I synthesized nanoparticles but I am getting aggregation of nanoparticles. I tried different variables such as solvent media, time, pH, temperature but could not get rid of it.
Our experience shows that minimal number of chemicals should be used:
1) simple salt as precursor,
2) good selection of reducing agent,
3) optimization of solvent type and conditions,
4) no additives,
5) no stabilizers,
6) simple conditions.
A variety of different particles can be obtained.
--
Efficient General Procedure To Access a Diversity of Gold(0) Particles and Gold(I) Phosphine Complexes from a Simple HAuCl4 Source. Localization of Homogeneous/Heterogeneous System's Interface and Field-Emission Scanning Electron Microscopy Study,
J. Am. Chem. Soc., 2013, 135, 3550
http://dx.doi.org/10.1021/ja311258e
I would suggest using some stabilizing agent. Somewhere in the RG there is a huge topic about creating nanoparticles in room temperature. Check there if you can find some interesting information.
@ marta siek: Mines is green synthesis without any stabilizing or capping agent.
@ joao Conde: I dont use citrate reduction method, mines is single step synthesis, directly using antibiotic and media.
I don't konw in which condition the aggregation occur, but a method to reducing this aggregation in the dry state is dispersing the glod particles in water and then lyophilizing them.
Please show a TEM picture of the aggregation. You may be able to mechanically disperse the nanoparticles.
Dear researchers The crux of getting nano is encourage nucleation and not growth - please my book " Nano science and technology " CRC press( 2004) with prof A.Subramania and many good papers
Hitesh,
It will be easier to figure out the cause for aggregation of nanoparticle if you have mentioned the reaction details. In general, all the nanoparticles tend to get aggregated unless they are in suitable condition. The aggregation can be minimized or avoided with the choice of suitable surfactant/stabilizer (CTAB, PVP, Sodium Citrate, thiols, polymers... etc) and also reaction medium (pH), temperature etc. Storage of nanoparticles in solution form rather than powder form will also help to reduce aggregation in some cases.
Storage of nanoparticles in solution form rather than powder form will also help to reduce aggregation in some cases. it is wrong - They will grow
I am not generalizing the storage for all cases. Of course, CTAB stabilized nanoparticles will grow in solution form. But there are some examples (even from our own experience) that solution in proper environment (pH, solvent etc) will be stable (in some cases).
Experimental parameters are more important rather than using a surfactant or capping agent.
In some case we will not be able to use any surfactant due to experimental limitation. In that case if we want to use the nanoparticles we have to be adjust the pH with surface charge ~ +/- 30 mV. I think it will work. In case of metalic nanoparticle we can use the bimetalic procedure such as Au/Ni combination.
You can use some hydrofilic polymers like HPMC .....you can precipitate together. This polymer will help the material resuspension.
Regards
What kind of NP's u want to synthesize...?....one can also stabilize the NP's by using stabilizer/capping groups to attached with the surface of NP's...like citrate stabilized AuNP's...
Often, the stabilisation (mechanism) of nanoparticles is simply electrostatic. This stabilisation type is overcome by salt = high ionic strength. (In many cases, a buffer salt is enough to aggregate the nanoparticles.) Today, polymer colloid synthesis experts tend to change the stabilisation mechanism (by synthesis) from electrostatic to electrosteric. The result are so-called 'hairy' polymeric nanoparticles. They even do not aggregate or flocculate at pH 0 - 1.
You can use different stabilizers, such as polymers, SiO2, ...
and surfactants such as CTAB, SDS, AOT,...
Our experience shows that minimal number of chemicals should be used:
1) simple salt as precursor,
2) good selection of reducing agent,
3) optimization of solvent type and conditions,
4) no additives,
5) no stabilizers,
6) simple conditions.
A variety of different particles can be obtained.
--
Efficient General Procedure To Access a Diversity of Gold(0) Particles and Gold(I) Phosphine Complexes from a Simple HAuCl4 Source. Localization of Homogeneous/Heterogeneous System's Interface and Field-Emission Scanning Electron Microscopy Study,
J. Am. Chem. Soc., 2013, 135, 3550
http://dx.doi.org/10.1021/ja311258e
Reply by Valentine Ananikov in itself a complete direction towards the aforesaid question.
Apart from this if you want to avoid aggregation of nanoparticles (depends upon the type of particle in study) a general concept shows
1. Lower concentration
2. Store it under cool temperature (in fact it is in practice i could not give the reference for this)...do not vary the temperature range of storage.
3. Mild reducing agent and simple salt gives out stable nanoparticles solution phase .
Increasing the temperature will enhance the aggregation of nanoparticles.
Keeping them dispersed in a solvent rather than powder form, low concentration of dispersion, suitable stabilizer based on the type of nanoparticles (for example oleic acid, oleyl amine stabilized magnetic nanopartilces), mild reducing agent and the use of simple salt are some of the common ways to avoid nanoparticles aggregation.
Nanoparticle Aggregation: Principles and Modeling gives a brief overview in this area
http://link.springer.com/chapter/10.1007%2F978-94-017-8739-0_2
amino acids can be used as reducing ( aspartic acid or tryptophan) and capping/stabilizing ( lysine) agents. Oleylamide and decanethiol could be used as stabilizing agends as well.
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