Effects of Synthesis and Processing on Optoelectronic Properties of Titanium Carbonitride MXene

Abstract

MXenes, a relatively new class of two-dimensional (2D) transition-metal carbides, carbonitrides, and nitrides, exhibit unique properties such as high electronic conductivity, a wide range of optical characteristics, hydrophilicity, and mechanical stability. Because of the high electronic conductivity, MXenes have shown promise in many applications, such as energy storage, electromagnetic interference shielding, antennas, and transparent coatings. 2D titanium carbide (Ti 3 C 2 T x , where T x represents surface terminations), the first discovered and most studied MXene, has the highest electronic conductivity exceeding 10 000 S cm −1 . There have been several efforts to alter the conductivity of MXenes, such as manipulation of the transition-metal layer and control of surface terminations. However, the impact of the C and N site composition on electronic transport has not been explored. In this study, the effects of synthesis methods on optoelectronic properties of 2D titanium carbonitride, Ti 3 CNT x , were systematically investigated. We show that Ti 3 CNT x , which hosts a mix of carbon and nitrogen atoms in the X layer, has lower electronic conductivity and a blue shift of the main absorption feature within the UV−visible spectrum, compared to Ti 3 C 2 T x . Moreover, intercalants such as water and tetraalkylammonium hydroxides decrease the electronic conductivity of MXene due to increased interflake resistance, leading to an increase in resistivity with decreasing temperature as observed in ensemble transport measurements. When the intercalants are removed, Ti 3 CNT x exhibits its intrinsic metallic behavior in good agreement with Hall measurements and transport properties measured on single-flake field-effect transistor devices. The dependence of conductivity of Ti 3 CNT x on the presence of intercalants opens wide opportunities for creating MXene-based materials with tunable electronic properties.

Scalable Synthesis of Ti3C2Tx MXene

“…In general, MXene optoelectronic properties depend on solution concentration, flake size, and surface terminations. Both small and large batches have characteristic absorption peaks at 770 nm, matching previous reports for this material . The UV region absorption is strongly correlated with flake size and shape, in addition to surface terminations, confirming the results from DLS (Figure S3, Supporting Information) and XPS (Figure ).…”

Recent Advances in 2D MXenes for Photodetection

“…d) Reproduced with permission. [ 58 ] Copyright 2019, American Chemical Society. e) Reproduced with permission.…”

“…[ 57 ] The dependence of absorption spectra between 200 and 1000 nm (UV–VIS) on material synthesis and X elements is illustrated in Figure 2d. [ 58 ] When using a mixture of LiF and HCl as the etching solution, Ti 3 CNT x (the black curve) with an absorption peak at ≈670 nm shows overall larger local absorbance than Ti 3 C 2 T x (the blue curve) with an absorption peak at ≈770 nm, leading to their brown‐like and green‐like colors, respectively. When manipulating the etching solution, no dominant absorption peak is observed for Ti 3 CNT x (the red curve) prepared through HF + tetramethylammonium hydroxide (TMAOH).…”

Potential of MXenes in Water Desalination: Current Status and Perspectives

“…The interlayer spacing of MXenes is usually in the range of 1 nm and is dependent on the value of n in MXenes (M n+1 X n T x ) [13]. So far, nearby 30 MXenes compositions are reported in the literature that have been synthesized from the MAX phase precursors primarily by incorporating two or more transition metals in the M layers [5,[18][19][20][21]. Among them, titanium-based MXenes (such as Ti 3 C 2 T x and Ti 2 CT x ) are extensively employed in environmental applications [1,18].…”

“…Among them, titanium-based MXenes (such as Ti 3 C 2 T x and Ti 2 CT x ) are extensively employed in environmental applications [1,18]. Besides carbides, other MXenes structures with nitride and carbonitride have also been employed in various fields [19,[22][23][24][25]. Owing to their unique layered structures and 2D morphology, MXenes can be easily exploited to form a composite with other materials to enhance their properties [25][26][27][28][29][30].…”