Magnesium oxide nanoparticles-cellulose acetate based composite beads for lead uptake from contaminated stream: Experimental and DFT based study

Abstract

Groundwater, a primary source of drinking water, is becoming increasingly contaminated with toxic heavy metals, particularly lead. The unregulated discharge of industrial effluents into water bodies further exacerbates the problem. Accordingly, an effective system is required to treat these pollutants. Although there are existing solutions with certain challenges, this study aims to develop efficient composite polymeric beads composed of cellulose acetate and magnesium oxide nanoparticles for effective removal of lead from contaminated water. Prepared beads were spherical, synthesized by the phase inversion of polymer solution with the help of a needle-syringe assembly. As-prepared beads were characterized based on its morphological and chemical characteristics, revealing porous texture with considerable crystallinity. Presence of Pbsingle bondO bond in FTIR spectra post lead adsorption highlighted synergy between lead ions and Mgsingle bondOH groups. Uptake mechanism involved the substitution of hydrogen ions by lead ions, resulting in the formation of stable Mgsingle bondOsingle bondPb complexes. This was facilitated by lead's lower electronegativity in contaminated water. Lead uptake by composite beads was governed by monolayer adsorption as evident from isotherm studies. A maximum uptake capacity of 500 mg/g was observed at 298 K, which increased to 600 mg/g at 318 K. Optimum dosage of 1 g/l was identified as ideal for achieving equilibrium conditions. Thermodynamic parameters confirmed that the adsorption process was spontaneous and endothermic in nature. Regeneration studies showed effective reusability up to two cycles, after which the removal capacity reached saturation. Isoelectric point was obtained at a pH value of 9.7. Presence of MgO helped in stabilising lead ions and prevented precipitate formation in alkaline medium, providing a minor reduction in lead removal, as compared to conventional adsorbents. Furthermore, Density functional theory (DFT) based simulation was performed suggesting collective indication of consistent trends, with both approaches converging towards the same adsorption behaviour and Pbsingle bondO interaction patterns.