Atomic Force Microscopy to Characterize Size of Zeolitic Imidazolate Framework‑8 Nanocrystals

The crystal nucleation and growth mechanism of monodispersed metal–organic framework nanoparticles were studied using Dynamic Light Scattering (DLS) and Atomic Force Microscopy (AFM) characterization methods. We confirmed that zeolitic imidazolate framework-8 (ZIF-8) nanocrystals follow a nonclassical crystal growth pathway, where a fast nucleation occurs with dense liquid clusters or nanocrystals forming spontaneously when two precursors are mixed. Two modulators, including 1-methylimidazole (1-mIm), tris(hydroxymethyl)aminomethane (THAM) were studied with AFM. We found that 1-mIm dramatically increases the rate of nucleation of ZIF-8. With an increasing amount of 1-mIm, which functions as a coordination modulator, the size increases, and the zeta potential of ZIF-8 decreases. We discuss the size dependence of the nanoparticles on mica substrates using atomic force microscopy. The findings will be applicable to other nanocrystals in colloid systems, which are used for heterogeneous catalysis and guest molecular loadings.