Defective NH₂-UiO-66 for Efficient Adsorption of Anionic Dye

Abstract

The development of high-performance adsorbents for the efficient removal of anionic dyes from wastewater remains a critical challenge. Metal-organic frameworks (MOFs), especially amino-functionalized NH₂-UiO-66, are promising candidates for this application, and their adsorption properties can be further enhanced via defect engineering. In this study, defective NH₂-UiO-66 was synthesized through a facile solvothermal approach, and its adsorption performance toward Direct Scarlet dye was systematically evaluated. The defective NH₂-UiO-66 featured a hierarchical micro-mesoporous structure, originating from missing-linker defects, with a high specific surface area of 944.91 m²·g⁻¹, and excellent thermal stability. NH₂-UiO-66 exhibits a maximum Langmuir adsorption capacity of 534.76 mg·g⁻¹ for Direct Scarlet dye under neutral conditions. Adsorption kinetics and isotherms fitted well with the pseudo-second-order (R² = 0.9952) and Langmuir (R² = 0.9948) models, indicating a spontaneous, endothermic monolayer adsorption process. Notably, the NH₂-UiO-66 exhibits approximately 80% removal efficiency after five consecutive adsorption-desorption cycles, demonstrating excellent reusability. Importantly, the PXRD pattern of the recycled material confirms its robust structural stability. FT-IR analysis further verified that the enhanced adsorption performance was primarily driven by strengthened electrostatic interactions between protonated amino groups and anionic dye molecules. This work demonstrates that the strategic combination of amino functionality and defect-induced hierarchical porosity offers a synergistic enhancement in dye adsorption, providing a versatile strategy for designing advanced Zr-MOF adsorbents for water treatment applications.