d-Band Center Optimization of Ti₃C₂T_x MXene Nanosheets for Ultrahigh NO₂ Gas Sensitivity at Room Temperature

Abstract

MXene exhibits numerous advantageous properties such as high electronic conductivity, high surface area, and ease of surface modification via tailoring of functional groups. However, the mechanism by which MXene functionalization enhances gas sensing performance has not yet been well understood, let alone the development of a rational sensor design optimization strategy. This work presents a functionalization methodology for MXene based on d-band center modulation, which can be implemented by introducing Fe onto the surface of Ti 3 C 2 T x nanosheets, for significantly improved gas sensing response and selectivity. The strategy is demonstrated in the design of gas sensors. The optimized gas sensor shows a response of 50% toward 10 ppm of NO 2 at room temperature, which is over 6-fold improvement from its pristine counterpart, an unprecedented performance level among all reported MXene gas sensors. XPS characterizations, valence band analyses, and density functional theory (DFT) calculations all indicate that the underlying enhancement mechanism can be attributed to the tuning of the d-band center energy toward the Fermi level. This work provides a new design strategy based on the optimization of the d-band center energy and adds a much needed systematic and quantitative method to the design of two-dimensional materials based semiconducting gas sensors.

Advancing electrocatalytic reactions through mapping key intermediates to active sites via descriptors

“…The shift of the valence band of an element relative to the E f level following a catalyst change can be ascertained through techniques such as X-ray absorption near-edge spectroscopy (XANES) and ultraviolet photoemission spectroscopy (UPS), where the shift of the valence band corresponds to the shift of the d-band center, providing insights into the adsorption strength of the intermediates. 137,138 Nevertheless, practical challenges may arise from the discrepancies between theoretical calculations and experimental findings. Generally, DFT calculations often simplify catalysts and ignore the external influences, which may lead to deviations in experimental results.…”

Identification of Lung Cancer Biomarkers by Nanosensors Based on Titanium Carbide (Ti3C2Tx) MXenes

“…46,47 These successfully synthesized Ti 3 C 2 T x -type nanosheets exhibit ultrahigh sensitivity toward NO 2 gas at room temperature. 48 In a combined experimental and simulations work, Kim et al used a chemiresistive gas sensor to study the ultrahigh sensitivity of acetone, ethanol, ammonia, propanol, NO 2 , CO 2 , and SO 2 with (Ti 3 C 2 T x , T x : O, S, F, and OH) MXenes. 49 Similarly Wang et al used XPS characterization and DFT simulations to study NO 2 adsorption on pristine and Fesubstituted Ti 3 C 2 O 2 sheet, and the results show that Fe substitution improves sensing of NO 2 than the pristine sheet.…”

“…49 Similarly Wang et al used XPS characterization and DFT simulations to study NO 2 adsorption on pristine and Fesubstituted Ti 3 C 2 O 2 sheet, and the results show that Fe substitution improves sensing of NO 2 than the pristine sheet. 48 The utilization of three-dimensional porous MXenes/NiCo-LDH composite has also proven successful in creating highperformance nonenzymatic glucose sensors. 36 In this study, we used first-principles DFT level simulations to explore the sensing capabilities of functionalized titanium carbide MXenes (Ti 3 C 2 T x , T x : O, S, F, and OH) toward the mentioned VOCs.…”

“…In a combined experimental and simulations work, Kim et al used a chemiresistive gas sensor to study the ultrahigh sensitivity of acetone, ethanol, ammonia, propanol, NO 2 , CO 2 , and SO 2 with (Ti 3 C 2 T x , T x : O, S, F, and OH) MXenes . Similarly Wang et al used XPS characterization and DFT simulations to study NO 2 adsorption on pristine and Fe-substituted Ti 3 C 2 O 2 sheet, and the results show that Fe substitution improves sensing of NO 2 than the pristine sheet . The utilization of three-dimensional porous MXenes/NiCo-LDH composite has also proven successful in creating high-performance nonenzymatic glucose sensors …”

“…Using a DFT level simulation, the biocompatible transition-metal-based MXenes like Ti 2 CO 2 with (0001) a basal surface have high sensing propensity toward various nucleobases like DNA and RNA . Due to several advantageous features like adjustable surface properties and tunable band gap, the Ti 3 C 2 T x -type MXene hybrid structures are investigated for sensing applications with an ultralow detection limit. , These successfully synthesized Ti 3 C 2 T x -type nanosheets exhibit ultrahigh sensitivity toward NO 2 gas at room temperature …”