Effect of synthesis parameters on ZIF-8 morphology: Insights from experimental and statistical integrated analysis

Abstract

Zeolitic Imidazole Framework-8 (ZIF-8) is an important class of metal-organic frameworks (MOFs), which has gained significant attention due to its unique morphological properties, such as high surface area and tunable porosity, making it suitable for applications in catalysis and gas storage. The synthesis of ZIF-8 is highly sensitive to various parameters, including precursor concentration, which affects its morphology and functionality. While many studies have examined the effects of synthesis parameters on ZIF-8 synthesis, they typically adjust only one factor at a time, thus overlooking the potential combined effect of multiple parameters. This study focuses on the joint effect of three critical parameters, i.e., precursor concentration, temperature, and solvent composition, on ZIF-8 morphology. Specifically, a three-factor, three-level experimental design is used to guide our investigation by varying the molar ratio of Zn²⁺:Hmim:solvent (1:60:2228, 1:100:2228, and 1:140:2228), temperatures (0 °C, 24 °C, and 50 °C), and solvent mixtures (methanol:water in volume ratios of 50:50, 70:30, and 90:10). The results show that the size of ZIF-8 varied from 57 nm to 222 nm, with the largest surface area of 1380 m²/g observed for nanoparticles sized around 170 nm. Additionally, multivariate control chart analysis is performed to quantitatively evaluate the individual and combined effects of these parameters on morphology. This analysis suggests that the molar ratio is the most significant factor affecting the size, providing insights into the morphology optimization of ZIF-8 for different applications.