I was calcining MCM-41 at a heating rate of 2 degrees per minute. Experienced power failure when it got to 235 degrees. When power was restored i decided to check the samples and noticed they had gone light brown. This is quite unexpected as a rich white color is meant to be the outcome. Any idea why this happened?
Once the material calcined properly at required temperature one can expect the pure white color. I don't think that your material is calcined properly at 235 degrees which is way lower temperature used for calcination of MCM-41. The light brown color of the sample is obvious because of the absorption of gases evolved from the decomposition of template used in the synthesis procedure and also indicates the improper calcination conditions.
The materials should be calcined in presence of flowing air above 500 C so that the gas evolved from template decomposition are carried away from the material, the calcining the sample at low temperature or in absence of air decompose the template partially and these decomposed gases or organics adsorbed on the materials and look brownish or blackish.
I am partially agreeing with Vijaykumar...You should calcine your material at 550oC even static air atmosphere to remove all SDA. Though few reports suggested even at 400oC to remove SDA, i didn't succeeded to removing it less than 500oC.
Hari Babu Bathula K. Saravanan Vijaykumar Marakatti thanks so much for your reply. The plan was to heat to 550 for 6 hours but we experienced a blackout which interrupted the process. I continued the process and the materials came out white as expected. THere are still very slight traces of CTAB from FTIR inspection. But its the expected color. Thanks
Agree with @ Hari Babu Bathula. The calcination step plays vital role in synthesis of mesoporous family of Alumina/Silica materials (e.g. SBA-15, MCM-41). Washing with millipore water/ ethanol should be of several times to ensure there is no presence of surfactant. Calcined the prepared sample with sufficient time and proper temperature ramp to avoid appearence of light brown color.
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