Hydrogen will reduce the ever present oxide layer (top 5 - 10 atomic layers) on the particles - shown by ESCA. I'd recommend this route. See also:

September 2nd, 2015 Silver colloids and invisible ink https://www.brainshark.com/malvern/vu?pi=560497681&b=1&tx=120486&c1=22

February 18th, 2016 Metal colloids - their preparation, application and characterization https://www.brainshark.com/malvern/vu?pi=529368070&b=1&tx=120486&c1=22

Thank you very much Dr. Alan F Rawle for the information. In the above links, i could find the information only on the silver nanoparticle- synthesis and characterization, which is already known for me. As I know, many researchers have been using centrifugation followed by washing with ethanol and water for nanoparticle purification. I would like to make sure whether any other methods are available so far...

You did not write the substances that you used for the synthesis. After the presentation of substances, you can give recommendations for cleaning.

@ Ranjith Yes, there is overall indication of preparation in the webinars. But within the talks you’ll find the evidence that the surface of such ’silver’ nanoparticles isn’t silver at all but silver in the +1 oxidation state i.e. the oxide. Hydrogen will reduce this surface as shown by TPR, for example.

Thank you Dr. Yuri Mirgorod. In general, people use sodium borohydride or sodium citrate as a reducing agent for the synthesis of silver nanoparticle.

Thank you Dr. Alan. You may misunderstood my question. Sorry about that. I would like to know, how can i purify silver nano particles, which were synthesized by chemical reduction methods. What are the methods used for purification?

Yuri’s request for the precursors is important and correct. Borohydride reduction leads to contamination with boron and this cannot be removed in my experience. Chloride precursor (e.g. for gold colloids) lead to intractable chloride contamination that cannot be washed out with water, Other reducing agents in the preparation such as hydrazine hydrate or citrate may alleviate such issues. All ‘silver’ materials prepared in the presence of air or oxygen containing species (e.g. water) will be covered with a surface layer of oxide. This layer can be removed with hydrogen reduction but materials need to be isolated from air then (under hydrogen or nitrogen) to prevent this oxide layer reforming.

Thank you again Dr. Rawle for the detailed information.

@ Ranjith. You say 'purify'. What contaminant do you suspect?

@ Dr. Rawle, till now, I don't suspect any contamination on the silver nanoparticles. As far as, I know, most of them are using Amicon Ultra centrifugal Unit for purification of silver nano particles. Instead of contamination, I would suspect traces unreacted borohydride or PVP may be found after synthesis.

I am now very confused. You seem to be talking about size separation of your nanoparticles as opposed to chemical purity. If you have used borohydride reduction, you’ll find boron in your silver nanoparticles.

I am not talking about size separation and purification of silver nanoparticles. I would like to know only about how can i seperate silver nanoparticles (total) after reduction. As far as, I know, people use centrifugation followed by washing with solvent and water. In other case, as I mentioned earlier, Amicon Ultra centrifugal Unit has been used for the purification of nanoparticles. In addition, ultra centrifugation has been used for smaller nanoparticles (less than 10 nm). I would like to know, what is the best way for seperation and purification of nanoparticles.

@ Ranjth Your question states ‘How can I purify silver nanoparticles......’.

Above in your last reply you state ‘I am not talking about size separation and purification of silver nanoparticles’......

@Dr. Rawls, Sorry for the uncleared question. Would you mind, could you provide some details on the separation and purification of sil nanoparticle?

I recommend our procedure for your application. Easily you can wash the chemicals through centrifugation tube. Check our paper

Article Radiofrequency electric field hyperthermia with gold nanostr...

Thank you Dr. Seyed