Abstract
In this study, novel organic–inorganic composites were prepared by the complexation of dicarboxylic azo dye (AD) with aluminum–magnesium hydroxycarbonate (AlMg–LH). This procedure provides an effective method for the stabilization of dicarboxylic organic chromophores on an AlMg−LH host. The structures of the hybrid composites were examined by X-ray diffraction (XRD), secondary ion mass spectrometry (TOF-SIMS), 27-Al solid-state nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA) and scanning transmission electron microscopy (STEM). The TOF-SIMS method was applied to investigate the metal–dye interactions and to monitor the thermal stability of the organic–inorganic complexes. Secondary ion mass spectrometry confirmed the presence of a characteristic peak for C18H10O5N2Mg22+, indicating that both carboxylic groups interacted with AlMg−LH by forming complexes with two Mg2+ ions. Modification with hybrid pigments affected the crystal structure of the AlMg−LH mineral, as shown by the appearance of new peaks on the X-ray diffraction patterns. Adsorption of the dicarboxylic chromophore not only led to significantly enhanced solvent resistance but also improved the thermal and photostability of the hybrid pigments. We propose a possible arrangement of the azo dye in the inorganic matrix, as well as the presumed mechanism of stabilization.
Highlights
Azo dyes are an important class of modern dyes and are extensively used in textiles, leather, printing, food, drugs, and optical devices
We studied the interactions between alizarin and aluminum–magnesium hydroxycarbonates with different Mg/Al ratios [33]
Comparison of the TOF-SIMS spectra in Figure 1a,b demonstrates that the intensity of the C18 H10 O5 N2 Mg2 2+ peak grew as the concentration of azo dye in the inorganic matrix increased
Summary
Azo dyes are an important class of modern dyes and are extensively used in textiles, leather, printing, food, drugs, and optical devices. Some azo dyes have a limited range of applications, for example, due to their low melting points, high tendency to migrate, and poor thermo- or/and photostability, some dyes cannot be used in polymer materials. Most of these disadvantages can be overcome by complexation of the organic chromophores with inorganic hosts [1,2]. There has been great interest in multifunctional hybrid materials, which combine the advantages of both organic materials (light weight, versatility, intense color) and inorganic materials (high thermal and chemical resistance) [3,4]. Various procedures have been proposed for Molecules 2019, 24, 880; doi:10.3390/molecules24050880 www.mdpi.com/journal/molecules
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