Prakash Majee

Visible detection of explosive nitroaromatics facilitated by a large stokes shift of luminescence using europium and terbium doped yttrium based MOFs

To use the large stokes shift and low self quenching of luminescence, we have successfully constructed two luminescent yttrium based MOFs doped with europium and terbium, [Y0.9Eu0.1(OBA)(Ox)0.5(H2O)2], Y-MOF:Eu and [Y0.9Tb0.1(OBA)(Ox)0.5(H2O)2], Y-MOF:Tb through an isomorphous substitution technique using a two dimensional metal–organic framework (MOF) [Y1.0(OBA)(Ox)0.5(H2O)2], [OBA = 4,4′-oxybis(benzoic acid), Ox = oxalate], Y-MOF, as a structural basis. The structure and size of Y-MOF, Y-MOF:Eu and Y-MOF:Tb were systematically characterized by PXRD, TGA, SEM and EDX analysis. Y-MOF:Eu and Y-MOF:Tb shows high intensity visible red and green emission, respectively, on the exposure of UV light. These emissions of Y-MOF:Eu and Y-MOF:Tb were used for the visible detection of nitro explosives such as 2,4,6-trinitrophenol (TNP), 1,3-dinitro benzene (DNB), 2,4-dinitro toluene (DNT), nitro benzene (NB), 4-nitro toluene (NT) in acetonitrile through luminescence quenching. Y-MOF:Eu and Y-MOF:Tb shows superior sensitivity towards TNP and NT compared to other nitroaromatic explosives. The large stokes shift of Y-MOF:Eu and Y-MOF:Tb allows naked eye detection of these nitroaromatics. The observed KSV (quenching constant obtained from Stern–Volmer plots) values are in the range 3.2 × 104 to 0.4 × 104 M−1 for Y-MOF:Eu and 3.19 × 104 to 0.47 × 104 M−1 for Y-MOF:Tb. Using these materials ppm level detection of nitro explosives has been achieved.

A Co(II) complex of a vitamer of vitamin B6 acts as a sensor for Hg2+ and pH in aqueous media

A Co(II) complex of molecular formula C48H96.8N12O22.4Co2Cl2, 1, was synthesized from the Schiff base [H2pydmdp]Cl by a template reaction of pyridoxal (pyd), a vitamer of vitamin B6, N-methyl-1,3-diaminopropane (mdp) and cobalt(II) acetate. It was characterized by elemental analysis, 1H NMR, IR and UV-Vis spectroscopy, thermal analysis, electrochemistry and single crystal X-ray diffraction. The experimental results suggested that in complex 1, the central Co(II) is bonded to two phenolato-oxygens, two imine nitrogens and two amine nitrogens in an octahedral geometry. In aqueous media complex 1 exhibits an intense fluorescence emission peak at 506 nm when it was excited at 425 nm. The fluorescence behavior of complex 1 in aqueous media was employed to determine whether it acts as a chemosensor for some selective toxic metal ions. The studies showed that the present complex behaves as a promising sensor for Hg2+ even at the sub-micromolar level. In addition in aqueous solution, complex 1 acts as a sensor for the pH of the medium. A detailed study on the mechanism of sensing behavior established that Hg2+ interacts with complex 1 via weak non-covalent interaction with the N-atom of the pyridine moiety of the molecule. The pyridine nitrogen also plays a vital role in sensing the pH of the medium.

Detection of Pesticides in Aqueous Medium and in Fruit Extracts Using a Three-Dimensional Metal–Organic Framework: Experimental and Computational Study

A new, three-dimensional cadmium based metal-organic framework [Cd3(PDA)1(tz)3Cl(H2O)4]·3H2O {PDA = 1,4-phenylenediacetate and tz = 1,2,4-triazolate}, 1, has been successfully synthesized using slow diffusion method at room temperature. The structure of compound 1 has been determined using single crystal X-ray diffraction. The triazolate ligands connect three different types of octahedral Cd2+ ions to form a two-dimensional structure. The chloride ion and PDA ligands connect the two-dimensional layers to form a three-dimensional structure. The phase purity of 1 was confirmed by powder X-ray diffraction, thermogravimetric analysis, and IR spectroscopy. Aqueous dispersion of compound 1 gives intense luminescence emission at 290 nm upon excitation at 225 nm. This emission was used for the luminescence based detection of pesticides, especially azinphos-methyl, chlorpyrifos, and parathion in aqueous medium. The selectivity of pesticide detection remains unaltered even in the presence of surfactant molecules. The mechanisms of luminescence quenching were successfully explained by the combination of absorption of excitation light, resonance energy transfer, and the possibility of electron transfer. Experimental findings are also well supported by the density functional theory calculations. Selectivity of pesticides detection in real samples such as apple and tomato juice has also been observed.