Important roles of surface functionalized groups of MXenes on adsorption capacities of Sr and Cs: A theoretical study

It is important and challenging to capture the radioactive strontium (90Sr) and cesium (137Cs) from nuclear wastes for radionuclide remediation due to their long half-lives and hazardous nature. Adsorption method has been widely used to remove radioactive nuclides as it's low-cost and easy operation. Transition metal carbide and nitride (MXenes) nanomaterials with functional groups possess excellent properties, which can be used as promising adsorbents. However, the influence of surface functional groups of MXenes on adsorption properties of radioactive nuclides is not clear. In this work, a serial of surface functional groups (O/OH) decorated MXenes have been systematically investigated to adsorb Sr and Cs based on density functional theory calculations. The best O/OH (3/16) ratio of MXenes has been used to remove Sr and Cs, and we have found that Sr and Cs can adsorb on the surfaces of MXenes with the adsorption energies ranging from −2.07 ∼ −4.34 eV and −1.42 ∼ −2.58 eV, respectively. Among these MXenes, Sc2C monolayer exhibits the strongest adsorption capacity for Sr and Cs with the largest value of electron transfers, which can be achieved by forming three SrO and CsO covalent bonds between the radioactive nuclides and O atoms of Sc2C monolayer.