Hi Esraa Abdelsalam , to obtain mesoporous silica, calcination is performed in a tube furnace with a flow of compressed air. This will remove the CTAB and give mesoporous silica, which is a white powder. In your case, since you used muffle furnace, whatever is burned in the furnace stayed there as activated carbon (black colour), mixed with silica support. That is why you ended up with a blackish product. Also, there is a chance of burning both CTAB and silica in muffle furnace.

Dear all, the following RG free access document gives a review of the different techniques and methodologies followed for the preparation of mesoporous silica gels. My Regards

https://www.researchgate.net/publication/235604111_Synthesis_of_Mesoporous_Silica_Nanoparticles

Dear Esraa Abdelsalam

This subject to the type of furnace used in the sintering. However, changing the color can be generally due to the the change in the microstructure of the sample. As the grain boundaries are formed and the porosity is changing after the sintering, the absorption and scattering of the light by the sample also change.

Besides, in your case if you were using the furnace with air, it definitely is due to burning the raw materials, they disintegrate and turn carbon into CO2 gas.

I have similar experience during my Master project. the white color of Calcium silicate ceramic was changed to gray and finally black with increasing the calcination temperature. This happened for all the samples, I used a copolymer (P.123) as the template for some samples and some other samples did not have it.

It would help if you had airflow in the furnace. Use a tube furnace with air circulation or add a ventilation system to your muffle furnace (e.g., attach a fan to the furnace exhaust).

And also, 550 degrees is not enough temperature to remove CTAB completely. Increase the temperature up to 700 degrees.

Best regards.