Determination of Debye Temperatures and Lamb-Mössbauer Factors for LnFeO3 Orthoferrite Perovskites (Ln = La, Nd, Sm, Eu, Gd)

Lanthanide orthoferrites have wide-ranging industrial uses including solar, catalytic and electronic applications. Here a series of lanthanide orthoferrite perovskites, LnFeO3 (Ln = La; Nd; Sm; Eu; Gd), prepared through a standard stoichiometric wet ball milling route using oxide precursors, has been studied. Characterisation through X-ray diffraction and X-ray fluorescence confirmed the synthesis of phase-pure or near-pure LnFeO3 compounds. 57Fe Mössbauer spectroscopy was performed over a temperature range of 10 K to 293 K to observe hyperfine structure and to enable calculation of the recoil-free fraction and Debye temperature (θD) of each orthoferrite. Debye temperatures (Ln = La 474 K; Nd 459 K; Sm 457 K; Eu 452 K; Gd 473 K) and recoil-free fractions (Ln = La 0.827; Nd 0.817; Sm 0.816; Eu 0.812; Gd 0.826) were approximated through minimising the difference in the temperature dependent experimental Centre Shift (CS) and theoretical Isomer Shift (IS), by allowing the Debye temperature and Isomer Shift values to vary. This method of minimising the difference between theoretical and actual values yields Debye temperatures consistent with results from other studies determined through thermal analysis methods. This displays the ability of variable-temperature Mössbauer spectroscopy to approximate Debye temperatures and recoil-free fractions, whilst observing temperature induced transitions over the temperature range observed. X-ray diffraction and Rietveld refinement show an inverse relationship between FeO6 octahedral volume and approximated Debye temperatures. Raman spectroscopy show an increase in the band positions attributed to soft modes of Ag symmetry, Ag(3) and Ag(5) from La to GdFeO3 corresponding to octahedral rotations and tilts in the [010] and [101] planes respectively

UO<img src='http://www.niscair.res.in/jinfo/twoplustwo.gif' border=0> uptake by calcium silicate hydrate: 11 Å tobermorite

893-894Synthetic crystalline calcium silicate hydrate: Ca5Si6O16 (OH)2, 4H2O which is identical to the silicate Mineral 11 Å tobermorite shows UO uptake in aqueous solutions. When placed in solutions initially of 100-3000 ppm in UO , 11 Å tobermorite takes up significant amount of the uranyl ion after equilibration for 10 days at 29°C. The uptake appears to be a combined effect of cation exchange with release of Ca2+ in solution alongwith sorption of UO on this synthetic material

Catalytic oxidation and selective sensing of carbon monoxide for sense and shoot device using ZnO–CuO hybrids

In the present work, we have demonstrated that ZnO–CuO based hetero-composites exhibit selective CO sensing with T 100 is in close proximity to T opt to yield simultaneous CO sensing together with its 100% catalytic oxidation for sense and shoot devices. When these heterocomposites are exposed to CO, reduction of Cu 2 + ions in CuO grains leads to a strong metal semiconductor interaction (SMSI) between Cu 2 + /Cu + /Cu 0 species (in CuO grains) and ZnO grains across the ZnO-CuO interface. The SMSI interaction promotes the generation of oxygen vacancies in neighboring ZnO lattice. Eventually activated oxygen (O ∗ ads ) and CO (CO ∗ ads ) are preferentially chemisorbed on zinc oxide (in its vacant oxygen sites) and CuO (on the surface of Cu 2 + /Cu + /Cu 0 ions) respectively. The activated oxygen reacts immediately with adsorbed CO to yield selective CO sensing together with 100% CO oxidation. For ZnO–CuO (1:1) composites, the measured T opt ( ∼175 °C) and T 100 ( ∼200 °C) temperatures are significantly lowered as compared to the respective temperatures measured for indium doped ZnO (T opt ∼300 °C, T 100 ∼550 °C) and CuO (T opt ∼200 °C,T 100 ∼300 °C) catalysts. Fine tuning of the mole fraction of ZnO and CuO are necessary for these hetero-composites to yield T 100 of catalytic activity close to T opt for maximum CO sensing

New frontiers for high value utilisation of fly ash : production of zeolites

This paper outlines technologies for production of flyash based zeolite (FAZ) A, X & Y with significant reduction in the cost of production of FAZs due to substitution of conventionalraw material, viz. sodium silicate and aluminate with flyash. The cost of production of FAZs is estimated to be 25% lower than the indegenously available commercial zeolites. The high exchange capacity of FAZ-A indicates its potential as a substitute for phosphatic detergent builder. The high surface area and thermal stability of FAZ-Y indicates its suitability as a catalyst in specific areas such as automotive exhaust and detergent

Dragon's blood-aided synthesis of Ag/Ag2O core/shell nanostructures and Ag/Ag2O decked multi layered graphene for efficient As(iii) uptake from water and antibacterial activity

There has been a great interest to engineer surface characteristics of nanomaterials that are useful for various environmental applications. In this context, synthesis of nanomaterials using green methods is of great significance. Herein, new, easy, rapid and environmentally benign synthesis protocols to obtain Ag/Ag2O core/shell and Ag/Ag2O decorated multi -layered graphene (MLG) nanostructures are reported. The end products are obtained with the aid of "Dragon's blood", a resin extracted from the bark of the mysterious tree, Dracaena cinnabari. Dragon's blood has a variety of antioxidant flavonoids and tannins, amongst many other constituents, which act as reducing and stabilizing agents. Ag/Ag2O core/shell and Ag/Ag2O decorated MLG nanostructures exhibited excellent adsorption characteristics in removing arsenite (As(III)) ions from water. The nanostructures also showed strong activity against E. coli and S. aureus bacteria

Water conservation due to greywater treatment and reuse in urban setting with specific context to developing countries

In India, the per capita water availability is reducing day by day due to rapid growth in population and increasing water demand. Greywater treatment and reuse is one of the feasible options in developing countries like India to overcome this problem. A greywater collection, treatment and reuse system was designed and implemented in an urban household having a water requirement of 165 liter per capita per day (lpcd) and a greywater generation rate of 80 lpcd. An upflow–downflow greywater treatment plant having a screening, sedimentation, filtration and disinfection as major treatment processes was constructed and treated greywater is used for toilet flushing and to irrigate the vegetables in the backyard of the household. Greywater characterisation indicates that COD and BOD are sufficiently reduced during the treatment and there is also substantially reduction in Escherichia coli count. The payback period of this greywater treatment and reuse system is estimated to be 1.6 year