Sorption Enhancement of Lead Ions from Water by Surface Charged Polystyrene-Supported Nano-Zirconium Oxide Composites

A novel hybrid nanomaterial was fabricated by encapsulating ZrO2 nanoparticles into spherical polystyrene beads (MPS) covalently bound with charged sulfonate groups (-SO3-). The resultant adsorbent, Zr-MPS, exhibited more preferential sorption toward Pb(II) than the simple equivalent mixture of MPS and ZrO2. Such observation might be ascribed to the presence of sulfonate groups of the polymeric host, which could enhance nano-ZrO2 dispersion and Pb(II) diffusion kinetics. To further elucidate the role of surface functional groups, we encapsulated nano-ZrO2 onto another two macroporous polystyrene with different surface groups (i.e., -N(CH3)(3)(+)/-CH2Cl, respectively) and a conventional activated carbon. The three obtained nanocomposites were denoted as Zr-MPN, Zr-MPC, and Zr-GAC. The presence of -SO3- and -N(CH3)(3)(+) was more favorable for nano-ZrO2 dispersion than the neutral -CH2Cl, resulting in the sequence of sorption capacities as Zr-MPS > Zr-MPN > Zr-GAC > Zr-MPC. Column Pb(II) sorption by the four nanocomposites further demonstrated the excellent Pb(II) retention by Zr-MPS. Comparatively, Zr-MPN of well-dispersed nano-ZrO2 and high sorption capacities showed much faster breakthrough for Pb(II) sequestration than Zr-MPS, because the electrostatic repulsion of surface quaternary ammonium group of MPN and Pb(II) ion would result in a poor sorption kinetics. This study suggests that charged groups in the host resins improve the dispersion of embedded nanoparticles and enhance the reactivity and capacity for sorption of metal ions. Suitably charged functional groups in the hosts are crucial in the fabrication of efficient nanocomposites for the decontamination of water from toxic metals and other charged pollutants.