Have you verified the performance of the system with the appropriate wavelength and concentration standards before commencing your work?  If you have and the system is working correctly as I suspect will be the case then something is changing in your samples. How were the samples made or synthesized?  Both TiO2 and FeOx are dense materials and if you made your samples from a powder (a collection of fused post and sub-micron material), then settling is inevitable and your results will change.  You need to keep your materials in colloidal suspension without drying in order to preserve the nano nature.  See:

Nov 11th, 2008. Dispersion and nanotechnology  http://tinyurl.com/hpywsge

and: November 3rd, 2015 Adhesion and cohesion  http://tinyurl.com/zwb2wlh

Dear Dibyanshu,

If you mean you are getting different results for different concentrations, then that's correct, because you will always get different results/Absorptions levels for different concentrations.

But,

if you are getting different results for repeat samples then you need to find out the reason, which could possibly be errors in sample preparations or most probably your nanoparticles suspensions are not stable, etc.

And that is obviously with the conditions that you are using exactly the same method on UV-VIS each time?

It would be good to share some results here for people to see what you mean by "different results" and please clarify whether you are comparing results of repeats or of different concentrations?

All the best

Rehan

Sir, two times I have done the same experiment . I am attaching the result I got.

Have you verified the performance of the system with the appropriate wavelength and concentration standards before commencing your work?  If you have and the system is working correctly as I suspect will be the case then something is changing in your samples. How were the samples made or synthesized?  Both TiO2 and FeOx are dense materials and if you made your samples from a powder (a collection of fused post and sub-micron material), then settling is inevitable and your results will change.  You need to keep your materials in colloidal suspension without drying in order to preserve the nano nature.  See:

Nov 11th, 2008. Dispersion and nanotechnology  http://tinyurl.com/hpywsge

and: November 3rd, 2015 Adhesion and cohesion  http://tinyurl.com/zwb2wlh

yes, obviously you have no well dispersed nanoparticles, with FeO having poorer dispersion quality leading to higher deviation from expected.

So , everytime I will get different result  , then its absorbance capacity cannot be known

The results you have attached are very drastic. I would like to suggest to do analysis with the standard, either it may possible instrument is not functioning properly. If the instrument is running the standard properly then there may be the fault in your dispersion. Make dilute dispersion of your nanoparticles, divide into 2 parts and then perform UV of 2 divided dispersions separately. I hope it will help you. Otherwise, You may move towards another UV instrument for analysis.