B. Vijaya Kumar

Recyclable Bi2WO6-nanoparticle mediated one-pot multicomponent reactions in aqueous medium at room temperature

Different types of multicomponent reactions (MCRs) are reported using Bi2O3, BiVO4, and Bi2WO6 (nanoparticle) as heterogeneous catalysts. Among these, Bi2WO6 nanoparticles showed excellent reactivity for the synthesis of functionalized dihydropyridine, polyhydroquinoline, 4H-chromene and 2-amino-4H-benzo[b]pyran derivatives at ambient temperature in aqueous medium. All the reactions gave good to excellent yields in 10–45 minutes in the presence of 5 mol% (optimized) of the catalyst. The catalyst was regenerated and reused up to 5 times without losing catalytic activity. The gram scale synthesis of dihydropyridine gave the desired product in 82% yield in 2 h.

Preparation, characterization, emission (Eu3+), and electron spin resonance (Gd3+) studies of Y2−xLnxTi2O7 (Ln=Eu and Gd, x=0.0,0.05)

Bulk and nanopyrochlore materials of composition Y2−xLnxTi2O7 (Ln=Eu and Gd, x=0.0,0.05) have been prepared by sol-gel method via peroxo titanium complex precursor. All the samples were characterized by powder x-ray diffraction (XRD), Raman spectra, and transmission electron microscopy (TEM). The unit cell parameters were obtained from Rietveld analysis of XRD patterns. The influence of particle size on the emission of Eu3+ (in Y2−xEuxTi2O7), the electron spin resonance (ESR) of Gd3+ (in Y2−xGdxTi2O7) and optical absorption spectra have been studied. The band gap energy of Y1.95Ln0.05Ti2O7 (Ln=Eu and Gd) was determined and compared with parent Y2Ti2O7. The variation in the emission intensity of Eu3+ is accounted with the particle size and short range order. The spin-Hamiltonian parameters of Gd3+ were obtained from the powder ESR spectra. The single-ion anisotropy was taken in to account in the analysis of powder ESR spectra. The crystallite size was obtained from powder XRD and TEM images.

Synthesis of functionalized 1,2,3-triazoles using Bi2WO6 nanoparticles as efficient and reusable heterogeneous catalyst in aqueous medium

Synthesis of functionalized triazoles is reported via Bi2WO6 nanoparticle (10 mol%) mediated 1,3-dipolar cycloaddition reactions of β-nitrostyrenes, phenylacetylene and chalcones with azides (80 °C, 2–6 h) in water. The regioselective formation of 1,4-disubstituted triazoles was achieved in 5–20 minutes using azides and alkynes in presence of CuSO4·5H2O (2 mol%), sodium ascorbate (10 mol%) and Bi2WO6 nanoparticles (10 mol%) at room temperature in water. Similarly, regioselective synthesis of 1,4,5-trisubstituted triazoles was achieved from chalcones in aqueous medium.

Low temperature preparation of NaTi2(PO4)3 by sol-gel method

Bulk and nano sized rhombohedral NaTi2(PO4)3 belonging to NASICON family have been prepared by sol-gel method at low temperatures. The products are characterised by powder X-ray diffraction, Raman, SEM and TEM methods. The phase formation of NaTi2(PO4)3 was started at 550°C. The crystallite sizes of NaTi2(PO4)3 prepared at 550°C and 600°C were found to be 35 nm and 37 nm respectively. The nano nature of the samples was confirmed from the line width of powder XRD and Raman lines. The Raman spectra are characterised by bands due to isolated phosphate groups and Ti-O vibrational modes. The morphology of nano crystallites was found to be irregular. The average particle size calculated from TEM was found to be 30 nm and 35 nm for the samples heated at 550°C and 600°C respectively. The high resolution TEM image clearly shows the lattice fringes corresponding to the rhombohedral lattice of NaTi2(PO4)3.

Solid-State Syntheses of Rare-Earth–Doped Sr1-xLn2x/3MgP2O7 (Ln = Gd, Eu, Dy, Sm, Pr, and Nd; x = 0.05) by Metathesis Reactions and their Spectroscopic Characterization

ABSTRACT Rare-earth–doped strontium magnesium diphosphates of composition Sr1-xLn2x/3MgP2O7 (Ln = Gd, Eu, Dy, Sm, Pr, and Nd; x = 0.05) were prepared by metathesis reaction. These diphosphates were characterized by powder X-ray diffraction (XRD), energy dispersive spectra (EDS), and infrared spectroscopy. All these compounds were found to crystallize in monoclinic lattice with P21/n space group. The compositions of all the samples were confirmed from their EDS spectra. The infrared spectra of all the samples were characterized by bands due to units. The 31P MAS-NMR of these compounds suggests the presence of two types of phosphorous ions in the lattice. The electron-spin resonance spectrum of Sr1-xGd2x/3MgP2O7 (x = 0.05) gave “U”-type spectrum due to the low symmetry of the Gd3+ ion in the host lattice. The local symmetry of Eu3+, Dy3+, and Sm3+ in Sr1-xLn2x/3MgP2O7 (Ln = Eu, Dy, and Sm; x = 0.05) was obtained from their room-temperature luminescence spectra.

Photocatalytic and Conductivity Studies of Bi3+Substituted La2Zr2O7

ABSTRACT Trivalent bismuth substituted La2Zr2O7 pyrochlores of compositions La2-xBixZr2O7 (x = 0.2, 0.4 and 0.6) have been prepared by sol-gel method. All the samples were characterized by powder X-ray diffraction, IR spectroscopy, and SEM-EDS. These materials were found to crystallize in cubic lattice with space group . The unit cell parameters were deduced from the Rietveld refinement. The dc conductivity of all samples was measured in the temperature range 200–700°C. The photocatalytic activities of the samples were studied against methylene blue decomposition under sunlight. La2-xBixZr2O7 compounds showed enhanced photoactivity compared to La2Zr2O7.

Low Temperature Sol-Gel Synthesis of Bulk and Nano-sized NbTi(PO4)3

Bulk and nano-sized NbTi(PO4)3 has been prepared by citrate gel pyrolysis using peroxo titanium complex as one of the reactants, and ethylene glycol as gelating reagent. The compound was analyzed by powder XRD and infrared methods. It is found to crystallize in rhombohedral lattice with space group . The infrared spectra of samples prepared at different temperatures consist of mainly bands due to phosphate (PO4) group. The morphological characterization was carried out by transmission electron microscopy. The crystallite size was estimated from the line width of intense powder diffraction line using Scherrers formula and TEM images.