Hello,

I like to suggest  few opinions to your very interesting question.

Usually synthesis of silver nanoparticles are done with the help of a stabilizing agent (PVP) to control the aggregation of the particles. I dont know the reagents used in your synthesis but from the above question I think it may be Phyto mediated chemical reduction method. When you store this solution the particles aggregate together and deviate from the 'nano dimension' and the aggregation is indicated by increase in brown colouration (in the case of nano Ag). This can be prevented by employing suitable capping or stabilizing agent (EDTA or PVP) in the method.

I have synthesised nano Ag from AgNO3 by MW reduction technique using Glycol as the solvent and PVP as stabilizer. Check the images of the brown colloid in the attachment. All the best

Regards

Vishnu

I have used 5:20 ml plant extract and AgNO3 solution at alkaline condition (1M NaOH) at 80 degree celsius for 10 minutes...Brown coloration is observed just now. Please find the image attached..uv-vis spectrum is to be taken immediately after reaction? 

Awaiting your kind suggestions.

-Regards-

Neethu Kannan B

What does the plant extract contain? Any idea on the extract composition? IFF the extract contains reducing agents the silver nano particles will be formed. What is the concentration of AgNO3 used?

Hello Karthik,

Aqueous plant extract prepared by boiling at 60-degree celsius. 

1mM AgNO3 is used.

5: 20ML-PLANT: SILVER NITRATE

Try to reduce the AgNO3 volume and may be if you a different color then the reason could be aggregation of SNP to larger particles.

Try to reduce the AgNO3 volume and may be if you a different color then the reason could be aggregation of SNP to larger particles. What is the UV Vis peak that you are getting

I didnt get specefic peak... Can i store this solution for taking UV-Vis spectrum later. ?Will the storage affects the results in spectrum?

You can store the solution but unless you get a peak immediately after adding the extract and  silver nitrate i dont hink it has any use. Which plant extract are you using since the plant must have some reducing agent in order to form SNP.

Plant is cynanchum. It is a medicinal plant having so many bioactivities.  I didnt get peak with a previous attempt. This is a new one I did. So, I have to take spectrum with this.

If at all the SNP are synthesized then a peak should appear. It may be broad if the size range of SNP synthesized is vast. I am not able to tell if the extract has the material required for SNP synthesis.

Try to repeat the experiment without NaOH and check if the color formation is differennt

I think the plant extract is responsible for the brown colouration as shown in the figure. If there is SNP in the medium it will probably give a peak. Try to find what are the changes of plant extract on heating so that you can find what cause brown colouration. If you want to confirm the presence of SNP, I recommend to take a SEM image so that you will get a clear picture about what had happened. 

thanks alot for suggestions...

Hello neethu, there are different things you can modify in your synthesis protocol. You can use extract of fresh plant parts(instead of dried) while retaining your ratio. You can exempt NaOH. Also, the colour change between your plant extract and your final snp can easily provide early distinction. if you got a different colour(mostly reddish brown) from your plant extract, you can be assured your snp is formed. Do UV-vis analysis asap. 

hi Neethu,

No prominent UV-Vis spectrum suggest that Nps with different energy distribution. that may be because of broad range size distribution of Nps. Check Np size distribution by DLS.

Yeh you can

Easiest Synthesis of Silver Nanoparticles by Leaf Extract,

http://www.instanano.com/nanomaterial-synthesis/metal-nanoparticles/synthesis-silver-nanoparticles/