Adsorption performance and mechanism of MnO₂/Ti₃C₂T_X composite towards U(VI) in water

To address the shortcomings of Ti₃C₂T_X nanosheets, which tend to stack and have limited adsorption sites, a MnO₂/Ti₃C₂T_X composite was prepared using the hydrothermal method. The influence of uranium initial concentration, dosage, pH, time, and interfering ions on U(VI) adsorption was investigated through single-factor adsorption experiments. Modern characterization techniques were employed to analyze the surface properties of MnO₂/Ti₃C₂T_X and the mechanism of U(VI) adsorption. Experimental results revealed that with an initial U(VI) concentration of 5 mg·L⁻¹, MnO₂/Ti₃C₂T_X dosage of 0.1 g·L⁻¹, and a temperature of 303 K, pH of 6, the U(VI) concentration dropped to 0.41 mg·L⁻¹ within 30 s. Adsorption equilibrium was reached after 30 min, with an adsorption rate of 99.15% and an adsorption capacity of 49.58 mg·g⁻¹. After five cycles, the adsorption efficiency of MnO₂/Ti₃C₂T_X remained at 96.3%, demonstrating its potential for regeneration and reuse. The entire adsorption process was endothermic and spontaneous, fitting the pseudo-second-order kinetic model and the Freundlich isotherm model. BET analysis showed that the specific surface area of MnO₂/Ti₃C₂T_X reached 318.3 m²·g⁻¹, which is 55.9 times higher than that of Ti₃C₂T_X. FTIR and XPS analyses indicated that the primary mechanism of U(VI) adsorption on MnO₂/Ti₃C₂T_X is the coordination complexation between surface oxygen-containing groups and uranium.