Interaction of Methylene Blue on the Functionalized Hybrid Mg/Fe Layered Double Hydroxide—A Kinetic and Thermodynamic Interpretation

Abstract

The escalating presence of harmful dyes in industrial wastewater is a critical issue, with textiles, food, paper, and pharmaceutical industries identified major contributors. This study enhances the adsorption capabilities of Mg/Fe layered double hydroxide (LDH), a recognized adsorbent, by incorporating jute charcoal. Resulting hybrid, created with a 3 : 1 Mg/Fe molar ratio using co-precipitation, proves more efficient in removing Methylene Blue (MB) dye than pristine Mg/Fe LDH. Described by the Freundlich model, the hybrid displays a higher K value (0.87) than Mg/Fe LDH (0.13), indicating enhanced adsorption capacity. The pseudo-second-order kinetic model identifies chemisorption as the rate-determining step. Across temperatures (10 to 60°C), equilibrium MB removal reaches 343–454 µmol/g (Mg/Fe LDH) and 528–666 µmol/g (hybrid Mg/Fe LDH). The activation energy is significantly lower for the hybrid (18.63 kJ/mol) than Mg/Fe LDH (111.33 kJ/mol), signaling a favorable process. The hybrid’s efficacy in MB removal is attributed to π–π interactions, cation–π interactions, H-bonding, and electrostatic forces. Spontaneous adsorption is confirmed by negative ∆G° values (–5.5 to –9.69 kJ/mol for Mg/Fe LDH and –4.7 to –5.5 kJ/mol for the hybrid), exothermic reactions (∆H° values –5.5, –8.5 kJ/mol), and increased disorderliness (∆S° values 7.39, 11.71 kJ/molK), underscoring the hybrid’s potential in combating textile pollution.