Selective and Highly Efficient Adsorption of a Mixture of Anionic and Cationic Dyes as Synthetic Wastewater Absorbents on Layered Double Hydroxide: Experimental and Computational Studies

Abstract Background: In the current work, the removal of cationic and anionic dyes from water was studied both experimentally and computationally. We examine the selectivity of the adsorbent, Zn–Fe layered double hydroxide (LDH) toward three cationic and anionic dyes. Methods: The chemical and physical properties of the prepared adsorbent before and after adsorption were investigated using FT-IR, X-ray diffraction, zeta potential, energy dispersive X-ray, X-ray photoelectron spectroscopy, particle size, HRTEM, and FESEM analysis; optical and electric properties were estimated. The influence of pH on the adsorption process was estimated. Monte Carlo simulations were performed to understand the adsorption mechanism and compute the adsorption energies. Significant Findings : Single dye adsorption tests revealed that Zn–Fe LDH effectively takes up anionic methyl orange (MO) more than the cationic dyes methylene blue (MB) and malachite green (MG). From MO/MB/MG mixture experiments, LDH selectively adsorbed in the following order: MO>MB>MG. The adsorption capacity of a single dye solution was 230.68, 133.29, and 57.34 mg/g for MO, MB, and MG, respectively; for the ternary solution, the adsorption capacity was 217.97, 93.122, and 49.57 mg/g for MO, MB, and MG, respectively. Zn–Fe LDH was also used as a photocatalyst, giving 92.2% and 84.7% degradation at concentrations of 10 and 20 mg/L, respectively.