You should be used the difusse reflectance spectroscopy (DRS) for that. And plot with Kubelka Munk fucntion for band gap calculation

Nope, you've gotta use a dried sample only

You should be used the difusse reflectance spectroscopy (DRS) for that. And plot with Kubelka Munk fucntion for band gap calculation

Hello Dr. Kamani,

Indeed it is posible to estimate band gap using that relation while using coloidal samples. For that you have to know the material content in the colloids. Please follow our published work: Science of Advanced Materials Vol. 4 (2012) 591-596.

Please let me know if you have any difficulty further.

We can record the UV-visible absorption spectra in solution phase also provided first baseline correction has been done by keeping ethanol in reference & standard cell position. Ideally one should trust more on solid state sample. Is it not possible to spin coat your film on glass substrate and then record the spectra.

Dear Dr. Kamani: 

In a broad sense, for organic molecules, the absorption of a photon from UV-Vis radiation with specific wavelength turn the molecule excited being possible further effects on the excitations of bonding electron (electrons belonging to chemical bonds type “pi and Sigma”) and other electrons type of valence electrons (nonbonding electrons termed “n”).

From experimental view-point, the parameter absorptivity assigned to specific electronic transitions should be high sufficient to give a high sensitivity at measurement.

Water has been further considered as a functional solvent being the energy necessary to pi-pi* tend to small value. Thus, in an aqueous colloid or aqueous nano-fluid the absorption of UV-Vis by particle-oxides should higher than solvent molecules allowing further analysis. Seems that ethanol gives an an absorbance peak below 400 nm. Thus, as a golden-role when suspension particles/nanoparticles require further characterization via UV-Vis a fluid of low absorptivity is a proper fluid. The increasing of particle/nanoparticles does not give best results since system fluid/nanoparticles stay opaque to the UV-Vis beam. As mentioned in a previous answer, the spectrum of fluid can be previously collected and in the sequence subtracted of spectrum of fluid (standard) and particles/nanoparticles. But such procedure, a priori, only isolates the signal ascribed to particle/nanoparticles. In another words, if ratio signal to noise is bad, data have small accuracy.

I would like to comment that is possible both types of TiO2 termed of anatase and rutile which can absorb UV radiation near to visible portion of spectra. However, TiO2 phase type Rutile exhibits absorption on broad range of wavelength, at least an interval with higher extension that Anatase. Both types of structures have different characteristics at bands structure. Please, to taking a further insight about band structures, consider the paper below:

Nature Materials 12, 798–801 (2013) doi:10.1038/nmat3697

Then, it s important to determine that type of structure you has or having a mixture of phases what is the proportion of each. In the practice, this procedure will allow further data comparison, when some data base is accessed. At moment, seems that chemical routes for synthesis of TiO2 indicates the existence of a scale-phenomenon which determine the type of structure, being expected a phase transition Anatase to Rutile at temperatures of calcination close at 500 oC. In this sense, this materials exhibit a broad and asymmetrical peak between 300 and 350 nm.

Kind regards

Marcos Nobre (M. A. L. Nobre)

Thanks to all authors.

DRS gives 2 columns.

One of them is diffraction and another is landa(nm).

How can get the alfa(absorption constant) for drawing the plot with Kubelka Munk function?

that's impossible to obtain diffraction - the reflection (R, %) only. Than try to read any paper where the K-M function's used. Your disinclination for reading and studying is obvious. But I'll help you. Absorption (K) shown as K-M is calculated from the equation: K = (1-R)2/2R. Your welcome 

For DRS analysis you can check the article:

Use of diffuse reflectance spectroscopy for optical characterization of un-supported nanostructures.- AE Morales, ES Mora, U Pal

Revista Mexicana de Fisica S 53 (5), 18

Mr. Kamani, please, check your e-mail box where the results of the calculations had been sent.

Thank you Mr Nazarkovsky.I received your valuable answer.

My reply's found in the yesterday's letter. Check it

Hello Mr Nazarkovsky

I have not your letter yet.May I ask you sen it again.

thanks