Optimisation of methyl orange from aqueous solution onto magnesium-aluminium layered double hydroxide using response surface methodology

The discharge of dye containing wastewater from textile industries poses serious environmental and health concerns due to the persistence and toxicity of synthetic dyes such as methyl orange. Methyl orange was selected as the target pollutant because it is a common anionic azo dye that widely used in textile related industries. This study investigates the adsorption performance of magnesium–aluminium layered double hydroxide (MgAl-LDH) for the removal of methyl orange from aqueous solutions. MgAl-LDH was synthesised via the co-precipitation method and characterised using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX). The characterisation results confirmed the successful formation of a hydrotalcite-like layered structure with characteristic functional groups, plate-like morphology and homogeneous elemental composition. The adsorption process was optimised using response surface methodology (RSM) to evaluate the effects of adsorbent dosage, pH solution, initial methyl orange concentration and contact time on methyl orange removal efficiency. Statistical analysis showed that the developed quadratic model was significant and reliable, with optimum adsorption conditions obtained at approximately 0.65 g of MgAl-LDH, 7.78 of pH, 40 mg/L of initial methyl orange concentration and 20 minutes of contact time, achieving a maximum predicted methyl orange removal of 92.19%. Experimental validation conducted under the optimum conditions resulted in a higher methyl orange removal efficiency of 94.4% with relative standard error values below 5%, demonstrating good agreement with the model prediction and confirming the reliability of the RSM approach. Adsorption isotherm analysis indicated that the equilibrium data were better described by the Freundlich model, suggesting heterogeneous and multilayer adsorption behaviour. Kinetic studies showed that the adsorption process followed the pseudo-second-order model, indicating chemisorption as the dominant mechanism. The applicability of MgAl-LDH was further evaluated using textile wastewater where highest removal efficiency was 78.80% were achieved under the optimised conditions. Desorption and reusability studies revealed a gradual decrease in adsorption efficiency over repeated cycles, highlighting the need for improved regeneration strategies. Overall, this study demonstrates that MgAl-LDH is an effective adsorbent for methyl orange removal and has promising potential for wastewater treatment applications.