Chloride sorption of nano-SiO2@MgAl-layered double hydroxides core-shell nanocomposite in simulated concrete pore solution: Equilibrium, thermodynamic and kinetic studies

Nano-SiO₂@MgAl-layered double hydroxides (NS@MgAl-LDH) core-shell nano-composites were successfully synthesized by a co-precipitation method. The as-synthesized NS@MgAl-LDH was characterized by SEM, TEM, EDX, TGA and BET. The equilibrium, thermodynamic and kinetic studies on the chloride sorption of NS@MgAl-LDH were performed in simulated concrete pore solution (SCPS). The results show that NS@MgAl-LDH exhibits a higher specific surface area (SSA) compared to MgAl-LDH. Besides, the chloride sorption capacity of NS@MgAl-LDH is significantly higher than that of pure MgAl-LDH, which is obviously influenced by initial pH-value and amount of adsorbents addition. Also, the chloride sorption process can be fitted by the Langmuir-model thermodynamically and the pseudo-second-order kinetics kinetically. The negative values of Gibbs-free energy (ΔG⁰) and standard enthalpy change (ΔH⁰) indicate that the chloride sorption is spontaneous and exothermic. Furthermore, the outstanding chloride sorption capacity of NS@MgAl-LDH is mainly contributed to the ion-exchange of chloride ions with interlayer ions in the highly dispersed MgAl-LDH.