Tailoring MXene Thickness and Functionalization for Enhanced Room‑Temperature Trace NO2 Sensing

Abstract

In this study, precise control over the thickness and termination of Ti3C2TX MXene flakes is achieved to enhance their electrical properties, environmental stability, and gas-sensing performance. Utilizing a hybrid method involving high-pressure processing, stirring, and immiscible solutions, sub-100 nm MXene flake thickness is achieved within the MXene film on the Si-wafer. Functionalization control is achieved by defunctionalizing MXene at 650 degrees C under vacuum and H-2 gas in a CVD furnace, followed by refunctionalization with iodine and bromine vaporization from a bubbler attached to the CVD. Notably, the introduction of iodine, which has a larger atomic size, lower electronegativity, reduce shielding effect, and lower hydrophilicity (contact angle: 99 degrees), profoundly affecting MXene. It improves the surface area (36.2 cm(2) g(-1)), oxidation stability in aqueous/ambient environments (21 days/80 days), and film conductivity (749 S m(-1)). Additionally, it significantly enhances the gas-sensing performance, including the sensitivity (0.1119 Omega ppm(-1)), response (0.2% and 23% to 50 ppb and 200 ppm NO2), and response/recovery times (90/100 s). The reduced shielding effect of the -I-terminals and the metallic characteristics of MXene enhance the selectivity of I-MXene toward NO2. This approach paves the way for the development of stable and high-performance gas-sensing two-dimensional materials with promising prospects for future studies.