Partially Oxidized Ti₃C₂T_x MXenes for Fast and Selective Detection of Organic Vapors at Part-per-Million Concentrations

Abstract

MXenes, two-dimensional transition metal carbides or nitrides, have recently shown great promise for gas sensing applications. We demonstrate that the sensitivity of intrinsically metallic Ti3C2T x MXene can be considerably improved via its partial oxidation in air at 350 °C. The annealed films of MXene sheets remain electrically conductive, while their decoration with semiconducting TiO2 considerably improves their chemiresistive response to organic analytes at low-ppm concentrations in dry air, which was used to emulate practical sensing environments. We demonstrate that partially oxidized MXene has a faster and a qualitatively different sensor response to volatile analytes compared to pristine Ti3C2T x . We fabricated multisensor arrays of partially oxidized Ti3C2T x MXene devices and demonstrate that in addition to their high sensitivity they enable a selective recognition of analytes of nearly the same chemical nature, such as low molecular weight alcohols. We investigated the oxidation behavior of Ti3C2T x in air in a wide temperature range and discuss the mechanism of sensor response of partially oxidized MXene films, which is qualitatively different from that of pristine Ti3C2T x .

High electrical conductivity and breakdown current density of individual monolayer Ti3C2T MXene flakes

“…In its pristine form, the flake thickness is about 2.4 nm, which is similar to the values reported in our previous works for monolayer Ti 3 C 2 T x measured on a Si/SiO 2 substrate. 6,35 Interestingly, we previously observed a smaller AFM height of about 1.6 nm for the monolayer Ti 3 C 2 T x flakes lying on top of other flakes. 7,35 We suggested that the flakes lying directly on Si/SiO 2 appear thicker in AFM measurements than the flakes lying on other flakes because apparently there is a larger number of adsorbed molecules, such as water, at the Ti 3 C 2 T x /SiO 2 interface than between the Ti 3 C 2 T x layers.…”

“…6,35 Interestingly, we previously observed a smaller AFM height of about 1.6 nm for the monolayer Ti 3 C 2 T x flakes lying on top of other flakes. 7,35 We suggested that the flakes lying directly on Si/SiO 2 appear thicker in AFM measurements than the flakes lying on other flakes because apparently there is a larger number of adsorbed molecules, such as water, at the Ti 3 C 2 T x /SiO 2 interface than between the Ti 3 C 2 T x layers. 7 Figure 4C shows that, after the current breakdown, the majority of the flake has the thickness reduced by about 0.8 nm down to 1.6 nm.…”

2D Molybdenum Carbide MXenes for Enhanced Selective Detection of Humidity in Air

“…[16] So far, Ti 3 C 2 T x has proved being sensitive to rather low concentrations of ketones (< to 50 ppb), alcohols (< to 100 ppb), and ammonia (< to 100 ppb) vapors at room temperature maturing from the impact of the analyte's physical adsorption changing the electronic properties in these low-noise materials. [17][18][19][20][21][22] To further improve sensing properties of Ti 3 C 2 T x MXenes with respect to organic vapors, various approaches have been proposed including partial oxidizing at elevated temperatures up to 350 °C [23] and composing hybrid hetero-composites. [24] While most studies focus on Ti 3 C 2 T x , investigations are not limited to Ti-based MXenes; other M-elements are currently successfully employed with extensive functional characterization.…”

Prospects and Challenges of MXenes as Emerging Sensing Materials for Flexible and Wearable Breath‐Based Biomarker Diagnosis

“…Energy band diagram of the interface between pristine and oxidized MXene regions based on the UPS data; WF is a work function, F is a Fermi level, E c and E v are conduction and valence bands, respectively. Adapted with permission [136]. Copyright 2018, American Chemical Society.…”