Synergistic Effect of TiS3 and Ti3C2Tx MXene for Temperature-Tunable p-/n-Type Gas Sensing

Abstract

We propose a strategy for highly tunable gas sensors, in which a MXene is combined with a sacrificial material that could be controllably oxidized upon mild annealing to form oxide nanoparticles that alter the sensing response. A controlled annealing of such composite generally retains the integrity of MXene sheets while gradually converting the sacrificial material to a metal oxide that could form semiconductor heterojunctions with MXene, fine-tuning its sensor properties. This strategy is demonstrated using gas sensors based on Ti3C2Tx MXene mixed with TiS3, a semiconducting transition metal trichalcogenide. Compared to pristine MXene, the Ti3C2Tx-TiS3 composite exhibited a significantly improved sensor response to ethanol, which served as a model analyte, both at room temperature and upon annealing. Furthermore, as a less thermally stable material than the MXene, TiS3 oxidizes faster than Ti3C2Tx at elevated temperatures, producing TiO2 nanoparticles that strongly affect the sensing response. A pristine Ti3C2Tx exhibits a p-type sensor response to ethanol at room temperature. Upon annealing, Ti3C2Tx gradually degrades to TiO2, changing the sensor response to n-type above ∼300 °C. The addition of TiS3 allows for the general preservation of MXene as the sensor material, as the temperature of the p–n transition decreases to about 200 °C, at which Ti3C2Tx is generally stable. This approach can likely be applied to a great variety of combinations of various MXenes and sacrificial compounds with sensor properties that could be tuned via annealing for specific analytes or applications.