Synthesis, structural features, and adsorption performance of ZIF-8@hydroxyapatite hybrid composites for continuous adsorption systems

Abstract A hybrid composite based on a metal–organic framework (MOF), zeolitic imidazolate framework-8 (ZIF–8), and hydroxyapatite (HAp) was successfully synthesized via a straightforward and reproducible approach to address the limitations of MOFs in practical applications. While MOFs are well known for their high surface area and tunable porosity, their limited stability can restrict their use in aqueous systems. The integration of ZIF–8 with hydroxyapatite provides a synergistic platform that enhances structural robustness and surface reactivity while maintaining the intrinsic adsorption properties of the MOF. The resulting ZIF–8@HAp composite was characterized by powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), which confirmed both the preservation of the crystalline of the ZIF–8 and its successful integration onto the HAp matrix, while interfacial interaction mechanisms in the ZIF-8@HAp composite were elucidated via NCI, RDG, HS, and fingerprint plot analyses. Brunauer–Emmett–Teller (BET) analysis revealed a high specific surface area along with a well-structured and accessible pores. The adsorption performance of the composite was investigated using malachite green as a model organic dye. To evaluate process efficiency and optimize operational conditions, particular emphasis was placed on continuous fixed-bed column adsorption. The influence of key parameters, namely flow rate and bed height, was systematically examined to determine optimal working conditions. The results clearly indicated that these variables play a critical role in governing adsorption efficiency. Under optimal conditions (Q = 0.1 mL/min and H = 30 cm), a maximum adsorption capacity of 100.08 mg/g was achieved, underscoring the strong potential of this material for wastewater treatment. Overall, these findings demonstrate that ZIF–8@HAp is a promising, efficient, and stable MOF-based adsorbent for environmental remediation applications.