Zeolitic Imidazolate Frameworks (ZIFs): Metal–Organic Framework Nanomaterials for Selective Adsorption and Recovery of Polyphenols from Water

Water contamination from industrial and agro-industrial effluents remains a pressing environmental challenge. Among the diverse pollutants detected in wastewater, polyphenols present a distinctive dual characteristic: while elevated concentrations can disrupt aquatic ecosystems [1], they are highly valued for their antioxidant, antimicrobial, and nutraceutical properties [2]. Therefore, their selective recovery from water represents not only an environmental imperative, but also a strategic opportunity for resource valorisation from a circular economy perspective [3, 4]. In this context, Zeolitic Imidazolate Frameworks (ZIFs), a subclass of porous metal–organic framework (MOF) nanomaterials, were explored as advanced adsorbents for polyphenol recovery [5]. Three materials were synthesized and comparatively assessed: ZIF-8 (Zn-based), ZIF-67 (Co-based), and a hybrid bimetallic ZIF-67/8. Comprehensive physicochemical characterization (XRD, XPS, HRTEM, FESEM-EDS, N₂ physisorption, and TGA) was performed and correlated with adsorption performance using gallic acid as a model compound, alongside with structurally related polyphenols to elucidate structure–affinity relationships. Adsorption was predominantly governed by hydrogen bonding and coordination interactions, as evidenced by the strong dependence on polyphenol functional groups. All ZIFs exhibited remarkably fast adsorption kinetics at low and moderate concentrations (10–100 mg/L), achieving complete removal within minutes. However, performance declined with higher pollutant loads.Stability investigations revealed a critical limitation. The crystal structure of ZIF-67 undergoes complete structural collapse upon prolonged exposure to water (more than 5 h). Moreover, despite the comparatively higher water resistance of ZIF-8, all frameworks underwent partial structural degradation during adsorption, accompanied by loss of crystallinity and microporosity. The hybrid ZIF-67/8 displayed intermediate behaviors, balancing adsorption efficiency with improved aqueous stability. These results emphasize that high performance must be accompanied by long-term structural resilience, guiding future efforts toward more water-stable MOF systems and hybrid materials for scalable and sustainable polyphenol recovery. References [1] Y. Pan, Y. Zhang, M. Hou, J. Xue, R. Qin, M. Zhou, Y. Zhang, Sep. Purif. Technol. 2023, 317, 2023123905. [2] G. Riccucci, S. Ferraris, C. Reggio, A. Bosso, G. Orlygsson, C.H. Ng, S. Spriano, Langmuir 2021c, 37 (51), 14793. [3] M. G. Galloni, V. Nikonova, G. Cerrato, A. Giordana, P. Pleva, P. Humpolicek, E. Falletta, C.L. Bianchi, J. Environ. Manage. 2024, 369 122365. https://doi.org/10.1016/j.jenvman.2024.122365 [4] L. Franzen Ramos, J. Pluschk, A. Moura Bernardes, S.-U. Geißen, CLCB 2023, 5, 100048 [5] Z. Zheng, Z. Rong, H.L. Nguyen, O.M. Yagh, Inorg. Chem. 2023, 62, 51, 20861