I have synthesised GNPs by plasma reduction method using HAuCl4 mixed with distilled water at different molar concentrations (from 0.05 to 1 mM).
As a next step, I want to determine the Au NPs concentrations within the aqueous solutions of my synthesized samples. So, I follow the evaporation method to get dry Au NPs to be weighed then.
But my problem as I've experienced before, when I try to scratch the substrate surface for collecting the dry Au NPs, normally I lose a large portion of the NPs which leads to inaccurate results at the end.
So, I am just wondering if there is any an effective way to collect the dry Au NPs to avoid losing much.
P.S. I will re-disperse the dry Au NPs in Ethylene glycol after.
Thanks in advance.
Once you dry the nanoparticles it will be impossible to redisperse in any liquid. Do not dry them, trasfer them by dilution. Hope they remain stable.
@omar
I can't use dilution because I want to get red off the water and replace it the same volume of ethylene glycol.
Use centrifugation and redisperse in ethylene glycol. Do this several times and you will replace water. As I said before hope that there are no stability issues or solvent interaction issues.
To dry the nanoparticles from the collidel withou any losing , you can use the centrifuge device
@Wasna'a M. Abdulridha
I already tried the centrifugation but the result was like a bulky medium (agglomerated I mean)
You need to ensure protection such that you can redisperse the nps after centrifugation. what is your stabilizing agent? Also check if the nps disperse using a tip sonicator.
@Omar Gonzalez-Ortega
One of my aims is to not use any kind of stabilizing agents (free-surfactant NPs)
If you have nanoparticles something is stabilizing them. What is it? How did you prepare the nanoparticles?
@ Omar Gonzalez-Ortega
All what I have is the colloid after reducing the gold salt (HAuCl4.3H2O) in a distilled water into colloidal Au nanoparticles using atmospheric microplasma on the surface of the solution without adding any surfactants. So, now I want to separate the Au NPs without losing some of them (in case of evaporation followed by scratching the dry NPs) and without agglomeration (in case of the centrifugation)
Freeze-drying (also called lyophilisation) will definitely remove water and leave dry NPs, but could be tough to redisperse.
You need to increase particle repulsion. Add citrate or something that can not be considered a surfactant.
To determine concentration of the NPs by lyophilisation:
Weigh an empty eppendorf and then record the mass. Add a known volume (e.g. 1mL) of the water-based NPs to the eppendorf, freeze the sample and then lyophilise the NPs (i.e. the solid ice is sublimed directly to water vapour and leaves only dry NPs in the eppendorf). Re-weigh the eppendorf, the mass will increase and the mass difference (X) of the eppendorf before and after lyophilisation is from the dry NPs. If you put 1mL of NPs pre-lyophilisation then the concentration is X mg per mL of your stock solution.
You probably won't be able to resuspend the dried NPs back to their original size and will be not be useable, so the amount NPs you choose will have to be determined by how many you are willing to lose for the lyophilisation and concentration determination.
@Omar Gonzalez-Ortega
@Wasna'a M. Abdulridha
@Colin Moore
Thank you all for your answers, really appreciate :)
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