Pathways and Challenges for Biomimetic Desalination Membranes with Sub-Nanometer Channels – The Future of Desalination?

The authors acknowledge the support received from the National Science Foundation through the Engineering Research Center for Nanotechnology-Enabled Water Treatment (EEC1449500) and via Grant CBET 1437630. The authors also acknowledge funding from the National Science Foundation Graduate Research Fellowship Program under grant no. DGE-1752134, awarded to C.J.P. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

ABSTRACT

Transmembrane protein channels, including ion channels and aquaporins that are responsible for fast and selective transport of water, have inspired membrane scientists to exploit and mimic their performance in membrane technologies. These biomimetic membranes comprise discrete nanochannels aligned within amphiphilic matrices on a robust support. While biological components have been used directly, extensive work has also been conducted to produce stable synthetic mimics of protein channels and lipid bilayers.

However, the experimental performance of biomimetic membranes remains far below that of biological membranes. In this review, we critically assess the status and potential of biomimetic desalination membranes. We first review channel chemistries and their transport behavior, identifying key characteristics to optimize water permeability and salt rejection.

We compare various channel types within an industrial context, considering transport performance, processability, and stability. Through a re-examination of previous vesicular stopped-flow studies, we demonstrate that incorrect permeability equations result in an overestimation of the water permeability of nanochannels. We find in particular that the most optimized aquaporin-bearing bilayer had a pure water permeability of 2.1 L m^–2 h^–1 bar^–1, which is comparable to that of current state-of-the-art polymeric desalination membranes.

Through a quantitative assessment of biomimetic membrane formats, we analytically show that formats incorporating intact vesicles offer minimal benefit, whereas planar biomimetic selective layers could allow for dramatically improved salt rejections. We then show that the persistence of nanoscale defects explains observed subpar performance. We conclude with a discussion on optimal strategies for minimizing these defects, which could enable breakthrough performance.

Biomimetic Desalination Membranes

As stressors like population growth, industrialization, and climate change threaten to deplete and contaminate our freshwater resources, larger bodies of saline water could provide a vast supply of water for drinking, agricultural, and industrial use.(1) However, desalination of these waters requires more energy and financial resources than traditional freshwater purification methods.(2) Currently, the state-of-the-art technology for desalination is reverse osmosis (RO) using thin-film-composite (TFC) polyamide membranes.(3,4) Fully aromatic TFC-RO membranes are readily produced at industrial scale through interfacial polymerization, whereby a rapid reaction occurs at the interface of immiscible organic and aqueous phases to form a highly cross-linked polyamide selective layer on a porous support(5) (Figure 1). With the advent of the TFC-RO membrane and energy recovery devices, seawater desalination energy requirements for the RO stage have drastically reduced from ∼15 kWh m^–3 using the original cellulose acetate membranes of the 1970s down to only ∼2 kWh m^–3, only ∼25% above the practical minimum energy.(2)

Figure 1. Transition in desalination research from focusing on dense polymers that reject salt by a solution-diffusion mechanism to considering sub-nanometer channels capable of molecularly sieving ions. In the solution-diffusion panel (left), common reactants for TFC-RO membranes are represented, which rapidly react at an organic–aqueous interface during interfacial polymerization to form a cross-linked, fully aromatic polyamide selective layer with characteristic ridge-valley morphology. Salt rejection determined by a solution-diffusion mechanism results from the higher partitioning and/or diffusion rates of water over ions. In the ion sieving panel (right), common molecular sieves that have been considered for desalination are shown, with ideal water pathways illustrated. In pores similar in size to water, single-file water transport is induced. Nanotubes and nanochannels can be synthetic (e.g., carbon nanotubes) or biological (e.g., aquaporins). To produce nanoporous sheets, sub-nanometer pores where only a few atoms are vacant have been etched in single-layer graphene using chemical oxidation, electron beam irradiation, doping, and ion bombardment.(12) For 2D laminates, the water pathway is through interlayer spaces between sheets. Studies so far have primarily considered graphene oxide nanosheets for 2D laminates.(13,14) The molecular sieving mechanism for ion rejection is by size exclusion, where highly uniform pores exclude larger solutes and ideally transport only molecules similar in size to water.

Reduced Operational Costs, Improved Reliability and Efficiency and Enhanced Product Water Quality

Despite the substantial reduction in energy consumption and overall cost, seawater RO still has room for improvement. While current water permeabilities enable near-optimal performance, increased water-solute selectivity would allow for reduced operational costs, improved reliability and efficiency, and enhanced product water quality.(4) For example, TFC-RO membranes inadequately retain chloride and some small neutral solutes, such as boron in seawater desalination and trace organic contaminants in wastewater reuse, necessitating extra purification steps which increase the cost of desalination.(4)Transport through the polyamide layer is well described by the solution-diffusion model, in which permeants (i.e., water and solutes) partition into the dense polyamide layer and diffuse through it (Figure 1).(6) 

The resultant permselectivity of the membrane is attributed to differences in abilities and rates of species to dissolve into and diffuse through the polyamide membrane material.(7) Although intrinsic water permeability can far exceed salt permeability during solution diffusion, as it does for polyamide, historical data suggest that it will be difficult to significantly advance performance with polymeric systems. Commercial desalination and water purification membranes typically exhibit a permeability–selectivity trade-off, similar to the Robeson plot for polymeric gas separations.(8−11) 

Furthermore, despite many decades of extensive research, no polymeric material has yet surpassed the desalination performance (i.e., water permeability, water-salt selectivity, and cost-effectiveness) of fully aromatic polyamide.

To overcome the limitations of the solution-diffusion-based polyamide membranes, research focus has shifted toward the development of desalination membranes that remove solutes via molecular sieving. In this mechanism of ion rejection, highly uniform, rigid pores that are smaller than the diameter of hydrated salt ions transport water and nearly completely reject ions by size exclusion (Figure 1). Recent formats of molecular sieves considered for desalination include nanotubes and nanochannels, two-dimensional (2D) laminates, and nanoporous sheets (Figure 1).(14) 

However, these top-down efforts have failed so far to achieve adequate salt rejection due to the persistence of defects coupled with the daunting challenges of tuning interlayer spacing or pore size.(12,13,15) 

Biomimetic membranes, or composites comprising an amphiphilic matrix with discrete, aligned nanochannels on a robust support, may provide a platform for industrial-scale molecular sieves that overcome the limitations of solution-diffusion-based polyamide membranes.

After over 3.5 billion years of evolution,(16,17) the cell membranes of modern organisms can perform an array of highly complicated functions, which rely on a system of complex transmembrane proteins aligned within the amphiphilic lipid bilayer. In this system, water and only select ions pass through channel pores and pumps, depending on the energy and nutrient needs of the cell.(18,19) In pioneering work, Preston et al. determined that an integral membrane protein formed a biological channel that selectively transports water in and out of many types of cells. This protein was the CHannel-forming Integral Protein of 28 kDa (CHIP28),(20,21) later called the aquaporin. For these discoveries, Peter Agre and Roderick MacKinnon shared the 2003 Nobel Prize in Chemistry. Through additional biophysical studies, ion channels also showed impressive selectivity, inspiring the design of synthetic ion channels.(22−25) 

Eventually, researchers realized the potential implications of these channels for industrial-scale water purification, especially aquaporin in the use of desalination, and attempted to produce biomimetic membranes, or materials that mimic the structure and performance of biological membranes.(26−35) 

While much of the work has focused on water-solute separations, the biomimetic membrane format also presents opportunities to develop membranes with tunable selectivity based on a chosen channel type.However, translating biological mechanisms into industrial-scale technology necessitates scale-up by orders of magnitude—from the microscopic size of a cell membrane to tens of square meters.(36) For industrial relevance, the synthesis of a biomimetic membrane would need to be cost-effective and simple. Simultaneously, such a membrane would need to be mechanically stable under RO pressures exceeding 70 bar and chemically stable during repeated membrane cleaning and usage.(37) Notably, even at the lab scale, sufficiently high-salt rejection has not yet been achieved for biomimetic desalination membranes after over a decade of research.(37,38) 

Therefore, channels, selective layer formats, synthesis strategies, and support layer types must be carefully considered to attain the capabilities of this technology. While certain aspects of biomimetic desalination membranes have been reviewed recently,(37−42) a critical analysis of their performance and their potential application in water-treatment processes remains necessary.In this critical review, we examine efforts toward biomimetic desalination membranes for water purification in order to identify the best strategies to realize their full potential for both desalination and solute–solute selectivity. We first examine molecular transport, contrasting solution-diffusion with molecular sieving and assessing transport through the mixed matrix of biomimetic selective layers. We next identify the key characteristics of the aquaporin that explain its ultraselectivity and fast water transport, comparing this biological channel to several synthetic channels and placing each in industrial context. Using corrected analysis of reported permeability measurements, we then show that the water permeabilities of many channels have been overestimated. Subsequently, we predict best-case-scenario outcomes for common biomimetic formats, including membranes with intact vesicles and membranes with planar biomimetic layers. For the more promising planar format, the biggest challenge is the presence of nanoscale defects. Through mathematical models, we estimate the defect density for several reported biomimetic membranes. We then discuss synthesis pathways that could limit both the presence of defects and the effect of defects on transport performance.

We conclude with a discussion on the practicality of biomimetic desalination membranes and how to best exploit the strengths of discrete nanochannels as molecular sieves in other applications beyond desalination.

• 

Figure 2. Channel types for biomimetic membranes, including biological as well as bioinspired and bioderived. (a) Single channel water permeability versus pore interior diameter. The pore interior diameter here is defined as the inner diameter of the most constricted region. For PAH[4], the pore diameter shown refers to the average width of dynamic voids that formed in channel clusters.

Channel permeabilities from stopped-flow data and simulations were adjusted to 25 °C and corrected for any previous errors in permeability calculation (see SI, Section S1 for details). (b) (left) Overhead view of AqpZ tetramer and (right) side view of single AqpZ channel with characteristic hourglass shape. (c) GramA dimer as it exists in biological and vesicular environments. In organic solvents, the monomers can intertwine to form a parallel or antiparallel helix. AqpZ and GramA diagrams were drawn using PyMOL(69) with protein sequences from the Research Collaboratory for Structural Bioinformatics Protein Data Bank (RCSB-PDB, https://www.rcsb.org/), PDB-ID codes 1RC2(70) and 1NRM.(71) (d) Dependence of water diffusivity through pores on the number of interior hydrogen-bond points.

Data extracted from ref (56). (e) Cyclic peptide nanotubes. (left) Hydrogen-bonding pattern of pore-forming, stacked cyclic peptides. A polyglycine structure is shown for simplicity; side residues would typically be present. (right) Modified cyclic peptide with interior peptide-mimicking functional groups. The analogous unmodified cyclic peptide is radially symmetrical with a fourth primary amine side chain (cyclo[(d-Ala-Lys)₄]).(72) (f) Single-walled carbon nanotube porins (wide and narrow) with armchair pattern. Number of carbons approximate those of wCNTP and nCNTP. (g) (left) PAP[5] and (right) PAH[4] nanochannels with peptide appendages that form interarm hydrogen bonds. (h) (left) Aquafoldamer subunits with “sticky” ends. Differences in end groups that comprise Aqf1 and Aqf2 subunits are illustrated. (right) Weak hydrogen-bonding pattern of pore-forming, stacked aquafoldamers. Six subunits are needed to cross a DOPC membrane. (i) Pure water permeability versus total channel areal coverage in a DOPC bilayer. Single channel permeabilities from (a) were divided by channel cross-sectional area and converted into channel water permeability (A) coefficients using eq 3. Overall biomimetic layer A coefficients were calculated for various densities of channels within a DOPC bilayer using eq 7. DOPC bilayer hydraulic permeability was taken as 0.15 L m^–2 h^–1 bar^–1.(73) The shaded region indicates the water permeability of current commercial TFC-RO membranes, an adequate range for desalination performance. Permeabilities are listed in Table S1.

** Read the Complete Paper and Conclusions from AZ Nano by Following the Link Below

https://pubs.acs.org/doi/10.1021/acsnano.0c05753#

Authors

• Cassandra J. Porter: Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 
• Jay R. Werber: Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut and Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 

• Mingjiang Zhong: Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 
• Corey J. Wilson: School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
• Menachem Elimelech: Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 

Tiny Nanoparticles Offer Large Potential for Brain Cancer Treatment

For patients with malignant brain tumors, the prognosis remains dismal. With the most aggressive treatments available, patients are usually only expected to live about 14 months after a diagnosis

This is because, chemotherapy, the most common form of treatment for cancer, is uniquely challenging for brain tumor patients. The delicate organ in our skulls is protected by a network of vessels and tissue called the blood-brain barrier that keeps most foreign substances out. Furthermore, chemotherapy drugs can cause significant damage to the rest of the body if they are not able to target the tumor in a pharmacologically significant dose.

These challenges have plagued scientists for years, but a team of researchers for Yale School of Medicine and Beijing Normal University just published a breakthrough study detailing a new method that offers a promise at treatment. The solution? Nanoparticles.

Nanoparticles, particles that are smaller than wavelengths of visible light and can only be seen under a special microscope, have the potential to pass through the blood-brain barrier. They can also carry drugs to targeted areas of the body, reducing the side effects on the rest of the body. But previous nanoparticles were very complex and not very efficient in penetrating in the brain.

This most recent paper, published in Nature Biomedical Engineering on March 30, 2020, describes a small carbon nanoparticle engineered by the two labs that could both deliver chemotherapy drugs across the blood-brain barrier and mark tumor cells with fluorescence in mice. What’s more, this nanoparticle is incredibly simple—made up of only one single compound.

“The major problems we’ve solved is to improve the delivery efficiency and specificity of nanoparticles,” says Jiangbing Zhou, Ph.D., associate Professor of Neurosurgery and of Biomedical Engineering at Yale School of Medicine. “We created nanoparticles like building a missile. There’s usually a GPS on every missile to guide it into a specific location and we’re able to guide particles to penetrate the brain and find tumors.”

The GPS-like targeting occurs because the nanoparticles engineered to be recognized by a molecule called LAT1, which is present in the blood-brain barrier as well as many tumors, but not in most other normal organs. As a result, chemotherapy drugs can be loaded on the dots and target tumors while barely affecting the rest of the body. The nanoparticles gain entry to the brain because they’ve been engineered to look like amino acids, which are allowed past the blood-brain barrier as nutrients.

The nanoparticles have wider implications than drug delivery. They can be stimulated to emit a fluorescence, which helps surgeons locate tumor to remove with greater accuracy.

Still, there’s a long road ahead before this research can be applied in a clinical setting, says Dr. Zhou. “It takes a long time before the technology can be translated into clinical applications,” he says. “But this finding suggests a new direction for developing nanoparticles for drug delivery to the brain by targeting LAT1 molecules.”

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Explore further

Improving drug delivery for brain tumor treatment

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More information: Shuhua Li et al. Targeted tumour theranostics in mice via carbon quantum dots structurally mimicking large amino acids, Nature Biomedical Engineering (2020). DOI: 10.1038/s41551-020-0540-y

Journal information: Nature Biomedical Engineering

Why This New Quantum Computing Startup Has a Real Shot at Beating Its Competition

A startup called Quantum Circuits plans to compete with the likes of IBM, Google, Microsoft, and Intel to bring quantum computing out of the lab and into the wider world.

There’s one good reason to think it might be able to beat them all.

That’s because Quantum Circuits was founded by Robert Schoelkopf, a professor at Yale, whose work in many ways has helped kick-start this exciting new era of quantum advances.

Quantum computers exploit two strange features of quantum physics, entanglement and superposition, to process information in a fundamentally different way from traditional computers.

The approach allows the power of such machines to scale dramatically with even just a few quantum bits, or qubits. Those racing to build practical quantum computers are nearing the point where quantum machines will be capable of doing things that no conventional machine could—an inflection point known as quantum supremacy.

The promise of reaching such a milestone has transformed the field from a mostly academic endeavor into a high-stakes competition between the research arms of several big companies and a few startups. And everyone is using the superconducting circuits Schoelkopf pioneered.

He and colleagues were the first to create a “quantum bus” for entangling qubits using wires, as well as the first to demonstrate quantum algorithms and error correction techniques for quantum circuits.

Quantum Circuits’s other two founders are Michel Devoret, a professor of applied physics at Yale, and Luigi Frunzio, a research scientist in Schoelkopf’s lab (all three are in the photo above, with Frunzio, Schoelkopf, and Devoret starting from left).

“No team has done more to pioneer the superconducting approach,” Isaac Chuang, an MIT professor working on quantum computing and an advisor to the company, said in a release issued by Yale. “[The people behind Quantum Circuits] are responsible for a majority of the breakthroughs in solid-state quantum computing in the past decade.”

SOURCE: YALE UNIVERSIT

Nanogel that Delivers “1 -2” Punch to Cancer – Starts Clinical Trial

An Immune-Therapy drug delivery system created at Yale that can carry multiple drugs inside a tiny particle is heading toward its first phase of clinical trials for a possible new treatment for cancer.

The delivery system, a nanogel developed in the lab of associate professor Tarek Fahmy, can be used for multiple combinations of drugs for many different cancers and some immune disorders. The platform is designed to deliver multiple drugs with different chemical properties. A single particle can carry hundreds of drug molecules that concentrate in the tumor, increasing the efficacy of the drug combination while decreasing its toxicity.

A cutaway illustration of the nanogel developed by professor Tarek Fahmy. The small particle can carry multiple drug agents to a specific target, such as the site of a tumor. (Illustration by Nicolle Rager Fuller, NSF)

Fahmy describes the delivery system as a kind of “rational” therapy, in that it fuses established biological and clinical findings to the emerging field of nanotechnology.

“It creates a new solution that could potentially deal a significant blow to cancer and even autoimmune disease in future applications,” said Fahmy, who teaches biomedical engineering and immunobiology.

The first use of this delivery system will be a drug known as IMM-01. A multi-pronged treatment for metastatic cancer, it contains two agents: Interleukin-2 (IL-2) and an inhibitor of tissue growth factor (TGF beta). IL-2 amplifies the body’s immune system, while the TGF-beta inhibitor dampens the cancer cells’ ability to hide from the immune system. Because their size and makeup differ greatly, the two agents would normally be incompatible. Fahmy, however, developed a novel biodegradable gel that can contain both drugs and then release them in the tumor.

TVM Life Science Ventures VII is providing funding to Modulate Therapeutics Inc. to develop the drug to clinical proof of concept. Modulate secured the rights to IMM-01 from Yale and the Yale start-up company Immunova L.L.C., which was co-founded by Fahmy, Johns Hopkins University professor of oncology Ephraim Fuchs, and entrepreneur Bernard Friedman.

Friedman noted that the complexity of disease biology often hinders treatments. “Successful therapies must strike multiple targets,” he said. “The technology developed by Dr. Fahmy provides an elegant solution.”

“It’s about leveraging the biology of the system, not fighting it,” added Brian Horsburgh, CEO of Immunova and Modulate. “You want to wake up the immune system and harness that.”

Yale’s Office of Cooperative Research (OCR) helped launch Immunova in 2012 and develop Fahmy’s drug delivery technology. Fahmy is a member of the Yale Cancer Center.

“It’s great to see this technology moving forward to the clinic, and we’re hopeful that this will be the first of many life-saving drugs to use this technology,” said Dr. John Puziss, director of technology licensing in OCR.

Source: By William Weir, Yale University

Read more: Nanogel that delivers one-two punch to cancer heads to clinical trial

NEWT (Nano Enabled Water Treatment) Nanoscale solutions to a very large problem

ERCs produce both transformational technology and innovative-minded engineering graduates.
Credit and Larger Version

NSF-funded Nanosystems Engineering Research Center to enable deployment of mobile, efficient water treatment and desalination systems 

** NEWT is a joint designated collaboration between Rice University, ASU, UTEP and Yale University 

 

Water, water is everywhere, but we need more drops to drink.

The primary mission of the recently founded Nanotechnology Enabled Water Treatment (NEWT) Center, a consortium based at Rice University and led by environmental engineer Pedro Alvarez, is to produce more drinkable drops where they’re needed the most.

According to Alvarez, treated water is too often unavailable in parts of the world that cannot afford large treatment plants or miles of pipes to deliver it. Moreover, large-scale treatment and distribution uses a great deal of energy. “About 25 percent of the energy bill for a typical city is associated with the cost of moving water,” he said.

The center, funded by a five-year, $18.5 million National Science Foundation (NSF) award was founded to transform the economics of water treatment by using nanotechnology to develop compact, mobile, off-grid systems to provide clean water to millions of people around the world. A second goal is to make U.S. energy production more sustainable and cost-effective in regards to its water use.

NEWT is the first NSF Engineering Research Center (ERC) based in Houston. ERCs are interdisciplinary, multi-institutional centers that join academia, industry and government in partnership to produce both transformational technology and innovative-minded engineering graduates primed to lead the global economy. ERCs often become self-sustaining and typically leverage more than $40 million in federal and industry research funding during their first decade.

Water has long been a passion for Alvarez, who studies treatment and reuse, remediation strategies for contaminated aquifers and the water footprints of biofuels. His work also covers the environmental implications of using nanotechnology, and the transport — and eventual fate of — toxic chemicals in the environment. As NEWT director, he partners with researchers at Arizona State University (ASU), Yale University and the University of Texas at El Paso.

The consortium set as its first goal the development of modular water treatment systems that can deploy almost anywhere in the world. But Alvarez said the potential to make a significant impact is already expanding, with opportunities to address wastewater treatment at oil and gas drilling sites, nano-infused desalination in urban environments, and improved water treatment through more efficient filtration at existing plants.

Alvarez paused between classes recently to talk about the center’s plans.

Q. Where do you think NEWT’s greatest impact will be in 10 years?

A. It will be in drinking water, providing cleaner water to millions of people who now lack it. I think it’s going to be in developing small, portable units that will not only provide humanitarian water but also emergency response.

There will be other Flints. There will be other Elk River spills that will impact municipalities and water. I think we will be able to respond to those things.

We will probably have tremendous impact on desalination. Low-energy desalination will be one of our hallmarks, I believe. Of course, we will be very good also at treating some of the oil-and-gas water issues, but that’s a more difficult problem.

I expect we’ll also have high institutional impact because people may be more ready to consider unconventional water sources using portable systems that are easier to deploy. People are going to start considering more and more decentralized water-treatment approaches, especially as new cities and neighborhoods and developments evolve.

Q. What kind of sources will your technology be able to treat?

A. Briny ground water, for example, could be a source of drinking water in areas experiencing drought. Or in coastal areas. I think we will see more of that. We’ll see more harvesting of storm water, certainly, and for some uses, even greywater.

Those are the kinds of things our technologies will enable, but it’s not just about technology. It’s about the philosophy of changing to more sustainable, integratable water management, where we reuse more water, where we tap water that we thought was of too low quality but, as it turns out, is perfectly fine and safe and more economical for a sole intended use.

Q. In what directions are the initial projects headed?

A. I think the first thing we’re going to have out there is an adsorbent filter being developed by [NEWT deputy director] Paul Westerhoff at ASU. It’s a block of carbon with embedded nanoparticles. These particles adsorb — that is, they grab onto and hold — oxyanion contaminants like nitrate, arsenic and chromate, and effectively remove them from the water supply. [Oxyanions are negatively charged ions that contain oxygen.] It will be part of a drinking-water treatment unit.

Q. Would the technology apply to large water treatment plants?

A. Yes. Though we originally intended to carve a niche in the decentralized water treatment market, we do aspire to bigger things as our products, materials and processes gain momentum.

I am sure there will be a lot that can be used by the municipal water treatment community. It’s a more difficult industry to penetrate because it’s very conservative. You have to convince them that a technology is going to save them a lot of money and that they don’t have to change too much of the infrastructure or the configuration of the plant.

We have some very good ideas of things that will fit them. If they’re already using membranes for filtration, for example, our membranes may offer better rejection of contaminants and perhaps less susceptibility to being fouled, so they will last longer without having to be replaced. They won’t clog up as easily. They will not use as much energy.

Q. Why did you pursue hosting this NSF center?

A. I think that we as scientists and as engineers, especially in developed countries, have a social debt toward many poor people who lack access to clean water because they are denied the right to a life consistent with their inalienable dignity.

The lack of clean water is a major hindrance to human capacity. It goes beyond public health: It’s directly tied to the need for economic development.

That is certainly one important factor in my passion to provide water to many. It’s related to the concept of world affirmation, the idea that the world can be a better place and we can do something about it. Providing clean water is one way to do it.

The other big incentive was to try to move towards energy self-sufficiency in the United States in a manner that is more cost-effective and more sustainable with regards to the water footprint.

A major challenge for our energy industry is that they need to operate and extract oil and gas in areas that are relatively dry and semi-arid, where water is scarce. And they need relatively large quantities of water to obtain this energy. To get a barrel of oil in Texas, you need about 10 barrels of water. To frack a well to get shale gas or shale oil, you may need up to 6 million gallons of water, again in areas where water is scarce.

Once it’s used, disposal of that water becomes a major challenge and a potentially serious source of pollution. So the solution to both scarcity and minimizing impact is to reuse this water. That’s one of the things we’re trying to do: develop systems that are small and easily deployed that can enable industrial wastewater reuse in remote areas.

Q. What can you do with nanoparticles that you couldn’t have done before?

A. We need to recognize that at the nanoscale, the properties of matter change. Some elements, such as gold, that are very inert can become hypercatalytic at that scale, and materials that are good insulators like carbon can become superconductors.

When you exploit these extraordinary size-dependent properties, it allows you to introduce multifunctionality at both the reactor and materials level. This combination of multifunctionality — for example, membranes that have self-cleaning and self-healing properties — with the nanotechnology-enabled ability to selectively remove pollutants allows you to have smaller reactors. These can treat even unconventional sources of water, difficult sources, that currently would require huge reactors and very large and complex treatment trains that are impossible to take to remote locations.

Making them smaller, multifunctional and modular brings you tremendous versatility to handle a wide variety of challenges in water purification. Nanotechnology allows us to do that. It’s essential to our vision of decentralized water treatment systems.

Q. You’re an environmental engineer who knows aquatic chemistry, and you rely on other kinds of engineers and scientists for different parts of the water systems.

A. Absolutely. This has to be a multidisciplinary collaborative effort to build this innovation ecosystem. We need people who know how to make materials and people who know how to characterize them, how to immobilize them, how to manipulate them — how to assess their reactivity and bioavailability and mobility, and eventually scale them up.

We want people who are good at designing and building reactors all the way to systems to think about the whole lifecycle, the techno-economic implications of these materials, to make sure they’re feasible and improve on current practices.

They have to do it in a way that’s sustainable and avoids unintended, undesirable consequences as well.

Alvarez is the George R. Brown Professor of Environmental Engineering in the Department of Civil and Environmental Engineering at Rice University.

Investigators

Pedro Alvarez
Menachem Elimelech
Naomi Halas
Qilin Li
Paul Westerhoff

Related Institutions/Organizations
William Marsh Rice University
Arizona State University
University of Texas-El Paso
Yale University

Locations
Arizona
Connecticut
Texas

Related Programs
Engineering Research Centers

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Yale Study Confirms: Fracking Does Not Contaminate Drinking Water

Yale researchers have confirmed that hydraulic fracturing – also known as “fracking” – does not contaminate drinking water. (Photo : Flickr: Konstantin Stepanov)

Yale researchers have confirmed that hydraulic fracturing – also known as “fracking” – does not contaminate drinking water. The process of extracting natural gas from deep underground wells using water has been given a bad reputation when it comes to the impact it has on water resources but Yale researchers recently disproved this myth in a new study that confirms a previous report by the Environmental Protection Agency (EPA) conducted earlier this year.

After analyzing 64 samples of groundwater collected from private residences in northeastern Pennsylvania, researchers determined that groundwater contamination was more closely related to surface toxins seeping down into the water than from fracking operations seeping upwards. Their findings were recently published in the journal Proceedings of the National Academy of Science.

 

“We’re not trying to say whether it’s a bad or good thing,” Desiree Plata, an assistant professor of chemical and environmental engineering at Yale University, told News Three in a Skype interview. “We saw there was a correlation between the concentration and the nearest gas well that has had an environmental health and safety violation in the past.”

Researchers also noted that shale underlying the Pennsylvania surface did not cause any organic chemicals to seep into groundwater aquifers. However, these findings may not be applicable to all locations worldwide.

“Geology across the country is very different. So if you’re living over in the New Albany-area shale of Illinois, that might be distinct from living in the Marcellus shale in Pennsylvania,” Plata explained.

Researchers from Duke University also recently gave people a reason to trust fracking companies. In a study published in Environmental Science & Technology Letters, scientists explained that hydraulic fracturing accounts for less than one percent of water used nationwide for industrial purposes. This suggested that the natural gas extraction processes are far less water-intensive than we previously thought.

It’s hoped that these studies will help people better understand the safety of fracking.

Carbon Release from the Oceans Helped End the Ice Age

New techniques are allowing scientists to understand how carbon dioxide, released from the deep ocean, helped to end the last ice age and create our current climate.

An international team, including Yale paleoclimatologist Michael Henehan, studied the shells of ancient marine organisms that lived in surface waters of the southern Atlantic and eastern equatorial Pacific oceans thousands of years ago. The researchers determined that high concentrations of dissolved carbon dioxide in those waters coincided with rises in atmospheric carbon dioxide and global temperatures at the end of the last ice age.

The findings give scientists valuable insights into how the ocean can affect the carbon cycle and climate change, say the researchers.

A study describing the research appears in Nature. Joint lead authors of the study are Miguel Martínez-Botí of the Univ. of Southampton and Gianluca Marino of the Australian National Univ. The Univ. of Southampton led the effort.

“This is an exciting time for research into past climates,” said Henehan, who is a postdoctoral associate in the Dept. of Geology and Geophysics. “Advances in technologies and improvements in our methods have allowed us in this study to show just how critical carbon dioxide release from the oceans was in kicking the Earth out of the last ice age and into the climate state we have today.”

Henehan said Yale scientists are using the same technique to look even further back in time, investigating whether changes in atmospheric carbon dioxide played a role in the mass extinction of species at the end of the Cretaceous period.

Source: Yale Univ.

New class of Synthetic Molecules Mimics Antibodies

A Yale Univ. laboratory has crafted the first synthetic molecules that have both the targeting and response functions of antibodies.

The new molecules—synthetic antibody mimics (SyAMs)—attach themselves simultaneously to disease cells and disease-fighting cells. The result is a highly targeted immune response, similar to the action of natural human antibodies.

“Unlike antibodies, however, our molecules are synthetic organic compounds that are approximately one-twentieth the size of antibodies,” said David A. Spiegel, a professor of chemistry at Yale whose laboratory developed the molecules. “They are unlikely to cause unwanted immune reactions due to their structure, are thermally stable, and have the potential to be administered orally, just like traditional, small-molecule drugs.”

Spiegel and his team describe the research in a paper published online by the Journal of the American Chemical Society.

The paper looks specifically at SyAM molecules used to attack prostate cancer. Called SyAM-Ps, they work first by recognizing cancer cells and binding with a specific protein on their surface. Next, they also bind with a receptor on an immune cell. This induces a targeted response that leads to the destruction of the cancer cell.

Spiegel said the process of synthesizing and optimizing the structure of the molecules required considerable time and effort. “We now know that synthetic molecules of intermediate size possess perhaps the most important functional properties of antibodies—targeting and stimulation of immune cells,” he said.

“It’s also noteworthy that molecules of such a small size can bring together two objects as enormous as cells, and trigger a specific functional response, entirely as a result of specific receptor interactions,” Spiegel added.

Beyond their potential for treating prostate cancer, SyAMs may have applications for treating other forms of cancer, HIV and various bacterial diseases.

Source: Yale Univ.

Engineer to build “hot” solar cells

Yale Univ. associate professor of electrical engineering Minjoo Larry Lee has been awarded $2,540,000 to develop dual-junction solar cells that can operate efficiently at extreme temperatures above 750 F. In addition to converting a portion of the sunlight directly into electricity, the solar cells will use the remainder of the light to heat high-temperature fluids that can drive a steam turbine or be stored for later use.

“Our project aims to make a photovoltaic device that can operate at temperatures as hot as the inside of a brick oven,” says Lee, who will collaborate on this project with Emcore Corp. and the National Renewable Energy Laboratory. “This is definitely high-risk research, as solar cells have never been run this hot, and they’ll need to be both reliable and efficient at that temperature for a long time. But the potential payoffs are huge.”

Lee’s project, sponsored by a grant from the U.S. Dept. of Energy (DOE)’s Advanced Research Projects Agency for Energy, builds on the technology of photovoltaic solar panels. However, while current photovoltaic panels efficiently convert part of the solar spectrum directly into electricity, they become significantly less efficient as they get hotter—an inevitable side effect of absorbing sunlight.

Unlike traditional photovoltaics, which maintain their efficiency by dispersing the heat away from the panel or cooling the panel in some way, Lee’s panels will be built from materials that can operate efficiently at temperatures far higher than the typical panel and will integrate with a solar thermal collector that absorbs the unused portion of the light spectrum and converts it into heat.

The panels will use technology from concentrated solar power—a different method for capturing solar energy used in several large solar power plants—to transfer the heat to high-temperature fluids that can be used to power a steam turbine and generate electricity. These fluids can also be easily stored so that the heat energy can be dispatched when the sun is not shining or whenever electrical demand rises; this method of storing solar energy is more cost-effective than storing energy in batteries, notes Lee.

“The current high cost of storing solar electricity in batteries, combined with the natural variation of available sunlight, will weaken the economic drive for photovoltaic market growth,” says Lee. “Our project addresses both these challenges by taking the best elements of photovoltaic panels and combining them with the best elements of concentrated solar power.”

Source: Yale Univ.