An Investigation on Thermal Decomposition Behavior of Water-Soluble Azo Dyes

In order to investigate the thermal decomposition behavior of water-soluble azo dyes, a series of structurally isomeric water-soluble hydroxyl azo dyes were synthesized and their thermal decomposition phenomena were examined using TGA and DSC. Their thermal decomposition mechanism was also studied by measuring UV-Vis absorbance of the prepared dyes at various heating temperatures. From thermal analysis and spectroscopy, we found that the dyes decomposed gradually without a melting process, and those with strong inter-molecular interactions had high decomposition temperatures. Moreover, we suggested a new thermal decomposition mechanism different from that of the water-insoluble dye, in which dye molecules rapidly decomposed within a narrow temperature range following a melting process. We also found that dyes with stronger inter-molecular interactions had higher degradation temperatures using density analysis, X-ray diffraction (XRD), dynamic light scattering (DLS), and density functional theory (DFT) calculation.