Radha Velchuri

Synthesis, Characterization and Photocatalytic Activity of KAl0.33W1.67O6 and Sn0.5Al0.33W1.67O6xH2O

Nano sized defect pyrochlore, KAl0.33W1.67O6 (KAW), is prepared through sol–gel method. Divalent tin‐doped KAW is obtained at room temperature by ion exchange method using acidified SnCl2 and parent KAW. These materials are characterized by powder X‐ray diffraction, thermogravimetric analysis (TGA), scanning electron microscopy—energy dispersive spectra (SEM‐EDS), Raman Spectroscopy and X‐ray photo electronic spectroscopy. The composition of tin‐doped KAW is obtained from chemical analysis, SEM‐EDS and TGA methods and written as Sn0.5Al0.33W1.67O6 xH2O (x = 1.4–1.5) (SnAW). It crystallizes in cubic lattice with Fd3¯m space group. The band gap energies are found to be 2.82 and 2.21 eV for KAW and SnAW respectively. The observed reduction in the band gap with the introduction of Sn2+ in defect pyrochlore lattice is due to mixing of 5s state of Sn2+ with O 2p states leading to an upward shift in the valence band. The Raman spectra of these materials gave more bands than the number expected for defect pyrochlores due to substitutional disorder in 16c sites and displacive disorder of A ions. The photoactivity of SnAW is higher compared to KAW.

Metathesis synthesis, characterization, spectral and photoactivity studies of Ln2/3MoO4 (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er and Y)

Abstract Rare earth ortho-oxomolybdates of composition Ln2/3MoO4 (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er and Y) were prepared by metathesis reaction. All these materials were characterized by powder X-ray diffraction, Fourier transform-infrared spectroscopy (FT-IR) and UV-Vis diffuse reflectance spectra. The Rietveld analysis of all the samples was carried out to obtain the unit cell parameters and reliability factors. All the materials were crystallized in tetragonal lattice with I41/a space group. The infrared spectra of all the samples were characterized by bands due to MoO42– units. The bandgap energies of all the samples were obtained from UV-Vis DRS spectra. The luminescence spectra of Ln2/3MoO4 (Ln=Pr, Eu and Dy) showed characteristic transitions of the rare earth ions. The visible light photocatalytic activity of all the samples was studied against degradation of methylene blue.

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.

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.

Enhanced photoactivity of antimony phosphates by substitution of H+, Cu2+ and N3− in the K3Sb3P2O14·xH2O crystal lattice

Abstract Substitutional doping of framework heteroatoms in photocatalysis is one of the approaches for harvesting visible light. Tunnel structure potassium antimony phosphate (K3Sb3P2O14·xH2O) and Cu2+, H+ , and N3- substituted K3Sb3P2O14·xH2O were prepared. These materials were characterized by powder X-ray diffraction, energy dispersive spectra, infrared spectra, and UV–Vis diffuse reflectance spectra. All these compositions were crystallized in the rhombohedral crystal lattice with

Photocatalytic degradation of organic dyes with Sn2+- and Ag+-substituted K3Nb3WO9(PO4)2 under visible light irradiation

R\overline{3} m

Low temperature synthesis of fluorite-type Ce-based oxides of composition

R3¯m space group. The absorption edges of doped compositions were shifted to longer wavelength region considerably upon substitution of Cu2+, H+ , and N3−. The photocatalytic activity of these materials was tested against the degradation of methyl violet. The higher visible light photocatalytic activity of doped K3Sb3P2O14·xH2O compositions compared to parent material was discussed. N3−-doped K3Sb3P2O14·xH2O photocatalyst is stable even after the fourth cycle of photodegradation.