Amino-functionalized POSS nanocage-intercalated titanium carbide (Ti3C2Tx) MXene stacks for efficient cesium and strontium radionuclide sequestration

In this work, we prepared two-dimensional (2D) stack-structured aminopropylIsobutyl polyhedral oligomeric silsesquioxane (POSS-NH 2 ) intercalated titanium carbide (Ti 3 C 2 T x ) MXene material (Ti 3 C 2 T x /POSS-NH 2 ) using a post-intercalation strategy as a potential adsorbent for the removal of cesium (Cs + ) and strontium (Sr 2+ ) ions from aqueous solutions. Ti 3 C 2 T x /POSS-NH 2 exhibited unprecedented adsorption capacities of 148 and 172 mg g −1 for Cs + and Sr 2+ ions, respectively. Batch adsorption experimental data well fitted the Freundlich isotherm model, which revealed multilayer adsorption of Cs + and Sr 2+ ions onto heterogeneous –OH, –F, –O, and –NH 2 adsorption sites of Ti 3 C 2 T x /POSS-NH 2 with different energies. Ti 3 C 2 T x /POSS-NH 2 exhibited rapid Cs + /Sr 2+ ions adsorption kinetics and attained equilibrium within 30 min. Also, Ti 3 C 2 T x /POSS-NH 2 exhibited recyclable capability over three cycles and remarkable selectivities of 89% and 93% for Cs + and Sr 2+ ions, respectively, in the presence of co-existing mono- and divalent cations. We suggest the high adsorption capacity of Ti 3 C 2 T x /POSS-NH 2 might be due to the synergistic effects of (i) increased inter-lamellar distance between Ti 3 C 2 T x galleries due to POSS-NH 2 intercalation, enabling diffusion and encapsulation of large numbers of Cs + /Sr 2+ ions, (ii) strong complexation of amine (–NH 2 ) groups of POSS-NH 2 with Cs + /Sr 2+ ions, and (iii) the presence of large numbers of heterogeneous surface functional groups (e.g., –OH, –F, and –O), which resulted in the adsorptions of Cs + /Sr 2+ ions through electrostatic, ion exchange, and surface complexation mechanisms. Given the extraordinary adsorption capacities observed, intercalation appears to be a promising strategy for the effective removal of radioactive Cs + and Sr 2+ ions from aqueous media. • Unprecedented Cs + and Sr 2+ adsorption of Ti 3 C 2 T x MXene through POSS-NH 2 intercalation. • Strong complexation of –NH 2 groups of POSS-NH 2 with Cs + and Sr 2+ ions. • Intercalation increases Ti 3 C 2 T x interlayer distance and encapsulates more Cs and Sr. • Adsorption via synergistic electrostatic, complexation, and ion exchange processes. • Maximum Cs + and Sr 2+ adsorption capacities of 148 and 172 mg g −1 , respectively.