• K Hemalatha

      Articles written in Bulletin of Materials Science

    • Uptake of permanganate from aqueous environment by surfactant modified montmorillonite batch and fixed bed studies

      N Mahadevaiah B Vijayakumar K Hemalatha B S Jai Prakash

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      Organo-clay was prepared by incorporating different amounts (in terms of CEC, ranging from 134–840 mg of quaternary ammonium cation (QACs) such as hexadecytrimethylammonium bromide ([C19H42N]Br) into the montmorillonite clay. Prepared organo-clays are characterized by CHN analyser and XRD to measure the amount of elemental content and interlayer spacing of surfactant modified clay. The batch experiments of sorption of permanganate from aqueous media by organo-clays was studied at different acidic strengths (pH 1–7). The experimental results show that the rate and amount of adsorption of permanganate was higher at lower pH compared to raw montmorillonite. Laboratory fixed bed experiments were conducted to evaluate the breakthrough time and nature of breakthrough curves. The shape of the breakthrough curves shows that the initial cationic surfactant loadings at 1.0 CEC of the clay is enough to enter the permanganate ions in to the interlamellar region of the surfactant modified smectile clays. These fixed bed studies were also applied to quantify the effect of bed-depth and breakthrough time during the uptake of permanganate. Calculation of thermodynamic parameters shows that the sorption of permanganate is spontaneous and follows the first order kinetics.

    • Nitrates–melt synthesized LiNi0.8Co0.2O2 and its performance as cathode in Li-ion cells

      M Sathiya K Hemalatha K Ramesha A K Shukla A S Prakash

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      Layered LiNi0.8Co0.2O2 crystallizing in 𝑅$\bar{3}$𝑚 space group is synthesized by decomposing the constituent metal–nitrate precursors. Oxidizing nature of metal nitrates stabilizes nickel in +3 oxidation state, enabling a high degree of cation ordering in the layered LiNi0.8Co0.2O2. The powder sample characterized by XRD Rietveld refinement reveals < 2% Li–Ni site exchange in the layers. Scanning electron microscopic studies on the as-synthesized LiNi0.8Co0.2O2 sample reflect well defined particles of cubic morphology with particle size ranging between 200 and 250 nm. Cyclic voltammograms suggest that LiNi0.8Co0.2O2 undergoes phase transformation on first charge with resultant phase being completely reversible in subsequent cycles. The first-charge-cycle phase transition is further supported by impedance spectroscopy that shows substantial reduction in resistance during initial de-intercalation. Galvanostatic charge–discharge cycles reflect a firstdischarge capacity of 184 mAh g-1 which is stabilized at 170 mAh g-1 over 50 cycles.

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