Insights into U(VI) adsorption behavior onto polypyrrole coated 3R-MoS₂ nanosheets prepared with the molten salt electrolysis method

To improve the separation capacity of uranium in aqueous solutions, 3R-MoS₂ nanosheets were prepared with molten salt electrolysis and further modified with polypyrrole (PPy) to synthesize a hybrid nanoadsorbent (PPy/3R-MoS₂). The preparation conditions of PPy/3R-MoS₂ were investigated and the obtained nanosheets were characterized with SEM, HRTEM, XRD, FTIR, and XPS. The results show that PPy/3R-MoS₂ exhibited enhanced adsorption capacity towards U(VI) compared to pure 3R-MoS₂ and PPy; the maximum adsorption was 200.4 mg/g. The adsorption mechanism was elucidated with XPS and FTIR: 1) negatively charged PPy/3R-MoS₂ nanosheets attracted UO₂²⁺ by electrostatic attraction; 2) exposed C, N, Mo, and S atoms complexed with U(VI) through coordination; 3) Mo in the complex partly reduced the adsorbed U(VI) to U(IV), which further regenerated the adsorption point and continuously adsorbed U(VI). The design of the PPy/3R-MoS₂ composite with high adsorption capacity and chemical stability provides a new direction for the removal of radionuclide.