Thorium(IV) adsorption onto multilayered Ti3C2Tx MXene: a batch, X-ray diffraction and EXAFS combined study

The interlayer regulation of layered environmental adsorption materials such as two-dimensional early transition metal carbides and carbonitrides (MXenes) plays an important role in their purification performance for specific pollutants. Here the enhanced uptake of Th IV by multilayered titanium carbides (Ti 3 C 2 T x ) through a hydrated intercalation strategy is reported. Th IV adsorption behaviors of three Ti 3 C 2 T x samples with different c lattice parameters were studied as a function of contact time, pH, initial concentration, temperature and ion strength in batch experiments. The results indicated that the Th IV uptake was pH and ionic strength dependent, and the adsorption process followed the pseudo-second-order kinetics and the heterogeneous isotherm (Freundlich) model. Thermodynamic data suggested that the adsorption process of all MXene samples was a spontaneous endothermic reaction. The dimethyl sulfoxide intercalated hydrated Ti 3 C 2 T x featured the largest interlayer space and exhibited the highest Th IV adsorption capacity (162 mg g −1 at pH 3.4 or 112 mg g −1 at pH 3.0), reflecting the significant increase in available adsorption sites from Ti 3 C 2 T x interlayers. The adsorption mechanism has been clarified based on adsorption experiments and spectroscopic characterizations. An ion exchange process was proposed for the interaction between hydrated MXenes and Th IV , where H + from surface [Ti−O] − H + groups were the primary active sites on Ti 3 C 2 T x . Extended X-ray absorption fine structure (EXAFS) fitting results, in combination with X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses, clearly indicated that Th IV mainly formed the outer-sphere complexes on Ti 3 C 2 T x surface through electrostatic interaction under strong acid conditions, while at pH > 3.0 the adsorption mechanism was determined by inner-sphere coordination and electrostatic interaction together.