PCA-spectroscopy study of common salt effect on solubility of direct dye

Purpose This work aims to explain the effect of common salt on absorbance spectra and solubility of textile direct dyes, which is important in analysing and reusing wastewater of dyeing process. Design/methodology/approach Several textile dyes such as Direct red 243, Direct yellow 86 and Direct blue 201 solutions with and without NaCl salt were used to study the effect of common salt on solubility of textile direct dyes. Several methods such as derivative spectrophotometry, principal component analysis and colorimetric techniques were used to analyse the absorbance spectra of dye solution. Findings The obtained results indicate that the effect of common salt on absorbance spectra and solubility of textile direct dye depends on the chemical structure of dyes. The NaCl salt significantly affects the solubility of Direct red 243 (red dye) and Direct yellow 86 (yellow dye) which have Azo compounds containing four SO3 functional groups. But the NaCl salt does not change the solubility of Direct blue 201 (Blue dye) which has Azo compound containing two SO3 functional groups. Also, the NaCl salt decreases the accuracy of dye concentration prediction. Practical implications During reusing wastewater of dyeing process, the amount of dyes has been evaluated via absorbance spectra of dye solution. Originality/value This work explains the effect of common salt on solubility of textile direct dyes and the accuracy of dyes concentration prediction.