Design of Hetero-Nanostructures on MoS₂ Nanosheets To Boost NO₂ Room-Temperature Sensing

Abstract

Molybdenum disulfide (MoS), as a promising gas-sensing material, has gained intense interest because of its large surface-to-volume ratio, air stability, and various active sites for functionalization. However, MoS-based gas sensors still suffer from low sensitivity, slow response, and weak recovery at room temperature, especially for NO. Fabrication of heterostructures may be an effective way to modulate the intrinsic electronic properties of MoS nanosheets (NSs), thereby achieving high sensitivity and excellent recovery properties. In this work, we design a novel p-n hetero-nanostructure on MoS NSs using interface engineering via a simple wet chemical method. After surface modification with zinc oxide nanoparticles (ZnO NPs), the MoS/ZnO hetero-nanostructure is endowed with an excellent response (5 ppm nitrogen dioxide, 3050%), which is 11 times greater than that of pure MoS NSs. To the best of our knowledge, such a response value is much higher than the response values reported for MoS gas sensors. Moreover, the fabricated hetero-nanostructure also improves recoverability to more than 90%, which is rare for room-temperature gas sensors. Our optimal sensor also possesses the characteristics of an ultrafast response time of 40 s, a reliable long-term stability within 10 weeks, an excellent selectivity, and a low detection concentration of 50 ppb. The enhanced sensing performances of the MoS/ZnO hetero-nanostructure can be ascribed to unique 2D/0D hetero-nanostructures, synergistic effects, and p-n heterojunctions between ZnO NPs and MoS NSs. Such achievements of MoS/ZnO hetero-nanostructure sensors imply that it is possible to use this novel nanostructure in ultrasensitive sensor applications.

Controlled synthesis of ultrathin MoS2nanoflowers for highly enhanced NO2sensing at room temperature

“…Normally, the defect-dominated process on the surface of MoS 2 contributes to the signicant response and recovery times because of the high adsorption energy of the target gas with the defects as reactive sites. 36 Previous works reported that sensors based on pristine MoS 2 of different nanostructures have incomplete recovery at RT possibly because of the high adsorption energy of NO 2 on the MoS 2 surface or the strong binding between NO 2 and the reactive sites of MoS 2 . 17,37 However, some other works indicated that in spite of slow rates of gas adsorption and desorption, the pristine MoS 2 -based sensors showed the complete recovery at RT to target gases.…”

“…The gas-sensing characteristics of the MoS 2 nanostructures can be explained by the Langmuir-Hinshelwood mechanism for chemical reaction of the tested gas with adsorbed oxygen molecules on the surface of the sensing layer, leading to change in the sensor's resistance. 36,42,43 As shown in Fig. 7(a), when the p-type semiconducting MoS 2 nanostructures were exposed to ambient air, oxygen molecules were adsorbed on the MoS 2 surface and electrons were captured from the valence band of the MoS 2 to form the oxygen ion species (O 2 À , O À and O 2À ) (eqn (5)-(8)) as follows:…”

“…A large number of defects such as S vacancies (V S ++ ) at RT can be found in pristine MoS 2 , and these defects serve as reactive sites for target gas adsorption. 19,36 The interaction mechanism between NO 2 gas molecules and S vacancies is shown in, eqn (9) and (11) which generated signicant holes into the valence band, thereby highly increasing the gas response at RT. When the temperature was increased, the electron mobility increased but the number of electrons may not be increased signicantly; inversely, the number of S vacancies decreased drastically.…”

Environmental Analysis with 2D Transition-Metal Dichalcogenide-Based Field-Effect Transistors

“…As the representative TMDC, MoS 2 shows a high carrier mobility (60 cm 2 /V s at 250 K), a layer-dependent bandgap (1.2-1.8 eV), a high transistor on/off ratio (~ 10 8 ), and reasonable environmental stability [11]. Recent reports have demonstrated that 2D MoS 2 is a desirable channel material in FET sensor with breakthroughs in sensing performance for various analytes including NO 2 [12][13][14][15], NH 3 [16,17], chemical vapor [18,19], metal ion [20][21][22], small molecule [23][24][25], as well as biomaterials such as nucleic acid [26][27][28][29], protein [30][31][32], and microorganism [33]. Compared with MOSFET sensors, 2D-TMDCbased FET sensors normally show higher sensitivities due to the 2D nanosheet structure of TMDC.…”

Room‐Temperature NO2 Gas Sensing with Ultra‐Sensitivity Activated by Ultraviolet Light Based on SnO2 Monolayer Array Film

“…At present, it can realize low temperature NO 2 sensing by the UV‐light activation or without the presence of the UV‐light irradiation. However, for the case of the absence of the UV‐light activation, the NO 2 sensors usually show the very slow response/recovery speed, which is bad for the practical detection application. Alternatively, the emergence of UV‐light illuminated mode can effectively avoid above shortcomings, because it offers a very low working temperature and fast response/recovery speed.…”