I have used nanocomposite material for the photoreduction of CO2 into CH4. How do you claim the conversion in quantum yield? And/or find the amount of fuel energy converted relative to the solar power? I know the formula for quantum yield:
Quantum yield (%) = the number of reacted electrons / number of incident photons X 100
But how do you find the number of reacted electrons and the number of incident photons?
I would be grateful for the valuable help!
Dear Ehsan,
The number of incident photos is quite simple. It can be determined experimentally by an actinometric experiment [1] - which is the most reliable way - or you can estimate them from radiance measurements; though that is not advisable, since the photon availability depends heavily on the geometry of your system (but it should be ok for an estimation, if you have a simple system!).
Now, the reacted charges is a bit more tricky! You can estimate that by putting down the whole reaction mechanism and evaluating the stoichiometric requirements of charges for carrying out the whole mechanism. Once knowing the stoichiometric relationship, you can estimate the number of reacted charges by using the observed conversion in your experiments. I just read a paper about CO2 photoconversion that has quite a clean mechanism, in case you wanna cross-check with your references [2].
Best regards!
[1] (http://www.i-aps.org/pdf/iupac_photocatalysis.pdf)
[2] Li, K. et al. Catalysis Today 224 (2014) 3-12.
Dear Ehsan,
The number of incident photos is quite simple. It can be determined experimentally by an actinometric experiment [1] - which is the most reliable way - or you can estimate them from radiance measurements; though that is not advisable, since the photon availability depends heavily on the geometry of your system (but it should be ok for an estimation, if you have a simple system!).
Now, the reacted charges is a bit more tricky! You can estimate that by putting down the whole reaction mechanism and evaluating the stoichiometric requirements of charges for carrying out the whole mechanism. Once knowing the stoichiometric relationship, you can estimate the number of reacted charges by using the observed conversion in your experiments. I just read a paper about CO2 photoconversion that has quite a clean mechanism, in case you wanna cross-check with your references [2].
Best regards!
[1] (http://www.i-aps.org/pdf/iupac_photocatalysis.pdf)
[2] Li, K. et al. Catalysis Today 224 (2014) 3-12.
Dear Muhammad,
The answers of Bruno and Moisés were really very good. I would like just to emphasize the importance of geometry of the system used to get the data of photoreduction. I was having a look in the following paper that I hope being useful for your work:
Chemical Engineering Science 58 (2003) 979 – 985
www.elsevier.com/locate/ces
Absolute quantum yields in photocatalytic slurry reactors
Rodolfo J. Brandi, Miguel A. Citroni, Orlando M. Alfano, Alberto E. Cassano∗
Dear All,
Thank you for sharing/helping with some informative answers!
But what we are talking here, gives us the apparent quantum yield where we deal with the incident photons. I got this for my system. But when we have to deal with the number of absorbed photons for the actual quantum yield, that is complicated. But I wish I'll get that as well inshaAllah!
Anyway, thank you once again to all of you :)
Fahad
Almost everyone has a correct answer for a specific question, but no one has addressed Fahad's real question of how to measure absorbed photons in a heterogenous slurry where the photocatalyst is a nano something. The best answer I can offer is to configure the reactor as a double shelled tube with an actinometer solution in the outer shell and the reaction mixture in the inner one with the reactor window admitting light only to the reaction compartment (tape off the outer compartment from all outside light). Fill the inner shell with water or whatever solvent is used in the reaction and measure the conversion of actinometer, Redo this experiment with the photoreaction mixture in the inner shell and again measure the conversion of actinometer. If done correctly, absorbed light in the reactor will be the difference between the two actinometer readings. You also have to measure the extent of conversion of CO2 to CH4 during the time the light is on. The total photon flux is given by the conversion of actinom/QY act; you can figure out the rest from here
Ted
May I ask about the AQE of photocatalytic ammonia synthesis reaction, why AQE=6* the evolved ammonia moleculars/the number of incident photos, why 6?
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