Sorption properties of U(VI) and Th(IV) on two-dimensional Molybdenum Disulfide (MoS₂) nanosheets: Effects of pH, ionic strength, contact time, humic acids and temperature

Herein, the two-dimensional MoS₂ nanosheet was characterized and its performance as an adsorbent for U(VI) and Th(IV) removal from water was evaluated in batch experiments. The results showed that MoS₂nanosheets have a thin thickness and few negligible impurities. Both U(VI) and Th(IV) sorption on MoS₂were obviously enhanced by high pH and the oxygen-containing group on the surface of MoS₂ increased with an increase of pH. However, the sorption was not affected by ionic strength, suggesting that inner-sphere surface complexation dominated the two sorption processes. The removal efficiency of Th(IV) by MoS₂ was higher than that of U(VI) in solutions containing different cations and anions. The adsorption equilibrium for U(VI)/Th(IV) was achieved within 2 h and pseudo-second-order equation showed favorable fit. HA significantly increased the uptake of U(VI)/Th(IV) at pH <7.5/6, while decreased the sorption at pH >7.5/6. Freundlich model provided more fit to the equilibrium data than Langmuir model at pH 5.5. The maximum sorption amount of MoS₂ for U(VI)/Th(IV) run up to 492.72/454.72 mg⋅g⁻¹, obviously higher than the amounts of some other materials. The U(VI)/Th(IV) sorption was a spontaneous and endothermic process. All these results suggested the potential applicable value of MoS₂ nanosheets in removing U(VI) or Th(IV) from aqueous solutions.