Amino-functionalized POSS nanocage-intercalated titanium carbide (Ti₃C₂T_x) MXene stacks for efficient cesium and...

In this work, we prepared two-dimensional (2D) stack-structured aminopropylIsobutyl polyhedral oligomeric silsesquioxane (POSS-NH₂) intercalated titanium carbide (Ti₃C₂T_x) MXene material (Ti₃C₂T_x/POSS-NH₂) using a post-intercalation strategy as a potential adsorbent for the removal of cesium (Cs⁺) and strontium (Sr²⁺) ions from aqueous solutions. Ti₃C₂T_x/POSS-NH₂ exhibited unprecedented adsorption capacities of 148 and 172 mg g^-1 for Cs⁺ and Sr²⁺ ions, respectively. Batch adsorption experimental data well fitted the Freundlich isotherm model, which revealed multilayer adsorption of Cs⁺ and Sr²⁺ ions onto heterogeneous -OH, -F, -O, and -NH₂ adsorption sites of Ti₃C₂T_x/POSS-NH₂ with different energies. Ti₃C₂T_x/POSS-NH₂ exhibited rapid Cs⁺/Sr²⁺ ions adsorption kinetics and attained equilibrium within 30 min. Also, Ti₃C₂T_x/POSS-NH₂ exhibited recyclable capability over three cycles and remarkable selectivities of 89% and 93% for Cs⁺ and Sr²⁺ ions, respectively, in the presence of co-existing mono- and divalent cations. We suggest the high adsorption capacity of Ti₃C₂T_x/POSS-NH₂ might be due to the synergistic effects of (i) increased inter-lamellar distance between Ti₃C₂T_x galleries due to POSS-NH₂ intercalation, enabling diffusion and encapsulation of large numbers of Cs⁺/Sr²⁺ ions, (ii) strong complexation of amine (-NH₂) groups of POSS-NH₂ with Cs⁺/Sr²⁺ 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⁺/Sr²⁺ 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 Sr²⁺ ions from aqueous media.