desorb) these pollutants.”
The team also is working on another grade of OHM sponge that can selectively absorb (and later recover) excess dissolved nutrients, such as phosphates, from fertilizer runoff and agricultural pollution. Stephanie Ribet, a Ph.D. candidate in Dravid’s lab and paper coauthor is pursuing this topic. The team plans to develop and commercialize OHM technology for environmental clean-up.
Bravo to professor Vinayak Dravid and his team. I’m sure I’m not alone in wishing you and your team the best of luck as you continue to develop this remediation technology.
