NH2-MIL-53(Al) with Hierarchical Micro–Mesoporosity for Highly Efficient Capture of Direct Scarlet Anionic Dye: Insights into Structure–Property Correlations

Fabricating nanoscale metal–organic frameworks (MOFs) with hierarchical pores is an effective strategy to engineer high-performance adsorbents. Herein, hierarchically porous NH2-MIL-53(Al) nanorods were synthesized through a straightforward one-pot solvothermal approach, featuring inherently interconnected micro-/mesoporous with an average pore width of 19.51 nm and abundant amino-functionalized active sites. Toward the anionic Direct Scarlet dye, the material delivers a Langmuir maximum adsorption capacity of 694.99 mg·g−1, with its adsorption kinetics and isotherms well described by the pseudo-second-order kinetics and Langmuir isotherm model. Combined spectroscopic, thermodynamic, and diffusion analyses suggest monolayer electrostatic chemisorption between protonated –NH3+ and dye sulfonate groups. The material exhibits favorable reusability, retaining over 85% of its original dye removal efficiency after five adsorption–desorption cycles, and PXRD and SEM results verify well-preserved morphology and crystalline lattice. This work clarifies the intrinsic correlation between structure and adsorption performance of NH2-MIL-53(Al), offering a facile nanoscale pore-tuning strategy for the design and fabrication of high-performance MOF adsorbents.