I am trying to do experiment to get TiO2 nanocatalyst. I know, ramp temperature is very important. I am just wondering what is the ideal ramp rate for calcination step of TiO2 nanocatalyst ?
For anatase form it's better to do calcination below 300 oC with a ramp of 5 oC/min.
Suggest the ramp set at 0.5K//min to 10 K/min. Normally , a low heating rate is good for maintaining an order morphology. And rapid heating leads to an amorphous form .The termination temperature depends on the desired crystal form. Anatase is lower than rutile, with the bound estimated at 600-800 oC. At the same time, the higher temperatures may lead to larger particle sizes.
see paper in
https://doi.org/10.1016/j.ijhydene.2011.07.112
DOI: 10.1016/j.ijhydene.2011.07.112
5 oC/min is commonly reported ramp, that should be alright. I would recommend you first run TGA full scan at different ramps and see how the phase changes for your sample. That will help you in controlling phase transformation and guide you in choosing the best ramp and final temperature for your sample.
A lower ramp rate should give you a larger crystallite size. You can determine crystallite size from the Scherrer Equation using XRD raw data. Usually, you want a larger crystallite size in order to reduce your electron-hole recombination rate (application dependant). As mentioned above, anatase phase formation favors a calcination temperature generally 400-500C (for about 2 hours) and a ramp rate between 5-10 K/min. A ramp rate higher than 15 K/min can have negative effects on your morphology especially if your amorphous state is of a higher dimension (nanowires, nanoflowers, etc.)
Rate is important and typically low values (1-2 K min-1) are OK although I guess below 4-5 K min-1 you can obtain good morphology (high surface area and porosity). Of course, the rate as well as the final temperature of treatment will control the polymorph obtained. For most preparation methods, anatase can be obtained with low rates and temperatures of calcination below ca. 600 C. Even higher temperatures of calcination can be utilized (750-800 C) if the solid precursor is treated with sulfates and other terminal groups.
5 degree celcius/minute of ramp rate is ok. You can synthesise anatase form of TiO2 at 500 degree celcius. When you go for more than 500, the activity will be low for photocatalysis usually. But you need to check the activity at various temperatures for better result becasue everyone’ purpose varies. After 800 degree celcius you can ontain the rutile form and so you can also check your activity for the rutile form of titanium.
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