Thorium(IV) adsorption onto multilayered Ti₃C₂T_x MXene: a batch, X-ray diffraction and EXAFS combined study

Abstract

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 ThIV by multilayered titanium carbides (Ti3C2Tx) through a hydrated intercalation strategy is reported. ThIV adsorption behaviors of three Ti3C2Tx 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 ThIV 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 Ti3C2Tx featured the largest interlayer space and exhibited the highest ThIV 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 Ti3C2Tx 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 ThIV, where H+ from surface [Ti−O]−H+ groups were the primary active sites on Ti3C2Tx. 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 ThIV mainly formed the outer-sphere complexes on Ti3C2Tx 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.

Foreword to the special virtual issue on Actinide physics and chemistry with synchrotron radiation

“…(3) Lin Wang and co-authors combined X-ray diffraction and extended X-ray absorption fine-structure (EXAFS) methods to study thorium(IV) adsorption onto multilayered titanium carbides, Ti 3 C 2 T x (Wang et al, 2021). Jian Sun and co-authors studied two series of uranium-doped Nd 2 Zr 2 O 7 pyrochlore materials as potential nuclear waste host matrices by the combination of the X-ray diffraction, Raman and EXAFS techniques (Sun et al, 2022).…”