A new class of two-dimensional nanomaterials, MXenes, which are carbides/nitrides/carbonitrides of transition and refractory metals, has been critically analyzed. Since the synthesis of the first family member in 2011 by Yury Gogotsi and colleagues, MXenes have quickly become attractive for a variety of research fields due to their exceptional properties. Despite the fact that this new family of 2D materials was discovered only about ten years ago, the number of scientific publications related to MXene almost doubles every year. Thus, in 2021 alone, more than 2000 papers are expected to be published, which indicates the relevance and prospects of MXenes. The current paper critically analyzes the structural features, properties, and methods of synthesis of MXenes based on recent available research data. We demonstrate the recent trends of MXene applications in various fields, such as environmental pollution removal and water desalination, energy storage and harvesting, quantum dots, sensors, electrodes, and optical devices. We focus on the most important medical applications: photo-thermal cancer therapy, diagnostics, and antibacterial treatment. The first results on obtaining and studying the structure of high-entropy MXenes are also presented.

MXenes are a 2D materials (2DM) class with high industrialization potential, owing to their superb properties and compositional variety. However, ensuring high etching efficiency in the synthesis process without involving toxic, hazardous or non‐sustainable chemicals are challenging. In this work, an upscalable electrochemical MXene synthesis is presented. This novel protocol uses a non‐toxic and sustainable sodium tetrafluoroborate/hydrochloric acid (NaBF ₄ /HCl) electrolyte and increases etching efficiency by applying cathodic pulsing via pulse voltammetry. Hydrogen bubble formation restores electrochemical activity, and effectively supports 2D‐sheet removal, allowing continuous etching at higher yields in situ. In detail, yields of up to 60% electrochemical MXene (EC‐MXene) with no byproducts from a single exfoliation cycle are achieved. EC‐MXene had an excellent quality with high purity as assessed using chemical mapping by scanning electron microscopy with energy dispersive electron spectroscopy (SEM/EDX) and surface termination analysis performed with X‐ray photoelectron spectroscopy (XPS) and, for the first time, with low energy ion scattering (LEIS). Further properties of EC‐MXenes such as dimensions and adhesion energy of single flakes, vibrational peaks, and interlayer spacing are provided by atomic force microscopy (AFM), X‐ray diffraction (XRD), Raman spectroscopy (Raman), and transmission electron microscopy (TEM) respectively. Pulsed electrochemical synthesis is key to surface reactivation at the electrodes' interface, which results in improved exfoliation and quality of EC‐MXenes. This paves the way for scaling up and green industrialization of MXenes.

As the most representative member of a new emerging family of 2D material, titanium carbides or nitrides (MXenes), Ti ₃ C ₂ T _x and its 2D assembly format, Ti ₃ C ₂ T _x film, have displayed outstanding performance in a broad range of practical applications. However the mechanical behaviors of Ti ₃ C ₂ T _x films are rarely reported. We report a systematic study of the tensile behavior of Ti ₃ C ₂ T _x films. Ti ₃ C ₂ T _x films with various thicknesses (2–17 µ m) were prepared by the vacuum filtration method. Quasi-static tension and cyclic tension tests were performed to investigate the deformation and fracture mechanism of Ti ₃ C ₂ T _x films. It was found that: (1) the relative sliding between Ti ₃ C ₂ T _x flakes is the dominant deformation mechanism of Ti ₃ C ₂ T _x films. Cyclic loading-releasing in tension suppresses the inter-layer sliding of Ti ₃ C ₂ T _x flakes effectively and thus the tensile strength of thicker Ti ₃ C ₂ T _x film (5 µ m) film improves from 57 MPa to 67 MPa. (2) The mechanical properties of Ti ₃ C ₂ T _x films are found to be thickness dependent. When the film thickness increases from 2.3 to 17 µ m, the tensile strength and elastic modulus drop from 61 to 36 MPa and from 17 to 8 GPa, respectively. This is interpreted as more structural defects presented in the through-the-thickness direction as film thickness is increased. (3) Moderate ultrasonication pretreatment (30 min) reduces the Ti ₃ C ₂ T _x flake size significantly while improving the compactness of the Ti ₃ C ₂ T _x film; and the resulting Ti ₃ C ₂ T _x film shows a linear stress-strain relationship without plastic-like deformation. As a result, the tensile strength of 5 µ m thick Ti ₃ C ₂ T _x film is enhanced to 85 MPa; (4) Structural defects of the Ti ₃ C ₂ T _x film have significant effects on both the brittle-like fracture behavior and the distribution of tensile strength.