I fabricated Mn-Oxides with SiO2 as a composite to use for catalytic ozonation. surface Oh groups play an important role in this kind of catalysis. can anyone suggest me a reliable method to quantify them. i read many papers but so complicated and no detail about procedure. so i need a clear procedure.
Here is a paper that is absolutely useful for the type of stuff. Although the work in question focuses on methanol adsorption, the techniques are absolutely sound. Basically incorporation of FTIR techniques (transmission mode). With FTIR, the O-H groups are clear since it is clear which O-H groups belong to the metal oxide and adsorbed water. By applying Beers Law, you can get a good estimate for the amount of O-H in the sample.
There are other indirect methods such as TPD (Temperature Programmed Desorption), where you adsorb some gas molecule onto the functional sites. Quantification is great with this technique, but you have to know the nature of the O-H groups. If the O-H groups are believed to be all functioning as an acid, you adsorb NH3 and perform a TPD. In this method, you know how much sample there is, and you should have previously performed a calibration of NH3 detection.
We calibrated using ZSM-5. Since ZSM-5 zeolite acid sites are fixed (based on Al content), we saturate ZSM-5 with NH3, vacuum, then perform the TPD from 30-500C at 5C/min (VERY IMPORTANT). By integrating the peak profile, you will have the total number of NH3 desorbed from ZSM-5. Repeat this with different amounts of sample. Less sample means smaller areas. More sample means bigger areas. Thus you should get a linear plot.
You can find these techniques in most Heterogeneous Catalysis textbooks.
Hope this helps in some way.
use TPD and you can refer our work J. Nanoparticle res.
J Nanopart Res (2013) 15:1669
DOI 10.1007/s11051-013-1669-3
TGA, silicon NMR or inverse gas chromatography can also be used for OH determination.
By far the best source in the literature is the extensive book on silisca :
Colloidal Silica
Fundamentals and Applicationd
Horaccio E. Bergma and William O. Roberts editor
Taylor and Franci (2006)
Beside thermogravimetry, infrared abosrption and NMR techniques are thorougly discussed.
Dear Hussain Shah.
Try TGA analysis and Boehm titration. These methods will give you quantifiable amount of surface -OH.
Good luck!
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