Dispersion and diffusivity of halloysite and bentonite nanoclays in aqueous Pb (II): Effect of particle concentration, temperature, and pH

Abstract

This study investigates the influence of particle concentration, temperature, and pH to the dispersion properties and diffusivity of nanoparticles – halloysite and bentonite nanoclays in water, with and without the presence of lead (II) ions. Light scattering analyses were conducted to observe the changes on hydrodynamic radius, zeta potential, and diffusion coefficient of the nanoparticles. Results showed that with the increase of particle concentration and as pH increases, the average hydrodynamic radii for the two nanoclays seems to decrease, and were much smaller in the presence of Pb (II) ions. Conversely, the size of the nanoparticles appears to increase as temperature increases for the halloysite sample while the opposite was found for the bentonite dispersion. Sizes increase and decrease even more upon Pb (II) additions for the halloysite and bentonite dispersions respectively. In terms of zeta potential, both lead-free nanoparticles showed a more negative surface net charge as concentration and pH increases indicating an improvement in suspension stability. This was not the case with respect to temperature changes where halloysite dispersions become more unstable. Pb (II)–bentonite samples on the other hand exhibit a rather unpredictable trend in the zeta potential as the temperature increases but were both more stable than pure bentonite. Lastly, the diffusion coefficients were obtained and data suggest that temperature has the highest influence among all parameters while the addition of Pb (II) ions increases the overall diffusivities except for low-zeta potential dispersions.