For iron oxide nanoparticles, the color would be pale yellow and the absorbance lies in between 200-300 nm. but due to d-d transition you don't see the strong absorbance.

For infrared region, FT-IR are used for nanoparticles. Scanning 400 to 4000 cm-1 range is useful. A vibration belonging to a Fe2O4 spinel can easily be seen about 590 cm-1. C-O stretchings at 1500 cm-1  and water peak at 3500 cm-1 are familiar. 

I don't know if  we take into account 104 cm-1 scan range. What kind of vibrations do you expect? I dont know this part. 

Unlike its composite form, iron nanoparticles doesn't absorb a specific wavelength at UV-vis range. Moreover, its commonly color was at range dark brown to black.

In agreement with Zakki, the absorption keeps increasing when you go for spectrum scan. But you dont find any peak unless you are coated your particles with some compound to infer charge.

THANKS TO ALL

Another problem that am facing.I coated my nanoparticles with aminosilane coating agent but these are not dissolving completely .These particles settle down immediately.I want to use them as optical nanosensor but after functionalizing with UV active molecules they remain insoluble.what should I do for this?because for to use them I need a stable clear solution.What should be the concentration range and what should be the procedure for making solution of magnetic nanoparticles.

What is mean by infering charge on nanoparticles

Yeah thats what Aiman, you have coated your particles with aminosilane right. Usually iron oxide nanoparticles are electrically neutral. Hence it is impossible to make dispersion unless you coat with some chemical which infers charge on it and makes dispersion in water by avoiding agglomeration. But   in your case, particles are settling down even after coating with aminosilane may be because of gravitational force. Usually iron oxide nanoparticles tend to settle down under gravitational force also.

Hi friends this is S Vasantharaj.

I am working in the field of iron oxide nanoparticle from plant.What is the specific UV range to confirm the Biosynthesis.

how to break down iron particles of micron to nano size without using probe sonicator and ball milling

@Dimple Rani - dissolve and precipitate under appropriate conditions

For iron oxide nanoparticles, the color would be pale yellow and the absorbance lies in between 200-300 nm. but due to d-d transition you don't see the strong absorbance.

I am also working and obtained result in same range i.e. 200-300nm.

Open-source UV-Vis Spectroscopy Library for Nanomaterials,

https://www.instanano.com/2021/01/uv-vis-open-source-reference-liberary.html