High-efficiency AB113 dye removal using calcined CuMgAl-LDH: memory effect and CCD-RSM optimization

In this study, CuMgAl-layered double hydroxide (LDH) was synthesized by co-precipitation at pH 10, an amount of the prepared material was calcined at 823 K for 5 h. Structural and morphological analyses confirmed the successful synthesis of CuMgAl-LDH with good crystallinity, and showed that calcination resulted in the formation of randomly distributed open pores. The synthesized material exhibited excellent performance in removing the azo dye Acid Blue 113 (AB113), achieving an adsorption efficiency of 98.1 % under batch conditions (10 mg, 50 mg L⁻¹, 20 min, and 296 ± 2 K). The AB113 dye removal was not sensitive to the initial solution pH, temperature, and the presence of co-existing ions. On the other hand, Calcination led to a marked improvement in the dye removal efficiency, especially at high concentrations. Kinetic and isotherm modeling revealed that the experimental data fit well with pseudo-second-order and Langmuir model. The thermodynamic study indicates that the process was spontaneous and endothermic. Adsorption mechanism of AB113 dye onto CuMgAl-LDH involved electrostatic attraction and hydrogen bonding interactions. The central composite design (CCD) within response surface methodology (RSM) was used to optimize the experimental conditions for the adsorption process. The most influential factors were the CuMgAl-LDH mass (A), the initial concentration of AB113 dye (B), quadratic terms (A², B²), and interaction term (AB). An adsorption efficiency of AB113 dye under optimal conditions (10 mg, 50 mg L⁻¹, pH 8, 20 min, and 298 K) was 98.67 %, which is in good agreement with the batch experiments results. CuMgAl-LDH retained a high AB113 dye removal efficiency over six successive reuse cycles, owing to its memory effect. The results show that CuMgAl-LDH is a promising adsorbent for removing pollutants from dye wastewater.