In removal of dye from an aqueous system, mostly adsorption procedure is applied. Decrease in colour intensity is usually observed. So at the equilibrium time, it is concluded that adsorption of the dye onto the adsorbent has occurred.
It is first necessary to find a solvent for the colorants in question and then use paper chromatography by spotting out your dissolved sample onto filter paper. Any colorants present will cause slowly moving coloured rings to develop each of which is characteristic of a specific of a given colourant.
You may monitor concentration of the dye in solution after its sorption on adsorbent by recording the absorbance of solution at it's maximum absorbance wavelength (lamda max ) and compare it from the standard curve of the dye drawn at its maximum absorbance wave length (lamda max.) under similar pH and electrolyte concentration. Since the adsorbate is a dye it must be having it's maximum absorbance in the visible region so any visible range spectrophotometer will be helpful in your work.
When you employ any method for dye removal it can either get absorbed on the surface of the materials or it can get degraded to other products or eventually to CO2 and H2O. There are two methods widely used to monitor dye removal from water. UV-vis spectroscopy and HPLC. You can prepare the standard solution of the dye of different concentration and plot a calibration curve. Then use the actual solution after degradation to find out what is the amount of dye still left in the solution. HPLC can also help you to obtain information about degradation product. HPLC-MS can identify the degradation products.
The concentration of a given dye can be determined by various analytical methods, e.g. with the aid of chromatography, and not only by colorimetry. Also, avoid using the term "equilibrium time" because it has no physical meaning. It's better to talk about e.g. t0.95 or t0.99.
Complete removal also observed by a simple laboratory test. Take small quantity of degraded solution on a watch glass than heat it with help of water bath till the complete evaporation. If there is no residue (like salt) left on watch glass then it will be found that the dye is completely removed. It is an optional method.
Analytical technique LCMS/MS can be used for determining degraded fragments.
George Oindo Achieng' Atina
Recording the UV-vis spectrum for dye solution is the best way to evident the removal of dye from the aqueous solution. each dye has its own characteristic excitation wavelength, so monitor that peak intensity in the UV-vis spectrum. If that peak intensity is decreasing gradually over time then the dye content is adsorbing on the catalyst.
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