Synthesis of hexagonal mesoporous MgAl LDH nanoplatelets adsorbent for the effective adsorption of Brilliant Yellow.

Hexagonal mesoporous MgAl layered double hydroxide (LDH) was synthesized through a simple hydrothermal method and was employed without calcination as adsorbent in the removal of the direct anionic azo dye, Brilliant Yellow (BY). The adsorbent was characterized by XRD, FT-IR, SEM and BET surface area. Hexagonal platelets of MgAl LDH were fabricated with nanometric building blocks. Batch experiments were carried out for study effects of contact time, amount of adsorbent, solution pH and solution temperature on the removal efficiency of BY. The adsorption of BY onto the MgAl LDH was pH dependent and the highest value of adsorption capacity was observed at pH=6. The equilibrium adsorption data were obtained using the Langmuir, Freundlich and Temkin isotherms. The results indicated that the experimental adsorption data were fitted to Langmuir and Freundlich models. The maximum adsorption capacity of BY onto the MgAl LDH was found to be 115mg/g. The kinetic data of adsorption were evaluated by pseudo-first order and pseudo-second order, which described well by pseudo-second order model. The negative values of ΔG° at all temperature indicated that the adsorption process was spontaneous. The values of ΔH° and ΔS° were calculated 19.3kJ/mol and 80.5J/mol·K, respectively. The positive value of ΔH° shows that the adsorption was endothermic, while positive ΔS° value reflects increased disorder at the solid-solution interface during the adsorption.
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