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tldr: A new method uses copper-doped, cadmium sulfide semiconductor nanocrystals and LED light (405 nm) to break down PFAS quickly and cheaply. Significant dec

tldr: A new method uses copper-doped, cadmium sulfide semiconductor nanocrystals and LED light (405 nm) to break down PFAS quickly and cheaply. Significant decomposition occurs in 1 hour, with complete defluorination in up to 8 hours. This process uses multiphoton absorption to generate highly excited electrons from highly excited states in the nanocrystals. These electrons are capable of breaking down the strong carbon-fluorine bonds in PFAS. Article: https://cleantechnica.com/2024/07/23/researchers-claim-new-process-destroys-forever-chemicals-forever/ https://cleantechnica.com/2024/07/23/researchers-claim-new-p...

kragen 2y ago
i'm guessing that usually a mercury-vapor lamp would be a more economical source of radiation in the 400-nanometer range for this purpose? or have violet leds gotten much cheaper, longer-lived, and brighter since i last checked? oh actually they address this in the paper; they say using mercury vapor lamps is becoming 'less feasible due to regulatory constraints' but if i understand correctly doesn't require the photocatalyst because of the shorter wavelength maybe you could use a less annoying semiconductor (i'm assuming they tried titanium dioxide first, though they don't mention it), but with this method, you'd have to be pretty careful with how you treated the effluent. nanocrystals are a huge pain to filter out of things, and i'd much rather have pfas in my food and water than cadmium sulfide nanocrystals (depending on dose, of course) i sure fucking hope those regulatory constraints don't result in cadmium sulfide nanocrystals in my food
- bejdjndbe 2y ago
  While LED improve continuously, they do not yet achieve neither power nor power/$ of mercury lamps Mercury lamps do however have a strong disadvantage: Mercury There are only a few domains in EU where mercury UV lamps are still allowed (like water treatment) and to my knowledge the phase out is already decided
  - kragen 2y ago
    that's ridiculous, we're talking about metallic mercury in milligram quantities. you can swallow metallic mercury in kilogram quantities without apparent ill effects because its bioavailability is so low thanks for explaining the dismayingly superstitious situation!
    - magicalhippo 2y ago
      Isn't the issue inhaling mercury vapor[1], not eating it for lunch? And lamps will have it in vapor form if they break while running, no? [1]: https://en.wikipedia.org/wiki/Mercury_poisoning#Elemental_mercury https://en.wikipedia.org/wiki/Mercury_poisoning#Elemental_me...
      - kragen 2y ago
        yes, inhaling large amounts of mercury vapor is pretty bad, although still not in the same league as something like methylmercury or cadmium sulfide nanocrystals. i'm not really sure what happens if the lamp breaks while it's running, but i don't think it's a significant risk remember, what we're talking about here are perfectly normal fluorescent tubes, just without the phosphor and the ultraviolet-blocking glass. same thing that was in every office and classroom throughout the latter half of the 20th century. if the tube breaks the broken glass is a much bigger risk than the mercury
hanniabu 2y ago
My question is what are the byproducts after they've broken down?
- deleted 2y ago
  [deleted]
- GenerWork 2y ago
  The paper says that they're decomposed into fluorine ions. Probably some other byproducts as well, but they specifically called out fluorine ions.
  - bamboozled 2y ago
    Are these supposed to be less harmful to living things?
    - bejdjndbe 2y ago
      Significantly. Almost any toothpaste contains Flourine compounds and the US even dumps tons of Flourine into the drinking water to give residents whiter tooth. It's not harmless (nothing is) but much less harmful
      - kurthr 2y ago
        Whitening involves peroxide not fluoride. Fluoride hardens enamel and reduces dental caries (cavities).
    - deleted 2y ago
      [deleted]
    - kragen 2y ago
      not in themselves, but the paper explains that you can easily precipitate them with calcium ions to form fluorite, which is inert and not harmful to living things. in fact reacting with calcium ions to form inert fluorite is the main reason fluoride ions are toxic to living things, because without calcium ions, lots of biological processes fail, most urgently including neurons firing; if you get a possible fluoride overdose they inject you with calcium salts to compensate because of this rapid precipitation, fluoride ions don't really bioaccumulate in the conventional way, but since some of them do deposit in your teeth and bones, chronic exposure can result in fluorosis, which discolors teeth and makes bones harder but more brittle. very high chronic exposure levels cause neurological damage, dementia, etc. 100% natural dementia from mineral water!

kragen 2y ago

i'm guessing that usually a mercury-vapor lamp would be a more economical source of radiation in the 400-nanometer range for this purpose? or have violet leds gotten much cheaper, longer-lived, and brighter since i last checked? oh actually they address this in the paper; they say using mercury vapor lamps is becoming 'less feasible due to regulatory constraints' but if i understand correctly doesn't require the photocatalyst because of the shorter wavelength maybe you could use a less annoying semiconductor (i'm assuming they tried titanium dioxide first, though they don't mention it), but with this method, you'd have to be pretty careful with how you treated the effluent. nanocrystals are a huge pain to filter out of things, and i'd much rather have pfas in my food and water than cadmium sulfide nanocrystals (depending on dose, of course) i sure fucking hope those regulatory constraints don't result in cadmium sulfide nanocrystals in my food

bejdjndbe 2y ago
While LED improve continuously, they do not yet achieve neither power nor power/$ of mercury lamps Mercury lamps do however have a strong disadvantage: Mercury There are only a few domains in EU where mercury UV lamps are still allowed (like water treatment) and to my knowledge the phase out is already decided
- kragen 2y ago
  that's ridiculous, we're talking about metallic mercury in milligram quantities. you can swallow metallic mercury in kilogram quantities without apparent ill effects because its bioavailability is so low thanks for explaining the dismayingly superstitious situation!
  - magicalhippo 2y ago
    Isn't the issue inhaling mercury vapor[1], not eating it for lunch? And lamps will have it in vapor form if they break while running, no? [1]: https://en.wikipedia.org/wiki/Mercury_poisoning#Elemental_mercury https://en.wikipedia.org/wiki/Mercury_poisoning#Elemental_me...
    - kragen 2y ago
      yes, inhaling large amounts of mercury vapor is pretty bad, although still not in the same league as something like methylmercury or cadmium sulfide nanocrystals. i'm not really sure what happens if the lamp breaks while it's running, but i don't think it's a significant risk remember, what we're talking about here are perfectly normal fluorescent tubes, just without the phosphor and the ultraviolet-blocking glass. same thing that was in every office and classroom throughout the latter half of the 20th century. if the tube breaks the broken glass is a much bigger risk than the mercury

hanniabu 2y ago

My question is what are the byproducts after they've broken down?

deleted 2y ago
[deleted]
GenerWork 2y ago
The paper says that they're decomposed into fluorine ions. Probably some other byproducts as well, but they specifically called out fluorine ions.
- bamboozled 2y ago
  Are these supposed to be less harmful to living things?
  - bejdjndbe 2y ago
    Significantly. Almost any toothpaste contains Flourine compounds and the US even dumps tons of Flourine into the drinking water to give residents whiter tooth. It's not harmless (nothing is) but much less harmful
    - kurthr 2y ago
      Whitening involves peroxide not fluoride. Fluoride hardens enamel and reduces dental caries (cavities).
  - deleted 2y ago
    [deleted]
  - kragen 2y ago
    not in themselves, but the paper explains that you can easily precipitate them with calcium ions to form fluorite, which is inert and not harmful to living things. in fact reacting with calcium ions to form inert fluorite is the main reason fluoride ions are toxic to living things, because without calcium ions, lots of biological processes fail, most urgently including neurons firing; if you get a possible fluoride overdose they inject you with calcium salts to compensate because of this rapid precipitation, fluoride ions don't really bioaccumulate in the conventional way, but since some of them do deposit in your teeth and bones, chronic exposure can result in fluorosis, which discolors teeth and makes bones harder but more brittle. very high chronic exposure levels cause neurological damage, dementia, etc. 100% natural dementia from mineral water!