Fabrication and characterization of magnetically responsive Fe₃O₄@TiO₂ core-shell adsorbent for enhanced thallium...

Thallium (Tl) contamination in natural waters can pose a severe risk to human health. In this study, a magnetically responsive Fe₃O₄@TiO₂ core-shell adsorbent was developed for the effective removal of thallium(I) from water. The isoelectric point of the adsorbent surface was decreased from 6.0 to 4.8 due to the loading of nano-sized TiO₂, leading to an enhanced electrostatic interaction between the adsorbent and Tl(I) ions in a wider pH range. The Fe₃O₄@TiO₂ magnetic adsorbent exhibited a threefold higher BET specific surface area compared to pristine Fe₃O₄ particles. The kinetics study showed that approximately 82% of the maximum Tl(I) loading amount could be achieved within 30 min at the initial Tl(I) concentration of 8 mg/L and adsorbent dosage of 0.1 g/L. The adsorption of Tl(I) was significantly increased with increasing solution pH. The experimental data was better fitted by the Langmuir and Temkin isotherms than the Freundlich isotherm and the maximum adsorption capacity of the magnetic adsorbent was 101.5 mg/g at pH 7.0. The interference of co-existing cations in the Tl(I) adsorption followed the subsequence: Cu²⁺ > Mg²⁺ > Ca²⁺ > Na⁺. The hydroxyl groups bonded on titanium atoms might play a key role in the uptake of Tl(I) ions. During the adsorption, the Tl(I) ions can be effectively adsorbed on the adsorbent surface via the formation of Ti-O-Tl linkages. Graphical Abstract.