Investigation the adsorption kinetic and isotherm studies of Remazol Red 5B dye on benzoic acid modified Al₂O₃/UiO-66 composite

This research used a defect engineering approach by introducing a benzoic acid modulator to synthesis Al₂O₃/UiO-66 composites. Adding 5 eq benzoic acid (Al/UiO-66(B5)) produces mesopores with irregular morphology. Increasing benzoic acid to 20 eq (Al/UiO-66(B20)) produces ordered octahedral crystals. Deformation of Al₂O₃/UiO-66 by benzoic acid can effectively remove Remazol Red 5B (RRB) dye from the aqueous solution. The adsorption performance of the synthesized material was investigated in terms of pH, temperature, initial concentration of RRB dye, and contact period. Al/UiO-66(B5) shows the best RRB adsorption capacity performance with Q_max = 333.33 mg/g at 30 °C due to the defects and mesopore structure formed. From 30° to 50 °C, the adsorption capacity decreases, and acidic media are more conducive to the adsorption of RRB dye. The presence of interfering anions such as Cl⁻, NO₃⁻, CO₃²⁻, and SO₄²⁻ can be a limiting factor in adsorption. The kinetics results show that a pseudo second order model describes absorption. The data on chemical and physical adsorption equilibrium on heterogeneous surfaces are well-fitted by the Freundlich isotherm model. Other kinetic models, such as Intraparticle Diffusion and Elovich, as well as other isotherm models, such as Temkin and Scatchard, were also evaluated in this study. RRB adsorption was hypothesized to be spontaneous, feasible and exothermic based on the assessed thermodynamic parameters ΔG°, ΔH° and ΔS°. Therefore, Al₂O₃/UiO-66 with benzoic acid modification can be a promising adsorbent in wastewater treatment. This work can provide new theoretical insights into the modification of composite MOFs for simultaneous removal of RRB dyes.