Fabrication of Cerium Metal–Organic Frameworks Functionalized with Glutamic Acid for Adsorption of Basic Red 46 from Aqueous Solutions: Kinetics, Thermodynamics, and Optimization

This research investigated the efficient removal of cationic Basic red 46 (BR46) dye from aqueous solutions, by means of cerium metal-organic frameworks (Ce-MOF) functionalized with glutamic acid to create NH₂-Ce-MOF. The NH₂-Ce-MOF was easily produced through a postsynthesis functionalization strategy and extensively analyzed through numerous methods with X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX), and N₂ adsorption/desorption isotherm. The findings revealed that the synthesized adsorbent had a high surface area of 1158.8 m²/g, a pore size of 1.511 nm, and a pore volume of 0.875 cm³/g. Upon adsorption of the BR46 dye, the surface area decreased to 872.6 m²/g, the pore size reduced to 1.18 nm, and the pore volume released to 0.53 cm³/g. The decreases in surface area, pore size, and volume demonstrate the material's strong ability to adsorb substances, as the dye molecules can fill the tiny pores. They exhibited an increased adsorption capability of 454.8 mg/g. The Langmuir isotherm and pseudo-second-order kinetic models performed the best at simulating adsorption isotherm and kinetic curves, respectively. The exhibition of chemisorption and adsorption energy of 28.4 kJ/mol was supported by various adsorption driving forces, including hydrogen bonding, electrostatic interaction, π-π conjugation, pore filling, and van der Waals force. After conducting thorough research on the impact of temperature, it was established that the adsorption procedure is both endothermic, indicated by a positive Δ<i>H</i>° of 83.7 kJ/mol.K, and spontaneous, as confirmed by the increase in negativity of Δ<i>G</i>° with rising temperatures. Additionally, the increase in randomness with increasing temperatures is evident in the Δ<i>S</i>° value of 289.32 J/mol. Employed Box-Behnken design (BBD) and response surface methodology (RSM) to enhance the results of the adsorption procedure. The NH₂-Ce-MOF proposal is a practical, affordable solution for eliminating BR46 dye from wastewater streams because the adsorbent was composed of reusable materials and reused over five times with excellent efficiency.