Adsorptive Properties of Ti3C2Tx MXenes with Optimal Surface Functionalization by (‒O, ‒F) Groups

Nanoadsorbents, including 2D MХenes, are being actively studied as materials for the removal of heavy metals from water. Adsorption is a cheap and effective way to reduce the pollution level with such-kind toxic substances. Ti3C2Tx MXenes are one of the most promising materials in this field, due to their large specific surface area rich in adsorption centers. Additionally, the composition of this material can be optimally selected to ensure the maximum adsorption efficiency, for example, by controlling their surface functionalization. Density functional theory (DFT) modeling is one of the most effective methods for studying and predicting the adsorption properties of MXenes. In this work, the DFT approach is used to determine the adsorption energies (Eads) of mercury and iron ions on the surface of Ti3C2O2 and Ti3C2F2 MXenes. It is found that the maximum adsorption energy (Eads = –3.59 eV for Fe and –0.357 eV for Hg) is exhibited by MXenes with oxygen surface functionalization. Also, the work describes the synthesis and characterization of Ti3C2Tx MXenes with a predominant content of –O functional groups. Characterization of the material includes the study of its optical properties, i.e., absorption spectra: their analysis is a simple way to subsequently detect the content of MXenes in treated water. It is found that Ti3C2Tx MXenes have a light-absorption peak at a wavelength of 795 nm, and the dependence of the intensity of this peak on the concentration is linear in the range from 10 to 100 μg/mL, which is convenient for subsequent use in optical detection.