Kinetics and thermodynamics for acid red 88 adsorption on calcined layered double hydroxides

The adsorption thermodynamics and mechanism of acid red 88 (AR88) in aqueous solution adsorbed by LDO were investigated. The adsorption isotherms were measured at different temperatures, and the thermodynamic functions were also calculated. The results indicate that the equilibrium isotherms of uptake of AR88 by LDO were well fitted to the Langmuir equation, and thermodynamic parameters such as ΔG , ΔH and ΔS were calculated from Langmuir constants. The negative values confirm the spontaneous and exothermic nature of the adsorption process. Three kinetics models were used to fit the kinetics experimental data, and it was found that the pseudo-second order kinetics model could be used to describe the uptake process appropriately. The value of Ea was calculated to be 54.53 kJ • mol-1. The size and arrangement of AR88 molecular on LDHs were simulated using the CASTEP and Focite program, and speculation on mechanisms was that adsorption of AR88 on LDHs surface accompanied with a little AR88 intercalated into the layer.