Adsorption of synthetic cationic dyes from water (experimental, DFT and Monte Carlo studies) and treatment of real industrial wastewater using dextrose compound-modified layered double hydroxide

Abstract

Dyes are a major water pollutant, and various methods have been employed to address the dye pollution in aqueous solutions. Currently, adsorption using inexpensive, abundant, and eco-friendly adsorbents like anionic clay is one of the simplest and most effective methods. This study aimed to investigate the fabrication of a novel layered double hydroxide modified with dextrose D@Mg1.5Zn0.5Al-LDH composite via co-precipitation route for removing both synthetic Rhodamine B (RhB) and Basic Fuchsin (BF) dyes from aqueous solutions. Various characterization techniques were employed to comprehensively understand the properties of the as-synthesized material, including XRD, FTIR, SEM-EDX, BET surface area analysis and zeta potential. To enhance the adsorption process of both basic dyes, experiments were conducted in a batch reactor to investigate the effects of key parameters such as reaction duration, initial dye concentration, pH, adsorbent dosage, and solution temperature. Cationic dyes uptake was predominantly observed within the first 10mins, reaching equilibrium in approximately 60mins. The D@Mg1.5Zn0.5Al-LDH composite achieved removal efficiencies of 99% for BF dye and 60% for RhB dye at pH 10, which are considerably higher than that of bare Mg1.5Zn0.5Al-LDH. The experimental adsorption data demonstrated excellent agreement with pseudo-second-order kinetics and the Langmuir isotherm. Density functional theory (DFT) calculations and molecular simulations had been employed to elucidate the adsorption mechanism of BF and RhB dyes onto the D@Mg1.5Zn0.5Al-LDH composite. Quantum parameters were calculated to characterize the electron density of the dyes which provided insights into their reaction behavior. Additionally, Monte Carlo simulations were employed to calculate the fluctuation energy, and to determine probability distributions of adsorption energy, and geometry of the small adsorption energy poses for BF/D@Mg1.5Zn0.5Al-LDH and RhB/ D@Mg1.5Zn0.5Al-LDH. These results offer equilibrium statistical conditions that explain the adsorption mechanism behaviors between the D@Mg1.5Zn0.5Al-LDH composite and BF/RhB dyes optimally. Importantly, the theoretical outcomes are in good agreement well with experimental results. Finally, the adsorption process is used to treat real industrial wastewater that mainly contains a mixture of Rhodamine B and Methylene Blue as the cationic dyes. The D@Mg1.5Zn0.5Al-LDH composite has shown good efficiency in the treatment of real industrial wastewater.