One of the most explored and studied routes for gold nanoparticles synthesis is the tetrachloroauric acid (HAuCl4) and citrate as a reducing agent, under stirring and heating. One of the major drawbacks researchers still try to cope with is mono dispersibility and reproducibility. Though the last is almost only a matter of doing everything exactly the same way as before, the former seems to be linked to reaction variables such as pressure, temperature and mixing. Nucleation and growth might take place at the same time, and that is not desirable for a near monodisperse nanoparticle synthesis: one wants all the nuclei to form as quick as possible in the beginning and then grow from that without further nucleation. I've been trying to stop a AuNP reaction a few moments after it starts, so as to get really small (2 - 4 nm) seeds/nuclei, even if there is still Au3+ ions left. What I do next is I change the reaction variables in a way that the reaction takes place under controlled parameters and in slow speed, so I can stop it. The major problem so far has been citrate. Even if I can withdraw free Gibbs energy from the system (as to stop any thermodynamic activated reaction), there's still citrate left there to now-and-then react with III-auric ion.Question is: is there something that would react with citrate and consume it and leave the Au ions alone? Maybe an oxidant?
Interesting question - maybe some capping agent may work - preventing the agglomeration of the AuNPs ... good luck, Dirk
Do not know because this is not my subject, has anyone tried anionic surfactants or polyelectrolytes?
I know that organic capping agents may work (see
J. Synchrotron Rad. (2007). 14, 477-482 [ doi:10.1107/S0909049507044743 ])
However the route is a bit different ...
And what is going on when you simply play with Au or citrate concentrations? Your reaction stops with the end of substrates, doesn`t it?
Problem with adding the oxidant is that you have 3:1 chance that it will oxidise your NPs. Similar situation could be with surfactants and polyelectrolytes - they probably will firstly attack the NPs.
Share the answer with us when you manage to do that :) Good luck :)
Tartarate can be used because it is milder in comparison to citrate
It is something difficult to stop the reaction physically we want to stop by off stirrer and with in few mins you have to centrifuge the solution to get particular size and mono-dispersed nanoparticles
Adjust concentrations of compounds.
Article Spectrophotometric evaluation of gold nanoparticles as red-o...
I prefer to make Au-mirror without any citrate, this procedure gives small size particles.
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Efficient General Procedure To Access a Diversity of Gold(0) Particles and Gold(I) Phosphine Complexes from a Simple HAuCl4 Source. Localization of Homogeneous/Heterogeneous System's Interface and Field-Emission Scanning Electron Microscopy Study,
J. Am. Chem. Soc., 2013, 135, 3550
http://dx.doi.org/10.1021/ja311258e
Fellows, what we have found so far is, as Arunas and Hitesh said, salt to reductor ratio is the best variable to control, followed by temperature and stirring. We have splitted nucleation and growth in two separate reaction environments, feeding the first to the second and using a milder reductor in the second.
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