Facile Synthesis and Characterization of Trimetallic CuCrFe-BTC MOF for the Adsorptive Removal of Diamond Green G: Kinetic, Isotherm, and Thermodynamic Study

Abstract

In this study, trimetallic organic frameworks (CuCrFe-BTC MOF) was synthesized via the solvothermal method and applied for the adsorptive removal of diamond green G dye from aqueous medium. The synthesized CuCrFe-BTC MOF was characterized by SEM, FTIR, XRD, TGA, Zeta potential analyzer, and surface area analyzer. The results revealed that the synthesized MOF has spherical particles in the nanoscale range (80 nm), FTIR analysis confirmed the presence of necessary functional groups, XRD indicated high crystallinity with distinct peaks and TGA analysis demonstrated the thermal stability up to 500°C. The moderate negative charge value (−14.7 mV) as predicted by zeta potential analysis suggests its suitability for remediation of cationic pollutants. BET analysis revealed a high surface area of 767 m²/g, with a microporous structure. The synthesized MOF were then employed for the removal of diamond green G dye from water using batch adsorption approach. The effect of contact time, adsorbent dosage, pH, initial dye concentration, and temperature on adsorption was also evaluated to optimize the adsorption process. The maximum adsorption was achieved at optimum contact time of 60 min, adsorbent dosage of 0.01 g, pH 8, initial dye concentration of 100 ppm, and temperature 298 K. Different isotherm and kinetic models were applied to the adsorption experimental data. Kinetic data analysis revealed the best fit of the data with pseudo-second-order model confirming the chemisorption nature of the adsorption process. The isotherm studies data fitted well into Langmuir isotherm model, indicating monolayer adsorption with a maximum adsorption capacity Q_m of 434 mg.g⁻¹. Thermodynamic studies revealed that the adsorption process was endothermic with an enthalpy change ∆H° of 14.74 kjmol⁻¹ and an entropy change ∆S° of 53.44 jmol⁻¹ K⁻¹. Gibbs free energy ∆G° was negative at all tested experimental temperatures. The Gibbs free energy value increased with increase in temperature (−0.921, −1.989, and −3.058 at 293, 313, and 333 K respectively) indicated the feasibility of the process at high temperature. The overall adsorption process might involve several potential mechanisms including chemisorption involving π-π bonding, pore-filling, electrostatic interactions, and hydrogen bonding. The adsorbent was regenerated with sodium hydroxide and ethanol for many cycles and very little differences in adsorption capacity were recorded till 7th cycle. The study verified the structural stability and performance of CuCrFe-BTC MOF and showed its regeneration potential in industrial applications and could therefore, be considered as best alternative of commercial activated carbon.