I have a core shell nanoparticle containing gold core and polymer shell. There is an intermediate silica layer and I am trying to etch the silica layer using NaOH. My question is how can we confirm that the silica has been etched? TEM is a way to confirm it, but I may not be able to see the intermediate layer as the polymer will be entirely covering the core. Is there any other simple way to confirm the etching? Thanks
Hi Ramya, I think (my opinion)....If you have gold as a core, you can run UV -Vis spectrophotometer (by comparing the individual peak) for only Au-core, Au core coated by silica (second layer), and Au-SiO2 coated by polymer (third layer). or you can run tunable dua peaks Vis - NIR extinction characteristics in the same way.
I guess, you need to check with AFM after doing the etching treatment. Since really powerful AFM's can give atom level resolution, you might be appreaciating some surface roughness over the silica layer with which you can confirm the etching.
After quantitative addition of NaOH, Wash with a very dilute solution of NaOH and go testing the presence of monomeric sodium silicate in the washings till a time comes when the last washing does no give any test of silicate which indicates the complete removal of silica. The presence of silicate is tested as follows:
Receive the washings in a test tube containing acidified ammonium molybdate solution to obtain yellow colored complex:
Reactions:
SiO2+2 NaOH----- Na2 SiO3+ H2O
Na2SiO3+ H2SO4 +H2O-------- Si(OH)4 + Na2SO4
7Si(OH)4 + 12H6Mo7O24·4H2O + 17H2O -- 7H4SiMo12O40·29H2O
The resulting silicomolybdic acid is a yellow compound
Note:1. sodium molybdate solution is prepared in H2SO4 ( pH=4-5). It is vey commonly used laboratory reagent.
Note2: Even the Silicate testing kits are also available. You can try the kit if you could get one.
Note:3. Better perform the above mentioned simple test yourself. Graduate/ PG students would perform this test for silicates in their qualitative analysis class.
Dear Manohar, Thanks for the answer and this is what I have been looking for. Very much appreciated. Really an easy test to determine if silica has been etched.
Arun and Rudy, thanks for the suggestions.
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