Adsorption of Sr(II) in aqueous solution by multilayer titanium carbon nitrogen (Ti3CNTx) MXene: Box-Behnken modeling design and experimental study

The discharge of low-level radioactive wastewater from nuclear power accidents is an important source of radionuclides that enter and pollute the environment, such as 90Sr, which has a long half-life and is harmful. The effectiveness of multilayer Ti3CNTx MXene as a novel adsorbent for the removal of wastewater containing Sr2+ was explored. The synthesized multilayer Ti3CNTx MXene was characterized by XPS, FTIR, SEM, BET, and XRD. The influence of basic process parameters, such as time, pH, coexisting ion concentration, and initial concentration, on strontium adsorption efficiency, was determined. Ti3CNTx showed rapid kinetics (nearly 90% strontium removal after 15 min) and a broad active pH range of 3–12. The adsorption capacity of Ti3CNTx was better than that of Ti3C2Tx under the same reaction conditions. The maximum adsorption capacity of Ti3CNTx was 26.53 mg∙g−1 at 313 K according to the Langmuir isotherm. And the adsorption was consistent with the pseudo-second-order kinetic. The experiments of initial concentration and coexisting ions showed that the Ti3CNTx has a high affinity for strontium at low concentration, and the inhibition of Ca2+ is the largest. Ti3CNTx adsorbed Sr2+ via complex formation, electrostatic attraction, and encapsulation as revealed by various instrument characterization and analysis. The reusability of Ti3CNTx was good, after four cycles, the removal efficiency was 73%. Finally, the RSM model was applied to explore the optimal conditions of adsorbent to provide a reference for practical application. In conclusion, the results showed that the multilayer Ti3CNTx MXene has a good adsorption performance for strontium. [Display omitted] •An environmentally friendly MAX phase etching approach was applied to adsorb strontium.•The hexagonal, well-separated, book-liking lamellar structure improved the adsorption performance.•Ti3CNTx exhibited rapid kinetics, high Kd value, and widely pH.•Efficient Sr2+ adsorption mechanism included complex formation, electrostatic attraction, and encapsulation.•Optimization of Ti3CNTx for strontium adsorption used RSM model design.