Defect Engineering in UiO-66: Correlating Structural Modifications with Phenol Adsorption Performance through Comprehensive Kinetic, Isotherm and Thermodynamic Analysis

Abstract

Aquatic habitats are seriously threatened by phenolic chemicals found in industrial effluents, which calls for effective remediation techniques. This study uses thorough kinetic, isotherm, and thermodynamic analyses to examine how defect engineering affects the adsorptive performance of UiO-66 metal-organic frameworks for phenol elimination. Hydrothermal synthesis was used to create both defective and non-defective UiO-66, with EDTA acting as a modifying agent to introduce defects. FT-IR, XRD, TGA, DSC, SEM, and nitrogen physisorption were used to characterise the materials. The faulty sample showed signs of missing-linker defects, such as hierarchical porosity, uncoordinated carboxylate groups, and noticeable peak broadening. Both adsorbents achieved >95 % phenol elimination in 30 minutes, according to batch adsorption experiments that assessed the effects of concentration, dose, pH, duration, and temperature. While defective UiO-66 demonstrated enhanced uptake at pH 1 (98.7 %) and minimal dosage (97.4 % at 0.1 g), which was attributed to hierarchical porosity from missing-linker defects, non-defective UiO-66 performed better at low concentrations (96.9 % at 10 mg/L) and across a range of pH conditions because of its uniform pore architecture. Although the defective framework also fitted Elovich and intraparticle diffusion models, demonstrating site heterogeneity, the kinetic data preferred pseudo-first-order models (R2≈1.000), suggesting physisorption dominance. Differential model preferences were revealed by isotherm analysis; non-defective UiO-66 aligned with Freundlich and Redlich-Peterson formalisms, while defective UiO-66 best fit Langmuir and Temkin. For both materials, thermodynamic characteristics verified entropy-driven, exothermic, and spontaneous adsorption. These results show that UiO-66 adsorption qualities may be strategically tuned through defect engineering, with non-defective versions performing best in quick, ambient-temperature water purification treatments and defective frameworks being best suited for high-temperature, prolonged-contact situations.