I'm currently studying the in-situ formation of nanoparticles in metal salt doped polymer thin films by UV or visible laser irradiation + annealing. In this synthesis, the first step is to photo-reduce the metal ions but I have some questions about the microscopy mechanisms that takes place:
Is it only an optical (photonic) mechanism or does it depend on the polymer matrix? Are there polymer that can influence, increase the photo induced reduction?
Does the polymer chain length can play a role?
Is there any interest in adding a reducing agent such as Sodium citrate?
Currently I'm working with HAuCl4 or AgNO3 in PMMA matrix. Solvent used for spin coating are Acetone or DMF.
Thanks!
Can you explain this optical (photonic) mechanism.
It is very likely that you induce a Kolbe reaction (RCOOAg decarboxylation) or Photo-Kolbe reaction of the carboxylic group.
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Thank you for your answers.
Up to know I mainly worked with HAuCl4 and PMMA dissolved in acetone. I do not observe spontaneous formation of gold nanoparticles in solution, or if so, the kinetic must be very slow. I then spin cast films on glass wafer and perform laser irradiation. At this stage, I can monitor the decrease of the absorption peak of the gold salt (which is reduced) by absorbance measurements at different irradiation times, and I start to generate a little amount of gold nanoparticles (plasmon band appears). What I don't understand is the the photo-induced reduction mechanism of the salt during irradiation. A final annealing then lead to the formation of numerous and larger nanoparticles (the film turn red). I assume it is caused by a migration of the reduced Au atoms or seeds that aggregate and form nanoparticles as the polymer matrix is excited.
Michael, could you tell me a bit more about this Photo Kolbe reaction, I looked and I don't get where the photons are involved?
Sinha, thank you for the tip concerning Ag seeds in DMF. I actually wanted to try this solvent because it would give better films quality by spin coating than acetone. I might reconsider that. In the case of PMMA, would you know what can be the photo-excited state? The electron transfer mechanism?
You will not be able to find the keyword in combination with the fragmentation of carboxylic groups without an additional chromophore(photo-semiconductor). The name “Photo-Kolbe” is most likely introduced by Kraeutler 1978/1979 because it is so similar to the decarboxylation using Ag+ salts. In the same year Kaiser (Prof. Hanns Fischer) perform detailed Photo-ESR studies on carboxylic acids resulting in reactive radicals. (I will send you the dissertation).
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