2D Materials for Gas-Sensing Applications

Winston Yenyu Chen, Purdue University

Abstract

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) and transition metal carbides/nitrides (MXenes), have been recently receiving attention for gas sensing applications due to their high specific area and rich surface functionalities. Using pristine 2D materials for gassensing applications, however, presents some drawbacks, including high operation temperatures, low gas response, and poor selectivity, limiting their applications in this area. Moreover, one of the long-standing challenges of MXenes is their poor stability against hydration and oxidation in a humid environment, which negatively influences their long-term storage and applications. Many studies have reported that the sensitivity and selectivity of 2D materials can be improved by surface functionalization and hybridization with other materials. In this work, the properties of these two materials classes (TMDCs and MXenes) have been investigated and the results viewed through the lens of their implantation into chemoresistive gas sensors. In one of the lines of research, 2D MoS2 nanoflakes were functionalized with Au nanoparticles through a facile solution mixing method. Au-decorated MoS2 was used as a material platform for an electrochemical sensor to detect various volatile organic compounds (VOCs) at room temperature. After Au functionalization, the enhancement of gas-sensing performance in terms of response and selectivity, especially in detecting oxygen-based VOCs (acetone, ethanol, and 2-propanol), was observed. The response of the gas sensor to acetone improved by 131% (changing from 13.7% for pristine MoS2 to 31.6% for MoS2- Au(0.5)) owing to Au doping. Sensing tests under various relative humidity values (10−80%), repeated bending cycles, or after long-term storage, indicated the sound robustness and flexibility of the sensor. Density functional theory (DFT) simulations showed that the adsorption energy of acetone on Au-MoS2 is significantly greater than that of on pristine MoS2, contributing to an enhancement of VOC sensing. This work put forward an understanding of the dominant sensing mechanism for the highly sensitive and selective detection of oxygen-based VOCs with Au doped MoS2 electrode materials. ext, a nanocomposite film composed of exfoliated MoS2, single-walled carbon nanotubes (SCNTs), and Cu(I)−tris(mercaptoimidazolyl)borate complexes (Cu−Tm) was the electrode material used for the design of a chemoresistive sensor for the real-time detection of ethylene (C2H4). The reported detection limit of this sensor was of 100 ppb. A co-percolation network of MoS2 and SCNTs was deposited onto interdigitated Ag electrodes, printed on plastic substrates and then coated with Cu−Tm, with a final electrode conductance in the 0.5 mS range. The thinfilm sensors were highly selective toward C2H4, and they responded weakly to other volatile organic compounds or water at similar partial pressures. A mechanism is proposed in which Cu−Tm acts as a chemically sensitive n-type dopant for MoS2, based on spectroscopic characterization and DFT simulations. Cu−Tm-coated MoS2/SCNT sensors were also connected to a battery-powered wireless transmitter and used to monitor C2H4production from various fruit samples, validating their utility as practical, field-deployable sensors.

Degree

Ph.D.

Advisors

Stanciu, Purdue University.

Subject Area

Energy|Analytical chemistry|Atmospheric sciences|Chemistry|Nanotechnology|Optics

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