Two-dimensional (2-D) titanium carbide MXene core (Ti 3 C 2 T x ) shell aerogel spheres (MX-SA) for mercuric ion removal were designed and fabricated with varying concentrations of Ti 3 C 2 T x MXene and sodium alginate (SA) using a facile method. Owing to their unique inside structures, high porosities, large specific surface areas, oxygenated functional groups of MXene nanosheets, and available active binding sites, the synthesized microspheres constitute a unique adsorbent for heavy metals removal in water. The MX-SA 4:20 spheres exhibit an exceptional adsorption capacity of 932.84 mg/g for Hg 2+ , which is among the highest value reported for adsorbents. The adsorbent exhibits high single-and multi-component removal efficiencies, with 100% efficiency for Hg 2+ and > 90% efficiency for five heavy metal ions. The synthesized materials are highly efficient for Hg 2+ removal under extreme pH conditions (0.5-1.0 M HNO 3 ) and have additional excellent reproducible properties. The micro-size and spherical shape of MX-SA 4:20 also allow it to be used in column-packed devices.

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A green approach was adopted to exfoliate a Ti 2 AlC MAX phase. The exfoliated nanostructures (Alk-Ti 2 C fibr and Alk-Ti 2 C sheet ) with exceptional mechanical, thermal, and water stabilites, as well as abundant oxygenated active binding sites, were synthesized via a controlled hydrothermal treatment in an alkaline environment. The successful synthesis of nanofibers and sheetlike nanostructures was inferred with scanning electron microscopy and X-ray diffraction analyses. Field emission scanning electron microscopy, field-emission transmission electron microscopy, Raman spectroscopy, Brunauer−Emmett− Teller surface area, ζ-potential analyses, and X-ray photoelectron spectroscopy were utilized to investigate the material's characteristics and its structural changes after metal ion adsorption. Heavy metal ion adsorption of the synthesized nanostructures was assessed in batch tests based on Cd 2+ ion sequestration; the maximum adsorption capacity for Cd 2+ was 325.89 mg/g, which is among the highest values reported for similar materials such as graphene oxide and its derivatives. The detailed quantitative investigation confirmed the interaction of hydroxyl groups with Cd 2+ ions by electrostatic interactions, adsorption-coupled oxidation, and complex formation. Owing to their unique structure, high porosity, large specific surface area, and oxygenated functional groups, Alk-Ti 2 C sheet nanosheets were highly time-efficient for Cd 2+ removal. Moreover, Alk-Ti 2 C fibr and Alk-Ti 2 C sheet nanostructures were tested for simulated groundwater, showing that synthesized nanostructures were capable for removing Cd 2+ ions at the ppb level. The results obtained from this study suggested that nanostructures synthesized using this route could provide a new approach to prepare and exfoliate additional MAX phases for the removal of heavy metal ions and other pollutants in the environment.

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