I have taken activated carbon for the adsorption of 2-Aminophenol.Its colour is yellow, After adsorption it yellow colour vanishes and there were no detectable peaks in Uv-visible spectra.Afterthat, I have kept the solution for two days and it regain its colour.
It's simple: First, there was adsorption. Desorption occurred two days later.
Hi Lalit Kumar
I assume the activated carbon was separated from your solution after the initial treatment. If so, the most likely explanation is as follows:
Your aminophenol - which by itself has probably a very slight absorbance in the visible - is contaminated by oxidation products that have much higher absorbance coefficients in the range that would give you yellow/orange color (~400-500 nm). These oxidation products have much higher affinity to the carbon black than the aminophenol itself, so they are absorbed selectively and the solution turns almost colorless. Some of the aminophenol is probably absorbed too, but some remains in solution. After two days however, some of this remaining aminophenol is oxidized and the strong color reappears.
I assume that you measured your spectra in the visible, >=400 nm, not in the UV-visible (>=200 nm). Otherwise you would have seen the peaks of residual aminophenol at =200 nm) and didn't see anything but then the color reappeared after two days in the visible, it is my considered opinion that a miracle has occurred.
It seems that after the color change, the activated carbon was removed from the environment. In this case, rather than desorption, I can make the following interpretation: Activated carbon acted as a catalyst and 2-aminophenol was chemically changed (was dimerized or keto-enol tautometrized). When the conjugation was interrupted, the wavelength became shorter and the color shifted out of the visible region. Because the resulting substance was unstable, it bounced back and the color reappeared. Thank you for your question. I work in an interdisciplinary field. With this topic, I remembered that I was actually a chemist.
Dear Emanuel, miracles unfortunately remained in the time of the prophets. I appreciate your strong comment though
Dear Mehmet Can Dal
Your interpretation makes sense. I didn't think of tautomerism or dimerization, but it could happen to oxidation products of 2-aminophenol. I would still expect these compounds to be picked up by the activated carbon, but the extent of the adsorption would depend on many factors and enough may remain in the solution for the reverse reaction to occur visibly over time. Some 200-500 nm spectra of before, after carbon black treatment and after 2 days could help clarify what happened.
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