Insight into the formation mechanism of azo dye-based hybrid colorant: Physico-chemical properties and potential applications

This paper presents a novel method for preparing organic-inorganic hybrid composites by precipitation of monocarboxylic azo dye (MCD) using aluminum-magnesium hydroxycarbonate (LH) as a host. Secondary ion mass spectrometry (TOF-SIMS), solid state nuclear magnetic resonance (C-13 MAS NMR), powder X-ray diffraction (XRD), thermogravimetric analysis (TG-DTA) and scanning electron microscopy (SEM) were performed to characterize the structure of the synthesized hybrid colorant. TOF-SIMS displayed the presence of C17H13N4O3- Mg2+ ions in the LH matrix. The X-ray diffraction pattern showed that the formation of azo dye-LH complexes strongly affected the crystal structure of the LH mineral suggesting existence a new organic-inorganic hybrid. Incorporation of the monocarboxylic dye into the LH mineral contributed to the appearance of new peaks in the diffraction pattern, which did not belong to either the azo dye or the LH carrier. The thermostability of the pure dye and LH/pigment was investigated using TOF-SIMS, TG-DTA and UV-Vis spectroscopy. The TOF-SIMS technique was found to be a very promising tool for evaluating the chemical composition of organic inorganic materials and monitoring their thermal stability. The thermal stability, photostability as well as solvent resistance of the chromophore were enhanced significantly. This is mainly attributed to strong interactions between the carboxylic group in the dye and the Mg2+ in the inorganic matrix. This simple strategy for the preparation of hybrid composites can be easily applied for the design of novel multifunctional organic-inorganic pigments.