Stability of a HAuCl4 solution

[kephra]

It was because of the 'antioxidant' properties of cinnamon that lead me to try it for making nanoparticles.  Excess does not do any harm in any amount I used.
I suggest first making a test batch with glucose or maltodextrin so you have a color sample.
Then make some with your herb of choice and find out how much it takes to match the color of your sample.
Then add 50% more to make sure you have a complete reduction.
Other than that, there is no way to calculate how much you would need.

[LionHeart]

Thats a good suggestion.

I tried making a batch with green tea extract, where I could estimate the amount to use, because I read that 8-12% of dried tea leaves are polyphenols, and the molar weight of some of the most abundant polyphenols in the green tea varies between 250-600 g/mol. So I added the estimated amount of green tea to reduce the gold chloride, assuming that those polyphenols are capable of reducing properly, and then added some extra. However the green tea extract made it impossible to see any color change, because of the dark green/black colors of the green tea, so I had to rely on my estimations. It seem to be an obstacle when using herb, since many will make the solution very dark, and therefore difficult to observe the colors created by gold particles. Any suggestions? Maybe add herbs slowly to the gold chloride to see what happens, and then when the color is changing, add 50 % extra as you suggest, just to be safe.

Im also interested in knowing particle size. Do you know which factors influence size? What is the size of citrate and maltodextrin reduced gold?

[kephra]

Citrate and maltodextrin reduced gold is less than 20 nm.  Color indicates size, which is one of the reasons I would not use highly colored herbals.  Cinnamon extract adds a little color, but not too much.  If your gold is not red, its useless, as Dr. Abraham tested violet an blue reductions and found no physiological effect.  Its harmless, but apparently useless.

[LionHeart]

I know. I will try to slowly add herbs to the gold chloride in my next batch.

You add sodium carbonate to increase pH, it's probably a good idea for me to that as well with the herbs. Does sodium bicarbonate work as effectively?

Do you have any suggestions to how I can store my colloidal gold made with herbs, so that it doesn't grow mold. I've considered adding some colloidal silver, but how about boiling the colloidal gold once it's made. Would that affect colloidal gold properties? particle size?

[kephra]

Forget sodium bicarbonate.  It is not as effective as sodium carbonate because it contains acid as well as base.  Why not use the better of the two? 

[LionHeart]

How about sodium hydroxide? would that do?

Does boiling colloidal gold change its properties?

[kephra]

How about sodium hydroxide? would that do?

Does boiling colloidal gold change its properties?

Sodium hydroxide or potassium hydroxide are ideal.
Once the gold is reduced and stabilized, boiling does not hurt it, and since gold has no antibacterial properties, its probably a good thing to do to help prevent unwanted things from griwing in it.

[LionHeart]

Great. I have some sodium hydroxide. I had to ask, because I wasn't sure if the extra amount of hydroxide ions would react with the antioxidants from the herbs, and use some of the reducing agents that were meant for the gold. But this is not an issue?

[kephra]

It has never been an issue for me.  Sodium hydroxide and sodium carbonate have the same amount of sodium per mole.
Sodium carbonate hydrolyzes to sodium hydroxide and carbonic acid, but carbonic acid is a weak acid, and most of the carbonate exists as carbon dioxide dissolved in the water (non-ionic).  Because of this, the maximum pH for sodium carbonate is a little less than sodium hydroxide.  I used to recommend using sodium hydroxide, but another member suggest sodium carbonate as a safer (to handle) choice, so that is what I do. 
I'm not sure using either is necessary for reduction of gold with polyphenols.  It is necessary when using glucose based reducing agents to convert the glucose ring structure to a linear molecule.  When in its ring form, its not a good reducing agent, but I don't think that applys to polyphenols.

[kephra]

I said:

Sodium hydroxide and sodium carbonate have the same amount of sodium per mole.

What was I thinking?
Sodium carbonate has twice as much sodium per mole as sodium hydroxide!
Na₂CO₃ vs NaOH

Sorry, a few synapses must have blown.

[RickinWI]

When making colloidal silver the electrolyte actually plays 3 roles (I think):
1. Facilitate current flow for the electrolysis.
2. Provide sodium ions to prevent silver from plating the cathode.
3. Raise pH to allow the fructose & dextrose (glucose) rings to break which then provides an electron for the IS to grab and then it can form into silver particles.

So my question is this: If you had a 1 Molar solution of each would they be interchangeable on a 1 : 1 basis ?  From what you just mentioned the Sodium carbonate would provide twice as much silver plate-out protection as NaOH (drop for drop), but what about the other 2 issues?

When it comes to making colloidal gold I guess the only issue is raising the pH to allow the Maltodextrin (or Karo) to work, so would each raise the pH the same amount drop for drop?

[LionHeart]

What was I thinking?
Sodium carbonate has twice as much sodium per mole as sodium hydroxide!
Na2CO3 vs NaOH

Sorry, a few synapses must have blown.

Hehe... That happens sometimes. But the sodium is not so important when reducing gold chloride, right? It is more for electrolysis.

It is necessary when using glucose based reducing agents to convert the glucose ring structure to a linear molecule.

So it is not necessary to raise pH, when using citrate as reducing agent?

When it comes to making colloidal gold I guess the only issue is raising the pH to allow the Maltodextrin (or Karo) to work, so would each raise the pH the same amount drop for drop?

That would depend on the concentrations. If the concentrations are identical, I'm pretty sure NaOH is a stronger base and would raise pH more than sodium carbonate if you added the same amount

[kephra]

So it is not necessary to raise pH, when using citrate as reducing agent?

No, you only need sodium citrate, which is itself basic (Strong base, weak acid).
The citrate method is known as the Turkevich method.  Its slow, requiring a long time at boiling tempseratures.

Hehe... That happens sometimes. But the sodium is not so important when reducing gold chloride, right? It is more for electrolysis.

If reducing the gold with a glucose based sugar, its necessary to raise the pH, so starting with acidic HAuCl₄ you need an alkalizing agent.  So yes, I think it is in this case.

That would depend on the concentrations. If the concentrations are identical, I'm pretty sure NaOH is a stronger base and would raise pH more than sodium carbonate if you added the same amount

Yes, as sodium hydroxide completely dissociates into OH ions, while sodium carbonate hydrolyzes to hydroxide ions and carbonic acid which lowers its pH.

[kephra]

When it comes to making colloidal gold I guess the only issue is raising the pH to allow the Maltodextrin (or Karo) to work, so would each raise the pH the same amount drop for drop?

Sodium carbonate does not raise the pH as much as sodium hydroxide, but does provide more cathode protection. 
Of the three effects the electrolytes give, cathode protection requires the most, so that is the one we are most concerned with.  For that, 1M sodium carbonate is better than 1M sodium hydroxide

[LionHeart]

Btw Kephra, do you know of any way to make smaller particles from a colloidal gold solution with bigger particles, like raising pH, boiling, etc.? I have a purple solution from my ginger method. But it should be possible to make it red, since that happened in the paper i followed. Can I transform it into red?

Im very curious to know about what generally affects particle sizes?