Ultrasound-Induced In Situ Self-Assembly of Bimodal Micro/Mesoporous UiO-66-NH₂ Aerogels for High-Performance Congo...

Metal-organic framework (MOF) powders possess remarkable adsorption capabilities, yet their practical application is severely hampered by poor processability, difficult recovery, and high mass-transfer resistance. Here, we report a green and rapid two-stage strategy for constructing UiO-66-NH₂ self-assembled aerogels with a bimodal micro-/mesoporous architecture. A brief thermal pretreatment (130 °C, 3 h) is used solely for precursor activation, after which the critical MOF crystallization and in situ self-assembly are driven under ambient conditions via ultrasonic cavitation (900 W, 15-60 min). This protocol simultaneously drives the nucleation, crystallization, and self-assembly of UiO-66-NH₂ nanocrystals into a monolithic, self-supporting architecture, thereby replacing the conventional prolonged high-temperature solvothermal MOF crystallization with a rapid room-temperature process. The sonication time critically governs the structural evolution, transforming initially amorphous aggregates into well-defined regular octahedral nanocrystals that form an interconnected framework. The optimized aerogel (UNA-T60) exhibits an exceptional specific surface area (1196.9 m² g^-1) and a synergistic bimodal pore structure comprising intrinsic micropores and intercrystalline mesopores. This architecture enables rapid mass transfer and active-site accessibility, resulting in a maximum Congo Red (CR) adsorption capacity of 660.56 mg g^-1, with kinetics conforming to the pseudo-second-order model (R² > 0.999). The robust monolithic structure endows the material with outstanding reusability, retaining 90.8% of its initial adsorption capacity after four regeneration cycles. This work presents a paradigm-shifting approach for the sustainable fabrication of pure MOF aerogels, offering a promising solution for advanced dye wastewater treatment.