Lead levels in drinking water spike when copper and lead pipes joined: Levels linked to galvanic corrosion, disinfectants, pH

Lead pipes once used routinely in municipal water distribution systems are a well-recognized source of dangerous lead contamination, but new research from Washington University in St. Louis suggests that the partial replacement of these pipes can make the problem worse.

The research shows that joining old lead pipes with new copper lines using brass fittings spurs galvanic corrosion that can dramatically increase the amount of lead released into drinking water supplies.

"Work done in our laboratory shows galvanic corrosion in joined service lines is significant and lasts for a long time," says Dan Giammar, PhD, the Harold D. Jolley Career Development Associate Professor in the Department of Energy, Environmental & Chemical Engineering at Washington University in St. Louis.

His study, published in the Proceedings of the 2011 Water Quality Technology Conference, suggests that safety-minded, lead-pipe-removal programs at water utilities across the country actually may be increasing the risk of lead exposure for water customers.

An experiment running in his aquatic chemistry lab shows why. It features 80- to 100-year-old lead water pipes that were dug out of the ground in Washington, D.C., and shipped to his St. Louis laboratory. Some of the lead pipes have been cut and then joined with brass couplings to brand new copper pipe.

This setup mimics what happens if a utility company is replacing lead service lines and homeowners decline to have their sections of the lines replaced.

A service line runs from the main to the home. The utility owns the part from the main to the homeowner's property line and the homeowner owns the part from the property line to the house. The utility cannot replace the homeowner's half of the line unless the homeowner gives permission and pays for replacement. In the U.S. only 10 percent of homeowners agree to the charge.

"Since you started with a whole lead pipe and you now have half a lead pipe, you might think your problem would be half of what it was or -- maybe -- completely unchanged," Giammar says.

His experiment reveals that instead, it could be far worse. The joined lead-copper pipe in his lab releases five times more lead than did the original lead pipe.

The lead is released by galvanic corrosion, a process set up whenever two dissimilar metals are immersed in a conducting liquid.

The same thing happens if lasagna or another acidic dish is made in a stainless steel pan, covered with aluminum foil, and placed in a refrigerator. The two metals and the lasagna act as a galvanic cell, and some of the aluminum may migrate out of the foil and plate out on the surface of the lasagna.

The old lead pipes from Washington, D.C., must be "conditioned" for several months before they'd start behaving the way they behaved when they were buried in the ground, Giammar (right) explains to doctoral candidates Yin Wang and Vrajesh Mehta. To condition them, the pipes are filled daily with water that simulates district water.

The Lead and Copper Rule

The project to measure galvanic corrosion of lead pipes was the third Giammar has done for the Water Research Foundation, an organization of water utilities that allows them to pool their money to support research on problems of common interest.

Giammar, who calls himself a heavy metals guy, did his doctoral work on uranium contamination of soil and groundwater, work relevant to the far-flung branches of the Manhattan Project that purified uranium for the atomic bomb during World War II.

He still works on uranium remediation, but when he moved to St. Louis in 2002, he thought that he really ought to work on lead as well, because Missouri has historically been one of the two largest lead-producing states in the country. The other is Alaska.

Giammar began with experiments directed at understanding exactly what happens when phosphates are worked into lead contaminated soil. Under the right conditions, the phosphate will bind to the lead and immobilize it.

Phosphate remediation of lead contaminated soils had been successful in Joplin, Mo., a town located in the Tri-State district, an historic lead-zinc mining district that takes in parts of Missouri, Kansas and Oklahoma.

While Giammar was working with phosphates and soils, the media began reporting that lead levels in the tap water in Washington, D.C., were higher than before and indeed were higher than national drinking water standards allowed.

Lead, as Giammar says, is a "xenobiotic" element (literally foreign to living systems). Unlike some metals, it serves no biological purpose and only does harm. But lead pipes weren't outlawed in new construction until 1978.

That the district knew it had a problem was remarkable in itself. The levels of lead in drinking water weren't regulated until 1991, when the Lead and Copper Rule was passed.

The lead levels in Washington, D.C., drinking water began to rise in 2001.

The case of water in Washington, D.C.

The lead levels rose for an interesting reason, says Giammar. The district water utility was trying to improve water quality.

In the U.S., he explains, water is delivered with a disinfectant still in it. There are two ways of chlorinating water to disinfect it. Utilities either use free chlorine, which is essentially bleach, or they use chloramines, which are essentially bleach combined with ammonia.

Free chlorine is a better disinfectant but it also forms higher concentrations of chlorinated disinfection byproducts -- things like chloroform -- that we don't want in our drinking water, Giammar says.

In an effort to decrease the concentrations of disinfection byproducts, the district switched from chlorine to chloramine.

This is where the water chemistry comes in. "The lead pipe, in itself, is not much of a concern," Giammar says. Pure lead, lead 0 as it's called, is not particularly reactive or soluble, which is one of the reasons people made plumbing out of it. Lead pipes last much longer than iron pipes.

But lead can oxidize -- essentially corrode. The lead species that then form determine how much lead ends up in the water. The various forms of lead in the +2 oxidation state are all more soluble than lead 0, but lead sulfate is more soluble than lead carbonate, which is in turn more soluble than lead phosphate. (The oxidation state of an element is a rough measure of how many electrons it has "lost to other, nearby elements that are attracting the electrons more strongly.)

When it comes to lead in the +4 oxidation state there's a twist.

"If you have a strong oxidant, you can form species with lead in the +4 oxidation state," Giammar says. "These have very low solubility but they're only stable in the presence of a strong oxidant. As soon as the strong oxidant goes away, the lead +4 is no longer stable. It starts to come back to lead +2, and it can release the lead quite quickly."

The free chlorine the district had been using is a very strong oxidant. The chloramines they switched to are less strong.

"So when they switched to chloramines, the pipe scale that had formed over years of chlorine treatment began to release lead into the water," Giammar says. It was a classic example of an unintended consequence.

What the district case demonstrates, Giammar says, is that tap water is a manufactured product, not a natural resource. The water leaving the treatment plant can have essentially no lead in it, but by the time it reaches the faucet that could have changed.

The lead comes from the piping, but whether it is released depends on the chemistry of the water running through the distribution system.

Looking at water chemistry

When he read about the district problem, Giammar wrote a proposal to the Water Research Board offering to study the chemistry of the insides of pipes, particularly the dissolution rates of lead phosphates, lead carbonates and the lead +4 oxides, as a function of pH, added phosphate and disinfectants.

"That was our first entry into the field of lead and drinking water," he says.

"We knew pH would be an important variable," he says. "You don't want your pH to fall too low, especially for the lead carbonates, which dissolve at lower pH."

"But we didn't realize how important pH was. We studied water samples with a pH of 10, 8.5 and 7.5. You wouldn't think there would be a much of a difference between a pH of 8.5 and 7.5, but there was.

"In some cases, the pH made the difference between a lead concentration that met the drinking water standard and one that didn't."

St, Louis water

"You might be surprised to know that the pH of St. Louis drinking water is 9 to 9.5," Giammar says, "much higher than the pH of distilled water, which is 7."

In fact, it is heading toward milk-of-magnesia territory.

He explains that the pH of the Missouri River is about 8, because the river flows through limestone, which makes the water somewhat alkaline.

The limestone also makes the water hard, meaning it contains high levels of calcium and magnesium. So when it reaches the St. Louis water treatment plants, the pH is raised to between 10 and 11 to precipitate out some of the calcium carbonate and soften the water. The water utility then lets the pH drift back down to somewhere between 9 and 9.5 before the water is delivered.

"It's a nice stable water with good water chemistry," Giammar says. "Quite non-corrosive, has a good stable pH. They do all right with their distribution system," he says.

By the way, St. Louis water is disinfected with chloramines rather than chlorine.

Phosphate also turned out to be important. "It had a huge impact on the dissolution rates of all the lead corrosion products we studied," says Giammar.

So one way to bring down lead levels is to add phosphate. But phosphate costs money, so the utilities want to add as little of it as they can to produce a good-quality water.

"It's never going to be a one-size-fits all solution because the source-water compositions are different," says Giammar, "but we came up with some pretty strong recommendations."

The final report on the project, "Influence of Water Chemistry on the Dissolution and Transformation Rates of Lead Corrosion Products," was published last year.

Should you let the tap run?

"Another thing we studied in that first project," Giammar says, "was whether we should be more worried about reaction rates or about the equilibrium state of the reactions.

"To put it another way, if you let the water sit in the pipes for six hours, will it be different from water that sat in the pipes for only an hour?"

It turned out that most lead species dissolve relatively quickly, so reaction rates are not particularly important. The water is the same no matter how long the water has been sitting in the pipes.

But this isn't true of the lead +4 oxides, the material that formed the scale inside the Washington, D.C., pipes. "They are never at equilibrium with the water flowing over them," Giammar says. "Instead everything depends on the rate at which those oxides form or the rate at which they dissolve."

So Giammar proposed a second project for the Water Research Foundation just to study the lead +4 oxides. "They're fascinating solids," he says.

Then Giammar's lab picked up a third project. "A little over a year ago, I got a call from an environmental engineer in Washington, D.C., who was looking at something called galvanic corrosion and its potential to release lead into drinking water," he says.

This is the project that led to the centenarian lead pipe experiment now taking up much of the bench space in his lab.

Unlike some of the other water problems he has studied, galvanic corrosion is national in scope. The Environmental Protection Agency is concerned enough that it has appointed a science advisory board to make recommendations on how best to deal with it, Giammar says.

How low can we go?

It's difficult to talk about lead in a sensible way. The current threshold for drinking water is 15 micrograms per liter, Giammar says. And while there's talk in the community about lowering the allowable levels of some water contaminants, lead is not among them.

Environmental lead is ubiquitous and everyone has measurable levels of lead in their blood. We are exposed to it through dust and air as well as through water, thanks in part to the tetraethyl lead added to gasoline as an antiknock compound for 80 years.

"If your dominant exposure is through dust, there's little benefit to ratcheting down your exposure to water even further," Giammar says.

But, he says, because of the Lead and Copper Rule, water utilities now monitor lead levels. And he learned at a recent conference that during the most recent monitoring period, only 30 utilities had lead levels above the drinking water standard.

That may seem like a lot, he said, but there are roughly 54,000 water utilities in the U.S.

Story Source:

The above story is reprinted from materials provided by Washington University in St. Louis. The original article was written by Diana Lutz.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Graphene grows better on certain copper crystals

New observations could improve industrial production of high-quality graphene, hastening the era of graphene-based consumer electronics, thanks to University of Illinois engineers.

By combining data from several imaging techniques, the team found that the quality of graphene depends on the crystal structure of the copper substrate it grows on. Led by electrical and computer engineering professors Joseph Lyding and Eric Pop, the researchers published their findings in the journal Nano Letters.

"Graphene is a very important material," Lyding said. "The future of electronics may depend on it. The quality of its production is one of the key unsolved problems in nanotechnology. This is a step in the direction of solving that problem."

To produce large sheets of graphene, methane gas is piped into a furnace containing a sheet of copper foil. When the methane strikes the copper, the carbon-hydrogen bonds crack. Hydrogen escapes as gas, while the carbon sticks to the copper surface. The carbon atoms move around until they find each other and bond to make graphene. Copper is an appealing substrate because it is relatively cheap and promotes single-layer graphene growth, which is important for electronics applications.

"It's a very cost-effective, straightforward way to make graphene on a large scale," said Joshua Wood, a graduate student and the lead author of the paper.

"However, this does not take into consideration the subtleties of growing graphene," he said. "Understanding these subtleties is important for making high-quality, high-performance electronics."

While graphene grown on copper tends to be better than graphene grown on other substrates, it remains riddled with defects and multi-layer sections, precluding high-performance applications. Researchers have speculated that the roughness of the copper surface may affect graphene growth, but the Illinois group found that the copper's crystal structure is more important.

Copper foils are a patchwork of different crystal structures. As the methane falls onto the foil surface, the shapes of the copper crystals it encounters affect how well the carbon atoms form graphene.

Different crystal shapes are assigned index numbers. Using several advanced imaging techniques, the Illinois team found that patches of copper with higher index numbers tend to have lower-quality graphene growth. They also found that two common crystal structures, numbered (100) and (111), have the worst and the best growth, respectively. The (100) crystals have a cubic shape, with wide gaps between atoms. Meanwhile, (111) has a densely packed hexagonal structure.

"In the (100) configuration the carbon atoms are more likely to stick in the holes in the copper on the atomic level, and then they stack vertically rather than diffusing out and growing laterally," Wood said. "The (111) surface is hexagonal, and graphene is also hexagonal. It's not to say there's a perfect match, but that there's a preferred match between the surfaces."

Researchers now are faced with balancing the cost of all (111) copper and the value of high-quality, defect-free graphene. It is possible to produce single-crystal copper, but it is difficult and prohibitively expensive.

The U. of I. team speculates that it may be possible to improve copper foil manufacturing so that it has a higher percentage of (111) crystals. Graphene grown on such foil would not be ideal, but may be "good enough" for most applications.

"The question is, how do you optimize it while still maintaining cost effectiveness for technological applications?" said Pop, a co-author of the paper. "As a community, we're still writing the cookbook for graphene. We're constantly refining our techniques, trying out new recipes. As with any technology in its infancy, we are still exploring what works and what doesn't."

Next, the researchers hope to use their methodology to study the growth of other two-dimensional materials, including insulators to improve graphene device performance. They also plan to follow up on their observations by growing graphene on single-crystal copper.

"There's a lot of confusion in the graphene business right now," Lyding said. "The fact that there is a clear observational difference between these different growth indices helps steer the research and will probably lead to more quantitative experiments as well as better modeling. This paper is funneling things in that direction."

Lyding and Pop are affiliated with the Beckman Institute for Advanced Science and Technology at the U. of I. The Office of Naval Research, the Air Force Office of Scientific Research, and the Army Research Office supported this research.

Story Source:

The above story is reprinted from materials provided by University of Illinois at Urbana-Champaign.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Joshua D. Wood, Scott W. Schmucker, Austin S. Lyons, Eric Pop, Joseph W. Lyding. Effects of Polycrystalline Cu Substrate on Graphene Growth by Chemical Vapor Deposition. Nano Letters, 2011; : 111004083339002 DOI: 10.1021/nl201566c

Click chemistry with copper -- a biocompatible version

Berkeley Lab researchers have found a way to make copper-catalyzed click chemistry biocompatible. By adding a ligand that minimizes the toxicity of copper but still allows it to catalyze the click chemistry reaction, the researchers can safely use their reaction in living cells.

Biomolecular imaging can reveal a great deal of information about the inner workings of cells and one of the most attractive targets for imaging are glycans – sugars that are ubiquitous to living organisms and abundant on cell surfaces. Imaging a glycan requires that it be tagged or labeled. One of the best techniques for doing this is a technique called click chemistry. The original version of click chemistry could only be used on cells in vitro, not in living organisms, because the technique involved catalysis with copper, which is toxic at high micromolar concentrations. A copper-free version of click chemistry that can safely be used in living organisms is available, but it is not always optimal in terms of reaction kinetics and target specificity. Now, a variation of click chemistry has been introduced that retains the copper catalyst of the original reaction - along with its speed and specificity – but is safe for cells in vivo.

Researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with researchers at the Albert Einstein College of Medicine at Yeshiva University in New York, have found a way to make copper-catalyzed click chemistry biocompatible. By adding a ligand that minimizes the toxicity of copper but still allows it to catalyze the click chemistry reaction, the researchers can safely use their reaction in living organisms. Compared to the copper-free click chemistry reaction, which can take up to an hour, the ligand-accelerated copper-catalyzed click chemistry reaction can achieve effective labeling within 3-5 minutes. The presence of the copper catalyst also enables this new formulation of click chemistry to be more target-specific with fewer background side reactions.

"The discovery of this new accelerating ligand for copper-catalyzed click chemistry should provide an effective complimentary tool to copper-free click chemistry," says Yi Liu, a chemist with Berkeley Lab's Molecular Foundry and the co-leader of this research with Peng Wu, of the Albert Einstein College of Medicine.

"While copper-free click chemistry may have advantages for whole animal imaging experiments such as imaging in mice," Liu says, "our ligand-accelerated copper reaction is better suited for enriching glycoproteins for their identification."

The ligand-accelerated copper-catalyzed reaction was used to label glycans in recombinant glycoproteins, glycoproteins in cell lysates, glycoproteins on live cell surfaces, and glycoconjugates in live zebrafish embryos. Because a zebrafish embryo is transparent in the first 24 hours of its development, it allows labeled glycans to be detected via molecular imaging techniques, making it a highly useful model for developmental biology studies.

"Based on our results," says Peng Wu, "we believe that ligand-accelerated copper-catalyzed click chemistry represents a powerful and highly adaptive bioconjugation tool that holds great promise for further improvement with the discovery of more versatile catalyst systems."

Click chemistry, which was introduced in 2002 by the Nobel laureate chemist Barry Sharpless of the Scripps Research Institute, utilizes a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction that makes it possible for certain chemical building blocks to "click" together in an irreversible linkage, analogous to the snapping together of Lego blocks. While the technique immediately proved valuable for attaching small molecular probes to various biomolecules in a test tube or on fixed cells, it could not be used for biomolecule labeling in live cells or organisms because of the copper catalyst.

In 2007, Carolyn Bertozzi, a chemist who holds joint appointments with Berkeley Lab, the University of California (UC) Berkeley, and the Howard Hughes Medical Institute, led a research effort that produced a copper-free version of click chemistry. In this version, glycans were metabolically labeled with azides - a functional group featuring three nitrogen atoms - via reactions that were carried out through the use of cyclooctyne reagents that required no copper catalyst. With their latest reagent, biarylazacyclooctynone (BARAC), Bertozzi and her group have provided a copper-free click chemistry technique that delivers relatively fast reaction kinetics and the bioorthogonality needed for biomolecule labeling. However, the technique can only be used on biomolecules that can be tagged with azides.

"Our bio-benign ligand-accelerated copper-catalyzed click chemistry reaction liberates bioconjugation from the limitation where ligations could only be accomplished with azide-tagged biomolecules," Liu says. "Now terminal alkyne residues can also be incorporated into biomolecules and detected in vivo."

Provided by Lawrence Berkeley National Laboratory (news : web)

Click chemistry with copper: A biocompatible version

Biomolecular imaging can reveal a great deal of information about the inner workings of cells and one of the most attractive targets for imaging are glycans -- sugars that are ubiquitous to living organisms and abundant on cell surfaces. Imaging a glycan requires that it be tagged or labeled. One of the best techniques for doing this is a technique called click chemistry. The original version of click chemistry could only be used on cells in vitro, not in living organisms, because the technique involved catalysis with copper, which is toxic at high micromolar concentrations.

A copper-free version of click chemistry that can safely be used in living organisms is available, but it is not always optimal in terms of reaction kinetics and target specificity. Now, a variation of click chemistry has been introduced that retains the copper catalyst of the original reaction -- along with its speed and specificity -- but is safe for cells in vivo.

Researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with researchers at the Albert Einstein College of Medicine at Yeshiva University in New York, have found a way to make copper-catalyzed click chemistry biocompatible. By adding a ligand that minimizes the toxicity of copper but still allows it to catalyze the click chemistry reaction, the researchers can safely use their reaction in living organisms. Compared to the copper-free click chemistry reaction, which can take up to an hour, the ligand-accelerated copper-catalyzed click chemistry reaction can achieve effective labeling within 3-5 minutes. The presence of the copper catalyst also enables this new formulation of click chemistry to be more target-specific with fewer background side reactions.

"The discovery of this new accelerating ligand for copper-catalyzed click chemistry should provide an effective complimentary tool to copper-free click chemistry," says Yi Liu, a chemist with Berkeley Lab's Molecular Foundry and the co-leader of this research with Peng Wu, of the Albert Einstein College of Medicine.

"While copper-free click chemistry may have advantages for whole animal imaging experiments such as imaging in mice," Liu says, "our ligand-accelerated copper reaction is better suited for enriching glycoproteins for their identification."

The ligand-accelerated copper-catalyzed reaction was used to label glycans in recombinant glycoproteins, glycoproteins in cell lysates, glycoproteins on live cell surfaces, and glycoconjugates in live zebrafish embryos. Because a zebrafish embryo is transparent in the first 24 hours of its development, it allows labeled glycans to be detected via molecular imaging techniques, making it a highly useful model for developmental biology studies.

"Based on our results," says Peng Wu, "we believe that ligand-accelerated copper-catalyzed click chemistry represents a powerful and highly adaptive bioconjugation tool that holds great promise for further improvement with the discovery of more versatile catalyst systems."

Click chemistry, which was introduced in 2002 by the Nobel laureate chemist Barry Sharpless of the Scripps Research Institute, utilizes a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction that makes it possible for certain chemical building blocks to "click" together in an irreversible linkage, analogous to the snapping together of Lego blocks. While the technique immediately proved valuable for attaching small molecular probes to various biomolecules in a test tube or on fixed cells, it could not be used for biomolecule labeling in live cells or organisms because of the copper catalyst.

In 2007, Carolyn Bertozzi, a chemist who holds joint appointments with Berkeley Lab, the University of California (UC) Berkeley, and the Howard Hughes Medical Institute, led a research effort that produced a copper-free version of click chemistry. In this version, glycans were metabolically labeled with azides -- a functional group featuring three nitrogen atoms -- via reactions that were carried out through the use of cyclooctyne reagents that required no copper catalyst. With their latest reagent, biarylazacyclooctynone (BARAC), Bertozzi and her group have provided a copper-free click chemistry technique that delivers relatively fast reaction kinetics and the bioorthogonality needed for biomolecule labeling. However, the technique can only be used on biomolecules that can be tagged with azides.

"Our bio-benign ligand-accelerated copper-catalyzed click chemistry reaction liberates bioconjugation from the limitation where ligations could only be accomplished with azide-tagged biomolecules," Liu says. "Now terminal alkyne residues can also be incorporated into biomolecules and detected in vivo."

This work was supported by a grant from the National Institutes of Health, and in part as a User Project at the Molecular Foundry, which is funded through DOE's Office of Science.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

Christen Besanceney-Webler, Hao Jiang, Tianqing Zheng, Lei Feng, David Soriano del Amo, Wei Wang, Liana M. Klivansky, Florence L. Marlow, Yi Liu, Peng Wu. Increasing the Efficacy of Bioorthogonal Click Reactions for Bioconjugation: A Comparative Study. Angewandte Chemie International Edition, 2011; DOI: 10.1002/anie.201101817

Copper ions as morphogens for the formation of polymer films by click chemistry

Scientists are envious of nature because of its ability to build up highly complex structures like organs and tissues in an ordered fashion without any problem; it takes a great deal of effort for scientists to produce defined microscale structures. Pierre Schaaf and a team of scientists from Strasbourg have now imitated a few of nature’s tricks in order to get a polymer film to "grow" onto a surface. As the researchers report in the journal Angewandte Chemie, they used morphogens as nature does. These signal molecules show a reaction which way it should go.

The growth of our bones, seashells, or the complicated forms of diatoms, requires the processes involved in biomineralization to occur along precisely controlled tracks. Molecules cannot simply be allowed to react in an uncontrolled fashion as soon as they encounter each other. In order for a complex organism to develop, every individual cell must know where it is located within a growing organ. Special signal molecules called morphogens inform the cell. They are formed in a specific location and then spread out into the surrounding tissue. This results in concentration gradients, which the cells can use to "orient" themselves.

Schaaf and his co-workers chose a similar strategy to form thin films on a substrate. They also used a sort of morphogen to steer the process. The reactants involved were polymers, one containing azide groups (–N3) and the other with alkyne groups (–C?CH) as side chains. In the presence of positively charged copper ions (CuI), these groups react with each other to form a carbon- and nitrogen-containing five-membered ring, crosslinking the polymers. This type of reaction is called “click chemistry”, because the reaction partners simply snap together.

In a solution containing both click partner and CuI ions, the reaction would immediately proceed at random. This would not result in a thin polymer film. The scientists’ idea was thus to place the CuI ions as a morphogen only on the surface to be coated. Their approach was to place CuII ions in the solution. They then applied an electric voltage to the surface. When CuII ions come into contact with this surface, they take an electron to become CuI. These are thus primarily to be found on the surface. Where there are CuI ions, the click reaction can proceed; the polymers only crosslink into a continuous film on the surface. The magnitude of the applied voltage can be used to control the number of CuI ions and thus the thickness of the film.

More information: Pierre Schaaf, Electrochemically Triggered Film Formation by Click Chemistry, Angewandte Chemie International Edition 2011, 50, No. 19, 4374–4377, http://dx.doi.org/ … ie.201007436

Provided by Wiley (news : web)