A remarkable increase in photocatalysis performance of Methylene blue degradation is observed when protein capped ZnO NPs were used in comparison to bare ZnO NPs. Can anyone explain the major driven force behind this observation? Also, how the presence of proteins make such a drastic difference in catalytic activity?
Thanks for response.....I am using UV light irradiation for my studies...
Being a biologist, I don't know how to measure Band gap experimentally. Kindly suggest some methods...
Thanks in advance
The process has usually two steps: the adsorption of the pollutant (MB in your case) followed by the oxidation reaction with HO. radicals resulted in photocatalysis. So, your significant increase (how much actually?) may be the result of a higher concentration of MB on/in the vicinity of the ZnO NP, as result of interactions MB - capping agent. Usually the pseudo-first order kinetics applies, thus the MB concentration increase is mirrored in a higher reaction rate and thus a higher efficiency for a given period of time. If this is the reason than, after reaching equilibrium, the efficiencies with and without capping agent should be almost equal.
If not, another reason may be the "production" of a higher amount of HO. radicals, as result of the protein capping. This should be tested in the absence of MB (in a blank).
It is also important to notice that MB is quite easily degradable in photocatalysis. One "harder" test is with methyl orange (MO, much more stable and therefore more difficult to degrade). This should be tested also because there is a quite large difference in the chemical formula of MO and MB. If the effect of capping is the same (significant increase in efficiency), than one may suppose that the reason is the higher amount of HO. radicals. If not, it may be the MB affinity for the protein.
Please test with other reactants other than MB. Use of MB in photocatalytic reaction is not advisable. In your case mostly protine is helping decolourisation. May be photocatalytic activity is enhanced but you need to evaluate the reaction. By changing the test reaction you may conclude the results.
Yes, there is possibility in enhancement of photocatalytic activity of ZnO nanoparticles. This may be due to several reasons such as the change of surface area of your pristine ZnO, which may facilitate more adsorption and which may further lead to higher photocatalytic degradation. In order to reach exact conclusion I would like to suggest to check followoing things.
1. Adsorption of MB on pristine ZnO
2. Adsorption of MB on protein capped ZnO (1 & 2 ,this study need to be done in dark)
3. Check surface area of the samples keeping low degassing temperature for longer time, so that your protein should nt get affected during degassing of your samples.
4. Check bandgap of both the samples (already suggested)
5. Try some other dye which do not have interaction with your protein or less adsorption.
6. Run blank photocatalytic experiment (without catalyst)
All the above thing may be helpful for you to understand the enhancement in the photocatalytic activity. If you need any help please write me, I will try to help at my level.
The activity of ZnO as photo-catalyst is well known mainly due to lower band-gap. Other factors such as active sites,surface area, morphology,pH of media are also important. However, the most draw back of ZnO is suffering from photo-corrosion and losing its activities after some time.
Dear Rajesh,
Can you recommend any publications which can help me in executing recommended calculations.
Thanks in advance.
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