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 Al-27, C-13 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 alpha- and beta-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. (C) 2006 Elsevier Inc. All rights reserved.