Tahira Mahmood

Cation exchange removal of Cd from aqueous solution by NiO

Detailed adsorption experiments of Cd from aqueous solution on NiO were conducted under batch process with different concentrations of Cd, time and temperature of the suspension. The solution pH is found to play a decisive role in the metal ions precipitation, surface dissolution and adsorption of metal ions onto the NiO. Preliminary adsorption experiments show that the selectivity of NiO towards different divalent metal ions follows the trend Pb>Zn>Co>Cd, which is related to their first hydrolysis equilibrium constant. The exchange between the proton from the NiO surface and the metal from solution is responsible for the adsorption. The cation/exchange mechanism essentially remains the same for Pb, Zn, Co and Cd ions. The sorption of Cd on NiO particles is described by the modified Langmuir adsorption isotherms. The isosteric heat of adsorption (ΔH) indicates the endothermic nature of the cation exchange process. Spectroscopic analyses provide evidence that Cd is chemisorbed onto the surface of NiO.

Equilibrium and kinetics studies of arsenate adsorption by FePO4

The present work is focusing on removal of arsenate from aqueous solution using FePO4. The equilibrium study regarding the removal of arsenic by FePO4 was carried out at 298, 308, 318 and 328K. Langmuir parameters were found to increase with the increase in temperature indicating that the adsorption is favorable at high temperature. Kinetic study of arsenate adsorption on FePO4 was also carried out at different temperatures and at pH 6 and 8. Different kinetic models were used to the kinetic data amongst which pseudo second order model was best fitted. The mechanism of the adsorption kinetics was investigated by employing intraparticle diffusion and Richenberg models. The energy of activation (Ea) was found to be 30 and 35.52kJmol(-1) at pH 6 and pH 8, respectively, suggesting chemisorption nature of the adsorption process. The negative entropic values of activation signified the existence of entropy barrier while the positive ΔG(#) values indicated the existence of energy barrier to be crossed over for the occurrence of a chemical reaction. Both the spectroscopic studies and increase in equilibrium pH reveal the anion exchange removal of arsenate from aqueous solution to the solid surface.

High-k Polymer Nanocomposites for Energy Storage Applications

High dielectric (high-k) polymer nanocomposites that can electrostatically store energy are widely used in electronics and electric power systems due to their high breakdown strengths (Eb), durability, and ability to configure in various shapes. However, these nanocomposites suffer from a limited working temperature regime, thus limiting their extreme applications, such as hybrid and electric vehicles, aerospace power electronics, and deep ground fuel exploration. Furthermore, the Eb and the electric displacement (D) of polymer nanocomposites must be simultaneously enhanced for high-density capacitor applications, which prove to be difficult to modify concurrently. This chapter thoroughly reviews (investigates) the recent developments in the high-k polymer nanocomposites synthesis, characterization, and energy storage applications. Consequently, the aim of this chapter is to provide an overview of the novel developmental strategies in order to develop high-dielectric nanocomposites perovskite ceramics that can be incorporated in high-energy-density (HED) applications.

Detailed kinetics study of arsenate adsorption by a sequentially precipitated binary oxide of iron and silicon

ABSTRACT This paper comprises a comprehensive kinetic study for the adsorptive removal of As (V) from aqueous medium by mixed oxide (MO) of iron and silicon. The multi-linearity of the intraparticle diffusion model pointed towards the likelihood of both the pore and film diffusion. The Boyd model validated film diffusion to be the principal mechanism responsible for controlling the rate of the arsenate adsorption on MO. The negative entropy of activation (ΔS#) suggested the adsorption mechanism to be associative in nature. The non-negative values of ΔG# suggested the presence of an energy barrier to be surmounted for the reaction to occur.