Chloride and Salt Contaminated Fresh Water Can Be Cleaned by New Molecule

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One-millionth of a gram of a new molecule in a metric ton of water will be able to capture all of the salt. The new salt-extraction molecule created at Indiana University
(IU) is composed of six triazole “motifs” — five-membered rings composed of nitrogen, carbon and hydrogen — which together form a three-dimensional “cage” perfectly shaped to trap chloride.

The molecule is designed to capture chloride, which is formed when the element chlorine pairs with another element to gain an electron. The most familiar chloride salt is sodium chloride, or common table salt. Other chloride salts are potassium chloride, calcium chloride and ammonium chloride.

It only takes one teaspoon of salt to permanently pollute five gallons of water.

At the same time that the human population continues to grow, the seepage of salt into freshwater systems is reducing access to drinkable water across the globe. In the U.S. alone, the U.S. Geological Survey estimates about 272 metric tons of dissolved solids, including salts, enter freshwater streams per year.

Researchers have created a powerful new molecule for the extraction of salt from liquid.

The molecule is also unique because it binds chloride using carbon-hydrogen bonds, previously regarded as too weak to create stable interactions with chloride compared to the traditional use of nitrogen-hydrogen bonds. Despite expectations, the researchers found that the use of triazoles created a cage so rigid as to form a vacuum in the center, which draws in chloride ions.

By contrast, cages with nitrogen-hydrogen bonds are often more flexible, and their vacuum-like center needed for chloride capture requires energy input, lowering their efficiency compared to a triazole-based cage.

“If you were to take our molecule and stack it up against other cages that use stronger bonds, we’re talking many orders of magnitude of performance increase,” Flood said. “This study really shows that rigidity is underappreciated in the design of molecular cages.”

Science – Chloride capture using a C–H hydrogen bonding cage

Tight binding and high selectivity are hallmarks of biomolecular recognition. Achieving these behaviors with synthetic receptors has usually been associated with OH and NH hydrogen bonding. Contrary to this conventional wisdom, we designed a chloride-selective receptor in the form of a cryptand-like cage using only CH hydrogen bonding. Crystallography showed chloride stabilized by six short 2.7-Å hydrogen bonds originating from the cage’s six 1,2,3-triazoles. Atto-molar affinity (10^17 M–1) was determined using liquid-liquid extractions of chloride from water into nonpolar dichloromethane solvents. Controls verified the additional role of triazoles in rigidifying the 3D structure to effect recognition affinity and selectivity. This cage shows anti-Hofmeister salt extraction and preliminary corrosion inhibition.

22 thoughts on “Chloride and Salt Contaminated Fresh Water Can Be Cleaned by New Molecule”

  1. That’s what I mean about option 4. We can come up with SOME story that makes sense, but only if you completely ignore at least some of what the actual story has written.

  4. Sea my calculation above. (Yes, I did that.)

    TL;DR No, they do not get to desalinate sea water with 1 millionth of a gram per tonne. That’s just stupid.

  5. I count that molecule as having about 40 carbon and nitrogen atoms.

    And it appears to capture one chloride ion per molecule. If we assume that means a Cl- ion then that’s 1 Chlorine atom (weight 35) for 40 carbon and nitrogen atoms (combine weight ~520) a weight ratio of 1: 15. If it’s a full salt NaCl then the mass ratio is 1:9

    One-millionth of a gram of a new molecule in a metric ton of water will be able to capture all of the salt. 

    Well if it only gets one NaCl per molecule then that means it can only capture 1/9 of a millionth of a gram. Then every molecule is full.

    So what could they possibly mean by this apparently nonsensical sentence?

    1. Maybe they mean with recycling? They dump in the salt getter, pull it out, remove the salt, dump it into the water again, continue until all the salt is gone.
    2. Maybe they capture more salt molecules than is shown in the model? Doesn’t really matter. Even if they capture 100 salt molecules per catcher molecule that still only gives them 10 millionths of a gram. Several orders of magnitude less than any salt content that anyone would care about, let alone consider “salty water”
    3. They are lying liars who lie. Possible, but such people generally don’t get to be research chemists. No easily spotted lies anyway.
    4. The journalist has completely mixed up what the original quote was trying to say. It actually meant something completely different. My best guess.

  6. I put about 1 teaspoon of salt in 1 liter (about 0.25 gallons) for drinking purposes if I’m going to be working hard in the sun. It’s perfectly drinkable at 20 times the concentration of 1 tsp/5gallons.

  7. Forward Osmosis is in commercial production, and you can buy FO units online just by googling the name.

    However, FO is rather limited in application. An inherent feature is that you don’t get fresh water, you get a solution of something other than what you started with. eg. Start with a salt water solution, get a sugar water solution.

    Hence it is not a general purpose desalination, and so the market opportunities are small and specialized.

    This is not a failure of the tech, it was all the tech ever offered in the first place.

  9. That is good news. It would take less than 2 metric tons to turn ALL the salt water into fresh water. I wonder how the sea life fare?

  10. There aren’t any OH- ions for it to react with, unless some are added to replace the Cl-. (Technically, there is a tiny amount in equilibrium with H3O+ and water, but we can pretty much ignore those.) If OH- is added, it would usually be added along with some cations (usually more sodium), so this doesn’t answer the question. If there’s some sort of ion exchange membrane or ion exchange resin involved, then maybe. Either way, this would raise the pH, which is usually undesirable.

    Also, in solution, there’s no reaction to form a salt, unless the salt is insoluble (or the concentration is too high, in which case it becomes partially insoluble). As long as all the possible salts are fully soluble, the positive and negative ions remain separate. If new ions are introduced, you just get a different mix of dissolved ions.

    Btw, if you did raise the pH, the bicarbonate and carbonate would be in equilibrium, with a mix of both depending on the pH. The higher the pH, the more carbonate.

  11. Probably initially reacts with OH- ions to form sodium hydroxide, then reacts with dissolved CO2 from the atmosphere to form some kind of “soda’, ie sodium carbonate or bicarbonate.

  12. One-millionth of a gram of a new molecule in a metric ton of water will be able to capture all of the salt.

    What, even if it’s a brine and just short of saturated?

    It only takes one teaspoon of salt to permanently pollute five gallons of water.

    That may be true for some industrial uses but most people would be unlikely to notice that much salt in drinking water. People can safely drink brackish water if they have to.

  13. Like solar power breakthroughs, water treatment ones are also dime a dozen. Whatever happened to Forward Osmosis, something NBF pimped a while back?

  14. He’s not confusing anything. Chloride is the negative ion Cl-, which is formed from chlorine (as the quote says). In any salt, it’s balanced by a positive ion, such as Na+ (sodium cation), K+ (potassium cation), etc.

    In salt water the charges are also balanced, so you have roughly as many positive ions as negative ones (not exactly as many, since some ions like Ca+2 have a bigger charge). The main positive ion in salt water is sodium. If the chloride ions are removed, the sodium ions have to go somewhere too, otherwise the remaining water will become charged.

    So the question remains – if the chloride is removed with this new molecule, where does the sodium go? How is it removed?

    EDIT: A possible answer:
    After some of the chloride is removed, an initial charge separation forms, and then the cations (sodium or otherwise) /should/ naturally flow towards the negatively charged area where the chloride anions have been collected.

  15. Questions?? Can this be made cheaply for desalinization? Is the molecule recyclable so that the system can be used cheaply etc. Otherwise just a nice science experiment.

  17. You’re confusing chloride and chlorine. From the article :

    “The molecule is designed to capture chloride, which is formed when the element chlorine pairs with another element to gain an electron. The most familiar chloride salt is sodium chloride, or common table salt. Other chloride salts are potassium chloride, calcium chloride and ammonium chloride.”

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