Understanding the Interaction of zinc oxide (ZnO) and cerium oxide (CeO₂) nanoparticles with bentonite clay particles in the aqueous environment

Mondal, Mithu (2019) Understanding the Interaction of zinc oxide (ZnO) and cerium oxide (CeO₂) nanoparticles with bentonite clay particles in the aqueous environment. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Over the past few years, substantial efforts have been made to develop many nanoparticles/Nano crystals for the advancement of new cutting-edge applications in energy storage, communications, sensing, data storage, optics, transmission, environmental protection, cosmetics, biology and medicine. Considering their limited size and a high density of corner or, edge surface sites, the Nano crystals can exhibit exclusive physical and chemical properties which includes optical, electrical and magnetic properties. The prime objectives of the present work are as follows: Separation of uniform Nano sized clay fraction from bentonite colloidal suspension using Centrifugation at specific speed; Characterization of ZnO, CeO2 and Bentonite clay particles using XRF, Zeta Sizer (DLS), TEM and XRD; To determine the stability constant of CeO2, ZnO and bentonite particles separately; To study the interaction of CeO2 and ZnO particles with Bentonite as a function of pH, Temperature and Ionic Strength using Dynamic Light Scattering (DLS) technique; To study the aggregation kinetics of bentonite particles after the interaction with CeO2 and ZnO particles by monitoring the particle concentration and size distribution, as a function of time, using DLS; and To use DLVO theory for qualitatively analyzing the experimental results in terms of the influence of pH, temperature and ionic strength on the surface potential of the bentonite particles. It shows that the stability of a bentonite colloid prepared from a natural bentonite was studied by investigating the surface charge properties of the bentonite colloids as a function of the pH, ionic strength and temperature; Temperature, pH and ionic strength influence the aggregation kinetics of colloidal bentonite particles by affecting the repulsive energy. Temperature affects the collision frequency between particles; Increase in ionic strength results in faster aggregation of Bentonite particles with faster and more aggregation by trivalent cations than mono valent ones; Lower concentration of CeO2 can result in co transportation with bentonite whereas at higher CeO₂ concentrations, PZC is in natural pH range which can result in co precipitation; Higher aggregation of bentonite with temperature in presence of ZnO than CeO₂; The influence in temperature on bentonite NPs stability was observed at 15⁰C, 25⁰C and 35⁰C .For NaCl, an increase in temperature CCC shift from 23 mM at 15⁰C to 20 mM at 35⁰C whereas in case of CaCl₂ CCC shift from 3mM at 150C to 2.6 mM at 350C, and for AlCl3 CCC remain almost constant (1.8 mM) for all three temperature (15°C, 25°C and 35°C). The higher CCC value at lower temperature reflects higher stability of the NPs; Presence of bicarbonate ions induce negative charge in the system causing CeO₂ NPs to aggregate while the effect is opposite due to increased repulsion in presence of negatively charged clay particles. Interestingly, presence of both CeO₂ and clay shows the affinity of bicarbonate ions for blocking the sorption sites over clay surface causing decrease in aggregation; and Humic acid link to the particle surface via adsorption or hydrophobic interaction which increase the steric repulsion and electrostatic repulsion between the particles thus providing stabilizing effect. This stabilizing effect help the metal oxide to transport through aqueous environment.

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