Analytical investigation of calcined layered double hydroxide for the efficient removal of selected organic dyes from aqueous solutions

A calcined layered double hydroxide (Mg Al-LDH, Mg4Al2(OH)14·13H2O) was synthesized and evaluated as an efficient adsorbent for the removal and determination of organic dyes from aqueous solutions. The synthesized adsorbent was characterized using Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM), confirming its successful formation and enhanced surface properties. The adsorption behaviour toward Congo Red (CR) and Alizarin Red (AR) dyes was investigated using a batch adsorption method under various experimental conditions, including initial dye concentration, pH, contact time, and temperature. Residual dye concentrations were determined by UV–Vis spectrophotometry at λmax values of 497 nm for Congo Red and 430 nm for Alizarin Red. Excellent analytical performance was achieved with linear calibration ranges of 0.5–50.0 mg L⁻¹ for both dyes, correlation coefficients (R²) higher than 0.999, limits of detection (LOD) of 0.12 mg L⁻¹ for Congo Red and 0.15 mg L⁻¹ for Alizarin Red, and relative standard deviations (%RSD, n = 5) below 3.5. Adsorption isotherm studies revealed that the adsorption process followed Giles' L-type (Group 2) classification and was best described by the Langmuir isotherm model. The adsorption kinetics were evaluated using pseudo-first-order and pseudo-second-order models, with the latter providing the best fit to the experimental data. Maximum adsorption capacities obtained from experimental measurements were 94.952 mg g⁻¹ for Congo Red and 81 mg g⁻¹ for Alizarin Red. The results demonstrate that the Mg Al-LDH adsorbent is an effective, environmentally friendly material for the removal and spectrophotometric determination of organic dyes from contaminated water samples.