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Analytical Chemistry

MXenes provide exceptional signal-to-noise ratios in gas sensing

Metallic conductivity and reactive surface groups take credit for 2-D material’s performance

by Mitch Jacoby
February 5, 2018 | A version of this story appeared in Volume 96, Issue 6

This drawing depicts the structure of a titanium carbide MXene compound and gas molecules adsorbing to it.
Credit: Adapted from ACS Nano
High conductivity and the presence of –O, –OH, and –F surface groups make this titanium carbide MXene useful for sensing gases (ethanol and ammonia shown). Ti = yellow, C = black, H = white, O = red, F = blue, N = green.

Gas sensors have long served critical roles in industrial applications, including monitoring air quality and engine emissions. Analyzing volatile organic compounds in breath to screen for disease markers is a developing application that is being advanced by highly sensitive “homemade” gas sensors, often based on semiconducting oxides, nanomaterials, and two-dimensional materials. That field may advance even more quickly now thanks to a study showing that a titanium carbide MXene compound can be fashioned into a gas sensor that provides part-per-billion-level sensitivity and record-setting signal-to-noise ratios (ACS Nano 2018, DOI: 10.1021/acsnano.7b07460). Various 2-D materials, including black phosphorus and molybdenum disulfide, rank among the top-performing gas-sensing media. That motivated a team led by Hee-Tae Jung of Korea Advanced Institute of Science & Technology and Yury Gogotsi of Drexel University to see how MXenes, a family of 2-D metal carbides and nitrides, stack up in that application. Head-to-head comparisons in tests with acetone, ethanol, ammonia, propanal, and other gases relevant to breath analysis show that the MXene compound evaluated, Ti3C2, provides signal-to-noise ratios roughly 100 times as high as those of the other 2-D materials. The team attributes the excellent performance to the MXene’s porosity, metal-like conductivity, and abundant surface groups that adsorb analytes.


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