Stronger and more flexible than graphene, a single-atom layer of boron could revolutionize sensors, batteries, and catalytic chemistry.
From MIT Technology Review March 2019
From MIT Technology Review March 2019
In this special anniversary episode of Stories from the NNI, Dr. Lisa Friedersdorf, Director of NNCO, talks to Prof. Pedro Alvarez, of Rice University. Pedro and Lisa discuss the role nanotechnology plays in water security, exciting research results and applications, and his thoughts on the NNI.
Rice engineers led by materials scientists Pulickel Ajayan and Jun Lou have developed a method to make atom-flat sensors that seamlessly integrate with devices to report on what they perceive.
Electronically active 2-D materials have been the subject of much research since the introduction of graphene in 2004. Even though they are often touted for their strength, they’re difficult to move to where they’re needed without destroying them.
The Ajayan and Lou groups, along with the lab of Rice engineer Jacob Robinson, have a new way to keep the materials and their associated circuitry, including electrodes, intact as they’re moved to curved or other smooth surfaces.
The results of their work appear in the American Chemical Society journal ACS Nano.
The Rice team tested the concept by making a 10-nanometer-thick indium selenide photodetector with gold electrodes and placing it onto an optical fiber. Because it was so close, the near-field sensor effectively coupled with an evanescent field—the oscillating electromagnetic wave that rides the surface of the fiber—and accurately detected the flow of information inside.
The benefit is that these sensors can now be imbedded into such fibers where they can monitor performance without adding weight or hindering the signal flow.
“This paper proposes several interesting possibilities for applying 2-D devices in real applications,” Lou said. “For example, optical fibers at the bottom of the ocean are thousands of miles long, and if there’s a problem, it’s hard to know where it occurred. If you have these sensors at different locations, you can sense the damage to the fiber.”
Lou said labs have gotten good at transferring the growing roster of 2-D materials from one surface to another, but the addition of electrodes and other components complicates the process. “Think about a transistor,” he said. “It has source, drain and gate electrodes and a dielectric (insulator) on top, and all of these have to be transferred intact. That’s a very big challenge, because all of those materials are different.”
Raw 2-D materials are often moved with a layer of polymethyl methacrylate (PMMA), more commonly known as Plexiglas, on top, and the Rice researchers make use of that technique. But they needed a robust bottom layer that would not only keep the circuit intact during the move but could also be removed before attaching the device to its target. (The PMMA is also removed when the circuit reaches its destination.)
The ideal solution was poly-dimethyl-glutarimide (PMGI), which can be used as a device fabrication platform and easily etched away before transfer to the target. “We’ve spent quite some time to develop this sacrificial layer,” Lou said. PMGI appears to work for any 2-D material, as the researchers experimented successfully with molybdenum diselenide and other materials as well.
The Rice labs have only developed passive sensors so far, but the researchers believe their technique will make active sensors or devices possible for telecommunication, biosensing, plasmonics and other applications.
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More information: Zehua Jin et al, Near-Field Coupled Integrable Two-Dimensional InSe Photosensor on Optical Fiber, ACS Nano (2018). DOI: 10.1021/acsnano.8b07159
October 25, 2018
Rice University scientists are counting on films of carbon nanotubes to make high-powered, fast-charging lithium metal batteries a logical replacement for common lithium-ion batteries.
The Rice lab of chemist James Tour showed thin nanotube films effectively stop dendrites that grow naturally from unprotected lithium metal anodes in batteries. Over time, these tentacle-like dendrites can pierce the battery’s electrolyte core and reach the cathode, causing the battery to fail.
That problem has both dampened the use of lithium metal in commercial applications and encouraged researchers worldwide to solve it.
Rice University graduate student Gladys López-Silva holds a lithium metal anode with a film of carbon nanotubes. Once the film is attached, it becomes infiltrated by lithium ions and turns red. Photo by Jeff Fitlow
Lithium metal charges much faster and holds about 10 times more energy by volume than the lithium-ion electrodes found in just about every electronic device, including cellphones and electric cars.
“One of the ways to slow dendrites in lithium-ion batteries is to limit how fast they charge,” Tour said. “People don’t like that. They want to be able to charge their batteries quickly.”
The Rice team’s answer, detailed in Advanced Materials, is simple, inexpensive and highly effective at stopping dendrite growth, Tour said.
“What we’ve done turns out to be really easy,” he said. “You just coat a lithium metal foil with a multiwalled carbon nanotube film. The lithium dopes the nanotube film, which turns from black to red, and the film in turn diffuses the lithium ions.”
“Physical contact with lithium metal reduces the nanotube film, but balances it by adding lithium ions,” said Rice postdoctoral researcher Rodrigo Salvatierra, co-lead author of the paper with graduate student Gladys López-Silva. “The ions distribute themselves throughout the nanotube film.”
An illustration shows how lithium metal anodes developed at Rice University are protected from dendrite growth by a film of carbon nanotubes. Courtesy of the Tour Group
When the battery is in use, the film discharges stored ions and the underlying lithium anode refills it, maintaining the film’s ability to stop dendrite growth.
The tangled-nanotube film effectively quenched dendrites over 580 charge/discharge cycles of a test battery with a sulfurized-carbon cathode the lab developed in previous experiments.
The researchers reported the full lithium metal cells retained 99.8 percent of their coulombic efficiency, the measure of how well electrons move within an electrochemical system.
Rice University scientists have discovered that a film of multiwalled carbon nanotubes quenches the growth of dendrites in lithium metal-based batteries. Courtesy of the Tour Group
Co-authors of the paper are Rice alumni Almaz Jalilov of the King Fahd University of Petroleum and Minerals, Saudi Arabia; Jongwon Yoon, a senior researcher at the Korea Basic Science Institute; and Gang Wu, an instructor, and Ah-Lim Tsai, a professor of hematology, both at the McGovern Medical School at the University of Texas Health Science Center at Houston.
Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer science and of materials science and nanoengineering at Rice.
The research was supported by the Air Force Office of Scientific Research, the National Institutes of Health, the National Council of Science and Technology, Mexico; the National Council for Scientific and Technological Development, Ministry of Science, Technology and Innovation and Coordination for the Improvement of Higher Education Personnel, Brazil; and Celgard, LLC.
Rice University chemist James Tour, left, graduate student Gladys López-Silva and postdoctoral researcher Rodrigo Salvatierra use a film of carbon nanotubes to prevent dendrite growth in lithium metal batteries, which charge faster and hold more power than current lithium-ion batteries. Photo by Jeff Fitlow.
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Rice University scientists have developed something akin to the Venus’ flytrap of particles for water remediation.
The research is detailed in the American Chemical Society journal Environmental Science & Technology.
BPA is commonly used to coat the insides of food cans, bottle tops and water supply lines, and was once a component of baby bottles. While BPA that seeps into food and drink is considered safe in low doses, prolonged exposure is suspected of affecting the health of children and contributing to high blood pressure.
The good news is that reactive oxygen species (ROS) – in this case, hydroxyl radicals – are bad news for BPA. Inexpensive titanium dioxide releases ROS when triggered by ultraviolet light. But because oxi-dating molecules fade quickly, BPA has to be close enough to attack.
That’s where the trap comes in.
Close up, the spheres reveal themselves as flower-like collections of titanium dioxide petals. The supple petals provide plenty of surface area for the Rice researchers to anchor cyclodextrin molecules.
Cyclodextrin is a benign sugar-based molecule often used in food and drugs. It has a two-faced structure, with a hydrophobic (water-avoiding) cavity and a hydrophilic (water-attracting) outer surface. BPA is also hydrophobic and naturally attracted to the cavity. Once trapped, ROS produced by the spheres degrades BPA into harmless chemicals.
In the lab, the researchers determined that 200 milligrams of the spheres per liter of contaminated water degraded 90 percent of BPA in an hour, a process that would take more than twice as long with unenhanced titanium dioxide.
The work fits into technologies developed by the Rice-based and National Science Foundation-supported Center for Nanotechnology-Enabled Water Treatment because the spheres self-assemble from titanium dioxide nanosheets.
“Most of the processes reported in the literature involve nanoparticles,” said Rice graduate student and lead author Danning Zhang. “The size of the particles is less than 100 nanometers. Because of their very small size, they’re very difficult to recover from suspension in water.”
Because ROS also wears down cyclodextrin, the spheres begin to lose their trapping ability after about 400 hours of continued ultraviolet exposure, Zhang said. But once recovered, they can be easily recharged.
“This new material helps overcome two significant technological barriers for photocatalytic water treatment,” Alvarez said. “First, it enhances treatment efficiency by minimizing scavenging of ROS by non-target constituents in water. Here, the ROS are mainly used to destroy BPA.
“Second, it enables low-cost separation and reuse of the catalyst, contributing to lower treatment cost,” he said. “This is an example of how advanced materials can help convert academic hypes into feasible processes that enhance water security.”
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More information: Danning Zhang et al. Easily-recoverable, micron-sized TiO2 hierarchical spheres decorated with cyclodextrin for enhanced photocatalytic degradation of organic micropollutants, Environmental Science & Technology (2018). DOI: 10.1021/acs.est.8b04301
De Lange Conference XI | December 4-5, 2018 | Rice University De Lange Conference XI will bring together biologists, engineers, medical researchers, policy scholars, humanists, and industrial representatives from the nascent bioelectronics industry and federal agencies will serve to identify the grand challenges in the field, including technological, ethical, legal, and societal issues. The biennial De Lange Conferences, funded by the De Lange Endowment, were established by C.M. and Demaris Hudspeth in honor of Demaris’ parents, Albert and Demaris De Lange. For more information, visit delange.rice.edu
|The term bioelectronics, or bionics for short, describes a research field that is concerned with the integration of biological components with electronics; specifically, the application of biological materials and processes in electronics, and the use of electronic devices in living systems.|
|One day, bionics research could result in neural prostheses that augment or restore damaged or lost functions of the nervous system – restore vision, healing spinal cord injuries, and ameliorate neurodegenerative diseases such as Parkinson’s.|
Engineer Qilin Li at Rice University’s lab is building a treatment system that can be tuned to selectively pull toxins from wastewater from factories, sewage systems and oil and gas wells, as well as drinking water. The researchers said their technology will cut costs and save energy compared to conventional systems.
“Traditional methods to remove everything, such as reverse osmosis, are expensive and energy intensive,” said Li, the lead scientist and co-author of a study about the new technology in the American Chemical Society journal Environmental Science & Technology. “If we figure out a way to just fish out these minor components, we can save a lot of energy.”
The heart of Rice’s system is a set of novel composite electrodes that enable capacitive deionization. The charged, porous electrodes selectively pull target ions from fluids passing through the maze-like system. When the pores get filled with toxins, the electrodes can be cleaned, restored to their original capacity and reused.
“This is part of a broad scope of research to figure out ways to selectively remove ionic contaminants,” said Li, a professor of civil and environmental engineering and of materials science and nanoengineering. “There are a lot of ions in water. Not everything is toxic. For example, sodium chloride (salt) is perfectly benign. We don’t have to remove it unless the concentration gets too high.”
In tests, an engineered coating of resin, polymer and activated carbon removed and trapped harmful sulfate ions, and other coatings can be used in the same platform to target other contaminants. Illustration by Kuichang Zuo
The proof-of-principal system developed by Li’s team removed sulfate ions. The system’s electrodes were coated with activated carbon, which was in turn coated by a thin film of tiny resin particles held together by quaternized polyvinyl alcohol. When sulfate-contaminated water flowed through a channel between the charged electrodes, sulfate ions were attracted by the electrodes, passed through the resin coating and stuck to the carbon. Tests in the Rice lab showed the positively charged coating on the cathode preferentially captured sulfate ions over salt at a ratio of more than 20 to 1. The electrodes retained their properties over 50 cycles. “But in fact, in the lab, we’ve run the system for several hundred cycles and I don’t see any breaking or peeling of the material,” said Kuichang Zuo, lead author of the paper and a postdoctoral researcher in Li’s lab. “It’s very robust.”
In Rice’s new water-treatment platform, electrode coatings can be swapped out to allow the device to selectively remove a range of contaminants from wastewater, drinking water and industrial fluids. Illustration by Kuichang Zuo
“The true merit of this work is not that we were able to selectively remove sulfate, because there are many other contaminants that are perhaps more important,” she said. “The merit is that we developed a technology platform that we can use to target other contaminants as well by varying the composition of the electrode coating.”
The research was supported by the Rice-based National Science Foundation-backed Center for Nanotechnology-Enabled Water Treatment, the Welch Foundation and the Shanghai Municipal International Cooperation Foundation.
Nidec Motor Corporation (NMC) named Henk van Duijnhoven as its CEO and global business leader of ACIM (Appliances, Commercial and Industrial Motors). Van Duijnhoven was most recently a partner and managing director of The Boston Consulting Group where he was responsible for business turnaround, mergers and acquisitions, and strategy planning for clients in the industrial and medtech markets. He holds a Bachelor of Science degree from the College of Automotive Engineering and a Master of Business Administration from the Massachusetts Institute of Technology.
Woodard & Curran named Peter Nangeroni as its new industrial and commercial strategic business unit leader. He brings experience managing large, multidisciplinary projects for industrial clients with emphasis on generating positive environmental outcomes, return on investment and improved risk management. He has been with Woodard & Curran for 13 years in various roles, most recently as director of technical practices. He takes over for the long-time leader of the business unit, Mike Curato, who is retiring after 11 years in the role and 20 with the firm.
Nangeroni is a Professional Engineer with a degree in civil engineering from Tufts University and more than 35 years of experience working with clients on engineering and construction management projects. In his new role, he will oversee staffing, business development and project execution at a strategic level for the industrial and commercial strategic business unit, which focuses on water treatment, manufacturing and process utilities for clients in a wide range of industrial sectors.
First, according to Rice University engineers, get a nanotube hole. Then insert water. If the nanotube is just the right width, the water molecules will align into a square rod.
Rice materials scientist Rouzbeh Shahsavari and his team used molecular models to demonstrate their theory that weak van der Waals forces between the inner surface of the nanotube and the water molecules are strong enough to snap the oxygen and hydrogen atoms into place.
Shahsavari referred to the contents as two-dimensional “ice,” because the molecules freeze regardless of the temperature. He said the research provides valuable insight on ways to leverage atomic interactions between nanotubes and water molecules to fabricate nanochannels and energy-storing nanocapacitors.
A paper on the research appears in the American Chemical Society journal Langmuir.
Shahsavari and his colleagues built molecular models of carbon and boron nitride nanotubes with adjustable widths. They discovered boron nitride is best at constraining the shape of water when the nanotubes are 10.5 angstroms wide. (One angstrom is one hundred-millionth of a centimeter.)
The researchers already knew that hydrogen atoms in tightly confined water take on interesting structural properties. Recent experiments by other labs showed strong evidence for the formation of nanotube ice and prompted the researchers to build density functional theory models to analyze the forces responsible.
Shahsavari’s team modeled water molecules, which are about 3 angstroms wide, inside carbon and boron nitride nanotubes of various chiralities (the angles of their atomic lattices) and between 8 and 12 angstroms in diameter. They discovered that nanotubes in the middle diameters had the most impact on the balance between molecular interactions and van der Waals pressure that prompted the transition from a square water tube to ice.
“If the nanotube is too small and you can only fit one water molecule, you can’t judge much,” Shahsavari said. “If it’s too large, the water keeps its amorphous shape. But at about 8 angstroms, the nanotubes’ van der Waals force starts to push water molecules into organized square shapes.”
He said the strongest interactions were found in boron nitride nanotubes due to the particular polarization of their atoms.
Shahsavari said nanotube ice could find use in molecular machines or as nanoscale capillaries, or foster ways to deliver a few molecules of water or sequestered drugs to targeted cells, like a nanoscale syringe.
More information: Farzaneh Shayeganfar et al, First Principles Study of Water Nanotubes Captured Inside Carbon/Boron Nitride Nanotubes, Langmuir (2018). DOI: 10.1021/acs.langmuir.8b00856
PHOTO: SIMON DAWSON/BLOOMBERG
The batteries that power our modern world—from phones to dronesto electric cars—will soon experience something not heard of in years: Their capacity to store electricity will jump by double-digit percentages, according to researchers, developers and manufacturers.
The next wave of batteries, long in the pipeline, is ready for commercialization. This will mean, among other things, phones with 10% to 30% more battery life, or phones with the same battery life but faster and lighter or with brighter screens. We’ll see more cellular-connected wearables. As this technology becomes widespread, makers of electric vehicles and home storage batteries will be able to knock thousands of dollars off their prices over the next five to 10 years. Makers of electric aircraft will be able to explore new designs.
There is a limit to how far lithium-ion batteries can take us; surprisingly, it’s about twice their current capacity. The small, single-digit percentage improvements we see year after year typically are because of improvements in how they are made, such as small tweaks to their chemistry or new techniques for filling battery cells with lithium-rich electrolyte. What’s coming is a more fundamental change to the materials that make up a battery.
First, some science: Every lithium-ion battery has an anode and a cathode. Lithium ions traveling between them yield the electrical current that powers our devices. When a battery is fully charged, the anode has sucked up lithium ions like a sponge. And as it discharges, those ions travel through the electrolyte, to the cathode.
Typically, anodes in lithium-ion batteries are made of graphite, which is carbon in a crystalline form. While graphite anodes hold a substantial number of lithium ions, researchers have long known a different material, silicon, can hold 25 times as many.
The trick is, silicon brings with it countless technical challenges. For instance, a pure silicon anode will soak up so many lithium ions that it gets “pulverized” after a single charge, says George Crabtree, director of the Joint Center for Energy Storage Research, established by the U.S. Department of Energy at the University of Chicago Argonne lab to accelerate battery research.
Current battery anodes can have small amounts of silicon, boosting their performance slightly. The amount of silicon in a company’s battery is a closely held trade secret, but Dr. Crabtree estimates that in any battery, silicon is at most 10% of the anode. In 2015, Tesla founder Elon Musk revealed that silicon in the Panasonic-made batteries of the auto maker’s Model S helped boost the car’s range by 6%.
Now, some startups say they are developing production-ready batteries with anodes that are mostly silicon. Sila Nanotechnologies,Angstron Materials , Enovix and Enevate, to name a few, offer materials for so-called lithium-silicon batteries, which are being tested by the world’s largest battery manufacturers, car companies and consumer-electronics companies.
For Sila, in Alameda, Calif., the secret is nanoparticles lots of empty space inside. This way, the lithium can be absorbed into the particle without making the anode swell and shatter, says Sila Chief Executive Gene Berdichevsky. Cells made with Sila’s particles could store 20% to 40% more energy, he adds.
Angstron Materials, in Dayton, Ohio, makes similar claims about its nanoparticles for lithium-ion batteries.
Dr. Crabtree says this approach is entirely plausible, though there’s a trade-off: By allowing more room inside the anode for lithium ions, manufacturers must produce a larger anode. This anode takes up more space in the battery, allowing less overall space to increase capacity. This is why the upper bound of increased energy density using this approach is about 40%.
The big challenge, as ever, is getting to market, says Dr. Crabtree.
China-based Amperex is also an investor in Sila, but Amperex Chief Operating Officer Joe Kit Chu Lam says his company is securing several suppliers of the nanoparticles necessary to produce lithium-silicon batteries. Having multiple suppliers is essential for securing enough volume, he says.
The first commercial consumer devices to have higher-capacity lithium-silicon batteries will likely be announced in the next two years, says Mr. Lam, who expects a wearable to be first. Other companies claim a similar timetable for consumer rollout.
Enevate produces complete silicon-dominant anodes for car manufacturers. CEO Robert Rango says its technology increases the range of electric vehicles by 30% compared with conventional lithium-ion batteries.
BMW plans to incorporate Sila’s silicon anode technology in a plug-in electric vehicle by 2023, says a company spokesman. BMW expects an increase of 10% to 15% in battery-pack capacity in a single leap. While this is the same technology destined for mobile electronics, the higher volumes and higher safety demands of the auto industry mean slower implementation there. In 2017, BMW said it would invest €200 million ($246 million) in its own battery-research center.
Enovix, whose investors include Intel and Qualcomm, has pioneered a different kind of 3-D structure for its batteries, says CEO Harrold Rust. With much higher energy density and anodes that are almost pure silicon, the company claims its batteries would contain 30% to 50% more energy in the size needed for a mobile phone, and two to three times as much in the size required for a smartwatch.
The downside: producing these will require a significant departure from the current manufacturing process.
Even though it’s a significant advance, to get beyond what’s possible with lithium-silicon batteries will require a change in battery composition—such as lithium-sulfur chemistry or solid-state batteries. Efforts to make these technologies viable are at a much earlier stage, however, and it isn’t clear when they’ll arrive.
Meanwhile, we can look forward to the possibility of a thinner or more capable Apple Watch, wireless headphones we don’t have to charge as often and electric vehicles that are actually affordable. The capacity of lithium-ion batteries has increased threefold since their introduction in 1991, and at every level of improvement, new and unexpected applications, devices and business opportunities pop up.
Corrections & Amplifications
Sila Nanotechnologies produces nanoparticles that contain silicon and other components, but don’t include graphite. A previous version of this column incorrectly described nanoparticles as a graphite-silicon composite. An earlier version also incorrectly identified Angstron Materials as Angstrom Materials. (Angstron error corrected: March 18, 2018. Nanoparticles error corrected: March 19, 2018
Appeared in the March 19, 2018, print edition as ‘Battery Life Powers Ahead Toward Sizable Gains.’
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Specks of titanium dioxide adhere to polyvinyl fibers in a mat developed at the Rice University-led NEWT Center to capture and destroy pollutants from wastewater or drinking water. After the mat attracts and binds pollutants, the titanium dioxide photocatalyst releases reactive oxygen species that destroy them. Credit: Rice University/NEWT
A polymer mat developed at Rice University has the ability to fish biologically harmful contaminants from water through a strategy known as “bait, hook and destroy.”
Tests with wastewater showed the mat can efficiently remove targeted pollutants, in this case a pair of biologically harmful endocrine disruptors, using a fraction of the energy required by other technology. The technique can also be used to treat drinking water.
The mat was developed by scientists with the Rice-led Nanotechnology-Enabled Water Treatment (NEWT) Center. The research is available online in the American Chemical Society journal Environmental Science and Technology.
The mat depends on the ability of a common material, titanium dioxide, to capture pollutants and, upon exposure to light, degrade them through oxidation into harmless byproducts.
Titanium dioxide is already used in some wastewater treatment systems. It is usually turned into a slurry, combined with wastewater and exposed to ultraviolet light to destroy contaminants. The slurry must then be filtered from the water.
The NEWT mat simplifies the process. The mat is made of spun polyvinyl fibers. The researchers made it highly porous by adding small plastic beads that were later dissolved with chemicals. The pores offer plenty of surface area for titanium oxide particles to inhabit and await their prey.
The mat’s hydrophobic (water-avoiding) fibers naturally attract hydrophobic contaminants like the endocrine disruptors used in the tests. Once bound to the mat, exposure to light activates the photocatalytic titanium dioxide, which produces reactive oxygen species (ROS) that destroy the contaminants.
Established by the National Science Foundation in 2015, NEWT is a national research center that aims to develop compact, mobile, off-grid water-treatment systems that can provide clean water to millions of people who lack it and make U.S. energy production more sustainable and cost-effective.
NEWT researchers said their mat can be cleaned and reused, scaled to any size, and its chemistry can be tuned for various pollutants.
“Current photocatalytic treatment suffers from two limitations,” said Rice environmental engineer and NEWT Center Director Pedro Alvarez. “One is inefficiency because the oxidants produced are scavenged by things that are much more abundant than the target pollutant, so they don’t destroy the pollutant.
The Rice University-led NEWT Center created a nanoparticle-infused polymer mat that both attracts and destroys pollutants in wastewater or drinking water. A mat, top left, is immersed in water with methylene blue as a contaminant. The contaminant is then absorbed at top right by the mat and, in the bottom images, destroyed by exposure to light. The mat is then ready for reuse. Credit: Rice University/NEWT
“Second, it costs a lot of money to retain and separate slurry photocatalysts and prevent them from leaking into the treated water,” he said. “In some cases, the energy cost of filtering that slurry is more than what’s needed to power the UV lights.
“We solved both limitations by immobilizing the catalyst to make it very easy to reuse and retain,” Alvarez said. “We don’t allow it to leach out of the mat and impact the water.”
Alvarez said the porous polymer mat plays an important role because it attracts the target pollutants. “That’s the bait and hook,” he said. “Then the photocatalyst destroys the pollutant by producing hydroxyl radicals.”
“The nanoscale pores are introduced by dissolving a sacrificial polymer on the electrospun fibers,” lead author and former Rice postdoctoral researcher Chang-Gu Lee said. “The pores enhance the contaminants’ access to titanium dioxide.”
The experiments showed dramatic energy reduction compared to wastewater treatment using slurry.
“Not only do we destroy the pollutants faster, but we also significantly decrease our electrical energy per order of reaction,” Alvarez said. “This is a measure of how much energy you need to remove one order of magnitude of the pollutant, how many kilowatt hours you need to remove 90 percent or 99 percent or 99.9 percent.
“We show that for the slurry, as you move from treating distilled water to wastewater treatment plant effluent, the amount of energy required increases 11-fold. But when you do this with our immobilized bait-and-hook photocatalyst, the comparable increase is only two-fold. It’s a significant savings.”
The mat also would allow treatment plants to perform pollutant removal and destruction in two discrete steps, which isn’t possible with the slurry, Alvarez said. “It can be desirable to do that if the water is murky and light penetration is a challenge. You can fish out the contaminants adsorbed by the mat and transfer it to another reactor with clearer water. There, you can destroy the pollutants, clean out the mat and then return it so it can fish for more.”
Tuning the mat would involve changing its hydrophobic or hydrophilic properties to match target pollutants. “That way you could treat more water with a smaller reactor that is more selective, and therefore miniaturize these reactors and reduce their carbon footprints,” he said. “It’s an opportunity not only to reduce energy requirements, but also space requirements for photocatalytic water treatment.”
Alvarez said collaboration by NEWT’s research partners helped the project come together in a matter of months. “NEWT allowed us to do something that separately would have been very difficult to accomplish in this short amount of time,” he said.
“I think the mat will significantly enhance the menu from which we select solutions to our water purification challenges,” Alvarez said.
More information: Chang-Gu Lee et al, Porous electrospun fibers embedding TiO2 for adsorption and photocatalytic degradation of water pollutants, Environmental Science & Technology (2018). DOI: 10.1021/acs.est.7b06508
Provided by Rice University
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