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A facile method to prepare activated ZnFe2O4 nanoparticles through novel metal ion doping using Bi3+ is demonstrated. The enhanced activity of the Bi3+-doped ZnFe2O4 nanoparticle was evaluated through Cr(VI) ions adsorption capability analysis from aqueous samples since industrial effluents have the metal ion as a major source of concern. ZnFe2-xBixO4 (x = 0.0, 0.05, 0.10, 0.15, 0.2) were synthesized using sol gel method, and a comparative adsorption efficiency study of Bi3+-doped and undoped ZnFe2O4 was performed. To understand the variation in adsorption efficiency and mechanism of adsorption on the Bi3+-doped ZnFe2O4, the adsorption study was conducted under varying adsorption conditions including pH, adsorbent dosage, contact time, initial ion concentration, and temperature. All the quantification studies regarding the adsorption were done using atomic adsorption spectroscopy (AAS). The studies suggested enhanced adsorption capability via Bi3+ doping as it can enhance the effective surface area and electrostatic charge density on the surface. Adsorption equilibrium information from this study was modeled using prominent adsorption kinetics and isotherm models, for extracting information regarding the performance of the adsorbent, rate of the adsorption and adsorption mechanism, which are imperative in the design and operation of adsorption systems. Scope of regeneration and reusability of the spent adsorbents in water treatment, which is also investigated in this work, addresses the ecological and economic demands for sustainability and also makes the wastewater treatment process cost effective. [ABSTRACT FROM AUTHOR]

Nano metal ferrites (MFe2O4, M = Ni, Zn, Cu) were synthesized by sol–gel method and comparative studies of their adsorption efficiency on the removal of Cr (VI) ions from its aqueous solution were carried out. The ferrite samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The various factors affecting the uptake of Cr (VI) from its aqueous solution such as pH, time, adsorbent dose, adsorbate concentration, and temperature were investigated through batch adsorption studies. It is observed that the adsorption process follows a pseudo-second-order kinetics model, and the experimental data fitted well with Langmuir isotherm. Of the MFe2O4 (M = Ni, Zn, Cu) nanoparticles, ZnFe2O4 showed highest adsorption efficiency. By regenerability study, the extent of reuse of the ferrite samples was checked. Highlights: Nano metal ferrites (MFe2O4, M = Ni, Zn, Cu) were synthesized by sol–gel method. The various factors affecting the uptake of Cr (VI) from its aqueous solution were investigated through batch adsorption studies. The adsorption process follows a pseudo second order kinetics model. [ABSTRACT FROM AUTHOR]

New red phosphor materials of general formula Gd3−xMO7:xEu3+ (M = Nb, Sb, and Ta) were prepared using a high temperature solid state reaction route. Detailed structural studies using XRD, FT-IR and Raman spectroscopic techniques showed that niobate and tantalate samples crystallized in the weberite type structure whereas the antimonate sample in the fluorite structure. Photoluminescence properties of the three compositions are correlated with their crystal structures. It was observed that more ordering occurs in the lattice when an M site is doped from Sb to Nb to Ta. Although niobate and tantalate samples possess similar structures more distortions were noticed in the tantalate sample increasing the radiative transition probabilities. Due to the more ordered structure of the Gd3TaO7 host lattice resulting in a more uniform distribution of Eu3+ ions, the tantalate system showed better luminescence properties. The variation in the luminescence intensity with various Eu3+ concentrations in the Gd3TaO7 host lattice was also studied to calculate the optimum doping concentration. [ABSTRACT FROM AUTHOR]

A series of intense red emitting phosphors, CaZrMoSiO:0.2Eu ( x = 0.025, 0.05, 0.075, 0.1) that could be effectively excited in the UV region was prepared by conventional high temperature solid state reaction route. Structural, morphological and photoluminescence properties of the prepared samples were studied in detail. The incorporation of Zr and Si ions in CaMoO lattice maintained the powellite crystal structure. Luminescence properties were optimized for 7.5 mol% of Zr and Si concentration. Emission intensities improved more than twice in comparison with CaMoO:Eu. Life times of the prepared samples improved and the quantum efficiency enhanced to ~39 %. The improvement in emission intensity and quantum efficiency is explained in terms of the local distortion around the Eu ions resulting in improved absorption in the UV region. The CIE color co-ordinates of the red emission were in agreement with the values of the standard red phosphors providing potentiality to be used in phosphor converted (pc) white LEDs. [ABSTRACT FROM AUTHOR]

New stannate pyrochlore based red emitting phosphor materials: CaLaSnNbO: xEu were prepared by the conventional solid state route and characterized by Powder X-ray diffractometer, scanning electron microscope and fluorescence measurements. Optimization studies by way of varying the calcination temperatures show that CaLaSnNbO: Eu prepared at 1,400 °C displayed the maximum luminescence characteristics. The dominant emission peak of CaLaSnNbO: xEu phosphor is D → F forced hypersensitive electric dipole transition which indicates the deviation of pyrochlore A-site from inversion symmetry. The present quaternary pyrochlore phosphors show strong red luminescence (~612 nm) under near UV (394 nm) and blue light (465 nm) excitations. [ABSTRACT FROM AUTHOR]

Powellite type molybdate-based red phosphors CaGd1− x NbMoO8: x Eu3+ ( x = 0.05, 0.1, 0.15, 0.20, 0.25, and 0.30) were synthesized by a solid-state reaction ( SSR) route, and a citrate gel ( CG) route. The crystalline structure, morphology, absorbance, and luminescent properties of these phosphors were characterized using powder X-ray diffraction, scanning electron microscopy, UV visible absorption spectroscopy, and photoluminescence spectroscopy. The solid solution formation of the phosphor effectively takes place at a lower temperature by the CG route than the SSR route. Particle morphology of the phosphors prepared by the CG route reveals that they are less agglomerated, more spherical, and homogenous in nature with uniform particle size. Investigations on photoluminescence properties show that these phosphors emit strong red light (614 nm) under both near UV (395 nm), and blue (465 nm) excitations. The morphological variation of the developed phosphors with respect to synthesis method and heat treatment played an important role in their luminescence enhancement. The red phosphors prepared via CG route were characterized by enhanced and sharper red emission with longer life time compared to that of phosphors synthesized via SSR route. The CIE color coordinates of the developed red phosphors are (0.65, 0.34) that are closer to NTSC standard red phosphor. Thus, these phosphors could be a promising red candidate for the phosphor converted white light emitting diode applications. [ABSTRACT FROM AUTHOR]