Engineered MnO₂/UiO-66-x Heterostructure with Tailored Interfaces for Efficient Capture of NSAIDs: Performance and...

The widespread misuse of nonsteroidal anti-inflammatory drugs (NSAIDs) has become a growing concern due to their severe threats to aquatic ecosystems and human health. Current adsorption technologies face limitations including low capacity, poor efficiency for trace-level contaminants, and unclear removal mechanisms. These limitations stem from poorly optimized pore architectures and surface chemistries in existing materials, necessitating the development of multifunctional adsorbents with tailored active sites. Herein, a series of MnO₂/UiO-66-x composites were rationally designed via a solvothermal approach and comprehensively characterized using powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, N₂ physisorption, scanning electron microscopy (SEM), and zeta potential analysis. Systematic optimization demonstrated that MnO₂/UiO-66-1 (5 mg) achieved exceptional adsorption capacity (q_max = 659.49 mg·g^-1) for diclofenac sodium (DCF, 20 mg·L^-1, 30 mL), with >90% removal within 10 min (k₂ = 0.0081 g·mg^-1·min^-1). Mechanistic studies revealed that this performance was attributed to hierarchical porosity (micro-/mesopores), which enables size-selective uptake, synergistic binding, and pH-dependent electrostatic enhancement. Structure-activity relationships indicated that NSAIDs adsorption efficiency (naproxen ≈ ibuprofen ≈ ketoprofen > indomethacin > paracetamol) was governed by molecular structure, size, and pK_a values. Thermodynamic and kinetic studies confirmed a spontaneous (ΔG⁰ < 0), endothermic (ΔH⁰ > 0), and entropy-driven (ΔS⁰ > 0) process dominated by chemisorption through synergistic interactions (including coordination bonding, hydrogen bonding, Lewis acid-base effects, electrostatic attraction, and π-π stacking). This study establishes a new paradigm for metal-organic-framework-based adsorbent design through precise control of metal-organic interfaces and defect engineering. With 87% capacity retention after 5 regeneration cycles, MnO₂/UiO-66-x shows strong potential for practical water remediation applications.