I am using Methylene Blue (adsorbate) and activated carbon (adsorbent) and measuring different parameters like pH, adsorbent dosage and MB concentration.
I use the spectrophotometer for measuring the absorbance to find the percentage removal but why in some cases i got negative absorbance from the spectrophotometer?
please mention what you have considered as control for setting zero. spectrophotometric readings depends upon the control most.
That can happen if the final concentration of MB is very low and the solvent (calibration blank) is not purified.
Can you try to do one filtration of the solvent in your activated carbon, to obtain a very pure solvent, and then use that purified solution as new blank?
Vrajesh, I am using distilled water as blank and the wave length is 665nm
MB gets adsorbed on the cell ( quartz or glass) walls. If the cells are not cleaned very well, use of such a cell for the reference solvent may give such results when the MB concentration in the measuring cell is very low. One way to test the presence of adsorbed MB in the cells may be to add a few drops of methanol to the dry cells and see if the solvent becomes blue colored.
I mentioned in my paper it is due to impurities probably, as illustrated in the figures, after a while (elimination of impurities), Acid Yellow 17 (a dye) with negative removal efficiencies had positive removal efficiencies.
Article A comparative study on removal of four types of Acid Azo dye...
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