Adsorptive Decontamination of Methyl Violet 6B Using a Trimetallic CuCrFe–BDC Metal Organic Framework: Equilibrium Isotherms, Kinetic Modeling & Thermodynamic Insights

Abstract

This work presents the solvothermal synthesis of a trimetallic CuCrFe–BDC Metal-Organic Framework (CuCrFe-BDC MOF), designed for highly efficient and stable adsorption of Methyl Violet 6B (MV-6B) dye from aqueous media. Detailed characterization via SEM, XRD, FTIR, BET, TGA, zeta potential, EDX, and elemental mapping was carried out. FTIR analysis verified all pivotal functionalgroup signatures, while XRD confirmed a highly crystalline phase exhibiting sharp, well-defined diffraction peaks. TGA demonstrated exceptional thermal resilience up to 600°C. BET measurements revealed a remarkable specific surface area (626 m²/g) with pronounced microporosity, ideal for high-performance adsorption. The material was synthesized with an average nanoscale particle size of 87 nm, forming larger aggregates around 289 nm. Under optimized conditions of 0.01 g adsorbent dosage, 333 K, pH 8, and a 60 min contact time, the trimetallic CuCrFe-BDC MOF achieved over 91 % removal of MV-6B dye. Adsorption kinetics followed a pseudo-secondorder model (R² > 0.99), indicating chemisorption dominance. Equilibrium data conformed closely to the Langmuir isotherm (R²  =  0.99), with a maximum monolayer adsorption capacity of 416 mg/g at 333 K. Thermodynamic analysis revealed an endothermic process, by positive enthalpy change (ΔH°  = 17.79 kJ/mol ) that is spontaneous across the temperature range studied, as evidenced by consistently negative ΔG° values. The adsorption mechanism likely includes chemisorption combined with π–π stacking, pore-filling, electrostatic interactions, and hydrogen bonding. Importantly, the CuNiZnBDC MOF maintained its structural integrity and recyclability over seven adsorption–desorption cycles, retaining 65 % removal efficiency. These findings underline the potential of this robust, high-capacity MOF as an effective adsorbent for industrial wastewater applications.