You can XRD of doped sample, you should be first indentify the phase of TiO2 present, or even if its the cobalt titanate?

Another thing, depend of the semiconducting its direct or indirect  the tauc plot its different, for the case of anatase TiO2, its indirect, you should be graphicate  square root of hvF (R) vs hv and then calculate band gap.

Dear Johan sir,

Its a cobalt doped in Anatase TiO2 Phase. This is direct bandgap image 

1. How to check direct or indirect for following semiconductors (ex; TiO2, SnO2, ZnO)using Tauc plot ?

2. I think Y axis value also good in graph.

this correct tauc plot its similar using kubelka munk function, You should be change the Y axis for square root of hvF (R), in case anatase TiO2 is indirect semiconducting. Maybe the results change for the band gap.

Dear Raj Kumar,

Have you experimentally confirmed by XRD, as suggested by Dr. Gonzalez, that your sample is a single-phase one? Our experience in doping ferrite nanopowder with Cu tells us that it is difficult to obtain  single-phase Cu-doped ferrites. I wonder if you actually had a second phase which gave you another band gap. 

Another thing, in my experience antase phase obtain about 400 - 500 0C, above that obtain mixture with rutile phase, at a certain point only rutile TiO2