Photodegradation processes in two-dyes systems – Simultaneous analysis by first-order spectra derivative method

Wastewaters from textile industry contain a mixture of dyes with other organic and inorganic compounds. The paper proposes a new method of analysis of dyes in real wastewater than global standard parameters used for wastewaters characterisation. The first order derivative spectra method – as a multivariable calibration method – was developed to overcome the spectral overlapping, for the simultaneous analysis of two dyes in solutions. The photodegradation of Bemacid Gelb (BG), Bemacid Rot (BR) and Bemacid Blau (BB) by titanium dioxide films in two-dyes solutions (BG–BR, BG–BB, BR–BB) was investigated and the residual concentration was evaluated based on the first order derivative spectra method. The proposed method is characterised by accuracy for all the dyes (standard deviation of ±3%). The method does not involve expensive instrumentation and dyes separation. The method can be applied to determine any dye present in a binary mixture.

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► Three acid dyes in mixture have been individual determined after photocatalysis.
► A first-order derivative spectrophotometric method used for dyes evaluation in binary solutions.
► The recoveries and errors between the theoretical and experimental concentration were calculated.