Graphene microbubbles make perfect lenses – And Much More … Drug Delivery .. Water Treatment

In situ optical microscopic images showing the process of the microbubble generation and elimination. Credit: H. Lin et al

Tiny bubbles can solve large problems. Microbubbles—around 1-50 micrometers in diameter—have widespread applications. They’re used for drug delivery, membrane cleaning, biofilm control, and water treatment. They’ve been applied as actuators in lab-on-a-chip devices for microfluidic mixing, ink-jet printing, and logic circuitry, and in photonics lithography and optical resonators. And they’ve contributed remarkably to biomedical imaging and applications like DNA trapping and manipulation.

Given the broad range of applications for microbubbles, many methods for generating them have been developed, including air stream compression to dissolve air into liquid, ultrasound to induce bubbles in water, and laser pulses to expose substrates immersed in liquids. However, these bubbles tend to be randomly dispersed in liquid and rather unstable.

According to Baohua Jia, professor and founding director of the Centre for Translational Atomaterials at Swinburne University of Technology, “For applications requiring precise bubble position and size, as well as high stability—for example, in photonic applications like imaging and trapping—creation of bubbles at accurate positions with controllable volume, curvature, and stability is essential.” Jia explains that, for integration into biological or photonic platforms, it is highly desirable to have well controlled and stable microbubbles fabricated using a technique compatible with current processing technologies.

Balloons in graphene

Jia and fellow researchers from Swinburne University of Technology recently teamed up with researchers from National University of Singapore, Rutgers University, University of Melbourne, and Monash University, to develop a method to generate precisely controlled graphene microbubbles on a glass surface using laser pulses. Their report is published in the peer-reviewed, open-access journal, Advanced Photonics.

Photonic jet focused by a graphene oxide microbubble lens. Credit: H. Lin et al., doi 10.1117/1.AP.2.5.055001

The group used graphene oxide materials, which consist of graphene film decorated with oxygen functional groups. Gases cannot penetrate through graphene oxide materials, so the researchers used laser to locally irradiate the graphene oxide film to generate gases to be encapsulated inside the film to form microbubbles—like balloons. Han Lin, Senior Research Fellow at Swinburne University and first author on the paper, explains, “In this way, the positions of the microbubbles can be well controlled by the laser, and the microbubbles can be created and eliminated at will. In the meantime, the amount of gases can be controlled by the irradiating area and irradiating power. Therefore, high precision can be achieved.”

Such a high-quality bubble can be used for advanced optoelectronic and micromechanical devices with high precision requirements.

The researchers found that the high uniformity of the graphene oxide films creates microbubbles with a perfect spherical curvature that can be used as concave reflective lenses. As a showcase, they used the concave reflective lenses to focus light. The team reports that the lens presents a high-quality focal spot in a very good shape and can be used as light source for microscopic imaging.

Lin explains that the reflective lenses are also able to focus light at different wavelengths at the same focal point without chromatic aberration. The team demonstrates the focusing of a ultrabroadband white light, covering visible to near-infrared range, with the same high performance, which is particularly useful in compact microscopy and spectroscopy.

Jia remarks that the research provides “a pathway for generating highly controlled microbubbles at will and integration of graphene microbubbles as dynamic and high precision nanophotonic components for miniaturized lab-on-a-chip devices, along with broad potential applications in high resolution spectroscopy and medical imaging.”

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Monolayer transition metal dichalcogenide lens for high resolution imaging

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More information: Han Lin et al, Near-perfect microlenses based on graphene microbubbles, Advanced Photonics (2020). DOI: 10.1117/1.AP.2.5.055001

Provided by SPIE

Improving Access to Clean Water and the Role of Nanotechnology

Access to clean, safe drinking water is thought to be a basic human right. Yet, according to the World Health Organization (WHO), over 785 million people across the globe are without access to a basic drinking-water source. This has researchers around the world researching and developing a series of water treatment solutions and applications using nanotechnology.

Current WHO statistics are damning, making this an issue that must be addressed urgently as it is thought that around 2 billion people are using a contaminated water supply. In addition, over 485,000 people die each year from diarrhoeal related illnesses and diseases such as polio, typhoid, and cholera are once again being transmitted as a further consequence. Based on current trends and data, it is thought that by 2025 half of the total global population will be living in water-stressed or water-scarce areas.

 

While there are a wide-range of effective water purification methods and techniques including boiling, filtration, oxidation, and distillation, these often require high amounts of energy. Other treatment processes may include the use of chemical agents which is only possible in areas with an infrastructure that is up to par.

The more affordable and portable devices currently available are not always fit for purpose as they cannot guarantee 100% removal of harmful viruses, bacteria, dust, and even microplastics. So, it is thought that nanotechnology could offer affordable and accessible clean water solutions to the world’s most vulnerable populations.

Nanotechnology is a process that involves manipulating and controlling matter on the atomic scale. In the process of water purification, this involves using nanomembranes to soften the water and eradicate biological and chemical contaminants as well as other physical particles and molecules.

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What’s more is that nanotechnology is portable and can be incorporated into existing commercial devices which increases the likelihood that nanotech solutions could become a feasible option for areas of the developing world and places with limited infrastructure.

In recent years scientists have improved on conventional methods that use coagulants by taking their cues from nature, notably the ocean dwelling Actinia organism. Traditional coagulants, such as aluminum sulfate and other metallic salts can pull out larger contaminants by causing them to group together and settle. However, this method is not effective for smaller particles and molecules and often requires additional methods to ensure the water is clean. Thereby increasing the cost and use of energy as several techniques are required to ensure the water is safe.

Using nanocoagulants, scientists were able to synthesize organic and inorganic matter to replicate the structure of the Actina sea anemone. The researchers produced a reversable core-shell that can catch larger particles as well as the smaller ones when it turns inside-out. This is also a one-step process which removes the need for additional technologies and opens up the potential for minimizing water purification costs.

Another viable method of water purification currently in development that makes use of nanotechnology includes utilizing magnetically active nanoparticles to extract chemicals from water. The process enables the removal of toxins from drinking-water contaminants attracting nanoparticles that consist of magnetic phases. This solution would also be low-energy and could provide an economic advantage as well as health and environmental benefits.

Other proposals for nanotech solutions include using nanoparticles to break down microplastics and a rapid nano-filter that can clean dirty water 100 times faster than current methods. Researchers are also aware that most water purification methods require access to a constant electricity supply, but this can be a significant obstacle in places with limited infrastructure or areas damaged by extreme weather conditions.

One such approach is the creation of a self-sustaining biofoam that conducts heat and electricity by combining bacteria-produced cellulose with graphene oxide. The graphene-fused foam draws water up to the surface via the cellulose layer which accelerates evaporation. This results in a layer of freshwater which can be easily collected and is safe to drink. The biofoam is also lightweight and relatively inexpensive to manufacture making it an attractive alternative to conventional methods.

Thus, as the need for clean, safe water is very much still an urgent global issue, nanotech solutions offer new and essential possibilities for the water treatment industry. The next phase of development is the scaling up of nanotechnologies to improve access to clean water. Perhaps then the future can be one that offers a new hope to the expanding global population experiencing water-stressed and water-scarce conditions.

Re-Posted from AZ NAno – David J. Cross MA

Magnetic Nanoparticles ease Removal of ‘microcontaminants’ from Wastewater

Many wastewater treatment plants do not completely remove chemical substances from wastewater. Credit: Symbol image: Shutterstock

Microcontaminants place a considerable burden on our water courses, but removing them from wastewater requires considerable technical resources. Now, ETH researchers have developed an approach that allows the efficient removal of these problematic substances.

In our everyday lives, we all use a multitude of chemical substances, including cosmetics, medications, contraceptive pills, plant fertilisers and detergents—all of which help to make our lives easier. However, the use of such products has an adverse effect on the environment, because many of them cannot be fully removed from wastewater at today’s watertreatment plants. As micropollutants, they ultimately end up in the environment, where they place a burden on fauna and flora in our water courses.

As part of a revision of the Waters Protection Act, parliament therefore decided in 2014 to fit an additional purification stage to selected water treatment plants by 2040 with a view to removing microcontaminants. Although the funding for this has in principle been secured, the project presents a challenge for plant operators because it is only possible to remove the critical substances using complex procedures, which are typically based on ozone, activated carbon or light.

Nanoparticles aid degradation

Now, researchers at ETH Zurich’s Institute of Robotics and Intelligent Systems have developed an elegant approach that could allow these substances to be removed more easily. Using multiferroic nanoparticles, they have succeeded in inducing the decomposition of chemical residues in contaminated water. Here, the nanoparticles are not directly involved in the chemical reaction but rather act as a catalyst, speeding up the conversion of the substances into harmless compounds.

“Nanoparticles such as these are already used as a catalyst in chemical reactions in numerous areas of industry,” explains Salvador Pané, who has played a key role in advancing this research in his capacity as Senior Scientist. “Now, we’ve managed to show that they can also be useful for wastewater purification.”

Based on the example of various organic pigments, such as those used in the textile industry, the researchers are able to demonstrate the effectiveness of their approach. Picture left before treatment, right after treatment. Credit: ETH Zurich / Fajer Mushtaq

An 80 percent reduction

For their experiments, the researchers used aqueous solutions containing trace quantities of five common medications. The experiments confirmed that the nanoparticles can reduce the concentration of these substances in water by at least 80 percent. Fajer Mushtaq, a doctoral student in the group, underlines the importance of these results: “These substances also included two compounds that can’t be removed using the conventional ozone-based method.”

“Remarkably, we’re able to precisely tune the catalytic output of the nanoparticles using magnetic fields,” explains Xiangzhong Chen, a postdoc who also participated in the project. The particles have a cobalt ferrite core surrounded by a bismuth ferrite shell. If an external alternating magnetic field is applied, some regions of the particle surface adopt positive electric charges, while others become negatively charged. These charges lead to the formation of reactive oxygen species in water, which break down the organic pollutants into harmless compounds. The magnetic nanoparticles can then be easily removed from water using magnetic field, says Chen.

Positive responses from industry

The researchers believe that the new approach is a promising one, citing its easier technical implementation than that of ozone-based wastewater treatment, for example. “The wastewater industry is very interested in our findings,” says Pané.

However, it will be some time before the method can be applied in practice, as it has been investigated only in the laboratory so far. At any rate, Mushtaq says that approval has already been given for a BRIDGE project jointly funded by the Swiss National Science Foundation and Innosuisse with a view to support the method’s transfer into practical applications. In addition, plans are already in place to establish a spin-off company, in which the researchers intend to develop their idea to market maturity.

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Chemists suggest a new method to synthesise titanium nanoparticles for water purification

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More information: Fajer Mushtaq et al. Magnetoelectrically Driven Catalytic Degradation of Organics, Advanced Materials (2019). DOI: 10.1002/adma.201901378

Journal information: Advanced Materials

Provided by ETH Zurich

Using Nanotechnology to Clean Water: A Conversation with Pedro Alvarez of Rice University (NEWT – Nano Enabled Water Treatment)

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.

 

 

Read More: How Can Graphene Be Used in Desalination?

Novel Nanosheet allows for efficient ‘Molecular Sieving’ – Zeolite Membranes have enormous potential in Energy and Chemical industries

The process of fabricating the membrane and the principle of water- and proton-selective permeation through it. Credit: Zishu Cao

Zeolites have played an important role in the chemical industry in past decades. These microporous, aluminosilicate materials are well-known catalysts and adsorbents for catalytic reforming and separation of petrochemicals. More recently, zeolites have also been used to remove radioactive cesium from seawater following the Fukushima Daiichi nuclear disaster. Now, recent work from the University of Cincinnati, has opened even more doors for the material by tweaking its geometry and surface chemistry.

Zishu Cao and her colleagues fabricated membranes by tiling with 6-nanometre-thick zeolite flat sheets, they synthesized by a modified hydrothermal crystallization procedure. The resultant membrane was much thinner than a conventional zeolite membrane, with a thickness of less than 500 nanometres versus a traditional membrane’s thickness of several micrometres.

Tiling enhancements

Cao’s adviser, Junhang Dong of the Department of Chemical and Environmental Engineering, says Cao’s two-dimensional zeolite sheets overcome the major transport issues the conventional thicker zeolite membranes typically experience when they are several microns thick.

“The potential for zeolite membranes in the energy and chemical industries is enormous,” says Dong, “but the practical realization of their use is hindered by two serious issues caused by intercrystalline spaces in the films and their randomly oriented polycrystalline structure.”

These intercrystalline spaces, or gaps between the randomly oriented crystals that comprise the films, undermine the separation selectivity by causing nonselective permeation of molecules and ions. In addition, the random orientation of the crystals in the films results in longer and un-preferred diffusion paths making the membrane permeation inefficient.

The two-dimensional, zeolite nanosheet tiled membranes synthesized by Cao, however, provide an oriented straight channel structure that provides both reduced intercrystalline spaces and shortened diffusion lengths for enhanced selectivity and membrane flux.

“Imagine you are using blocks to waterproof a roof. Now we are using tiles or shingles to construct the roof,” says Dong.

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Biomimetic coagulant makes water safe to drink

Petrochemical inspiration

Their readily scalable membrane fabrication by zeolite nanosheet lamination was inspired by recent work from the University of Minnesota, where researchers synthesized organophilic pure-silica zeolite nanosheets suitable for petrochemical separations. In Cao’s work, they incorporated aluminium ions into the silica-based zeolite framework to make the surface ionic and strongly hydrophilic – both favorable properties for water and ion separations. To the group’s knowledge, the ionic zeolite nanosheet laminated membrane is the first of its kind.

In their recently published paper, Cao displayed its potential for water desalination. The group chose to study this application because of its relevance to a wide range of needs in treating high salinity wastewaters, from industrial activities such as oil and gas drilling and power plant desulphurization and cooling. They reported high water flux with high salt rejection rates for brines containing up to 24% dissolved sodium chloride by weight.

The group says many routes are possible – desalination was just an example of the membrane’s capabilities. From here, they are exploring high-performance battery ion separators, catalysts, adsorbents, and thin-film sensors.

More details can be found in Science Advances.

Hairy nano-cellulose provides green anti-scaling solution – More applications including drug delivery, antimicrobial agents, and fluorescent dyes for medical imaging – McGill University

Credit: McGill University

A new type of cellulose nanoparticle, invented by McGill University researchers, is at the heart of a more effective and less environmentally damaging solution to one of the biggest challenges facing water-based industries: preventing the buildup of scale.

Formed by the accumulation of sparingly soluble minerals, scale can seriously impair the operation of just about any equipment that conducts or stores water – from household appliances to industrial installations. Most of the anti-scaling agents currently in use are high in phosphorus derivatives, environmental pollutants that can have catastrophic consequences for aquatic ecosystems.

In a series of papers published in the Royal Society of Chemistry’s Materials Horizons and the American Chemical Society’s Applied Materials & Interfaces, a team of McGill chemists and chemical engineers describe how they have developed a phosphorus-free anti-scaling solution based on a nanotechnology breakthrough with an unusual name: hairy nanocellulose.

An unlikely candidate

Lead author Amir Sheikhi, now a postdoctoral fellow in the Department of Bioengineering at the University of California, Los Angeles, says despite its green credentials cellulose was not an obvious place to look for a way to fight scale.

“Cellulose is the most abundant biopolymer in the world. It’s renewable and biodegradable. But it’s probably one of the least attractive options for an anti-scaling agent because it’s neutral, it has no charged functional groups,” he says.

While working as a postdoctoral fellow with McGill chemistry professor Ashok Kakkar, Sheikhi developed a number of macromolecular antiscalants that were more effective than products widely used in industry – but all of his discoveries were phosphonate-based. His desire to push his research further and find a phosphorus-free alternative led him to take a closer look at cellulose.

“Nanoengineered hairy cellulose turned out to work even better than the phosphonated molecules,” he says.

The breakthrough came when the research team succeeded in nanoengineering negatively charged carboxyl groups onto cellulose nanoparticles. The result was a particle that was no longer neutral, but instead carried charged functional groups capable of controlling the tendency of positively charged calcium ions to form scale.

Hirsute wonder particle a chance discovery

Previous attempts to functionalize cellulose in this way focused on two earlier forms of nanoparticle – cellulose nanofibrils and cellulose nanocrystals. But these efforts produced only a minimal amount of useful product. The difference this time was that the McGill team worked with hairy nanocellulose – a new nanoparticle first discovered in the laboratory of McGill chemistry professor Theo van de Ven.

Van de Ven, who also participated in the anti-scaling research, recalls the moment in 2011 when Han Yang, then a doctoral student in his lab, stumbled upon the new form of nanocellulose.

“He came into my office with a test tube that looked like it had water in it and he said, ‘Sir! My suspension has disappeared!'” van de Ven says with a grin.

“He had a white suspension of kraft fibres and it had turned transparent. When something is transparent, you know immediately it has either dissolved or turned nano. We performed a number of characterizations and we realized he had made a new form of nanocellulose.”

Extreme versatility

The secret to making hairy nanocellulose lies in cutting cellulose nanofibrils – which are made up of an alternating series of crystalline and amorphous regions – at precise locations to produce nanoparticles with amorphous regions sprouting from either end like so many unruly strands of hair.

“By breaking the nanofibrils up the way we do, you get all these cellulose chains sticking out which are accessible to chemicals,” van de Ven explains. “That’s why our nanocellulose can be functionalized to a far greater extent than other kinds.”

Given the chemical versatility of hairy nanocellulose, the research team sees strong potential for applications beyond anti-scaling, including drug delivery, antimicrobial agents, and fluorescent dyes for medical imaging.

“We can link just about any molecule you can think of to hairy nanocellulose,” van de Ven says.

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More information: Amir Sheikhi et al. Overcoming Interfacial Scaling Using Engineered Nanocelluloses: A QCM-D Study, ACS Applied Materials & Interfaces (2018). DOI: 10.1021/acsami.8b07435

Amir Sheikhi et al. Nanoengineering colloidal and polymeric celluloses for threshold scale inhibition: towards universal biomass-based crystal modification, Materials Horizons (2018). DOI: 10.1039/C7MH00823F

Journal reference: ACS Applied Materials and Interfaces  

Provided by: McGill University

 

Win-Win Collaborations – Derisking Advanced Technology Commercialization: YouTube Video from David Lazovsky, Founder of Intermolecular

David Lazovsky, Founder of Intermolecular, addresses the audience of the Advanced Materials Commercialization Summit 2017, speaking on Win-Win Collaborations: De-risking Advanced Technology Commercialization. Read More About Intermolecular

” … We sought to establish collaborative development programs with the Companies that were the end Producers.” – David Lazovsky, Founder of Intermolecular

 

“In the end you cannot “commercialize” technology (only) … you can only commercialize a Product  (technology+application) that can be produced and scaled economically into the Marketplace. You must find a way to build a bridge to span the gap between ‘Discovery, Proof of Concept, Prototype and Scaling to Funding (Finance), Market Integration and Acceptance.”

– Bruce W. Hoy, CEO of Genesis Nanotechnology, Inc.

Australian scientists develop nanotechnology to purify water

Scientists in Australia have developed a ground-breaking new way to strip impurities from waste water, with the research set to have massive applications for a number of industries.

Scientists in Australia have developed a ground-breaking new way to strip impurities from waste water, with the research set to have massive applications for a number of industries.

By using a new type of crystalline alloy, researchers at Edith Cowan University (ECU) are able to extract the contaminants and pollutants that often end up in water during industrial processing.

“Mining and textile production produces huge amounts of waste water that is contaminated with heavy metals and dyes,” lead researcher Associate Professor Laichang Zhang from ECU’s School of Engineering technology said in a statement on Friday.

Although it is already possible to treat waste water with iron powder, according to Zhang, the cost is very high.

“Firstly, using iron powder leaves you with a large amount of iron sludge that must be stored and secondly it is expensive to produce and can only be used once,” he explained.

We can produce enough crystalline alloy to treat one tonne of waste water for just 15 Australian Dollars (10.8 US dollars), additionally, we can reuse the crystalline alloy up to five times while still maintaining its effectiveness.” Based on his previous work with “metal glass,” Zhang updated the nanotechnology to make it more effective.

“Whereas metallic glasses have a disordered atomic structure, the crystalline alloy we have developed has a more ordered atomic structure,” he said.

“We produced the crystalline alloy by heating metallic glass in a specific way.””This modifies the structure, allowing the electrons in the crystalline alloy to move more freely, thereby improving its ability to bind with dye molecules or heavy metals leaving behind usable water.”Zhang said he will continue to expand his research with industry partners to further improve the technology.

Rice University engineers develop system to remove contaminants from water

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 Corp. appoints CEO

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 names new business unit leader

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.

NEWT – Mat baits, hooks and destroys pollutants in water: Rice University

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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