Recent advances in ZIF-67-based composites for heavy and radioactive metal ion removal: synthesis, adsorption mechanisms, performance assessment, and future directions

The contamination of aquatic environments with heavy metals and radioactive ions has emerged as a critical global issue due to their toxicity, persistence, and bioaccumulative nature. Addressing this challenge requires the development of efficient, sustainable, and scalable remediation technologies. This review comprehensively examines recent advancements in the use of zeolitic imidazolate framework-67 (ZIF-67) and its nanocomposites for the adsorptive removal of heavy and radioactive metals from wastewater. Synthesis and functionalization strategies to enhance structural stability, adsorption capacity, and selectivity are critically discussed. Various composites incorporating graphene oxide, carbon nanotubes, biochar, polymers, and magnetic nanoparticles are analyzed, highlighting their synergistic effects in improving adsorption performance. Key operational factors influencing the adsorption process—such as solution pH, temperature, contact time, and adsorbent dosage—are systematically reviewed. Adsorption isotherms, kinetics, and thermodynamic parameters are assessed to elucidate the underlying mechanisms governing metal ion removal, including electrostatic interactions, complexation, and ion exchange. The regeneration and reusability of ZIF-67-based adsorbents are also evaluated, underscoring their practical potential for multiple adsorption cycles. Studies investigating the removal of heavy metals from real wastewater using ZIF-67 composites are examined, providing insights into real-world performance. Despite significant progress, challenges such as achieving consistent material stability, controlling pore structures, minimizing agglomeration, and developing cost-effective, scalable fabrication methods remain. Future research directions are proposed, focusing on the rational design of multifunctional composites, green synthesis strategies, and the integration of advanced modeling and characterization techniques. This review aims to guide innovations toward the practical deployment of ZIF-67-based adsorbents for sustainable water treatment technologies.