The band gaps can be calculated via UV-Vis spectroscopy using Tauc Plots. Attached you can find one file for your assistance. Here we plot the graph between (ahv)1/2 on y-axis and hv on x-axis. a (alpha) is the absorbance calculated from UV and hv can be calculated by following way... hv = 1240/wavelength. Then you will extraplot the vertical sagments of the plot to intersect on x-axis where y-axis is zero. That value is your band gap. It might be direct or indirect depending upon the formula.

In UV-Vis spectroscopy, there is an option called UV- Differential reflectance spectroscopy (DRS) mode. With the help of that mode, you can able to record the reflectance percentage, from that you can convert into absorbance followed by can calculate the bandgap as Zia Ullah Khan suggested formulas and Tauc plots.

Yeah, i aggree with Zia Ullah Khan

Thanks everyone for your valuable suggestions.

Simply, you can dissolve your sample in distilled water and perform UV-Visible Spectroscopy and calculated the bandgap of the material by ushing Tauc Plot.

You can take reference of my paper named "Synthesis and characterization of Sol-gel processed ferric oxide thin film followed by Humidity and Gas Sensing".

Thank you very much Kuldeep Singh Chauhan

Dear Sahoo

You can use the following information

Dear Malaya K Sahoo ,

If the grains are crystalline and its grains are relatively large then its energy gap will be more or less that of the single crystal. If the grains sizes are nanometers size then it is expected that the energy gap will be larger than that of the single crystal. The effect of the grain size on the energy gap is well studied in the literatures. If the oxide is conducting and you made it in powder form, it will be also still conducting except the the additional resistance of the grain boundaries.

I think it is better to think in the material this way.

Best wishes