I have synthesized silver nanoparticles using green technique called Tollens method in which a solution of Ag(NH3)2 were prepared then mixed with NaOH sol to rise the PH beside adding a stabilizer polymer (PVP) as capping agent. After that rosemary plant extract broth was added slowly as reducing agent. The TEM images that attached down here show silver nanoparticles of sizes in range of 50 to 10 nm that are irregular in its shape and polydispersity. So what do you think the reasons of this irregular shape and a weak dispersion of the nanoparticles?
Dear Elham,
Me and my other two colleagues synthesized AgNP’s by using trisodium citrate as a reducing agent and a stabilizer. The size, shape and particles aggregation of AgNP were affected by the change of pH values. We prepared AgNP's using:
1. TriSodium Citrate Na3C6H5O7.2H2O.
2. Silver Nitrate AgNO3.
3. Paraffin Oil: For oil bath.
4. Potassium hydroxide KOH and Sulfuric Acid H2SO4 used for PH adjustment.
5. Distilled Water (D.W.).
TEM analysis: A dilution factor 4:16 (4 ml sample to 16ml D.W.) was used, 1ml of different PH solutions was added to 1ml sample, and samples were put in sonicator
AgNPs aggregation:
An Ag particle in suspension has a positive zeta potential so at a low pH (pH
Hi Alham,
Green synthesis routes for the synthesis of nanoparticles would usually yield you particles of polydisperse nature since the reaction chemistry is not strict. That's because you are using a plant extract whose consituents and their exact concentration are not known. There maybe a couple of things that maybe done to synthesize a more monodisperse nanoparticle product :
1.) Try isolating the individual fractions through chromatography or other techniques and identify which of these constituents help in reduction and stabilization. Mere reduction of metal ions would not yeild you nanoparticles but instead you may get aggregates. Thus a fraction that stabilizes the nanoparticle is also required.
2.) Use strict reaction parameter controls like temperature, pH, concentration of precursor and plant extract, etc. Sometimes microwaving may also help one in getting monodispersed nanoparticles.
3.) Try different methods of extracting the plant extract. You may extract the aqueous components and the organic components separately using different solvents. The hydrophobic components would merely add to the weight and thereby affect the concentration of the plant extract if your reaction is being carried out in an aqueous phase.
A couple of optimization steps should probably help you in understanding how exactly the reaction works and you should be able to fine tune it yourself for getting monodispersed nanoparticles.
All the very best!.
Aggregation can be inhibited by the thick electrical double layers that form around metal nanoparticles in low-ionic-strength suspensions. For high ionic strengths or organic-phase suspensions, capping agents such as polymers, can be employed to protect the particles from aggregation. If the synthesis is carried out in the presence of capping agents, however, anisotropic particles may result due to the differing affinities of the ligands to the exposed crystal faces. This is sometimes a desired effect and several researchers have shown that various shapes can be produced through judicious use of stabilizing agents.
For getting monodispersed nano particles , synthetic method is the only way .
Thank you all for these valuable answers , I really appreciate that.
Best Regards
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