Unique selectivity and rapid uptake of molybdenum-disulfide-functionalized MXene nanocomposite for mercury adsorption

A heterogeneous nanoadsorbent composed of two-dimensional Ti₃C₂T_x MXene nanosheets (MX) functionalized with nanolayered molybdenum disulfide (MoS₂/MX-II) was synthesized by a facile hydrothermal treatment method and used to remove toxic mercuric ions (Hg²⁺). Mercury was adsorbed by the synergistic action of the sulfur (disulfide) and the oxygenated terminal groups of Ti₃C₂T_x in the MoS₂-MX-II composite. Ultrasonication increased the surface area and interlayer distance of the Ti₃C₂T_x nanosheets, which enhanced the removal capability of the composite. As a result, 50 μmol/L of Hg²⁺ was reduced to 0.01 μmol/L in just 120 s, which is unprecedented kinetic behavior for mercury adsorption. Furthermore, the Langmuir adsorption isotherm fitted well with the adsorption data and revealed a maximum adsorption capacity of 7.16 mmol/g. To provide a practical demonstration of MoS₂/MX-II, it was applied to mercury-contaminated wastewater, whose results showed that MoS₂/MX-II was capable of removing Hg²⁺ at the ppb level with a distribution coefficient of 7.87 × 10⁵ mL/g in the co-presence of various metal ions. Hydrothermal stability tests and SEM analysis confirmed the stability of MoS₂-MX-II after it adsorbed a high concentration of Hg²⁺. Furthermore, MoS₂-MX-II exhibited excellent recyclability as 0.08 mM of Hg²⁺ was completely removed even after five cycles. The results suggest the practical applicability of this type of heterogeneous nanocomposite for water purification.