Abstract
Metal organic frameworks (MOF) are a class of hybrid networks of supramolecular solid materials comprising a large number of inorganic and organic linkers, all bound to metal ions in a well-organized fashion. Zeolitic imidazolate frameworks (ZIFs) are a sub-group of MOFs with imidazole as an organic linker to metals; it is rich in carbon, nitrogen, and transition metals. ZIFs combine the classical zeolite characteristics of thermal and chemical stability with pore-size tunability and the rich topological diversity of MOFs. Due to the energy crisis and the existence of organic solvents that lead to environmental hazards, considerable research efforts have been devoted to devising clean and sustainable synthesis routes for ZIFs to reduce the environmental impact of their preparation. Green chemistry is the key to sustainable development, as it will lead to new solutions to existing problems. Moreover, it will present opportunities for new processes and products and, at its heart, is scientific and technological innovation. The green chemistry approach seeks to redesign the materials that make up the basis of our society and our economy, including the materials that generate, store, and transport our energy, in ways that are benign for humans and the environment and that possess intrinsic sustainability. This study covers the principles of green chemistry as used in designing strategies for synthesizing greener, less toxic ZIFs the consume less energy to produce. First, the necessity of green methods in today’s society, their replacement of the usual non-green methods and their benefits are discussed; then, various methods for the green synthesis of ZIF compounds, such as hydrothermally, ionothermally, and by the electrospray technique, are considered. These methods use the least harmful and toxic substances, especially concerning organic solvents, and are also more economical. When a compound is synthesized by a green method, a question arises as to whether these compounds can replace the same compounds as synthesized by non-green methods. For example, is the thermal stability of these compounds (which is one of the most important features of ZIFs) preserved? Therefore, after studying the methods of identifying these compounds, in the last part, there is an in-depth discussion on the various applications of these green-synthesized compounds.
Highlights
According to the literature, zeotypes have been considered the primary technological, nano-porous, inorganic substances, with more than 180 framework topologies
Sinnwell et al.’s investigations address Zeolitic imidazolate frameworks (ZIFs)-8 synthesis in scCO2. They have shown that in-situ powder X-ray diffraction (XRD), ex-situ microscopy, and simulation offer a detailed vision of the formation of ZIF-8, as well as intermediary zinc oxide (ZnO)@ZIF-8 composites in non-traditional solvents
We have shown the significance of ZIFs as one of the specific subclasses of Metal organic frameworks (MOF) with high chemical and thermal stabilities not observed in several MOFs
Summary
Zeotypes have been considered the primary technological, nano-porous, inorganic substances, with more than 180 framework topologies. Researchers have much considered metal organic porous materials due to their attractive uses in separation, molecular recognition, and catalysis [5] They have encountered challenges in constructing open MOFs, which include the enhancement and modulation of pore dimensions for creating porous metalorganic materials of higher stability. The above methods forgo the utilization of the detrimental solvents in the MOFs’ synthesis; and, they enjoy very good stability, adjustable porosity, higher rate of production, and continual generation in the resulting MOFs [22,23]. In order to have a sustainable production of MOFs, researchers must consider one of the green and affordable production processes, a number of them are the utilization of inexpensive, recyclable, and renewable starting metal salts and acid linkers, less solvent or green solvents such as water, affordable energy resources, and proper low-risk synthetic techniques like lower pressure and temperature [27]
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