MrDoctor
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Safest way to produce Silver Fluoride from Ammonium Bifluoride
I have a project that ideally requires silver fluoride to produce some nanoparticles of very specific shape and size.
I am unable to purchase silver I fluoride directly as the cost for just 1g is just insane, however, i have silver on hand, and also quite a bit of
ammonium bifluoride. it would be very simple to just make HF but, ive sunken quite a bit of time now into seeing if i couldnt just use the ammonium
bifluoride directly somehow. the furthest i got was that it might be the case that something such as silver chloride or carbonate, if heated with the
ammonium bifluoride, would net a reaction without requiring an aqueous displacement, although since it afaik happens because the ammonium bifluoride
is decomposing, the chemistry gets muddy so, i think its time to defer to people smarter than myself.
otherwise i dont know of any solvent or silver salt combination that could conceivably coax the fluoride away from the ammonia.
Is HF the only reasonable route or is there a way to use ammonium bifluoride (currently aqueous) to produce silver (I) fluoride so that i dont need to
distill HF?
[Edited on 3-3-2025 by MrDoctor]
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teodor
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There are several problems here. If you need the compound of a reasonable purity is definitely better to buy.
Reaction with NH4HF2 most probably will give AgF * 2NH3 * 2H2O on (slow) evaporation. On heating it you will get Ag3N, the fulminating silver
(explosive). (As far as I remember, generally, mixing silver halides and ammonia is not a good idea, the mixture can become explosive just on
standing).
Reaction of carbonate or oxide with aqueous HF will give you the solution but getting dry AgF is not easy. The evaporation should be performed in
vacuum over sulfuric acid and in the absence of light. Just evaporation will give the product contaminated with basic fluoride.
So, if you need relatively safe way I have no idea what is better than HF. But taking in consideration that many chemist here try to avoid just
keeping and handling it (and distillation is out of question for most of us) I can't recommend it until you know what are you doing.
Update: wikipedia gives interesting reaction of thermal decomposition of silver tetrafluoroborate:
AgBF4 -> AgF + BF3
This route requires some experience (BF3 is toxic).
Also it mentions precipitation AgF out of solution with acetone. Probably the way to avoid vacuum evaporation. It's better to check the source it
cites, but I think Ag2O + HF and acetone could be the easiest way.
[Edited on 3-3-2025 by teodor]
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j_sum1
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I am probably missing something obvious here. My silver chemistry is a bit limited.
What would be the problem with reacting solutions of silver nitrate and sodium fluoride and salting out with methanol or ethanol?
Yield would probably be very low if you wanted purity. But the silver is recoverable.
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teodor
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@j_sum1: I thing the salting out could be a problem. It's very soluble. And it fluorinates organic compounds. It fluorinates even I2 to IF5 at higher
temoerature. Not sure, may be somebody have to try.
@MrDoctor : I probably foundcwhat you were asking for. Check Brauer's book in the SM library. Electrolisys of solution of KF in acetic acid with
silver anode. AgF is not so soluble in the acid as it is in water, so it precipitates as crystalls. Looking pretty safe. But don't use NH4+
!! I am wondering, if AgF darkens on light exposure, what is the reaction?
[Edited on 3-3-2025 by teodor]
[Edited on 3-3-2025 by teodor]
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bnull
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It apparently needs water to decompose. The anhydrous salt is quite insensitive, whereas the hydrates are almost as good as the other halides. AgF is
a fluorinating agent, so one possible reaction is 2AgF⋅(H2O)n+ℏν→2Ag++2F−+2nH2O→+Ag2O+(2n−1)H2O+2HF.
In the case of anhydrous silver fluoride, the water that is attacked comes from air.
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teodor
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I supposed so but I'd like to check that. I found some interesting peculiarities in decomposition of fluorides, I will describe them later in the
thread about getting F2. Could you point to any references where they say AgF decomposition is water-dependent?
@Sulaiman : Exactly. Thank you.
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Sulaiman
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just in case it went unnoticed
I realuse that the conditions may not favour it, but from
Wikipedia :
"Silver nitride is often produced inadvertently during experiments involving silver compounds and ammonia, leading to surprise detonations. Whether
silver nitride is formed depends on the concentration of ammonia in the solution. Silver oxide in 1.52 M ammonia solution readily converts to the
nitride, while silver oxide in 0.76 M solution does not form nitride.
Silver oxide can also react with dry ammonia to form Ag3N. Silver nitride is more dangerous when dry; dry silver nitride is a contact explosive which
may detonate from the slightest touch, even a falling water droplet.
It is also explosive when wet, although less so, and explosions do not propagate well in wet deposits of the compound. Because of its long-term
instability, undetonated deposits of Ag3N will lose their sensitivity over time."
CAUTION : Hobby Chemist, not Professional or even Amateur
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woelen
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I myself have some experience with silver, combination with ammonia.
I can say that the danger only exists when you have free ammonia. Ammonium ions do not react with silver ions, e.g. dissolving some silver nitrate in
a solution of ammonium nitrate is not dangerous and does not lead to fulminating silver. If the solution is even more acidic (which is the case in
NH4HF2) then the risk is non-existent. Of course, adding Ag2O may be dangerous, because that leads to formation of ammonia with the ammonium ions. But
if you add a non-alkaline silver salt to the NH4HF2 then I think that is safe. Making AgF from this, however, may be hard.
I think that the "safest" route, which also has good yield, is dissolving Ag2O in aqueous HF and then evaporating to dryness. Using acetone for
crashing out AgF from solution may be a useful thing, but before doing so, I would add a little excess amount of Ag2O to the HF, allow that mix to
stand for several days, so that all HF has reacted with the Ag2O and then allow the excess Ag2O to settle at the bottom. Then you can drive off water
vapor from the solution and in the final stage you add acetone. Still, if you boil off the solution, do this outside, or in a good fume hood, I can
imagine that even with some excess Ag2O, there may still be some unreacted HF. Reactions between oxides of metals and aqueous acids tend to be very
slow, near the end of the reaction and complete neutralization of the acid is hard to reach.
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teodor
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I think it is hard to get AgF from neutral solution because it is prone to hydrolisys and forming basic fluoride. I unable to say how much but in the
first preparation report HF solution was evaporated with stirring. Don't try to follow the procedure :
https://www.jstor.org/stable/112729
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bnull
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No. That's why I used "apparently". So far nothing substantial about the photodecomposition of silver fluoride has appeared. It seems that, due to its
being somewhat less interesting than the other halides with respect to photochemical applications (especially photography), the matter is
under-researched. There were some articles about the use of AgF in caries treatment, the formation of deposits of metallic silver on the surface of
teeth due to interaction of the salt with whatever organics are in the mouth, and none about the salt itself except for a brief mention that it is
more sensitive to UV.
Edit:Typos.
[Edited on 3-3-2025 by bnull]
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clearly_not_atara
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Quote: Originally posted by j_sum1  | I am probably missing something obvious here. My silver chemistry is a bit limited.
What would be the problem with reacting solutions of silver nitrate and sodium fluoride and salting out with methanol or ethanol?
Yield would probably be very low if you wanted purity. But the silver is recoverable. |
I thought you were supposed to salt out AgF with acetone? But you might want to check that you don't ppt NaNO3 along with it. I remember someone
posted a way to do it many years ago.
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MrDoctor
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purity and contamination isnt an issue and the end product desired is an aqueous solution. silver nanoparticles get made which have to be filtered and
washed, so i think the only limitation imposed there is that the reaction shouldnt reverse if water is introduced.
I dont mind converting to sodium/potassium fluoride if that helps. Ill take a look too of what the electrolysis entails.
Im following a paper which creates very specifically shaped silver-gallium nanoparticles, since under sonication, they can convert dissolved CO2 into
graphene and oxygen with supposedly rather high efficiency comparable to large scale existing reactions with, i think supercritical CO2 that is only
viable at scale, but in this case, even gram scale works.
i want to see if i can expand on this, because while they confirmed it works great, the scope was a bit narrow.
[Edited on 4-3-2025 by MrDoctor]
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Precipitates
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Perhaps:
Silver sulphate + calcium fluoride* -> calcium sulphate + silver fluoride?
CaSO4 has extremely poor solubility in methanol, whereas AgF solubility is low (1.5 g/100ml), but manageable. Filter to remove
CaSO4 (and unreacted CaF2), collect the filtrate, evaporate off the methanol and you're done (providing the AgF doesn't react
with methanol, as hinted above).
CaSO4 contamination is likely to be negligible, although depending on the sensitivity of your experiments, may still be noticeable.
*CaF2 has very poor solubility, (Ag2SO4 solubility isn't great either), so this reaction may proceed very slowly. I
would plan to use a quantity of water sufficient to dissolve the products, so should the reaction occur, it would be easy to see whether it has gone
to completion i.e., the solution is no longer hazy.
CaF2 may be produced from ammonium bifluoride by reacting this chemical with calcium chloride.
I may give this preparation a go at some point - but need to buy some calcium fluoride first, and I'm not extremely hopeful that it will work, and
personally have no use for silver fluoride!
Edit: Safest way, but probably won't work 
[Edited on 6-3-2025 by Precipitates]
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MrDoctor
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for some reason i didnt even look at calcium options. calcium sulfate contamination wont be an issue at all, although im seeing a bit of variability
in the figures floating around. i dont trust "insoluble" when the other values are fractions of a gram per liter.
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clearly_not_atara
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| Quote: Originally posted by Precipitates | Perhaps:
Silver sulphate + calcium fluoride* -> calcium sulphate + silver fluoride?
CaSO4 contamination is likely to be negligible, although depending on the sensitivity of your experiments, may still be noticeable.
* |
instead:
Silver perchlorate + potassium fluoride >> KClO4 (s) + AgF (aq)
Obviously the problem is that you need HClO4 (aq).
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RU_KLO
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in the insoluble sulfate idea:
Barium fluoride + silver sulfate.
from wiki:
1) barium fluoride is soluble in methanol/ethanol
2) silver sulfate is soluble in alcohols
3) solubility of barium sulfate in alcohol (It is virtually insoluble in water (285 mg/l at 30 °C) and insoluble in alcohol)
also you may read this info, maybe it could help you:
https://www.sciencedirect.com/science/article/abs/pii/S09277...
Counter-ion effects of silver salt on the production yield of silver nanoparticles in alcohol reduction process
In the fabrication of silver nanoparticles, the reduction of silver ions is an essential step. In the large-scale synthesis of silver nanoparticles
for industrial applications, there are limitations such as economic aspect and side effect of unreduced silver ions. To develop the practical
fabrication methods, various fundamental studies for the reduction of silver ions have been reported. In this study, the effect of counter-ions on the
reduction yield in alcohol reduction process was investigated. AgClO4, AgNO3, AgBF4, AgPF6, and AgF were employed as silver precursors. The UV–vis
spectrum and ISE data show that reduction yield strongly depends on the counter-ions and has the following order: AgF > AgPF6 > AgBF4 > >
AgNO3 > AgClO4. This result was explained based on the role of fluoride ions during the reduction process of silver ions. The reduction yield was
increased as the amount of fluoride ions was increased due to the released free [H+].
Go SAFE, because stupidity and bad Luck exist.
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teodor
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