ZnCo Bimetallic Macro-Microporous Metal–Organic Frameworks for Efficient Adsorption of Dyes

The significant threat posed by dye wastewater has driven the development of efficient adsorbents, such as metal organic frameworks (MOFs). Specifically, we explore the synthesis and application of ZnCo-based bimetallic zeolite imidazolate frameworks with a macro-microporous structure (SOM-ZnCo-ZIF), which exhibit enhanced adsorption capacity for dyes due to their large specific surface area and ordered porous arrangement. When SOM-ZnCo-ZIF is immersed in DMA solutions of methylene blue, methyl orange, crystal violet, and rhodamine B, due to its high specific surface area and the synergistic effect of ZnCo bimetallic clusters, SOM-ZnCo-ZIF significantly enhances dye adsorption. Notably, its adsorption capacity for Rhodamine B reaches an impressive 6798.9 mg/g, and within just 1 min, 0.5 g/L of SOM-ZnCo-ZIF can remove over 97% of Rhodamine B from a 60 mg/L solution. Moreover, it maintained a 92.8% dye removal efficiency in ten cycles without regeneration, demonstrating the effective adsorption capacity of SOM-ZnCo-ZIF. Density functional theory calculations have shown that the adsorption energy of ZnCo bimetallic ZIF for Rhodamine B is approximately twice that of a single metal. SOM-ZnCo-ZIF exhibits strong adsorption of Rhodamine B mainly due to its macro-microporous structure, which provides larger pore sizes (∼250 nm) allowing the dye molecules to infiltrate the porous network, and its ability to facilitate π-π stacking interactions between the benzene rings of Rhodamine B and the imidazole rings of the ZIF. Additionally, the interaction is further enhanced by strong coordination bonds and electrostatic interactions between the cationic dye and the negatively charged framework. This work not only proposes an effective adsorbent to remove Rhodamine B but also provides valuable insights for the rational design and synthesis of environmentally sustainable MOF structures.