Highly Broadband Absorber Using Plasmonic Titanium Carbide (MXene)

Control of light transmission and reflection through nanostructured materials has led to demonstration of metamaterial absorbers that have augmented the performance of energy harvesting applications of several optoelectronic and nanophotonic systems. Here, for the first time, a broadband plasmonic metamaterial absorber is fabricated using two-dimensional titanium carbide (Ti₃C₂T_<i>x</i>) MXene. Arrays of nanodisks made of Ti₃C₂T_<i>x</i> exhibit strong localized surface plasmon resonances at near-infrared frequencies. By exploiting the scattering enhancement at the resonances and the optical losses inherent to Ti₃C₂T_<i>x</i> MXene, high-efficiency absorption (∼90%) for a wide wavelength window of incident illumination (∼1.55 μm) has been achieved

Charge- and Size-Selective Ion Sieving Through Ti₃C₂T_<i>x</i> MXene Membranes

Nanometer-thin sheets of 2D Ti₃C₂T_<i>x</i> (MXene) have been assembled into freestanding or supported membranes for the charge- and size-selective rejection of ions and molecules. MXene membranes with controllable thicknesses ranging from hundreds of nanometers to several micrometers exhibited flexibility, high mechanical strength, hydrophilic surfaces, and electrical conductivity that render them promising for separation applications. Micrometer-thick MXene membranes demonstrated ultrafast water flux of 37.4 L/(Bar·h·m²) and differential sieving of salts depending on both the hydration radius and charge of the ions. Cations with a larger charge and hydration radii smaller than the interlayer spacing of MXene (∼6 Å) demonstrate an order of magnitude slower permeation compared to single-charged cations. Our findings may open a door for developing efficient and highly selective separation membranes from 2D carbides

Guidelines for Synthesis and Processing of Two-Dimensional Titanium Carbide (Ti₃C₂T_<i>x</i> MXene)

Two-dimensional (2D) transition metal carbides, carbonitrides, and nitrides (MXenes) were discovered in 2011. Since the original discovery, more than 20 different compositions have been synthesized by the selective etching of MAX phase and other precursors and many more theoretically predicted. They offer a variety of different properties, making the family promising candidates in a wide range of applications, such as energy storage, electromagnetic interference shielding, water purification, electrocatalysis, and medicine. These solution-processable materials have the potential to be highly scalable, deposited by spin, spray, or dip coating, painted or printed, or fabricated in a variety of ways. Due to this promise, the amount of research on MXenes has been increasing, and methods of synthesis and processing are expanding quickly. The fast evolution of the material can also be noticed in the wide range of synthesis and processing protocols that determine the yield of delamination, as well as the quality of the 2D flakes produced. Here we describe the experimental methods and best practices we use to synthesize the most studied MXene, titanium carbide (Ti₃C₂T_<i>x</i>), using different etchants and delamination methods. We also explain effects of synthesis parameters on the size and quality of Ti₃C₂T_<i>x</i> and suggest the optimal processes for the desired application

Electrochemical in Situ Tracking of Volumetric Changes in Two-Dimensional Metal Carbides (MXenes) in Ionic Liquids

We report the volumetric changes of MXenes in contact with different ionic liquids and the swelling/contraction during electrochemical voltage cycling by complementing electrochemical dilatometry with in situ X-ray diffraction measurements. A drastic, initial, and irreversible volume expansion of MXenes occurs during first contact to ionic liquids (wetting). Voltage cycling evidenced a highly reversible expansion and contraction of electrodes at a very large amplitude of strain (corresponding with max. 12 vol %), which may allow the use of MXene as a high-performance electrochemical actuator

Atomic Defects in Monolayer Titanium Carbide (Ti₃C₂T_<i>x</i>) MXene

The 2D transition metal carbides or nitrides, or MXenes, are emerging as a group of materials showing great promise in lithium ion batteries and supercapacitors. Until now, characterization and properties of single-layer MXenes have been scarcely reported. Here, using scanning transmission electron microscopy, we determined the atomic structure of freestanding monolayer Ti₃C₂T_<i>x</i> flakes prepared <i>via</i> the minimally intensive layer delamination method and characterized different point defects that are prevalent in the monolayer flakes. We determine that the Ti vacancy concentration can be controlled by the etchant concentration during preparation. Density function theory-based calculations confirm the defect structures and predict that the defects can influence the surface morphology and termination groups, but do not strongly influence the metallic conductivity. Using devices fabricated from single- and few-layer Ti₃C₂T_<i>x</i> MXene flakes, the effect of the number of layers in the flake on conductivity has been demonstrated