Low-Cost Method to Decompose PFAS Using LED Light and Semiconductor Nanocrystals | Hacker News Reader

Low-Cost Method to Decompose PFAS Using LED Light and Semiconductor Nanocrystals

onlinelibrary.wiley.com

29 pointsJimmc41426 comments

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-p...

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

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

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!

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_me...

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

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

The paper says that they're decomposed into fluorine ions. Probably some other byproducts as well, but they specifically called out fluorine ions.

Are these supposed to be less harmful to living things?

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!

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

Whitening involves peroxide not fluoride.

Fluoride hardens enamel and reduces dental caries (cavities).

Is "forever" chemicals a stupid name for these things? I've seen a few different articles about how these things can be decomposed. I guess it's "forever" because there are no know "natural" processes that break these things down ?

The term of art is “persistent organic pollutants” which I think falls on the diametric opposite end of the spectrum: it’s far too clinical to covey any information to laymen. “Forever chemicals” at least somewhat conveys the core problem to the masses.

taken literally, though, 'forever chemicals' would seem to apply equally well to helium, neon, xenon, zircon, alumina, and maybe silica

silica could even be described as a 'carcinogenic forever chemical'. inhaling silica dust is almost certainly worse for you than inhaling teflon dust. should people who want to avoid forever chemicals move someplace without naturally occurring silica?

to the extent that they're actually 'forever' they're pretty inert and not much of a problem. the likely pollution problem is not teflon (though maybe it behaves differently as nanoparticles) but the much less inert species like pfoa, which have significant toxicity precisely because they're less stable

It’s a shorthand for news articles intended for laypeople but it gets the point across; no natural processes yet found break down these compounds and in small but measurable quantities they build up in our environment. It’s not practical to say, treat all sewage effluent or refuse going to recycling / landfill / incineration to break them down so they build up and we don’t really know what they will end up doing. So for most practical purposes, yes they’re not going anywhere.

As with plastics, they are forever in only a hyperbolic sense. However, there are few, if any, biological processes that decompose them, and they are quite stable even in rough environments like direct sunlight and ocean water.

On the timelines that they are stable, the risk is that they will enter the food chain bioaccumulation will poison everything.

It's not merely a risk; it's already materialized. They already have entered the food chain. Almost all Americans have it in their blood. They already have poisoned everything. They're a part of sewage that is used to fertilize fields and livestock. They're even used in pesticides now, intentionally sprayed on food.

I saw a report where condoms have high amount of PFAs in them, like wtf?

The chemicals are probably used in condoms to help latex repel moisture and liquid. [1]

This is where trust in intuitions is breaking down in my opinion, all through high school it's "always wear a condom", which is yes, good advice, but now it turns out your condom was poisoning you and your partner ?

Penis and vagina skin is thin and the organs have a high level of blood vessels, which makes them particularly dangerous organs to expose to PFAS, Linda Birnbaum, a science adviser for Mamavation who previously ran the Environmental Protection Agency’s toxicology program, wrote in the report.

“The vagina and penis are incredibly vascular areas and dermal exposure to these areas are often higher than other places of the body,” Birnbaum said.

How these products were allowed to proliferate literally everywhere with so little oversight is absolutely crazy to me.

I have seen fire fighters discharge this stuff into rivers for "training". The river is now closed for swimming due to dangerous levels of chemicals.

[1] https://www.theguardian.com/environment/article/2024/jul/28/...

As kids we used to play in the (presumably PFAS) foam the firefighters filled a meadow with during county fairs. It was fun.

https://www.mamavation.com/health/condoms-lubricants-pfas-fo...

There's a lot more research showing the consequences of exposure to your partner than there are to PFAS.

Corporations have a fiduciary duty to poison us. What are you? A communist.

https://en.wikipedia.org/wiki/Dodge_v._Ford_Motor_Co.

Chernobyl never poisoned anyone.

Whataboutism.

Pretty shitty really, I absolutely hate they we have done stuff like this.

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