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Airborne Spray that changes colour where Carbon Dioxide is present

  1. Jul 21, 2012 #1
    We are looking to produce a spray changes colour when it comes into contact with Carbon Dioxide. Ideally this would be colourless when sprayed, but become a visible "smoke" where carbon dioxide is present.

    Failing this, we are open to a white "smoke" that changes to coloured where Co2 is present.

    We have looked at the possibility of having Sodium hydroxide mixed with water and a PH indicator in an aerosol, but don't think this will work.

    We are liking "Dangers" comment "vented co2" in the thread https://www.physicsforums.com/showthread.php?t=230130

    Is there a possibility we use something like a smoke/fog machine solution in an aresol that also contains a ph indicator that changes colour where Co2 is present?

    Many thanks in advance,

  2. jcsd
  3. Jul 21, 2012 #2
    Ammonia will react with H2O and CO2 to make a white fog of ammonium carbonate or bicarbonate when all are present at appreciable quanties, but it is so hygroscopic that the xtals dissipate as small solution droplets that are essentially invisible. I would also steer clear of using aqueous caustic aerosols.

    An aerosol of minute droplets, even if it has a colored base liquid is not likely to show up as colored- however, a fluorescent pH indicator might be just the ticket for visualizing H+ in droplets. You would need darkness and a black light (UV) to visualize; the next step is how to determine the level of CO2 that one wants to distinguish, and to determine if the test is to be used for quantifying the CO2.

    The issue here is that ambient CO2 is at trace levels in air (3.5 ppth), and it has to penetrate the liquid droplet air/ water interface, then slowly react with water to form bicarbonate and H+ (a reversible equilibrium). Here you can take advantage of nature- the carbonic anhydrase enzyme is one of the fastest known enzymes, and catalyzes this reaction. According to the Wiki article, you have a whole range of types of carbonic anhydrases to choose, and the reaction could be sped up to a diffusion controlled process.

    Enzymes tend to be allergens in aerosol, have specific pH ranges and temperatures they function in, and can be denatured or inhibited by physical and chemical means so this wouldn't be a friendly way to do this without some research. As long as the fluorescent pH indicator doesn't act as an inhibitor to the enzyme, and the enzyme and its required factors don't act to quench the fluoresence, then you have a chance to try it in multi-well plates with minute amounts, to study the reaction and variations in buffer capacity of each well...

    Let LeChatlier's principle help you design the buffer capacity of the individual droplet to max the signal for the amount you wish to visualize. If the fluorescent pH indicator can be picked such that it will distinguish the pKa of the carbonic acid/ bicarbonate buffer, and the droplets made to have a quantifiable amount of buffer capacity, this could work even in ambient air, and slightly enriched (below 1% or 10ppth CO2)!

    It could then give you a go /no-go pump spray to visualize pockets of CO2 gas in a darkened box lit by black lights such as a terrarium. It actually sounds like a fun project ;-)
    Last edited: Jul 21, 2012
  4. Jul 24, 2012 #3
    Very interesting idea one of our fellows tried to get some that would glow under black light years ago without success it was either toxic or smelled really bad.Today we are still using the CO2meters with the NDIR sensor. Like these www.co2meter.com.
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