I put the methylene blue under solar light and make a cooling for it. However, the MB concentration still decreased a lot, about 10% for 1h with the concentration of MB 10-5M. However, the same MB solution is lighted by UV light, the concentration decreased very little, about 2% for 1h.
I think it is unnormal because the degradation of MB is higher under visible light than UV. Anyone had any experience these phenomena. Please help me.
Most likely, the observed phenomena can be explained by different intensities of the luminous fluxes from the sun and your UV lamp. Sunlight contains both UV and visible components - obviously, your lamp emits much less power. Make a simple experiment - expose the dye under sunlight without UV components. This is easily done using a glass filter (yellow will be better). You will see the percentage of reducing of the bleaching and will be able to evaluate the contribution of UV-range.
Hi Bac Luong, in addition to the previous answers, in general on photocatalysis of dyes, the band gap energy to promote electron from HOMO to LUMO of Catalyst is the key to proceed. However, the characteristic of dyes material such as easy to react under sunlight irradiation, is also affecting the photodegradation process. In my suggestion, let try the other simple experiment, exposure the solution of MB without catalyst under sunlight irradiation.
I hope this information will be useful
Best regard,
Rudy Situmeang
Hello Mr. Luong,
I am also working in the same field and also encountered with the same issue in rhodamine blue (RhB). There might be some contamination in your dye (without catalyst) which provided such a high decreased concentration of 10% ( as you have mentioned) under the exposure of solar irradiation. Because as per my knowledge, MeB does not get degraded under the exposure of UV-vis irradiation at such a high level (10%) in 1 hour.
I agree with the answers given by Mr. Shcherbakov and Mr. Situmeang. But, in my opinion, human error is the main source of problem in your case.
Best of Luck!!
I agree with all above respected person's view but I can suggest you, Bac that try to avoid to study of dyes and try to do phenolic compounds, PCCPs, etc..
I support Niranjan Biswal. Almost all dyes are photochemically active compounds (photosensitizers). The photochemistry of dyes should be taken into account.The results are strongly dependent on the light source spectrum, presence/absence of O2,, pH, etc.
Thank you very much for your kind answers.
A. B. Shcherbakov: I have done other checking by using a LED replacing the solar ligh irradiation. The MB degradation also decreased strongly. So that I think it is not due to the power which is a key in this.
Aayush Gupta: We have done this research carefully. Several checking also gave the same phenomenon.
I have read several published papers and they reported that the visible light gave a very small decrease of MB. That is why I did this experiment. It is important to research in the photocatalysis for organic pollutants degradation under visible light.
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