Recycling Spent Synthesis Liquor for Enhanced Production of ZIF‐67: Characterization and Morphological Insights

This study reports the preparation and characterization of zeolitic imidazolate framework‐67 (ZIF‐67) through the recycling of spent synthesis liquor containing unreacted 2‐methylimidazole. The recycling enhances the yield of ZIF‐67 while maintaining the dodecahedral rhombic morphology of the particles. In the first synthesis, a molar ratio of 1:26 (Co²:2‐methylimidazole) results in particles with an average diameter of 230 nm and a surface area of 1374 m² g⁻¹. The first recycling step produces ZIF‐67 particles that doubl in diameter and surface area, reaching 520 nm and 1690 m² g⁻¹, respectively. In the second recycling step, the particles further increase to 1040 nm in diameter and 1806 m² g⁻¹ in surface area. This increase in diameter is attributed to changes in the metal‐to‐ligand ratio, which affects the nucleation and growth rates. Increased surface area is linked to a reduction in the average micropore diameter, which decreases from 1.42 nm (first synthesis) to 1.37 nm (second recycling step). There is a 6 m² g⁻¹ increase in surface area for every 0.001 cm³ g⁻¹ increase in the volume of micropores. This indicates that the spent liquor can be utilized in consecutive batches to produce ZIF‐67, minimizing reagent waste.