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 13C nuclear magnetic resonance (CPMAS 13C NMR), and Fourier transform infrared spectroscopy (FTIR). In the adsorption experiments, Gibbs free energy ΔG values for the temperatures in a range between 10 and 40 °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 ΔG values at higher temperature further indicates that this process is even more favorable at these conditions. The enthalpy ΔH 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.

Graphical abstractThree anionic blue organic dyes have been intercalated/adsorbed into Zn2Al layered double hydroxides, confirmed by thermodynamic data, in which enthalpy values were between physisorption and chemisorption.Figure optionsDownload full-size imageDownload as PowerPoint slide