Engineering Water-Stable Iron-Based MOF-74/Silica Nanocomposite for Sequestration of Atrazine and Ciprofloxacin: Performance, Interfacial Mechanisms, and Reusability

The limited water and thermal stability of metal–organic frameworks (MOFs) remains a major barrier to their practical deployment in adsorption-based separations. In the present work, a water-stable adsorbent was fabricated based on Fe-MOF-74 integrated with SiO2, termed the Fe-MOF-74/SiO2 nanocomposite, through a straightforward postsynthetic incorporation strategy and evaluated for the adsorption of atrazine (ATZ) and ciprofloxacin (CIP). Comprehensive characterizations confirmed successful SiO2 incorporation and revealed the evolution of hierarchical micromesoporosity. The SiO2 network provides a robust structural scaffold, endowing the composite with exceptional aqueous durability, with 88.8% of the initial surface area remaining after 72 h of water exposure. Under optimal conditions, the maximum uptake capacities for ATZ and CIP reached 131.6 and 404.7 mg/g, respectively, exceeding those of bare Fe-MOF-74. Isotherm modeling revealed that ATZ adsorption best correlated with the Langmuir model, whereas CIP adsorption exhibited better agreement with the Freundlich model. The adsorption process followed pseudo-second-order kinetics and was spontaneous and exothermic. Importantly, experiments at trace levels demonstrated the feasibility of the composite for practical environmental applications, with almost complete removal (>98%) of pollutants at concentrations of 0.1–1.0 mg/L. The adsorbent displayed outstanding performance in real wastewater matrices and robust resilience against competitive interferences from natural organic matter (NOM) and background cations. Mechanistic investigations suggest the adsorption is governed by a hierarchy of electrostatic attraction, Lewis acid–base coordination, π–π interactions, hydrogen bonding, and pore filling. Furthermore, the composite exhibited excellent practical reusability across eight consecutive cycles. Postregeneration analysis showed that the small loss in capacity was due to incomplete desorption, not collapse of the structure, with trace metal and silica leaching being essentially negligible. These findings demonstrate that interfacial engineering with SiO2 provides a viable, environmentally safe route to deploying Fe-MOF-74 for the continuous remediation of emerging organic contaminants.