Dear Researchers
We attempted to degrade methylene blue (MB) with negatively charged nanoparticle (NP). Both NP and MB were in aqueous solution and they were mixed. Immediately after mixing or within 5 min, the MB turn into colorless solution. Aqueous MB gives two peaks at 610 and 664 nm in the absorption spectra, however these peaks disappeared and two new peaks around 575 and 695 nm appeared in the spectra of MB+NP mixture. According to the literature, the peaks at the lower wavelength (less than 600 nm) suggested the formation of MB dimer or their higher aggregates. However, MB aggregates are expected to be more intense in color. This contradicts the formation of dimer or aggregates. The reduced form of MB (leuco-MB) is colorless, but it does not show any peaks in the visible region according to literature. This contradicts the reduction of MB. Also the NP does not have any peaks in this visible region (not included in the picture). We are trying to figure out what is responsible for decolorization and those two peaks. Your suggestions will be greatly appreciated.
Dear Parani Sundararajan,
What kind of nanoparticles did you use?
Thanks
Xuhua
Dr Parani
Did you measure the pH before and after addition? Reducing agents will also turn methylene blue colorless.
Alan F Rawle
We did measure the pH.
The pH of MB increased from 6 to 6.2 after adding NPs. We also added the capping agent that we used to stabilize the NPs, however there was no decolorization and there was no changes in the MB peak position. No reducing agents were used in the synthesis of NPs
Thanks
You should consider the absorption flattening caused by the inhomogeneous distribution of the chromophores. A good start would be Duysens, 1956.
what type of metal (Ag, Au, Pd or else) is it? What are their shape and size?
Dear Dr Parani thank you for this interesting technical question. As an inorganic chemist I'm not an expert in this field, but I can suggest to you a few potentially useful articles which could help answering your question. Please have a look at the following relevant references entitled
1. The effect of surface charge on photocatalytic degradation of methylene blue dye using chargeable titania nanoparticles
Article The effect of surface charge on photocatalytic degradation o...
2. Photocatalytic degradation of methylene blue under natural sunlight using iron titanate nanoparticles prepared by a modified sol–gel method
Article Photocatalytic degradation of methylene blue under natural s...
3. Oxidative Degradation of Methylene Blue Using Mn3O4 Nanoparticles
Article Oxidative Degradation of Methylene Blue Using Mn3O4 Nanoparticles
All three articles are freely available as public full texts on ResearchGate
Do you have differences in the ionic strength of the solution which can be the reason for the variations observed in these spectra?
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