Development of Zeolitic Imidazolate Frameworks (ZIFs) for Dyes Adsorption Applications

Abstract

Water being a vital source of life on earth, supply of clean water is one of the utmost significant universal issues due to ongoing economic expansion and the continuous upsurge in the worldwide population. Clean water sources are reducing day by day because of various organic and inorganic contaminants such as fertilizers, organic dyes, phenols, plasticizers, detergents, pharmaceuticals, pesticides, and aromatic compounds. There is a high need to remove these pollutants from drinking and wastewater, as they adversely affect aquatic and human life. Among the different methods employed for dyes removal such as chemical and biological methods, adsorption process is much more competitive than other methods due to its low cost, ease of operation and wide area of applications. Metal Organic Frameworks (MOFs) have emerged as a new class of adsorbent materials, which have attained a considerable attention of researchers over the last two decades due to their large surface area, tunable pore size, ease of synthesis and selective adsorption of species. Zeolitic Imidazolate Frameworks (ZIFs) a subclass of MOFs, topologically isomorphic with zeolites, consists of two building blocks: the inorganic metal and the organic Imidazolate linker. ZIFs have strong potential to be used as adsorbent due to their high porosity, large surface area, and extraordinary chemical and thermal stability in aqueous media. In this work, a series of monometallic zinc, cobalt and bimetallic Zn/Co ZIFs have been synthesized by room temperature and solvothermal method. Morphology, crystal structure, thermal stability and surface area were evaluated through SEM, XRD, TGA and BET analysis respectively, while metal ligand coordination was confirmed by FTIR. Subsequently, adsorption capacity and kinetic study of these synthesized ZIFs for six organic dyes namely, Methylene Blue (MB), Methyl Orange (MO), Methyl Red (MR), Crystal Violet (CV), Reactive Red (RR) and Rhodamine B (RhB) was carried out in aqueous solution through batch process by using UV-Visible Spectroscopy. Among these, Zn/Co ZIF showed highest capacity for adsorption of dyes from aqueous solution. Adsorption and kinetic study of dyes adsorption by ZIFs illustrates that adsorption processes follow Langmuir isotherm model and pseudo second order kinetic model respectively. Keywords: Metal Organic Framework, Zeolitic Imidazolate Framework, Solvothermal Synthesis, Room Temperature Synthesis, Organic Dyes, Adsorption, Kinetics.