Effect of dye aggregation and azo–hydrazone tautomerism on the photocatalytic degradation of Solophenyl red 3BL azo dye using aqueous TiO2 suspension

Aggregation of Solophenyl red 3BL (C.I. Direct 80) polyazo dye in aqueous solution was investigated using UV–visible and infrared spectroscopy techniques. The results showed a J-aggregate feature in highly acidic aqueous solutions with a red shift compared to monomer in the UV–visible absorption spectra which is due to dimer molecules. Infrared spectra showed that the carbonyl functional group stretch band of the dye molecule was eliminated in highly acidic aqueous solutions which can be related to intermolecular H-bonding. Photocatalytic degradation of Solophenyl red 3BL in aqueous TiO2 suspension under UV light irradiation in different acidity conditions was also investigated, the results showed that the complete mineralization occurs in low acidic, neutral and basic aqueous solutions but in the highly acidic solutions incomplete photocatalytic degradation was observed which can be related to the aggregated form of 3BL dye molecule. Further studies showed that azo–hydrazone tautomerism did not have any significant effect on the photocatalytic degradation of Solophenyl red 3BL in aqueous solution.