Synthesis, characterization, and application of low-cost Mg-Al/CO3 and Ni-Al/CO3 layered double hydroxides (LDHs) as adsorbents for the removal of aniline blue dye from aqueous solutions: adsorption isotherms, kinetics, and thermodynamic studies

Low cost Mg-Al/CO₃ and Ni-Al/CO₃ layered double hydroxides (LDHs) were prepared using a co-precipitation technique to improve their dye adsorption efficiency. Characterization techniques were employed to assess their structure and surface properties, including FT-IR, XRD, SEM, BET surface analysis, and UV-vis spectroscopy. The BET analysis revealed surface areas of 82.63 m² g⁻¹ for Mg-Al/CO₃ and 5.95 m² g⁻¹ for Ni-Al/CO₃, highlighting their porous nature. The materials' capability to adsorb aniline blue from water was tested under various conditions, such as time, pH, dye concentration, and temperature. The adsorption data were analyzed using both Langmuir and Freundlich isotherm models. The Mg-Al/CO₃ LDH exhibited a notably higher maximum adsorption capacity of 704 mg g⁻¹, compared to 181 mg g⁻¹ for Ni-Al/CO₃ LDH, according to the Langmuir model. The correlation coefficients (R²) indicate that the Freundlich model better fits the Mg-Al/CO₃ LDH data (R² = 0.9829), while the Langmuir model offers a better fit for Ni-Al/CO₃ LDH (R² = 0.9576). While kinetic studies showed that the pseudo-second-order model provided the best fit. The process was spontaneous and endothermic based on thermodynamic analysis, with positive entropy changes suggesting increased randomness at the interface. These results underscore the promise of using Mg-Al/CO₃ and Ni-Al/CO₃ LDHs as economical adsorbents in water purification.