Bimetallic PCN-333 with Modulated Crystallization and a Porosity Structure for a Highly Efficient Removal of Congo Red

Abstract

Bimetallic metal–organic frameworks (BMOFs) have garnered significant attention in the field of environmental remediation due to their more diverse adsorption sites compared to monometallic metal–organic frameworks (MOFs). Different energy barriers must be overcome for different metal ions and organic linkers to form MOFs. However, the impact of the synthesis temperature on the crystallization and porosity structure of BMOFs has been rarely studied. In this work, PCN-333 series-based BMOFs with different Fe/Al ratios were prepared by a solvothermal method at temperatures of both 135 and 150 °C. The synthesis temperature and Fe/Al ratio have significant effects on the crystal structure and specific surface area of bimetallic PCN-333, leading to the different adsorption performance of the PCN-333 for Congo red (CR). The Fe/Al-PCN-333–135(3:1) and Fe-PCN-333–150 exhibited the maximum CR adsorption capacities of 3233 and 3933 mg/g, respectively, surpassing the capacities of most previously documented adsorbents. The Langmuir model and pseudo-second-order kinetics can well describe the adsorption process of CR on Fe/Al-PCN-333–135(3:1) and Fe-PCN-333–150. Combining the isotherm adsorption behavior with the thermodynamic parameters, CR adsorption on BMOFs is a single-layer endothermic chemical adsorption. Furthermore, Fe/Al-PCN-333–135(3:1) and Fe-PCN-333–150 exhibited regenerability and reusability for three cycles with reasonable efficiency. This work is of great significance in the field of engineering BMOF materials to treat dye wastewater.