Bare and Polymer Coated Iron Oxide Superparamagnetic Nanoparticles for Effective Removal of U (VI) from Acidic and Neutral Aqueous Medium

TL;DR

This study demonstrates that superparamagnetic gamma-Fe2O3 nanoparticles, both bare and polymer-coated, effectively adsorb and facilitate magnetic removal of U(VI) from acidic and neutral water, with distinct behaviors at different pH levels.

Contribution

It introduces the use of bare and PAA-coated superparamagnetic iron oxide nanoparticles for efficient U(VI) removal from water, highlighting their adsorption mechanisms and magnetic separation capabilities.

Findings

Bare nanoparticles adsorb U(VI) at pH 2, causing agglomeration.

PAA-coated nanoparticles adsorb U(VI) at pH 7, forming large aggregates.

Both nanoparticle types enable magnetic separation of uranium from water.

Abstract

Superparamagnetic {\gamma}-Fe2O3 nanoparticles (5 nm diameter) were synthesized in water. The bare particles exhibit good colloidal stability at ~ pH 2 because of the strong electrostatic repulsion with a surface charge of +25 mV. The polyacrylic acid (PAA)-coated particles exhibit remarkable colloidal stability at ~ pH 7 with abundant free carboxyl groups as reactive sites for subsequent functionalization. In this work, we used zeta potential analysis, transmission electron microscopy, small angle X-ray scattering, and Inductively coupled plasma mass spectrometry to investigate the adsorption behavior of U (VI) on bare and coated colloidal superparamagnetic nanoparticles at pH 2 and pH 7. At pH 2, uranyl ion (UO22+) absorbed on the surface of the bare particles with decreasing particle surface charge. This induced particle agglomeration. At pH 7, uranyl ion (UO22+) hydrolyzed and formed plate-like particles of uranium hydroxide that were ~ 50 nm in diameter. The PAA-coated iron oxide nanoparticles absorbed on the surface of these U (VI) hydroxide plates to form large aggregates that precipitate to the bottom of the dispersion. At both pH 2 and pH 7, the resulting U (VI)/nanoparticle complex can be easily collected and extracted from the aqueous environment via an external magnetic field. The results show that both bare and polymer-coated superparamagnetic {\gamma}-Fe2O3 nanoparticles are potential absorbents for removing U (VI) from water.