Does the rate of metal salt precursor addition during ZIF-8 nanoparticles preparation affect their morphology?: Application in dye adsorption

Zeolitic imidazolate framework (ZIF)-8 nanoparticles demonstrate excellent physicochemical properties, which make them suitable for a variety of applications. However, their scale-up manufacturing requires insight into the rate of addition of precursors. This study investigates the impact of Zn salt precursor rate of addition to an organic linker solution on the morphology and size of ZIF-8 nanoparticles, and their potential for the adsorptive removal of dyes (cationic and anionic). ZIF-8 nanoparticles were produced with a molar ratio of Zn/2-methyl imidazole (Hmim)/H₂O at 1/36/2206 by varying the flow rate of Zn precursor at 5, 10, 15, 20, and 25 mL/min into the Hmim solution. The physicochemical properties of the synthesized ZIF-8 nanoparticles were assessed using microscopy, analytical, and spectroscopy techniques. Owing to different flow rates of the precursor, variations in the ZIF-8 particles’ size and morphology were observed. It was found that the optimum flow rate was 15 mL/min (named Z-15), resulting in particle size of 261 nm, with a high specific surface area, thermal stability, and a substantially high yield of ∼89%. Furthermore, the dye adsorption studies, performed using Z-15 NPs, resulted in high methylene blue (∼82%) and methyl orange (∼76%) removal efficiency. The adsorption performance was maintained with dye-spiked simulated wastewater. The superior dye adsorption capacity of the ZIF-8 nanoparticles could be attributed to their microporous characteristics. Thus, this study demonstrates that the rate of addition of Zn precursor in the synthesis of ZIF-8, indeed, affects both their morphology and size, and the resulting nanoparticles exhibit promising adsorption performance toward dyes.