Tetramethylammonium-Intercalated M<sub>2</sub>CT<sub><i>x</i></sub> (M = Ti, V, Nb, Mo) MXene Nanosheet-Based Gas Sensors
M. Sai Bhargava Reddy, Naveen Kumar Bandari, Kailasa Saraswathi, Bharat C. G. Marupalli, Shiv Govind Singh, Shampa Aich
Abstract
Gas sensors have become indispensable tools across various fields, with advanced materials playing a crucial role in enhancing their reliability and efficiency. Among two-dimensional nanomaterials, MXenes stand out due to their high surface area, tunable surface chemistry, and unique electronic properties. While Ti 3 C 2 T x has dominated MXene-based gas sensing research, other MXenes remain relatively underexplored despite their strong theoretical potential. This study bridges this gap by investigating the roles of transition metal (M)-sites, intercalants, surface terminal groups (T x ), and gas-MXene interactions in M 2 CT x (M = Ti, V, Nb, Mo) systems. Employing an optimized synthesis approach, comprising selective etching of both MAX and non-MAX phase precursors followed by delamination using tetramethylammonium hydroxide (TMAOH), we successfully produced multi- and few-layered MXenes with enhanced gas sensing performance. TMA + intercalation expands interlayer spacing, amplifying swelling-driven responses in metallic MXenes (Ti/V/Nb), while inducing pseudosemiconducting behavior in Mo 2 CT x, as evidenced by a reversal in response trends. Among the tested MXenes, Ti 2 CT x, V 2 CT x, and Nb 2 CT x demonstrated excellent selectivity for nitrogen dioxide (NO 2 ), with Ti 2 CT x achieving an outstanding response of ∼ 660% to 50 ppm and a detection limit below 1 ppm. In contrast, Mo 2 CT x showed superior selectivity for carbon monoxide (CO: −3.2% for 50 ppm). These findings underscore the critical influence of M-site selection, intercalation, and surface chemistry on MXene-gas interactions, providing a roadmap for designing tailored sensors for applications such as air quality monitoring or hazardous leak detection.