August 2017 - ACS Axial | ACS Publications

ACS on Campus Visits Australia  

ACS on Campus recently visited Australia for the first time and had a successful two weeks of events, engaging with almost 400 students, authors, reviewers, and ACS members.

The number of published articles from Australian authors in ACS journals is steadily increasing year over year. The country has an impressive number of ACS Editors and Editorial Advisor Board (EAB) members within its borders, including Justin Gooding, Editor-in-Chief of ACS Sensorsalong with six associate editors, two executive and senior editors, and 40 EAB members. With that in mind and with the centenary chemistry congress for the Royal Australian Chemical Institute (RACI) in July, it was the perfect time for an ACS on Campus roadshow.

The first stop was at the University of New South Wales in Sydney on July 19. ACS on Campus brought some of the best ACS editors and local researchers for a packed day of innovative lectures, scholarly publishing, and student science presentations. There was networking aplenty amongst students, ACS editors, and ACS staff, and 25 students were able to share their science during the poster session.

The tour continued with an event at the University of Melbourne on July 21. The full day program consisted of more talks on scholarly publishing, science communication sessions, and student science presentations. A highlight was the career panel, where professionals such as a patent attorney, a staff scientist in industry, and a chief marketing officer of a chemical manufacturing company explored different careers within the chemical enterprise.

“While I think the “10 tips on getting your paper published” is probably the most useful session for students in the short term, I think the career panel was really likely to have more benefit in the long term,” said ACS Nano Associate Editor Paul Mulvaney, one of the hosts of the event. “Everyone seems to expect that life is some sort of linear fixed progression and we had speakers who showed that a chemistry PhD can take you amazing places and into unexpected directions.”

“What I really enjoyed was the opportunity to engage with students and younger researchers about the whole publishing process. With so many journals around, picking and choosing journals is quite bewildering.It is difficult for the current generation of students to understand how and why the publishing process works the way it does. The ACS Events allowed senior editors a chance to talk about their experiences as researchers, what makes a good paper and traps to avoid in publishing. I had very positive feedback from graduate students in particular,” said Mulvaney.

The final stop of the trip was the RACI National Centenary Conference in Melbourne. This was the RACI’s biggest conference yet, boasting an impressive international audience of researchers. ACS on Campus was honored to be a part of the official program on July 28 and have the opportunity to talk with attendees about professional development, how to get published, how to maximize your research, science communication tips, and use social media like a master.

The ACS booth was a central fixture in the exhibit hall at RACI, where ACS Publications held a “Meet-an-ACS-Editor” event with participation from Gooding, Mulvaney Editor-in-Chief Paul S. Weiss, ACS Chemical Biology Editor-in-Chief Laura L. Kiessling, Journal of Medicinal Chemistry Editor-in-Chief Gunda Georg, Jounral of Medicinal Chemistry Associate Editor Stuart Conway, and ACS Central Science Senior Editor Dongyuan Zhao that attracted over 200 researchers.

“It was great to have the ACS visit Australia for our centenary chemistry congress and to run some ACS on Campus events down under. Both the students at UNSW Sydney and the University of Melbourne really enjoyed the ACS on Campus events and several told me that they learnt a lot about publishing,” said  Gooding.

We want to give a big thanks to our university hosts, the RACI organizers, and the ACS Editors who served as our featured speakers: Gooding, Zhao, Mulvaney, Conway, Journal of the American Chemical Society Associate Editor Michelle Coote, Environmental Science & Technology Associate Editor Jennifer Field, Environmental Science & Technology Associate Editor David Waite, Organic Letters Associate Editor Andrew Holmes, Chemistry of Materials Executive Editor Frank Caruso, and The Journal of Physical Chemistry Deputy Editor Anne McCoy.


Drinking Water: Healthy, Tasty, or Toxic

Attendees of the 254th ACS National Meeting & Exposition in Washington DC had an opportunity to attend a lecture on the chemistry of drinking water by Dr. David Sedlak, Editor-in-Chief of Environmental Science & Technology and Environmental Science & Technology Letters. The lecture entitled, “Healthy, Tasty, or Toxic: A Chemist’s View of Drinking Water,” provides a tour of the U.S. through five very different glasses of drinking water, exploring the chemistry that determines the quality and availability of drinking water in each city. Dr. Sedalk’s lecture was seen by more than 900 people live and is now available online.

The following text is adapted from Dr. Sedlak’s prepared remarks for the lecture.

Healthy, Tasty, or Toxic: A Chemist’s View of Drinking Water

When ACS told me that they were going to find all these people to listen to me talk about drinking water in Washington, DC in late August, I thought that they were joking. I didn’t even think that there were that many people left in the city that late summer. Then I remembered that the city was going to be suffering from an influx of chemists—people who are quite happy to spend their days in windowless rooms suffering in the name of knowledge. So even if you are only here because you wandered in looking for an air conditioned room, I am happy to see you.

I also hope that you are thirsty because I want to share some drinking water with you. I’ll drink the water, and you can either drink your water or enjoy them vicariously. After I drink these five glasses of water, I hope you will have a better understanding of how we and solve problems related to our most precious resource.

As chemists, we tend to be quite literal when it comes to definitions. To us, water is a compound consisting of one atom of oxygen and two atoms of hydrogen. To the rest of the world, water is a much different thing. The stuff of life. Our most essential resource. Perhaps the most interesting observation is that water is defined by what it is not: no color. No light absorption. No odors.

The same thing holds for drinking water: It is suitable for consumption if it comes out of the faucet with no color, odor or substances that absorb visible light. Now a literal chemist might say, this drinking water thing is easy. Just serve people deionized water. But, for reasons that I will show you today, that is just not feasible. In addition to the aesthetic properties, I described, drinking water has to be available in your home 24 hours per day, and it has to cost less than about half a penny per gallon. That half a penny mostly pays for the water pipes and the salaries of the utility employees. The actual cost of water treatment is less than about a twentieth of a penny per gallon.

Now, I want to take share five glasses of drinking water with you. Each one is filled with colorless and odorless H2O. Sometimes we drink them because we are thirsty. We drink them because they maintain our health. We drink them because they taste good. And when we drink them we do not need to worry that they contain toxins or microbes that will make you sick. But they did not start out that way. All water has impurities. Those impurities are like footprints in the sand, telling us where the water has been and what it has done. Removing enough of the impurities to make the water healthy, tasty and non-toxic is the challenge of drinking water treatment. Let’s see if we can understand this challenge by translating it into the language of chemistry.

One of the first lessons of water chemistry is that we mix and match references states in the expression of equilibrium constants. Consider the dissociation of water—one of the simplest reactions in chemistry. For a water chemist, this reaction is second nature. As a result, we often forget that equilibrium constants are expressed according to different standard states. For water, we use molarity (moles per liter) when we describe solutes. The activity of each solute is simply the product of the activity coefficient and its concentration in moles per liter. Under the conditions, we find in drinking water the activity coefficients are close to one and thus are sometimes ignored. For water, we use the mole fraction scale instead of the molarity scale and a different symbol for the activity coefficient. Under the conditions found in drinking water, both the activity coefficient and the concentration are approximately equal to one.

This is quite a robust assumption. I calculated the mole fraction of water in our five glasses of drinking water are all > 0.9998. Even though the concentration of impurities in those glasses is negligible, I can assure you that it is the other stuff, the summation n, that makes all the difference. Let’s have a closer look at those impurities.

The most prominent of these impurities is salt. All water contains dissolved ions arising from the dissolution of minerals. If you evaporate seawater in the sun using the traditional method of making table salt, every liter will produce about 35 grams of sea salt (or 3.5%). These dissolved salts largely determine the taste of water. Of course, everyone knows that you cannot drink seawater.

Add as little as a half a gram of salt to water, and it is unpalatable. If you have drunk tap water ever in a city in the American Southwest and thought that it tasted a bit funny, it was probably because of salts. As the water made its way from its source to the water treatment plant under the hot desert sun, the concentration of dissolved salts increased due to evaporation. On the other end of the spectrum is distilled water. Water without salts also doesn’t taste very good either.

To assure that consumers have the same experience with their product anywhere in the world, some companies that sell bottled water first take out all of the salts and then add in a mix of salts that they have determined are tastiest to their customers. Other companies simply bottle water from natural springs in beautiful places. Drinking water in most cities falls within this range of salt concentrations that we find to be tasty. Your sensitivity and preferences are determined mostly by what you get used to.

This figure depicts the range of concentrations of four of the most common anions and cations that we encounter in water on a logarithmic scale, both in mole fraction and moles per liter. Sodium and chloride, the two most prominent ions in seawater also occur at the highest concentrations in freshwater. The divalent ions, calcium, and sulfate occur at lower concentrations and exhibit more variation determined by upon the local geology.

Drinking Water Glass #1: Tampa Florida

With this background in mind, the first glass of water that I would like to share with you comes from Tampa, Florida. Despite being located in a place where it rains more than a meter per year, the local rivers and groundwater aquifers do not provide a supply adequate for the 3 million people who live in the Tampa Bay metro area. To assure that there would be enough water, the city spent over $150 million to build a 100 million liter per day desalination plant in 2008. But this was only one chapter in a story that had started almost two thousand years earlier.

In ancient times, sailors realized that you could separate salts from seawater by boiling it and capturing the steam on a sponge. This was not a very practical solution for cities, but over time engineers working with the tools of the industrial revolution came up with more sophisticated ways of using distillation as a means of extracting fresh water from the ocean. By taking advantage of pressure, heat recovery and other properties of water they were able to make the process efficient enough for people with little or no water resources and a lot of fuel to burn (like the sugar plantations of the Caribbean or the oil-producing nations of the middle east to use it as a means of producing drinking water. But that wasn’t going to cut it for the rest of the world.

Back in 1961, JFK prioritized investment in an obscure US government agency called the office of saline waters. $150 million per year at its peak (in today’s dollars) jump-started a series of revolutionary ideas for separating fresh water from salts. Over the past fifty years, those the basic research seeded by the US government and others has gradually moved from the lab bench to pilot plants to the creation of a mature water desalination industry.

One of the key inventions originating from that period is the reverse osmosis membrane. The Principle of RO is relatively straightforward. As you might know, osmosis is the process through which water diffuses across a membrane from a region of low concentration to one of high concentration to even out the osmotic pressure. Reverse osmosis involves the application of pressure to the high salt concentration solution to overcome the osmotic pressure and drive water molecules through a membrane. With funding from the Office of Saline Waters, researchers working at UCLA developed a thin polymeric membrane that made reverse osmosis desalination of seawater possible. As you might imagine, pressurizing large volumes of seawater to 50-70 bar is an energy intensive process, and in the early years, the seawater RO plants required about as much energy as plants that used the distillation process.

But as the membranes moved out of the laboratory, engineers invented better materials and clever ways of recovering the energy that they invested to overcome the osmotic pressure. Over the last 40 years, the energy required to desalinate seawater by reverse osmosis has decreased by over a factor of five. Regarding energy consumption, modern, reverse osmosis desalination plants are approaching the minimum theoretical energy needed to separate salts from water. As a result, attention is now turning toward ways of improving the performance of membranes by increasing water flux and decreasing the need to take them out of service for cleaning.

As part of these investigations, chemists have learned that the workhorse polyamide membrane is more complicated than initially thought. It turns out that as the polymer forms, the crosslinking agents create layers of benzene rings that give rise to zones where water can diffuse more quickly across the membrane, These special, high water diffusion regions, shown in red, are where the bulk of the action happens regarding diffusion through the membrane. By using molecular simulations, like those shown here, we may be able to understand ways to increase the number of water diffusion fast lanes and thereby decrease the area of membranes needed to desalinate water. If we could do this, membrane modules would become less expensive, and the overall cost of desalination would shrink.

Drinking Water Glass #2: El Paso, Texas

The second glass of drinking water that I would like to share with you comes from El Paso, Texas. When it was still a small, border town, El Paso might have been able to rely on local sources of water, like the Rio Grande River, local reservoirs, and aquifers. But as the Metro area has grown to close to a million people it had to look for new supplies.

El Paso obtains about 5% of its water from a groundwater aquifer that up until 20 years ago was considered to be undrinkable because of the high levels of salts that it contained. But thanks to advances in the performance of reverse osmosis membranes (the cartridges are shown here), the city was able to build a $90 million desalination plant to in 2007.

According to the US Geological Survey, El Paso and some other cities sit on top of vast, untapped reserves of brackish groundwater. At 1 to 10 g/L of dissolved salts, brackish groundwater is too salty to drink. But it is still easier to desalinate than seawater. Brackish waters arise from the fact that groundwater gets trapped in contact with minerals and as the minerals dissolve over hundreds of years, the salts build up. We can mine these ancient water sources the same way we mine petroleum deposits. This map gives us an idea of some of the major known pools of brackish groundwater. Texas, Florida, and Arizona—three of our most water-stressed states have reserves of water that is mainly NaCl, likely from the dissolution of marine sediments that were rich in halites (sea salt). El Paso is not alone in its quest to mine brackish groundwater: San Antonio is building a desalination plant that will be even bigger than El Paso’. The center of the country is underlain by a band of water where calcium and sulfate are the main dissolved salts, mainly from the dissolution of CaSO4 (gypsum), BaSO4 (barite) and CaCO3 (calcite). Finally, CA’s central valley has reserves that are a mixture of these two types of salts.

Although a variety of technologies invented during the heyday of the Office of Saline Water can be used to desalinate brackish groundwater reverse osmosis is still the most common approach. As water molecules and a few salt ions that manage to get through imperfections in the membrane pass through the membrane the salt concentration on the other side increases. This stuff that remains, which we refer to as reverse osmosis concentrate, is a limiting factor in the desalination process. Operators of treatment plants want to recover as much freshwater as possible, both to increase the amount of drinking water that they produce to minimize the volume of reverse osmosis concentrate that they create. Cities that cannot simply pipe the reverse osmosis concentrate into the sea find that evaporating off the remaining water or finding places where it will not cause environmental problems can be the most expensive part of the whole treatment process. In addition to the need to apply higher pressures to overcome osmotic pressure as the salt levels increase in the concentrate, the problem with water recovery comes down to the formation of inorganic minerals on the surface of the membrane.

Consider what happens as the levels of calcium and sulfate increase as water passes through the reverse osmosis membrane. Even for waters where the main dissolved ions are Na and Cl, eventually, the solution will become supersaturated with gypsum (CaSO4). When this happens, the precipitate forms produces a layer of crystals on the surface oof the membrane that prevents the passage of water as shown in this electron microscope image. To address this problem, chemists have come up with a variety of strategies. The most common approach is to add chemicals known as antiscalants to the drinking water. These chemicals disrupt the formation of the mineral crystals on the membrane surface by adding charge to the nucleating crystals which can cause them to disperse into solution. The development of better antiscalants is a critical need, not just for treatment of brackish water, but for applications in energy production and industry where mineral precipitation causes problems.

It shouldn’t surprise us that when it comes to salts and mineral precipitation in water treatment, we are concerned about compounds containing calcium, silicon, iron, carbon, and oxygen. After all, they are among the most common elements in the earth’s crust as shown in this figure. What might be a little bit more surprising is all of the trouble caused by some of the less common elements scattered around the periodic table. In this case, the problems are mainly related to their toxicity. After all, biological systems did not need to evolve defenses against exposure to substances that they rarely encounter. Unfortunately, our quest for new sources of drinking water, as well as our desire to exploit the unique properties of some of these elements means that they sometimes occur in our drinking water at concentrations that cause health problems. Among these less common elements, three tend to cause the majority of the problems with drinking water: arsenic, chromium, and lead.

As you can see, the concentrations of these three elements in drinking water are typically a thousand times lower than those of the salts that we worry about during desalination. Nonetheless, arsenic and chromium have some things in common with the ions found in brackish groundwater: they often arise from the dissolution of minerals that remain in contact with water for long periods. It’s just that the arsenic and chromium-containing minerals are a lot less soluble than gypsum and halite. For such geogenic contaminants, our ability to pump water from deep aquifers often brings us into contact with these elements. All three of these elements are also used for industrial purposes, which has caused contamination of drinking water supplies. I think that no discussion of drinking water in the US in 2017 would be complete without a discussion of lead.

Lead has a melting point of 327.5 C. As a result, it was relatively easy for the Romans to make lead pipes (this one here is from an ancient Roman Bath, England. So for the Romans and plumbers up through the centuries, the lead was intertwined with drinking water. Even after we figured out how to make pipes out of copper, cast iron, steel, and cement, we still used lead to join pipes together (as solder) and in other applications where we needed a malleable material.

The first question you may be asking yourself is, “Have people been getting poisoned by lead in their drinking water for these last 2500 years?” After all, the moment you expose a lead pipe to oxygen and water the surface gets oxidized, which would allow the divalent lead to leach out. The answer to that question depends upon chemistry.

Fortunately for the Romans, they lived in an area where there were a lot of carbonate-containing minerals. This meant that as the drinking water flowed through the lead pipes, there was often enough calcium and carbonate to assure that a layer of calcite (CaCO3) precipitated on the surface, preventing the lead from coming into contact with the water. But even if parts of the Roman piping that were not coated with calcite, a layer of lead carbonate mineral form on the surface and coat it. Places in which the drinking water did not contain high levels of carbonate were not as lucky. For example, in parts of New England, where the drinking water doesn’t contain a lot of carbonates a significant fraction of the population had chronic lead poisoning: Using forensic tools and medical records, it has been estimated that 10% of the population of Massachusetts in the 1920s was showing symptoms of lead poisoning.

Luckily for people in those communities, US cities started to add chlorine (hypochlorous acid/hypochlorite) to their drinking water in the first few decades of the 20th century. This caused the divalent lead corrosion layer to undergo oxidation to a tetravalent lead oxide, which is incredibly insoluble.

For decades we have limped along with various remedies, like pH adjustment to encourage carbonate mineral formation. In the early 1990s, the US government passed a rule requiring that cities with lead pipes add a small amount of phosphate to create various lead phosphate minerals. This approach is used every day in hundreds of cities around the US. It allows them to continue to deliver water in their antiquated pipe networks, but as you are probably starting to see, it is not a simple process. And Flint, Michigan, has shown us that our current policy of serving millions of people water through a distribution network that contains lead pipes is a recipe for disaster. So I would not share a glass of Flint tap water with you.

Drinking Water Glass #3: Madison, Wisconsin

Instead, I want to share a glass of drinking water from Madison, Wisconsin. Like Flint, the old part of downtown Madison had sections of the city that had old lead pipes that were leaching. But when they tried to add phosphate to decrease lead levels it didn’t work very well. First, for reasons related to the local water chemistry, the phosphate didn’t lower the dissolved lead concentrations the way they were supposed to. Also, there was another problem related to phosphate addition.

As anyone who has ever been to Madison knows, the twin lakes that surround the city are a source of civic pride, beauty, and recreational opportunities. The city has been battling against algae blooms that turn the lakes green and render them unusable. The algae growth is caused by phosphorus that is released by upstream farms and local water users. So adding phosphate to the drinking water supply seemed like a bad idea because some of it would find its way into the lake or to the next sets of lakes downstream, where the city discharges its wastewater.

So rather than fooling around with the management of lead, the city ripped the lead pipes out and replaced them. Luckily for Madison, the problem was limited to a small section of the old city. As a result, it only cost about $15 million to do it or about $60 per person. According to the AWWA, the cost of repeating what Madison did in all of the cities in the United States with lead pipes would be over $30 billion, or about $90 per person if we shared it over the entire country. Madison solved their lead problem by investing in their infrastructure to solve the problem all at once rather than limping along with half measures. It remains to be seen if the rest of the country can follow their lead.

This problem of drinking water infrastructure investments to protect public health and the environment is the background behind our last two glasses of water. In these examples, the solutes that we are concerned about are organic chemicals that typically occur at concentrations that are typically ten to a hundred times lower than those of arsenic, chromium, and lead. To water chemists, they are known by their abbreviations, THMs (trihalomethanes), HAAs (haloacetic acids) and NDMA (nitrosodimethylamine). All of them are created when we disinfect water to remove harmful microbes, so it makes sense to start understanding them by considering the water disinfection process.

The main reason that we treat drinking water is to protect us from waterborne pathogens. During the 19th century cholera (caused by a virus) and typhoid fever (caused by the bacterium) were commonplace in US drinking water. With the advent of water filtration and chlorine disinfection in the turn of the century, the lives of people in North America increased by about seven years as shown in this figure of typhoid fever mortality in Baltimore in the early 20th century. In the early days, the science of disinfection was quite empirical: If you add more chlorine to the water, the pathogens go away faster. But as the practice became more common this wasn’t good enough because every water that was being treated behaved differently because of solutes in the water, like dissolved ferrous iron and organic matter, caused the chlorine to decay away at different rates.

Thankfully, a microbiologist named Harriet Chick used a quantitative chemistry approach to describe the relationship between chlorine exposure and microbe inactivation. If you can conceive of the disinfection process as a chemical reaction, like an electrophilic substitution of HOCl on a thiol group on a key membrane protein, it is the dose or the product of chlorine concentration and time that determines the inactivation for any specific organism. Chick and her collaborators showed that each organism had a unique sensitivity (the Chick-Watson coefficient, lambda. Therefore, the operator of water treatment plants just needed to quantify the kinetics of chlorine disappearance in their specific system and adjust the initial concentration until they had achieved an adequate dose for disinfection.

Let’s assume that the chlorine (hypochlorite at the pH of many water treatment plants undergoes a first order decay. After one hour a chlorine contact tank at the water treatment plant it is almost all gone, so there will be a little bit left when it goes into the underground pipe network, and the drinking water will not taste like a swimming pool.

One of the main reasons that the chlorine is disappearing in the treatment plant is that it is reacting with dissolved organic compounds. If the water came from a lake or river, those organic compounds would include polymeric materials produced when algae, leaves, and bacteria died and started to decay. This so called dissolved organic matter is a complex mixture of stuff that chemists have been studying for decades. Despite decades of study, chemists don’t entirely understand the structure of this natural organic matter. We know that it varies in composition from place to place and we also know that it contains an electron-rich functional group. Like phenols and amines that react with chlorine, causing it to disappear in the drinking water treatment plant. When these reactions occur, a small fraction (i.e., a few percent) are converted into small, chlorine-containing compounds. In particular, the trihalomethanes, like chloroform (CHCl3) and haloacetic acid s. The presence of these compounds, which we refer to as chlorine disinfection byproducts, has been correlated with increased risks of developing bladder cancer, miscarriages, and other health problems.

So the flip side chlorine disinfection is that the higher the dose of chlorine, the higher the concentration of chlorine disinfection byproducts will be formed. Normally, for a drinking water treatment plant, the designers employ their knowledge to balance the dose against the formation of disinfection byproducts. They must choose an initial chlorine concentration that is high enough to inactivate the pathogens, but not so much that they form disinfection byproducts at concentrations that endanger the health of community members.

Drinking Water Glass #4: Celina, Ohio

Our fourth glass of drinking water comes from the town of Celina, Ohio, a small city on the western side of the state where it wasn’t possible to find a suitable solution to the disinfection/disinfection byproduct balancing act. Like Madison, Celina is located on the shores of a beautiful lake.

And like Madison, the town struggles with algae blooms. But unlike Madison, the lake is the source of the city’s drinking water and all of that algae releases dissolved organic matter that produces disinfection byproducts when they are exposed to chlorine.

Celina couldn’t find a way to use chlorine to adequately disinfect their drinking water without forming unacceptable levels of disinfection byproducts. Celina’s solution has been to pass all of their drinking water through activated carbon. Activated carbon is essentially charcoal that is treated with acid before it is pyrolyzed. This causes it to develop a high surface area through the formation of pores. The hydrophobic and hydrophilic regions of this high surface area material create strong intermolecular reactions between the surface and that polymeric organic matter, causing it to adsorb to the material. Activated carbon also removes the musty flavored compounds that are often produced by algae.

You might be familiar with activated carbon if you use one of those filters in a pitcher for your drinking water. Doing this at the scale of an entire city is a different matter and requires tons of the stuff each year. The cost is less than 0.05 cents per gallon. It has made the city’s drinking water more expensive, but if they cannot control the nutrients that come into the lake from nearby farms, it would be unpalatable and unhealthy.

Drinking Water Glass #5: Anaheim, California

The last glass of drinking water that I would like to share with you comes from Anaheim, California. Anaheim is part of an area of southern California that sits in Orange County. Because it is not officially a part of LA or San Diego, it does not have the same access to imported water as its neighbors to the North and the South. Luckily the city does have access to groundwater, which supplies the majority of the drinking water to the city.

So starting in the early 1970s, the local water district began pioneering a new approach referred to as groundwater replenishment or potable water reuse. The way it works as follows: Water that people flush down the toilet goes to the wastewater treatment plant. After that, it is passed through reverse osmosis membranes (similar to the ones used for seawater desalination). The wastewater is used because it takes a lot less energy than seawater because it is only about 2% of the salinity of seawater. From the early days of the 1970s, the water was put back into the aquifer after RO. But in the early 1990s, the city discovered a new contaminant that passed through the RO membrane—NDMA.

But in the early 1990s, scientists working for the state of California discovered low levels of NDMA in the water produced by the advanced treatment plant. This was a major concern because toxicologists had determined the safe level of this potent carcinogen in drinking water to be several parts per trillion. As part of his Ph.D. dissertation, my student Bill Mitch discovered that the culprit was chlorine. You see, chlorine was added to the water before it went through the microfilters, which serve as the pre-treatment step to prepare it for reverse osmosis. The chlorine was added not to kill pathogens, but to minimize the growth of bacteria on the microfilters.

When chlorine is added to wastewater that contains ammonia, chloramines form. Those chloramines undergo an acid-catalyzed disproportionation reaction to produce dichloramines. The dichloramines then react with compounds like dimethylamine in the wastewater to produce a hydrazine compound that is then oxidized by oxygen to produce NDMA. The NDMA is so small and polar that it can slip through the RO membrane along with the water molecules. To solve this problem, the city installed a UV lamp and added about a millimole per liter of hydrogen peroxide after the reverse osmosis step. The hydroxyl radicals generated in this step rapidly oxidized the NDMA and any other compounds that snuck through the membrane.

So the new version of the advanced water treatment plant has the extra step of UV/H2O2 as an extra failsafe. This new approach to recycling water is catching on throughout the US southwest and is now providing the drinking water for several million people in California, Texas, and Arizona.

So there you have it: a glimpse into the world of drinking water in five glasses. As we have seen, the challenge of drinking water is providing thirsty cities with drinking water that is healthy, tasty and non-toxic. This challenge is complicated by the need to treat waters that start out with vastly different compositions. The challenge is also complicated by society’s assumption that the creation of drinking water is simple. I hope that this glimpse into some of the challenges associated with drinking water has shown you that the challenge of drinking water is one where chemists can and will continue to play a major role.

Take the ACS Reviewer Lab Challenge

If you’ve ever reviewed a paper for ACS, you know the review process is as demanding as it is essential. That’s why we’re proud to offer ACS Reviewer Lab, a free, 4-hour online course developed to educate researchers on the principles of quality peer-review. The course features interactive modules covering the basics of peer review and ethics, as well as real-life guidance on how to write a first-rate review.

Wondering if you’re in need of a little refresher course in correct review procedure? Why not take the ACS Reviewer Lab Challenge, a quick, five-question test of your grasp of reviewing principles:

Take the ACS Reviewer Lab Challenge:

ACS Reviewer Lab Quiz
Test your peer review knowledge and receive an email voucher for a special gift from ACS Publications at the ACS National Meeting in Washington, DC.
Test your peer review knowledge. Take the challenge!
Thank you for taking the Peer Review Challenge!
Be sure to print out your email voucher for a special gift at the ACS Publications Booth during the 254th ACS National Meeting & Exposition in Washington, D.C.

Looking for more peer review education? Check out the free, online course from ACS Publications, ACS Reviewer Lab.

Want more? You can check out ACS Reviewer Lab and get instruction on the basics of peer review, ethical dillemnas in peer reviews, preparing for review, assessing the signifigance and technical quality of a researcher paper, and writing your review.

Removing the Sunblock Contaminants That Damage Coral Reefs

Emerging evidence suggests that a certain important component in many sunblock lotions can be deadly to coral reefs. Now, researchers have developed a biodegradable bead that can soak up the sunblock ingredient, oxybenzone, like a thirsty sea sponge. They hope to use the agent to clean up seawater at beaches.

The beads’ matrix consists of materials that are familiar to the ocean: alginate, which is derived from algae, and chitosan, which is a waste product of fish. Inside this gelatinous matrix are the magnetic nanoparticles. The magnetic core of the nanoparticles is made from iron oxide and is coated with sodium oleate. By controlling the alginate/chitosan ratio, researchers can make these magnetic nanobiocomposites float or sink for added flexibility in the removal of contaminants.

Watch a video explaining this important new discovery for protecting coral reefs:

Dr. Felix R. Roman and Victor Fernandez-Alos, both of the University of Puerto Rico, Mayaguez,recently presented their work at the 254th ACS National Meeting in Washington, D.C.

Watch their press conference on using biodegradable beads to remove oxybenzone from beaches here:

Watch more great videos from the American Chemical Society.

Viruslike Nanoparticles Kill Drug-Resistant Bacteria

Viruslike polymer nanoparticles can target and kill different types of bacteria—including antibiotic-resistant strains—while sparing human cells, according to a new study. What’s more, fine-tuning the size and shape of these fuzzy polymer nanoparticles alters their potency. The strategy could represent a step towards a new class of antimicrobials that could fight infections while avoiding antibiotic resistance.

The rise of antibiotic-resistant superbugs has become a serious health issue. Conventional antibiotics employ several bacteria-killing strategies, such as interfering with cell wall construction, attacking protein synthesis, or messing with DNA replication. But the bugs can develop resistance by chemically altering the drugs, mutating their targets, or pumping drugs out of the cell.

So scientists have been trying to develop antimicrobials that avoid these resistance mechanisms and physically rip apart bacteria. Many are working with naturally occurring bacteria-fighting peptides. These positively charged, amphiphilic peptides bind tightly to negatively charged lipid molecules to rupture membranes and break apart the cell. Some researchers have tried to make antimicrobial nanoparticles out of the peptides, while others have synthesized peptide-mimicking polymers. But the hydrophobic parts of such peptides can also disrupt the membranes of mammalian cells, which limits their potential as new antibiotics.

Hongjun Liang of Texas Tech University thought that bacteriophages might offer some strategies that could make antimicrobial peptides more selective. These viruses with hairy surfaces target specific bacteria and penetrate the cells to infect them. “We were curious what role the phage nanostructures play,” Liang says.

The researchers made three different fuzzy polymer nanoparticles that mimic bacteriophages: an 8-nm-wide sphere, and two 7-nm-wide rod-shaped particles that were 18 nm and 70 nm long, respectively. They built particles containing a polymer core with hundreds of bristles composed of positively charged, hydrophilic poly(4-vinyl-N-methylpyridinium iodide) sticking out. By using only hydrophilic bristles, the team hoped to avoid the antimicrobial peptides’ toxicity to mammalian cells.


Scanning electron micrographs of E. coli bacteria with disrupted cell membranes.
Escherichia coli cells (left) incubated with rod-shaped nanoparticles (middle) are damaged less than those exposed to spherical nanoparticles (right).
Credit: ACS Infect. Dis.

The team tested the fuzzy particles’ antibiotic potency on Gram-negative Escherichia coli bacteria, Gram-positive Staphylococcus aureus, and various multidrug-resistant bacteria, as well as the particles’ toxicity to human cells.

The spherical particles worked best, killing over 99.9% of both Gram-positive and negative bacteria. It showed remarkable potency against multidrug-resistant Pseudomonas aeruginosa bacteria, requiring just 2 µg/ml to take out these microbes.

The longer particles showed lower antibacterial activity. However, they were more deadly to Gram-negative bacteria than to Gram-positive ones. That’s because the peptidoglycan layer that encapsulates Gram-positive bacteria is thick and has 5- to 50-nm-diameter pores that longer rods cannot cross. But rods can damage the thin, outer lipid membrane of Gram-negative bacteria. “So we can tune antibiotic activity just by changing the nanostructure’s size and shape,” Liang says.

Unlike antimicrobial peptides or their synthetic mimics, these polymer particles are not lethal to human cells. That’s because the particles rely on the shapes of lipids within the cell membrane to inflict damage. Bacterial membranes are rich in phosphoethanolamine lipids, which have an intrinsic curve, so these molecules easily bend and wrap around the tiny nanoparticle bristles, straining the membrane and causing the cell to burst. Meanwhile, human cells are primarily made of flat phosphocholine lipids. The particles can’t rupture those more rigid membranes because changing their shape would cost too much energy.

This is an exciting new approach to antimicrobials, says Jacinta C. Conrad of the University of Houston. Instead of tinkering with chemical toxicity, the researchers have mimicked the natural structure of viruses and demonstrated a potent, selective antimicrobial.

“This could be the critical new tool needed to fight drug-resistant bacteria, which may not be killed by other means,” she says. “Moreover, because these materials attack certain kinds of bacteria and not others, they may be less disruptive to bacteria in the human microbiome, which are often targeted by conventional antibiotics.”

Right now these particles are “far from meeting practical clinical standards,” Liang cautions. He says his team will have to go back and design nanostructures made of polymers that are more biocompatible and biodegradable. “We should go back to the drawing board and come up with something that has a good chance of passing rigorous safety tests.”

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on August 24, 2017.

ACS Editors’ Choice: Genomic Enzymology — and More!

This week: Genomic enzymology, ferric heme-nitrosyl complexes, synthesis of benzoxazoles — and more!

Each and every day, ACS grants free access to a new peer-reviewed research article from one of the Society’s journals. These articles are specially chosen by a team of scientific editors of ACS journals from around the world to highlight the transformative power of chemistry. Access to these articles will remain open to all as a public service.

Check out this week’s picks!
A Phosphonium Ylide as an Ionic Nucleophilic Catalyst for Primary Hydroxyl Group Selective Acylation of Diols

ACS Catal., 2017, 7, pp 6150–6154
DOI: 10.1021/acscatal.7b02281
Terahertz-Driven Luminescence and Colossal Stark Effect in CdSe–CdS Colloidal Quantum Dots

Nano Lett., Article ASAP
DOI: 10.1021/acs.nanolett.7b01837
Genomic Enzymology: Web Tools for Leveraging Protein Family Sequence–Function Space and Genome Context to Discover Novel Functions

Biochemistry, 2017, 56 (33), pp 4293–4308
DOI: 10.1021/acs.biochem.7b00614
Ferric Heme-Nitrosyl Complexes: Kinetically Robust or Unstable Intermediates?

Inorg. Chem., Article ASAP
DOI: 10.1021/acs.inorgchem.7b01493
Variation in Extracellular Detoxification Is a Link to Different Carcinogenicity among Chromates in Rodent and Human Lungs

Chem. Res. Toxicol., Article ASAP
DOI: 10.1021/acs.chemrestox.7b00172
Asymmetric Total Syntheses of Colchicine, β-Lumicolchicine, and Allocolchicinoid N-Acetylcolchinol-O-methyl Ether (NCME)

Org. Lett., Article ASAP
DOI: 10.1021/acs.orglett.7b02224
Synthesis of Benzoxazoles Using Electrochemically Generated Hypervalent Iodine

J. Org. Chem., Article ASAP
DOI: 10.1021/acs.joc.7b01686
Love ACS Editors’ Choice? Get a weekly e-mail of the latest ACS Editor’s Choice articles and never miss a breakthrough!

Foraging for Fetal Cells in Mothers’ Blood

Every pregnant woman who has considered getting a prenatal genetic test is familiar with the dilemma: Amniocentesis and chorionic villus sampling (CVS) are the only available diagnostic tests that can say for sure whether a fetus has a devastating genetic disorder—but these tests are invasive, and each carries a small risk of miscarriage. Now, researchers are developing a less invasive test that collects fetal cells from a maternal blood sample using an antibody-coated chip, allowing for conclusive testing for genetic disorders with a simple blood draw.

In amniocentesis and CVS, doctors insert needles or catheters into the uterus to collect placental cells. These cells, called trophoblasts, share the same genome as the developing fetus. But the trophoblasts don’t remain exclusively in the uterus. “During early pregnancy, the growth of the placenta is a little like the growth of a tumor,” says Hsian-Rong Tseng of the University of California, Los Angeles. The placenta grows into and essentially invades the uterus. The end result is that some of the trophoblasts end up circulating in the maternal blood. Tseng’s team had previously developed a chip that captures tumor cells from blood samples and realized they could adapt the method to capturing trophoblasts.

The researchers covered a piece of glass with a forest of nanosized poly(lactic-co-glycolic acid) pillars, which provide ample surface area for attaching the bait to capture cells of interest. To capture trophoblasts in particular, Tseng and colleagues attached an antibody that binds to a trophoblast surface protein to the nanopillars. Then, they applied blood samples obtained from six mothers carrying normal male fetuses and nine mothers carrying fetuses with genetic abnormalities, such as trisomy 21 (Down Syndrome), to the chip. The nanopillar chip captured 80% of the trophoblasts in blood samples spiked with a known trophoblast concentration, compared with 20 – 30% for a flat antibody-coated chip, says Tseng. That boost was critical, he says, with only two to six trophoblasts per 2 mL of maternal blood. The researchers still had to use 10 mL of blood to gather enough cells for genetic analysis.

To isolate the fetal cells from others stuck on the chip, the researchers tagged the trophoblasts with fluorescent antibodies and then used laser capture microdissection to collect only those cells that glowed. Using commercial microarrays, they analyzed the trophoblast genotypes, correctly identifying the sex and whether the fetus had genetic abnormalities for all 15 samples, as confirmed with amniocentesis or CVS.

“The fishing of the cells is innovative,” says Sascha Drewlo of Wayne State University, but he says the approach still needs to overcome significant hurdles before it’s ready for commercial application, including boosting the number of cells captured and lowering the amount of blood needed for analysis. Tseng is aware of these challenges, and hopes to improve his cell yield in future experiments by obtaining trophoblasts from cervical samples instead of maternal blood. “A pap smear sample can yield hundreds of trophoblasts,” says Tseng.

Tseng cofounded a company, FetoLumina Technologies, to commercialize the chip technology.

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on August 23, 2017.

ACS’ Most Prolific Author Zhong Lin Wang Shares His Productivity Tips

ACS journals feature the work of many amazing chemistry researchers, but none quite as productive as Dr. Zhong Lin Wang. At the 254th ACS National Meeting and Exposition, Wang was honored as ACS Publications’ most prolific author. The honor was announced via a photo mosaic, which used images submitted by event attendees to assemble a portrait of the most prolific author. While Dr. Wang was unable to attend the event in person, he did speak to attendees via video chat and his daughter, Aurelia Wang, was on hand to help celebrate his achievements.

What drives Wang’s remarkable productivity? What can ACS Axial readers learn from him about getting more done in the lab? Read an interview with Wang and discover his research published in ACS journals.

Dr. Wang’s answers have been lightly edited for clarity and flow.

What first attracted you to the study of chemistry? Do you remember what made you decide to pursue a career in the lab?

I was attracted to chemistry in my high school years. Although there was no experimental facility at all [at my school] back then, I was deeply impressed by watching chemical reactions occurs in a test tube. I remember asking my teacher a question: What is a hybridized valence state? He told me, “You cannot understand this now because you are too young, but wait until you get to college.”

What sparked your interest in energy research?

I have been engaged in nanomaterials and nanoscale characterization research since 1983. I always think about how can we utilize nanomaterials to make changes in our life. Besides the beauty provided by nanoscale structures, how they can be applied to serve the world? I first started in energy research in 2005. Ever since then, energy has been one of the most important focus areas of my research. But my energy research is different from most people, who are focused on organic catalysis, LEDs, solar cells, batteries, and supercapacitors. I use organic materials to convert body motion energy into electric power, which I call an organic nanogenerator.

What do you think the future of energy research looks like? Are there particular energy solutions you’re especially excited about?

We are making good progress in energy studies, but to solve the world’s energy needs at a large-scale is very challenging. I think the energy research we do today can only contribute a small portion of the world’s total energy consumption, in comparison with the energy we get from combustion-based fossil fuel use. However, with the new fields of the internet of things, sensor networks and big data, we need a huge number of small energy sources for powering mobile sensors and related networks. These so-called “micro-grid power sources” are desperately needed for the era of the internet of things. I think that our nanogenerator is ideal for this type of application since it harvests energy from our living environment for powering small sensors and mobile electronics.

What are the biggest remaining barriers to wide adoption of nanogenerators?

Converting mechanical energy into electric power was not a traditional area for chemists, but mechanical engineers. We chemists are used to studying organic solar cell and organic LEDs. But now chemists and materials scientists can fabricate triboelectric nanogenerators using the materials they have synthesized. I think that people have to overcome this mindset and realize that nanogenerators are a new and exciting field. They can have a wide range of applications in fields such as flexible electronics, wearable fiber electronics, health care, security, pollution control, and motion sensors.

With increased interest and worldwide research starting in the field of nanogenerators, our first challenge is we now have to find the killer applications of these nanogenerators. I think that breakthrough area will be found very soon, with the continuous increase in the output power of nanogenerators, particularly in the area of self-powered systems and sensors. The second challenge we need to overcome is the material’s durability and the device’s stability, as well as its lifetime. Solving this will open up new research areas for chemists and materials scientists, especially nanomaterials and polymer people. The third challenge would be the packaging technology and system integration, which is important for applying nanogenerators in our real life.

Did managing students and other researchers come naturally to you? What have you learned over your career of managing people that you wish you’d known at the start?

Our research attracts a wide range of students with all kinds of background, such as chemistry, physics, materials science, electrical engineering, mechanical engineering, and even medical sciences. We can fit them all into our research team because we are doing a systemic approach. Students are excited when they can directly see what they have made at work.

You’re being honored for being an incredibly prolific author. How do you manage to get so much done in the lab? Do you have a productivity tip for ACS Axial readers?

Nanogenerators and piezotronics are two fields that we pioneered. Our publications have been focused on the advances in these two new fields. I have been prolific not only because I work very hard, but also because I have many outstanding students, postdocs, and collaborators who also work very hard and dedicated.

I always stay on top of things and remain hands-on. I work very closely with my people and give them detailed advice. I always emphasize to them is that our research has to be high quality, with a high degree of innovation. We do research to advance our scientific understanding and technology innovations in nanogenerator and piezotronics fields, which we pioneered, rather than just publishing. Publications are the means for communicating and reporting to the world what we have done and establishing these new fields. Our goal is to make these two fields truly useful for the world.

The tips I can give are as follows:

  • If you have 5 minutes, do a task that takes 5 min things; each day is made of many 5 minutes.
  • Do not look at the same email twice. Process your email immediately as you receive it. If you can get it done today, do not wait until tomorrow.

You’ve published more than 300 papers in ACS journals. Do you have any favorite papers?

Yes! I have a number of very important papers published in ACS journals. Here are a few.

These two papers establish the physics foundation of piezotronics:

Piezoelectric-Potential-Controlled Polarity-Reversible Schottky Diodes and Switches of ZnO Wires
Nano Lett., 2008, 8 (11), pp 3973–3977
DOI: 10.1021/nl802497e

Flexible Piezotronic Strain Sensor
Nano Lett., 2008, 8 (9), pp 3035–3040
DOI: 10.1021/nl802367t

These three papers created the field of piezo-phototronics and its basic physics model:

Optimizing the Power Output of a ZnO Photocell by Piezopotential
ACS Nano, 2010, 4 (7), pp 4220–4224
DOI: 10.1021/nn101004

Enhancing Sensitivity of a Single ZnO Micro-/Nanowire Photodetector by Piezo-phototronic Effect
ACS Nano, 2010, 4 (10), pp 6285–6291
DOI: 10.1021/nn1022878

Enhancing Light Emission of ZnO Microwire-Based Diodes by Piezo-Phototronic Effect
Nano Lett., 2011, 11 (9), pp 4012–4017
DOI: 10.1021/nl202619d

This paper points out the killer application of the triboelectric nanogenerators at low-frequency in comparison to the traditional electromagnetic generator, which will have a huge impact on the engineering applications of nanogenerators.

Harvesting Low-Frequency (<5 Hz) Irregular Mechanical Energy: A Possible Killer Application of Triboelectric Nanogenerator
ACS Nano, 2016, 10 (4), pp 4797–4805
DOI: 10.1021/acsnano.6b01569

This was the first paper on a hybrid cell for harvesting multi-type of energy using a single device. It opens the field of hybrid energy cell.

Nanowire Structured Hybrid Cell for Concurrently Scavenging Solar and Mechanical Energies
J. Am. Chem. Soc., 2009, 131 (16), pp 5866–5872
DOI: 10.1021/ja810158x

Get more tips with your ACS ID on the ACS Publishing Center.

Explore All ACS has to Offer at the 254th ACS National Meeting & Exposition

The American Chemical Society will welcome nearly 12,000 chemists and related professionals to the 254th ACS National Meeting & Exposition in Washington D.C. fron Aug. 20-24. The program will feature topics related to the theme, “Chemistry’s Impact on the Global Economy.”

Be sure to attend the featured Kavli Foundation Lecture Series on Aug. 21. Attendees will be able to hear world-class presentations from Dr. Prashant K. Jain, Assistant Professor in the Department of Chemistry and the Materials Research Laboratory at the University of Illinois – Urbana Champaign and Dr. Joanna Aizenberg, Amy Smith-Berylson Professor of Materials Science, Professor of Chemistry and Chemical Biology and co-Director of the Kavli Institute of Bionano Science and Technology at Harvard University.

Throughout the meeting ACS will feature a wide array of programs and services including the ACS Career Navigator™, your home for ACS Career Services such as the ACS Career Pathways™ and ACS Leadership Development System® workshops as well as Professional Education courses. You can also network and interview with top employers at the ACS Career Fair. For a full list of all activities at the meeting visit the Washington DC career services page.

In the expo hall, ACS will feature numerous opportunities for attendees to participate in raffles and contests for a chance to win exciting prizes throughout the ACS booth!

Stop by to learn about the latest solutions from CAS including SciFinder®, STN®, PatentPak™, NCI™ Global, Science IP®, MethodsNow™ and ChemZent™.

Be Part of a GUINNESS WORLD RECORDS™ Official Attempt for the title of the Largest chemistry lesson at 10 am on August 21st in Ballroom A/B of the Washington Convention Center as ACS Publications tries to break the current record of 1,018 attendees. The attempt will feature a special lecture entitled “Healthy, Tasty, or Toxic: A Chemist’s View of Drinking Water” from Dr. David Sedlak, Editor-in-Chief of Environmental Science & Technology and Environmental Science & Technology Letters.

There will be a number of events at the ACS booth including C&EN’s 3rd annual C&EN Talented 12 honorees that will be unveiled Sunday, August 20. Full profiles will be featured in the Aug. 21 C&EN issue and each member will be presenting their science in a special C&EN Talented 12 Symposium on Aug. 21.

Learn about how you can become a Science Coach at a K-12 school from the ACS Education team and register and submit an abstract for any of the four upcoming ACS Regional Meetings at the ACS Meetings kiosk. You can also provide input about at the ACS Web kiosk to help improve the website so you can find the information you need faster and easier.

ACS members can share their story at and ask the team at the Membership kiosk any questions about the latest benefits of ACS membership.

One of the many benefits is the ACS Member Insurance Program, which offers life, disability, professional liability, and property insurance coverage. There is a special offer at the ACS booth for chemistry educators to receive a complimentary Chemical Educators Legal Liability Consultation.

Finally, don’t leave Washington DC without getting your must-have souvenirs such as Periodic Table of the Elements beach towels, mole key chains, t-shirts and so much more exclusively at the ACS Store.

We look forward to seeing you soon in DC!

Paperthin Device Produces Electricity from the Slowest Human Motions

A device made with sheets of black phosphorus, a two-dimensional semiconducting material, can generate electricity when it is bent or pressed at ultralow frequencies. Incorporated into clothing, the paperthin device could produce electricity by harnessing relatively slow motions like walking, bending, or standing up.

Converting movement into electricity could reduce the need for batteries for low-power wearable or portable devices. Some groups have tried to harvest motion using piezoelectric materials, which turn mechanical force into an electric potential. These devices work best at frequencies around 100 Hz, typical of mechanical vibrations and much higher than human motion. Other groups have developed triboelectric generators that convert friction into electricity. Zhong Lin Wang’s group at Georgia Tech, for example, has demonstrated friction-based devices that generate electricity from walking or other body motions with frequencies as slow as 0.1 Hz.

Researchers at Vanderbilt University developed a wearable device that generates electricity from low-frequency motions. The electrical current that it produces is displayed on a computer monitor.
Credit: Pint Laboratory/Vanderbilt University/YouTube

In the new study, mechanical engineering professor Cary L. Pint and his colleagues at Vanderbilt University report a device that can capture movements with frequencies as low as 0.01 Hz—one-hundredth the rate of a beating heart. That opens up the possibility of generating power during slow motions, such as when someone walks, flexes their muscles, or fidgets in their chair. And unlike other approaches, the foil-like device should be easy to integrate into fabric without affecting its look or feel.

The researchers developed their novel energy-harvesting method based on what’s called strain engineering. The premise is that subtly squeezing or stretching semiconducting materials changes their conductivity. Pint and his colleagues reported last year that bending or pressing electrode materials changes their output voltage and the rate at which ions migrate into or out of the material.

They wanted to see if they could harness that ion movement with battery electrodes made of black phosphorus, a 2-D material that is excellent at storing ions for generating current and responds well to strain. The researchers coated two pieces of copper foil with black phosphorus flakes. They loaded the black phosphorus with sodium ions by pressing the foils against sodium metal and applying an electric current. Then they put the two foil electrodes together, black phosphorus sides facing each other, separated by a thin polypropylene film.

Bending or pressing the device compresses one electrode and stretches the other. Sodium ions travel from the compressed region to the stretched one across the separator, causing electrons to flow and creating current.

The researchers tested the device by bending or pressing it for 10 to 100 seconds and then letting go. It can produce 42 nW of power per cm2 and up to 200 mV right now, which is higher than what state-of-the-art piezoelectric materials produce at that frequency. But Pint says his team is exploring ways to increase that output for charging applications. They are also testing the energy harvesters on human volunteers. The device could also find uses such as tracking human motion for virtual reality applications, Pint adds.

This is a novel method with great potential, says Daniel Deng of Pacific Northwest National Laboratory, who works on piezoelectric energy harvesting systems. Energy-harvesting devices at low frequencies typically have power outputs in the nanowatt range, just like this one does, so the challenge will be increasing the low power output. Deng says the researchers still have a lot of work to do to optimize the performance of their laboratory prototype and turn it into a practical gadget.

This article is reproduced with permission from C&EN (© American Chemical Society). The article was first published on August 15, 2017.