Azoic dyes hosted on hydrotalcite-like compounds: Non-toxic hybrid pigments

Layered double hydroxides with the hydrotalcite type structure and a Mg:Al ratio of three have been prepared with an azoic dye (methyl orange) stabilized on the external surface. Methyl orange was incorporated by reconstruction from a mildly calcined LDH-CO3 precursor. The solids have been characterized by powder X-ray diffraction and FTIR, UV–vis and 27Al, 13C CP/MAS NMR spectroscopies. Hartree–Fock calculations were performed in order to investigate the guest-host arrangement. Results show that the methyl orange molecule is in configuration trans and that the carbons in α- and β-positions, relative to the azo group, are interacting directly with brucite-like layers. Hydrotalcite shows a very high affinity for retention of azoic dyes. Another advantage offered by the stabilization of methyl orange anions in hydrotalcites compounds is that they are shielded from acid attacks.