I have synthesized some samples of gold nanoparticles (AuNPs) using gold salt HAuCL4.3h2O with distilled water at different gold salt concentrations under 10 minutes treatment without any surfactants. For the high concentration samples, some of the gold salt wasn't reduced to gold nanoparticles during the 10 minutes which is an invariable parameter in my experiment. To extract the AuNPs, I've dried the samples by evaporation under a heating process at a low temperature for no agglomeration. So, the unreduced gold salt remained with the dried nanoparticles. To re-disperse the AuNPs, I have to remove this unreduced gold salt.
*Note, I've tried centrifugation but because I don't use any surfactant, the result was bulky gold which couldn't be re-dispersed under ultrsonication. Thanks
Washing with DI water is the norm. However, one normally uses an excess of reducing agent to avoid losing the gold.
Your statement cannot be true ' To extract the AuNPs, I've dried the samples by evaporation under a heating process at a low temperature for no agglomeration '
Dear Alan, thanks for your answer .. but could you please let me know what is wrong with the statement? .. There are many ways to isolate NPs in a colloid but most of them didnt work with me like centrifugation (bulky gold which couldn't be re-dispersed) and filtering using a membtane (because the surfactnat-free NPs have many different sizes, wide range). The main objective of study is to investigate AuNPs without adding any reducing agents and you know in such case, It's not easy to isolate the NPs completely. So, I had only two options to isolate, drying by heating or by freeze drying (lyophilisation) but still the same problem (unreduced gold salt with the NPs after fully drying).
Aggregation and agglomeration are a given for dry or dried nanomaterial where the primary particle size is < 100 nm. See (open in IE):
Nov 11th, 2008. Dispersion and nanotechnology http://tinyurl.com/hpywsge
November 3rd, 2015 Adhesion and cohesion http://tinyurl.com/zwb2wlh
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