Enhanced NH3 Sensing Performance of Ti3C2T
x
Nanosheets Supported By TiO2 Nanoparticles at Room Temperature
Authors: Duan Zaihua , Jiang Yadong , Tai Huiling 
Published: May 2020

Introduction

With the rapid development of the chemical industry, the emission of the harmful NH3 has increased significantly, thus the research of high performance NH3 sensors has attracted extensive attention of the researchers [1]. Over the past decades, the emergence of novel materials has brought opportunities for the development of gas sensors. As a representative of another new family of materials, the 2D transition metal carbides, carbonitrides and nitrides (MXenes) have attracted great attention of the researchers in the field of gas sensors due to their unique chemical and physical properties being recently realized [2]. Taking the well-studied Ti3C2T
x
MXene as an example, it has been proved theoretically and experimentally that the Ti3C2T
x
has gas sensing properties at room temperature, especially for NH3 [3]. However, its NH3 sensing properties still need to be enhanced. In this work, the gas sensor based on TiO2/Ti3C2T
x
composite film is fabricated by a simple spraying method and its NH3 sensing properties are investigated at room temperature.

Method

The 2D Ti3C2T
x
nanosheets were prepared through etching Al from Ti3AlC2 in diluted HF and Tetramethylammonium hydroxide (TMAOH) solutions [4]. TiO2 nanoparticles in water dispersion were purchased from Sigma-Aldrich. The gas sensors were fabricated by a simple spray method. In brief, 0.4 mL diluted TiO2 nanoparticles solution (5 mg/mL) was sprayed on the polyimide (PI) substrate with seven pairs of Au interdigitated electrodes (electrodes width and distance: 0.2 mm) and dried at 60°C for 10 min for forming the TiO2 film. Then, 1 mL diluted Ti3C2T
x
nanosheets solution (2 mg/mL) was sprayed on the surface of the TiO2 film for fabricating TiO2-supported Ti3C2T
x
film gas sensor. For comparison, the gas sensors based on pure TiO2 nanoparticles (0.4 mL) and Ti3C2T
x
nanosheets (1 mL) were prepared by the same approach. The gas sensing properties of the sensors were tested at different NH3 concentration with 60.8% RH.

Results and Conclusions

Figure 1a shows the XRD patterns of the three samples, which the diffraction peaks match with the previous reports [5], indicating high purity of the Ti3C2T
x
and anatase TiO2. From the TEM image of the Ti3C2T
x
in Fig. 1b, Ti3C2T
x
is of few-layer nanosheet structure, proving that Ti3C2T
x
nanosheets is successfully prepared. Figure 1c shows the normalized response-recovery curves of three sensors to 10 ppm NH3. As can be seen, there is no NH3 response for the pure TiO2 sensor, and the responses of the Ti3C2T
x
and TiO2/Ti3C2T
x
sensors are about 1.9% and 3.1%, respectively. Compare with Ti3C2T
x
sensor, the baseline resistance of TiO2/Ti3C2T
x
sensor is more stable, and the enhanced response of TiO2/Ti3C2T
x
sensor is 1.63 times than that of pure Ti3C2T
x
sensor. Fig. 1d shows the good dynamic response-recovery curve of the TiO2/ Ti3C2T
x
sensor to different concentrations NH3 and the sensor can even respond to NH3 as low as 0.5 ppm.

In summary, we rationally designed the gas sensor based on based on TiO2/Ti3C2T
x
bilayer film for enhancing the NH3 sensing properties of pure 2D Ti3C2T
x
nanosheets and the results show that the response value and response/recovery speeds of TiO2/Ti3C2T
x
sensor are evidently improved. Meanwhile, the enhanced NH3 sensing response of the TiO2/Ti3C2T
x
sensor is explained by the model of self-built electric field (space charge layer) regulation. This work demonstrates that Ti3C2T
x
nanosheets supported by TiO2 nanoparticles can be used to enhance the NH3 sensing response, which is expected to provide useful reference for the development of high performance Ti3C2T
x
-based NH3 sensors.

References

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Figure 1