There are likely some impurities(organic) present in your synthesised nanoparticles.

Can you explain what kind of impurities and how we can improve the graph..

The impurities very much depend on what your raw materials are used. What about your starting materials to synthesize your silver nanoparticles?

silver nitrate and plant extract of pak choi 1:9 ratio

Have you checked your nanoparticles under SEM to see the features of their size?

Dear B R Siddharth ,

Such type of spectrum may be caused by impurities (as it was mentioned by Xuhua Wang ). But, from my point of view, the more probable reasons are:

1. big size of Ag particles, so scattering of light will prevail the absorption;

2. an interaction of Ag particles with organic stabilizer and forming some low-soluble heterogeneous "balls".

At the same time it would be nice to see the initial spectrum of plant extract to compare. And one more question - is the final solution transparent? Because if such graph caused by scattering, you will see visually impurities - absorption or scattering ~0.5 is very high value.

With kind regards,

Liliya

its instrumental problem UV range is not read at all.My solutions color turned brown after one hour incubation period but this is due to some instrumental error so that instrument is not showing absorbance in UV range.

Dear B R Siddharth,

You mentioned that your sample doesn't response to UV region. I don't think it is your spectrophotometer's problem. I came across this issue many times in the past. It depends on how to measure your samples. The reference beam has to be empty or air. You need to do baseline of scan for both sample beam arm and reference beam arm in air (which means empty). Then meaure solvent and your sample, respectively. You have to manually correct the spectrum of your solvent to obtain the spectrum of your sample. In this way you can overcome the problem. The theory behind is the optical reflection and transmission or absorption with the multiple path of your samples in the sample cuvette.

Dear B R Siddharth

UV range for AgNPs is optional - maximum of absorbance band is near 400 nm and the color of solution is yellow or brown. In some cases (depend on the stabilizer nature) maximum may be located near 500 nm, at this case solution will be blue.

There are 2 questions:

1. Is the color of your solutions turned brown in the presence of Ag+? At this case (if the solution is transparent) it's seems like AgNPs were formed. Can you do the photo of the solutions on the white (office paper, for example) background?

2. If the color of solution changed without Ag+ then something happened with stabilizer - maybe it oxidized by air oxygen. This must be tested more precisely.

Sincerely,

Liliya

Madam Xuhua Wang.

thank you for your response but i have searched a lot and at last i checked the UV reading in range of 300-700 nm range with Potassium permanganate and i came to know that the reading in UV range almost remained unchanged so that itself proves instrumental error because at least for different compound it should show different reading in UV range but the situation remained same there was reading in visible range but UV range remained unaffected.

Can you check the baseline of your instrument without anything inside both sample beam atm and reference beam arm, please? If there is no response in the UV region, so you can be sure that your instrument has a problem. Otherwise it is as I mentioned in the previous discussion of measurements' issue.

Dear Xuhua Wang

As I understand, B R Siddharth have no problems with baseline, but problems are with UV range. But for AgNPs UV range is optional - for example for studying of stabilizer transformations.

At the same time we can see some weak absorption band at ~540 nm. That is that some particles were formed. We observed surface plasmon resonance at ~520 nm for AgNPs stabilized by sodium polyacrylate (https://doi.org/10.1007/s00396-019-04488-4) as well as such fact was observed elsewere too (https://doi.org/10.102/jp991569t).

From my point of view such form of spectrum is caused by scattering - by impurities (as you mentioned above) or by formation of heterogeneities during the synthesis (big particles or aggregates / oxidation of stabilizer leading to its transformation to unsoluble products).

To clarify the problem it would be good to see the spectrum of initial stabilizer without Ag+ as well as photo of finish solution.

Best wishes,

Liliya

Thank you Madam Liliya Bazylyak here is the photo of finish solution -

B R Siddharth

Wow, it is really dark ;)

Initial solution of stabilizer is transparent? What spectrum is correspond to this mix?

Because, if it is blue lines then you obtained some amount of AgNPs, but it is must be proved by any another method (SEM, TEM or XRD of centrifuged precipitates). At the other cases it looks like that you obtained some complexes of your stabilizer with silver mono or polyatomic ions (Ag+, Ag(2)+, Ag(4)2+, etc. - absorption shoulder at near 300-340 nm, for more details you can see “J. Phys. Chem. B1998,102,10667-10671” or “Journal of Colloid and Interface Science 337 (2009) 427–438”). Such complexes may be insoluble.

We observed such artifacts (only that like blue lines of spectra) for sodium polyacrylate stabilized AgNPs, but in our case absorbance was within 0.1-0.5 and the solution was opalesce and visually inhomogeneous. For few days peak at 340 nm decreased up to baseline but peak at 500-520 nm increased.

Formation of some complexes with Ag ions we observed when we used biological stabilizers too. For example, UV spectrum of our stabilizer characterized by weak peak at 290 nm and after adding of Ag+ we observed some red shift to 300-310 nm and sharp increasing of absorbance (from ~0.05 to 0.5).

BUT!!! We never observed so high absorption at long-wave region as well as so weak peaks (rather the shoulders) with the exception of a few failed experiments.

That is, as a conclusion, we can say that you obtained inhomogeneous system, maybe it will be good to decrease the concentrations of reagents?

Good luck,

Liliya

P.S. I was found some our spectra for 2-10 nm AgNPs as well as for the failed experiment.