Design and Syntheses of Functional MOFs for Environmental Applications

Abstract

Metal-organic Frameworks (MOFs) are crystalline porous molecular solids retrofitted from widely explored classical coordination compounds through supramolecular self-assembly. These solid-state materials can be easily modulated through fine tuning of linkers, metal, guest species thereby rendering precise control over properties. Hitherto, MOFs are an excellent class of porous materials with potential applications ranging from separation, catalysis, capture, sensing. This thesis explores the design, syntheses and application studies of neutral nitrogen donor(N-donor) based MOFs with focus towards toxic guest encapsulation. In this regard, the first chapter describes the general principles of MOFs fabrication with focus towards the neutral nitrogen donor MOFs and its associated properties. Thereafter, a brief discussion regarding application of MOFs in the field of molecular decoding and toxic analyte capture is presented. In the second chapter, an interpenetrated luminescent MOF was exploited as molecular decoder for toxic pollutants viz. volatile organic compounds (VOCs) in the vapor phase. The material exhibited flexibility in presence of aromatic VOCs along with a characteristic photoluminescent response. This was rationalized based on distinct host-guest interactions as well as electronic nature of analyte. Learning from this host-guest response, in chapter three we targeted the development of MOF for allyl alcohol sensing that is very hazardous and lethal. A luminescent coordination polymer with metal-chlorine bond functional site were appended in conjunction with conjugated nature of the framework backbone. The material afforded a clear photoluminescent response toward allyl alcohol over other congener alcohols. In the second part of the work, for the first time we explored the suitability of cationic MOFs as scavengers for oxoanions of selenium and arsenic, which are associated with very weak binding affinity. In this respect, iMOF-1C exhibited an appreciable uptake towards Se(VI), As(V) along with a rare single-crystal-to-single-crystals transformation, that revealed hydrogen bonding interactions as preferred site for stabilization. This report served as the first example in the domain of ionic MOFs for selenium and arsenic capture. Subsequently, via rational design principle, we synthesized a cationic network, iMOF-3C, that exhibited extremely high binding affinity towards the oxoanions of selenium and arsenic (Se(IV), Se(VI), As(V)). This material performed well in sequestering oxoanions of selenium and arsenic from real systems such as river water to meet the EPA standards.