I synthesized tio2 by sol-gel method and got white tio2.
And I stored it in oven that maintains about 100 degrees celcius temperature.
After two weeks, I taked out tio2 and two samples turned week yellow.
At first, I did not think it was big trouble, so I conducted the dye decomposition experiment with it.
But the yellow tio2 did not show any activity.
The dye was not decomposed.
I used urea, NH4Cl to make tio2 that turned yellow, and just titanium isopropoxide for tio2 that did not turn yellow.
I don’t konw why I have this result.
If you know the cause of it, plz tell me.