Adsorption, Gas-Sensing, and Optical Properties of Molecules on a Diazine Monolayer: A First-Principles Study

A DFT study of the adsorption behavior and sensing properties of CO gas on monolayer MoSe2 in CO2-rich environment

CONTEXT

Carbon monoxide, also known as the "silent killer," is a colorless, odorless, tasteless, and non-irritable gas that, when inhaled, enters the bloodstream and lungs, binds with the hemoglobin, and blocks oxygen from reaching tissues and cells. In this work, the monolayer MoSe2-based CO gas sensors were designed using density functional theory calculation with several dopants including Al, Au, Pd, Ni, Cu, and P. Here, Cu and P were found to be the best dopants, with adsorption energies of -0.67 eV (Cu) and -0.54 eV (P) and recovery times of 1.66 s and 13.8 ms respectively. Cu conductivity for CO adsorption was found to be 2.74 times that of CO2 adsorption in the 1.0-2.26 eV range. P displayed the highest selectivity, followed by Pd and Ni. The dopants, Pd and Ni, were found suitable for building CO gas scavengers due to their high recovery times of 9.76 × 1020 s and 2.47 × 1011 s. Similarly, the adsorption of CO2 on doped monolayer MoSe2 was also investigated. In this study, it is found that monolayer MoSe2 could be employed to create high-performance CO sensors in a CO2-rich environment.

METHOD

The electrical characteristics of all doped MoSe2 monolayers are obtained using a DFT calculation with the PBE-GGA method from the Quantum ESPRESSO package. The self-consistent field (SCF) computations were performed using a 7 × 7 × 1 k-point grid and a norm-conserving pseudo potential (NCPP) file. To determine electrical conductivity, the semi-classical version of Boltzmann transport theory, implemented in the Boltz Trap code, was used.

First-Principles Investigation of Adsorption Behaviors and Electronic, Optical, and Gas-Sensing Properties of Pure and Pd-Decorated GeS2 Monolayers

The extensive applications of two-dimensional (2D) transition metal disulfides in gas sensing prompt us to explore the adsorption, electronic, optical, and gas-sensing properties of the pure and Pd-decorated GeS₂ monolayers interacting with NO₂, NO, CO₂, CO, SO₂, NH₃, H₂S, HCN, HF, CH₄, N₂, and H₂ gases by using first-principles methods. Our results showed that the pure GeS₂ monolayer is not appropriate to develop gas sensors. The stability of the Pd-decorated GeS₂ (Pd-GeS₂) monolayer was determined by binding energy, transition state theory, and molecular dynamics simulations, and the Pd decoration has a significant effect on adsorption strength and the change in electronic properties (especially electrical conductivity). The Pd-GeS₂ monolayer-based sensor has relatively high sensitivity toward NO and NO₂ gases with moderate recovery time. In addition, the adsorption of NO and NO₂ can conspicuously change the optical properties of the Pd-GeS₂ monolayer. Therefore, the Pd-GeS₂ monolayer is predicted to be reusable and a highly sensitive (optical) gas sensing material for the detection of NO and NO₂.

MoSe2/multiwalled carbon nanotube composite for ammonia sensing in natural humid environment

Herein, we report ammonia sensing in a natural highly humid environment using MoSe₂/multi-walled carbon nanotube (MWCNT) composite as sensing platform. The composite synthesis involved two steps, in the first step, MWCNTs were treated in an acidic medium to obtain -COOH group functionalized MWCNTs. In the second step, functionalized MWCNTs were probe sonicated with MoSe₂ to obtain MoSe₂/MWCNT composite. Proposed device exhibited superior sensing properties at a temperature down to 16^∘ C and relative humidity of 80%. Under these extreme natural environmental conditions, the device exhibited a relative response of 21% for 0.5 ppm of ammonia and superior noise free signal further suggests their use even below this concentration. Composite based device has also displayed better adsorption selectivity towards NH₃ as compared with other reducing and oxidizing gas molecules. Density functional theory simulations were further employed to understand the underlying adsorption process and selectivity behavior of the composite. Simulations predicted lowest negative adsorption energy for ammonia, implying physisorption (-0.387 eV) type exothermic adsorption process. Present results indicate that a composite with the rightly engineered MoSe₂ and MWCNTs weight ratio may serve as a potential candidate for ammonia sensing in a highly humid environment.

Selective and sensitive toxic gas sensors mechanism in 2D Janus MoSSe monolayer

With an inspiration of sensing toxic gases, this paper aims to explore potential of Janus MoSSe monolayer as gas sensor. Here, we focused on adsorption mechanism after the exposure of...