Preparation Of Phosphorylated Two-dimensional Layered Transition Metal Dichalcogenides And Their Adsorption Properties For Uranium

The two-dimensional layered transition metal dichalcogenides are graphene analog with excellent chemical stability,special crystal structure（three-layer sandwich structure）and high specific surface area.These materials are excellent matrix materials for radionuclide adsorption.In this paper,phosphorylated molybdenum disulfide（MoS₂-PO₄）,phosphorylated tungsten disulfide（WS₂-PO₄）and phosphorylated molybdenum selenide（MoSe₂-PO₄）were prepared by simple ultrasonic technology using molybdenum disulfide,tungsten disulfide and molybdenum selenide as substrates.And used to adsorb and separate uranyl ions in radioactive wastewater.The microstructure and physicochemical properties of the materials were characterized by SEM/EDS,TEM,AFM,Zeta potential,XRD,RAMAN and XPS.The phosphate groups were combined with S or Se at the defects in MoS₂,WS₂ and MoSe₂.The grafting density were 0.36,1.66 and 7.19 mmol·g^-1,respectively.Phosphate group functionalization did not change the original microscopic morphology.MoS₂-PO₄,WS₂-PO₄ and MoSe₂-PO₄ were still lamellar.The effects of solution pH,ionic strength,solid-liquid ratio,initial concentration,contact time,temperature and coexisting ions on the adsorption of uranium onto MoS2-PO4,WS₂-PO₄ and MoSe₂-PO₄ were systematically investigated.The results shown that the adsorption of U（VI）by MoS₂-PO₄,WS₂-PO₄ and MoSe₂-PO₄ were greatly affected by the pH value of the solution,the optimum pH value of these materials were 5.5.The adsorption rate of U（VI）by the three adsorbents were very fast.The adsorption equilibrium was reached at 3 min,8 min and 8 min,respectively.The removal rate of U（VI）by MoS₂-PO₄ was over80%at 12 s.The adsorption processes of MoS₂-PO₄,WS₂-PO₄ and MoSe₂-PO₄ for uranium conform to the pseudo-second-order kinetics model and Langmuir isothermal adsorption model.The results shown that the adsorption processes of MoS2-PO4,WS2-PO4 and MoSe2-PO₄ for uranium were single-layer chemical adsorption,and the maximum adsorption capacity were 338.98 mg·g^-1,268.82 mg·g^-1 and 88.97 mg·g^-1,respectively.The adsorption process is not affected by the ionic strength of the solution,which means that it is an inner sphere complexation.The adsorption of U（VI）by the three adsorbents are a spontaneous endothermic process,indicating that the elevated temperature is favorable for adsorption.The uranyl ion is mainly complexed with O in P=O and P-O.MoS₂-PO₄,WS₂-PO₄ and MoSe₂-PO₄ exhibit higher selectivity.The selectivity rates are 71.2%,78.7%and 82.3%,respectively.As a desorbent,0.4 mol·L^-1 HCl solution can effectively desorb uranium on the surface of three adsorbents,and the desorption rate is above 98%.In the adsorption-desorption process,MoS2-PO4,WS2-PO4 and MoSe2-PO4 have strong stability and the adsorption capacity retention rate exceeds 89%after 5 cycles of utilization.Based on this paper,the phosphorylated two-dimensional layered transition metal dichalcogenides adsorbents have simple preparation process,low cost,large adsorption capacity,high rate,high selectivity and strong stability,excellent uranium adsorption separation material.For the treatment of radioactive waste water,it can be especially used for emergency treatment of radionuclide leakage.