MSCA-COFUND-CLEAR-Doc - PhD Position #CD22-07: Functionalized Transition Metal Dichalcogenide (TMD) Nanosheets Based sensors for the detection of NOx and CO

Background and scientific context

Recently, atom-thick nano-sheets of transition metal dichalcogenides (TMDs), such as MoS2, WS2, MoSe2, as well as other 2D materials including black phosphorus have attracted attention due to their novel properties and potential applications. Thin TMD sheets have been suggested as efficient sensing materials for next generation of gas sensing [1]. This originates from their large surface-to-volume ratio, high electrical conductivities and low electrical noise, as well as appropriate band gap opening [2-3]. Compared to graphene, TMDs possess several advantageous properties such as the existence of a band gap in the near infrared to the visible region (depending on the number of layers), which contrasts with the zero band gap of graphene. Compared to graphene FET sensors, the novel TMDs based sensors displays a much higher sensitivity [4-5]. Indeed, MoS2 FET based sensors exhibited high sensitivity for NO gas, with a detection limit down to 0.8 ppm [4]. Compared to gas sensors based on carbon nanotubes, the MoS2-type sensor exhibits higher selectivity towards volatile organic compounds (VOCs) at room temperature [6]. The response of TMDs upon exposure to other gas molecules like NO2, NH3, H2S, H2, O2, H2O, CO, CH4, CO2, trimethylamine, acetone, methanol, dichloromethane, isopropanol and chloroform was studied [7-10]. As reported for graphene, sensors based on TMDs materials do not show any specific selectivity to gas. Various strategies have been studied to enhance the selectivity of 2D materials to detect specific gases such as functionalization by using chosen chemical species. Several recent theoretical and experimental studies reported that surface functionalization of TMDs can drastically improve the detection of toxic gases in terms of response and selectivity [11]. To improve TMDs gas-sensing performance, we propose an alternative approach based on functionalizing TMDs by porphyrins and/or phthalocyanines. This approach constitutes the first ever demonstration of functionalization of TMDs by metal complexes for gas sensing applications. We have previously reported that these molecules physi-adsorbed on the surface of carbon nanotubes and graphene and the presence of a weak charge transfer between those grafted molecules and the nanomaterials [12-14]. Furthermore, these organometallic molecules present exceptional properties such as high chemical stability, combined to unique physical and structural properties [15]. The originality of this approach lies in the nature of the ligand cavity of porphyrin or phthalocyanines that allows the coordination of different metal ions, thus enabling the sensing of different gas molecules and enhancing selectivity.

Thesis objectives

The main goal of this PhD proposal is to develop a new simple-to-use miniaturized gas sensor based on TMD materials (such as MoS2, WS2, etc.) that will be used to selectively and sensitively detect and quantify of NOx and CO pollutants in various environments. To this aim we will: 1) develop wet-method to produce exfoliated 2D-TMD materials, 2) study surface functionalization of new 2D materials with no-covalent binding of molecular probes for targeted gas, 3) study how surface functionalization modify the optoelectronic properties of 2D-materials; 4) fabrication of electrically transduced gas sensor and characterization of its behavior. The project covers all aspects from the fabrication and packaging of sensors to the range of functional testing in the laboratory in real conditions. If successful, this project will open up new possibilities to detect various pollutants and toxic industrial chemical compounds. This project is a collaborative work between three partners: NACRE (IMSE-UGE and LPICM-Ecole Polytechnique), MSME, and INL-Braga.

Research program and Role of the partners

1) Theoretical study (MSME-UGE): The sensing mechanism of the chemiresistive gas sensors relies on the charge transfer process.

The work will consist to study the adsorption of gas molecules on functionalized TMDs by porphyrins and/or phthalocyanines in order to better understand the binding, the charge transfer processes, and the effect of the gas molecule adsorption. The methodology has been well established for carbon nanomaterials and will be applied to TMDs.

2) Fabrication and functionalization of resistive devices (NACRE, INL): The objective is: i) to provide a protocol that enables fabrication of TMDs thin film and nanosheets produced using solution processing and to establish fundamental foundations needed to facilitate their implementation in chemiresistive gas sensor devices. ii) to fabricate and characterize chemiresistive devices and to understand how chemical surface functionalization can be correlated to device performance. To attain this objective, the following part will be implemented: a) production of TMDs materials by liquid-phase shear exfoliation, b) thin film processing, c) wet chemical functionalization of TMDs, d) chemiresistive sensors fabrication and characterization.

3) Assessing a sensitivity and selectivity to different gases (NACRE): Establishing rigorously the sensitivity to NOx and CO, the selectivity and the cross sensitivities to perturbing parameters for different devices: pristine and functionalized TMD-chemiresistive sensor will allow us to screen the best sensing layer materials and molecule. The best combinations (one for NOx, second one for CO sensing) will be chosen according to objective criteria; benchmarking the integrated devices. The characterization will be carried out using a brand new probe station under variable gases.

References:

[1] S. Cui et al. Nature Communications, 6, (2015) 8632.

[2] Q. H. Wang et al. Nat. Nanotechnol., 7 (2012) 699

[3] H. Li et al. Nat. Mater., 15 (2016) 48

[4] H. Li et al., Small 8 (2012) 63

[5] B. Liu et al., ACS Nano 8 (2014) 11

[6] W. Yang et al., Inorg. Chem. Front. 3

[7] N. Huo et al. Sci. Rep. 4 (2014) 5209

[8] H. Zhang et al., Sens. Actuators, B, 190 (2014) 472–478

[9] B. Liu et al. ACS Nano 8 (2014) 5304−5314

[10] W. Li et al., Sensors 19 (2019) 2123

[11] C. Nie et al., J.Phys. Chem. C 124 (2020) 16943−16950

[12 ] F. Bouanis et al, Organic Electronics 96 (2021) 106212

[13] F. Bouanis et al. DIB (2021) 107366

[14] M. Dieng et al. . Phys. Chem. C 2022, 126, 9, 4522–4533

[15] M. Ethirajan, Chem. Soc. Rev. 40 (2011) 340 –362