Efficient removal of Congo red from aqueous solutions using calcined and uncalcined MgZnFe ternary layered double hydroxide (LDH)

Abstract

This study investigates the textile industries' dye Congo-red removal from aqueous solution using the calcined and uncalcined $\left[M{g}_{0.5}^{2+}Z{n}_{0.25}^{2+}F{e}_{0.25}^{3+}{\left(OH\right)}_2\right].{\left(C{O}_3^{2-}\right)}_{0.125}.H_{2}O$ ternary layered double hydroxide (LDH). XRD confirms the successful formation of the crystalline structure of LDH. FTIR analysis shows that the peak position at 1108 cm⁻¹, which indicates the presence of S = O group. TEM analysis reveals the formation of a hexagonal shape morphology, whereas BET measurements demonstrate an improvement in surface area after calcination. This study analyzed dye adsorption, which is affected by interaction time, solution pH, and adsorbent dosage. The adsorption data is analyzed using the Langmuir isotherm and Freundlich isotherm, while the kinetics data is analyzed using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The change in enthalpy (ΔH₀) being positive and the change in Gibbs free energy (ΔG₀) being negative designates that the adsorption process is endothermic and occurs spontaneously. The Langmuir isotherm model analyzed the adsorption isotherm data and calculated the amount of adsorbate adsorbed by adsorbent. The maximum amount of Congo-red adsorbed by calcined and uncalcined layered double hydroxide are 205.76 and 89.76 mg g^-1. These results suggested that calcined layered double hydroxide is a significant adsorbent for removing effluents from wastewater.