Synthesis, Characterization and Applications of Nanocomposite-MOFs of Cobalt with 4, 4’-oxy bis-benzoic acid and Metal Oxide Nanoparticles

Abstract

Metal organic frameworks (MOFs) represent a new class of crystalline solids which find large number of applications in gas adsorption, molecular sensing, drug delivery, chemical catalysis and many more due to their tunable pores size. Recently, the robust framework of MOFs is coalesced with other nano materials to unlock their full potential for imparting synergistic properties to the new composites. Present work describes the synthesis of a known cobalt based MOF, [Co(OBA)(H2O)2] [(OBA =4,4’-oxybis(benzoate)], (1) and its application for the detection of nitro aromatics and aromatic organophosporous pesticides by optical methods of fluorescence quenching and fluorescence enhancement respectively. Highlight of the work was detection of trinitrophenol (TNP), a known explosive, up to 43 ppb using compound (1). Triazophos and chloropyrifos, the aromatic organophosporous pesticides, were detectable up to 0.6 and 0.7 ppm respectively. The work also describes the synthesis and characterization of modified compound (1) after loading it with ZnO and CeO2 nanoparticles. The new composite materials were characterized using techniques such as PXRD, HR-TEM, SEM-EDS, XPS and Raman Spectroscopy. ZnO incorporated three composites namely ZnO/MOF-I, ZnO/MOF- II and ZnO/MOF-III were found to be catalytically active for the advantageous reduction of nitroarenes by sodium borohydride under ambient conditions. Out of the three composites synthesized, the percentage conversion from p-nitro phenol to p-amino phenol was highest (97.8%) in case of ZnO/MOF-I due to their very small size and thus increased surface area. The same conversation due to higher size and decreased surface area, in case of ZnO/MOF-III, was lowest (70.6%). The applicability of composite containing compound (1) incorporated with CeO2 nano particles were shown towards oxygen evolution reaction (OER) by use as a thin film electrocatalyst. The film maintained its stability and activity over 16 hours. The electro catalyst was found to show lower over potential value of 180 mV at 10 mA cm-2, higher electrochemical surface area and a small Tafel slope of 39 mV dec-1