Abstract
Heavy metal contamination of water resources has become one of the most pressing problems of our time, and therefore it is necessary to invent new and effective materials for the removal of heavy metals from water. Although scientists consider two-dimensional transition metal carbides and nitrides (MXenes) as good adsorbents, natural structural defects are often found in the initial samples of these materials. The main obstacles to unlocking the full potential of the material are the close stacking of nanosheets and the lack of active centers on the surface. In this article, we will explain the role and mechanism of vacancy engineering in the removal of heavy metals by metal (VM), carbon/nitrogen (VX), and surface terminal vacancies (VTx). By specifically modifying the bonding and electronic structure of atoms, we can make vacancy defects not only reduce the adhesion of layers, but also act as active thermodynamic traps. Artificial atomic defects lead to the redistribution of electrons in a single location, and this phenomenon significantly reduces the Gibbs energy of binding to heavy metals. Such artificial defects activate the material, increasing its adsorption capacity several times (e.g., >400 mg/g for Pb²⁺) and lead to the spontaneous reduction of heavy metals such as Cr⁶⁺ in water. In this article, we discuss in detail new synthesis technologies that precisely introduce structural defects. Finally, we propose a strategic direction for the development of a new generation of MXene materials for pure water filters, while addressing the issues of industrial large-scale production and long-term storage.