Preparation and Gas-Sensing Properties of Two-Dimensional Molybdenum Disulfide/One-Dimensional Copper Phthalocyanine Heterojunction

Abstract

Although 2D MoS₂ alone shows excellent gas-sensing performance, it is prone to stacking when used as the sensitive layer, resulting in insufficient contact with the target gas and lower sensitivity. To solve this, a 2D-MoS₂/1D-CuPc heterojunction was prepared with different weight ratios of MoS₂ nanosheets to CuPc micro-nanowires, and its room-temperature gas-sensing properties were studied. The response of the 2D-MoS₂/1D-CuPc heterojunction to a target gas was related to the weight ratio of MoS₂ to CuPc. When the weight ratio of MoS₂ to CuPc was 20:7 (7-CM), the gas sensitivity of MoS₂/CuPc composites was the best. Compared with the pure MoS₂ sensor, the responses of 7-CM to 1000 ppm formaldehyde (CH₂O), acetone (C₃H₆O), ethanol (C₂H₆O), and 98% RH increased by 122.7, 734.6, 1639.8, and 440.5, respectively. The response of the heterojunction toward C₂H₆O was twice that of C₃H₆O and 13 times that of CH₂O. In addition, the response time of all sensors was less than 60 s, and the recovery time was less than 10 s. These results provide an experimental reference for the development of high-performance MoS₂-based gas sensors.

Keywords: CuPc; MoS2; VOC; ethanol; gas sensor; heterojunction.

Figure 1

Schematic of sensing test system.

Figure 2

SEM image of 2D-MoS₂/1D-CuPc heterojunction: (a) a weight ratio of 20:3 (3-CM); (b) a weight ratio of 20:5 (5-CM); (c,d) a weight ratio of 20:7 (7-CM); (e,f) weight ratios of 20:10 (10-CM) and 20:20 (20-CM), respectively.

Figure 3

XRD patterns of CuPc, MoS₂ NSs, and 2D-MoS₂/1D-CuPc heterojunction (7-CM).

Figure 4

Raman spectra of 3-CM, 5-CM, 7-CM, 10-CM, and 20-CM. (a) Enlargement of the MoS₂ peaks $E_{2\mathrm{g}}^1$ and $A_{1g}$ and (b) Enlargement of the MoS₂ peaks from 1360 cm⁻¹ to 1680 cm⁻¹.

Figure 5

XPS spectra of (a) Mo 3d and (b) S 2p of the different samples.

Figure 6

(a) Fourier transform infrared spectra of CuPc, MoS₂ NSs, 3-CM, 5-CM, 7-CM, 10-CM, and 20-CM. (b) Local magnification of figure (a).

Figure 7

Response curves of MoS₂-, 3-CM-, 5-CM-, 7-CM-, 10-CM-, and 20-CM-based sensors to 1000 ppm CH₂O, C₃H₆O, C₂H₆O, and 98% RH at room temperature.

Figure 8

(a) Mean response; (b) response time; and (c) recovery time for MoS₂, 3-CM, 5-CM, 7-CM, 10-CM, and 20-CM sensors to 1000 ppm CH₂O, C₃H₆O, C₂H₆O, and 98% RH.

Figure 9

Three-dimensional PCA plot derived from the average response of MoS₂, 3-CM, 5-CM, 7-CM, 10-CM, and 20-CM sensors.

Figure 10

Characteristic fingerprints derived from kinetic and thermodynamic parameters from (a) CH₂O, (b) C₃H₆O, (c) C₂H₆O, and (d) 98% RH at 1000 ppm at room temperature.

Figure 11

(a) Sensing curves of the 7-CM sensor to different concentrations of C₃H₆O; (b) fitted plots of the response vs. C₃H₆O concentration; (c) sensing curves of the 7-CM sensor to different concentrations of C₂H₆O; (d) fitted plots of the response vs. C₂H₆O concentration.

Figure 12

I–V curves of MoS₂-, 3-CM-, 5-CM-, 7-CM-, 10-CM-, and 20-CM-based sensors.

Figure 13

Schematic diagrams of (a) the band structure of MoS₂ and CuPc; (b) the gas-sensing mechanism of MoS₂/CuPc composites in the air; (c) the gas-sensing mechanism of MoS₂/CuPc composites in ethanol; (d) the band structure of MoS₂/CuPc composites in the air; (e) the band structure of MoS₂/CuPc composites in ethanol.