Green Full Conversion of ZnO Nanopowders to Well-Dispersed Zeolitic Imidazolate Framework-8 (ZIF-8) Nanopowders via a Stoichiometric Mechanochemical Reaction for Fast Dye Adsorption

In recent years, many nanofabrication methodologies to engineer metal organic frameworks (MOFs) have been investigated. However, there is only a small number of studies that explores scalable and environmentally friendly synthesis routes. This study reports the production of well-dispersed MOF nanopowders from an inexpensive precursor, in a green and scalable manner, with a high yield and minimal waste, for water remediation applications. One-step mechanochemical processing of a stoichiometric ratio of ZnO nanoparticles and 2-methylimidazole resulted in the full conversion of ZnO nanopowders into zeolitic imidazolate framework-8 (ZIF-8) of ca. 80 nm in diameter with little agglomeration. The particles had a surface area of 1885 m²/g, among the highest reported for ZIF-8 and close to the theoretical maximum of 1947 m²/g. For the first time, we studied the enhanced ability of our converted nanopowders to adsorb more model organic pollutants than ZIF-8 nanopowders synthesized via the most commonly used solution-based method. Details of the processing conditions, including milling-ball size, milling time, and postmilling treatment that influence the conversion yield, were systematically investigated using dry reactive grinding and liquid-assisted grinding. This work provides a new strategy for the commercial production of wide-ranging MOFs for environmental applications.