Ultrasound-assisted synthesis of layered zeolitic imidazolate framework: crystal formation and characteristics

Two-dimensional (2-D) Zn/Co, Zn, and Co zeolitic imidazolium frameworks (ZIF) were synthesized using straightforward ultrasound techniques. Dual metal Zn/Co ZIF-L, Zn ZIF-L and Co ZIF-L with leaf-like shape morphologies were prepared in 15 min. Various characterizations have been applied including X-ray diffraction, scanning electron microscopy and energy dispersive X-ray photoelectron spectroscopy to verify that the 2-D structures of these ZIF-L series have been established. The influence of various synthetic conditions such as different metal/ligand ratios as well as different synthesis times on crystal structure, morphology and porosity of Zn/Co ZIF-L were investigated. Cross-leaf morphology was obtained by reducing the metal/ligand ratio. Study of CO₂ adsorption revealed that these ZIF-L series have a considerable CO₂ adsorption capacity. In situ fabrication of TiO₂ nanoparticles within Zn/Co ZIF-L was realized via ultrasonication for 15 min as Zn/Co ZIF-L was created. TiO₂@Zn/Co ZIF-L was effectively applied as a catalyst in photodegradation of methyl orange under solar irradiation. The results indicate that ultrasound is an efficient way to synthesize high-quality metal matrix frameworks (MOFs) and immobilize nanoparticles in MOF structures with high yield, in a short time.