Zn2Al layered double hydroxides intercalated and adsorbed with anionic blue dyes: A physico-chemical characterization

Three different anionic blue organic dyes have been intercalated into the structure of Zn2Al layered double hydroxides, using the co-precipitation method at constant pH. Using the same synthetic procedure, Zn2Al-Cl has been prepared and used as an adsorptive phase to retain the blue dyes from an aqueous solution. All the organic/inorganic (O/I) hybrid LDH compounds were analyzed by X-ray powder diffraction (XRPD), thermal analysis (TG/DTA). elemental analysis, solid state C-13 nuclear magnetic resonance (CPMAS C-13 NMR), and Fourier transform infrared spectroscopy (FTIR). In the adsorption experiments, Gibbs free energy Delta G values for the temperatures in a range between 10 and 40 degrees C were found to be negative, which indicates that the nature of adsorption is spontaneous and shows the affinity of LDH material towards the blue anionic dyes. Additionally a decrease in Delta G values at higher temperature further indicates that this process is even more favorable at these conditions. The enthalpy Delta H values were between physisorption and chemisorption, and it may be concluded that the process was a physical adsorption enhanced by a chemical effect, characterized by a combined adsorption/intercalation reaction, making these O/I assemblies reminiscent of the Maya blue. (C) 2009 Elsevier Inc. All rights reserved.