[sharonttt]

Dear all,

As you can see, I am a newbie here, so still getting used to the rules etc. Anyway, I have a question which I am not very sure of right now, which is whether there is any reaction between gold tetrachloride and sodium hydroxide.

I am trying to get gold nanoparticles of preferably below 5nm in size. I have tried using sodium borohydride as the reducing agent for HAuCl4 to get Au and using thioglycolic acid as the capping agent, I was able to get my desired range of Au nanoparticles at room temperature. I was very happy indeed. However, my next step was to inject the gold nanoparticles into another reaction solution which is supposed to be at reflux temperature of 100 deg celsius.

From my 1st attempt, I realised the gold nanoparticles grow to rather big sizes after being heated up to such high temperatures in the reaction solution. Thus, I tried injecting simply HAuCl4 into my reaction solution as my reaction solution already is a basic solution (basisified to pH ~13 by NaOH) and there are capping agents like thioglycerol already present in it. However, after running a XRD on the final dried product, I was not able to find any peaks due to Au. Thus, I made the conclusion that Au nanoparticles were not formed in that condition.

To further confirm, I was wondering if anyone knows if there is any reducing reaction between HAuCl4 and NaOH? From my literature search, most people used either sodium borohydride or sodium citrate as a reducing agent to reduce gold tetrachloride. However, in this case, I need to find out if sodium hydroxide will be able to reduce HAuCl4.

Thank you so much for your help and I do hope to hear from you people soon! Thank you once again and sorry for the long posting.

Shar

[DevaDevil]

I am not sure that it will reduce gold in that way. I am certain that at first sodium hydroxide will transform your chlorauric acid into sodium aurichloride (NaAuCl₄), or at least in the aurichloride complex in solution. But after that with increased amounts of OH^- present... NaOH is basically a weak oxidising agent. And I am not aware of reactions that would have your gold precipitate with only NaOH.

And I have no experience doing it this way either  ; In the lab I was working in we always made Au Nanoparticles deposited on Pt, or whatever other metal by electrodeposition, which gives far less well-defined particles, but good enough for us.

-Dennis

[woelen]

At a pH of 13, so-called aurates are formed, which have formula AuO2(-). The gold is not reduced, however, it remains in solution.

[wildstar]

XRD isn't the best tool for detecting nanoparticles, because they can be amorphous and/or too small to diffract detectably. I had a similar experience with Ni nanoparticles, that didn't give any diffraction pattern, but they were present, as I later saw by transmission electron microscopy (TEM). So I suggest to observe the final product by TEM. The color of the solution gives also indication of the presence of gold nanoparticles, because these solutions are intensely red.

[trueapprentice]

in my experience, we can make au nanoparticles of that size by using NaBH4 + citrate + HAuCl4, but the particles tend to aggregate into bigger ones when u hav a high ionic support, so NaOH seems like it will cause aggregation, so people use thiols to cap the particles to stabilise them, but then the dried stuff u get has to be re-suspended in a non-polar solvent (toluene) with a phase-transfer catalyst

[butcher]

I suggest looking into ferrous sulfate or oxalic or sodium metabisulfate or SO2 gas slowly , metal of higher series ,ect study gold precipitants also minig ect.