Selective Detection of Carbon Monoxide on P-Block Doped Monolayers of MoTe2

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.

Efficient photoreduction of carbon dioxide to ethanol using diatomic nitrogen-doped black phosphorus

Successful conversion of CO2 into C2 products requires the development of new catalysts that overcome the difficulties in efficient light harvesting and CO-CO coupling. Herein, density functional theory (DFT) is used to assess the photoreduction properties of nitrogen-doped black phosphorus. The geometric structure, redox potential, first step of hydrogenation activation, CO desorption, and CO-CO coupling are systematically calculated, based on which the diatomic nitrogen-doped black phosphorus (N2@BPV) stands out. The calculated results of the CO2RR pathway demonstrate that N2@BPV has excellent selectivity and high activity for CH3CH2OH production. The results of the time-dependent ab initio nonadiabatic molecular dynamics simulation show that the diatomic N active sites of N2@BPV facilitate charge separation and inhibit electron-hole recombination. In addition, the activation mechanism of CO2 is studied. The main reason for CO2 activation is attributed to the imbalance in electron transfer that destroys the symmetry of CO2. We expect that our study will offer some theoretical guidance in CO2 conversion.

Theoretical insights into the structural, electronic and thermoelectric properties of the inorganic biphenylene monolayer

Being motivated by a recently synthesized biphenylene carbon monolayer (BPN), using first principles methods, we have studied its inorganic analogue (B-N analogue) named I-BPN. A comparative study of structural, electronic and mechanical properties between BPN and I-BPN was carried out. Like BPN, the stability of I-BPN was verified in terms of formation energy, phonon dispersion calculations, and mechanical parameters (Young's modulus and Poisson's ratio). The chemical inertness of I-BPN was also investigated by adsorbing an oxygen molecule in an oxygen-rich environment. It has been found that the B-B bond favours the oxygen molecule to be adsorbed through chemisorption. The lattice transport properties reveal that the phonon thermal conductivity of I-BPN is ten times lower than that of BPN. The electronic band structure reveals that I-BPN is a semiconductor with an indirect bandgap of 1.88 eV, while BPN shows metallic behaviour. In addition, we investigated various thermoelectric properties of I-BPN for possible thermoelectric applications. The thermoelectric parameters, such as the Seebeck coefficient, show the highest peak value of 0.00289 V K-1 at 300 K. Electronic transport properties reveal that I-BPN is highly anisotropic along the x and y-axes. Furthermore, the thermoelectric power factor as a function of chemical potential shows a peak value of 0.057 W m-1 K-2 along the x-axis in the p-type doping region. The electronic figure of merit shows a peak value of approximately unity. However, considering lattice thermal conductivity, the peak value of the total figure of merit (ZT) reduces to 0.68(0.46) for p-type and 0.56(0.48) for n-type doping regions along the x(y) direction at 900 K. It is worth noting that our calculated ZT value of I-BPN is higher than that of many other reported B-N composite materials.

Directionally-Resolved Phononic Properties of Monolayer 2D Molybdenum Ditelluride (MoTe2) under Uniaxial Elastic Strain

Understanding the phonon characteristics of two-dimensional (2D) molybdenum ditelluride (MoTe2) under strain is critical to manipulating its multiphysical properties. Although there have been numerous computational efforts to elucidate the strain-coupled phonon properties of monolayer MoTe2, empirical validation is still lacking. In this work, monolayer 1H-MoTe2 under uniaxial strain is studied via in situ micro-Raman spectroscopy. Directionally dependent monotonic softening of the doubly degenerate in-plane E2g1 phonon mode is observed with increasing uniaxial strain, where the E2g1 peak red-shifts -1.66 ± 0.04 cm-1/% along the armchair direction and -0.80 ± 0.07 cm-1/% along the zigzag direction. The corresponding Grüneisen parameters are calculated to be 1.09 and 0.52 along the armchair and zigzag directions, respectively. This work provides the first empirical quantification and validation of the orientation-dependent strain-coupled phonon response in monolayer 1H-MoTe2 and serves as a benchmark for other prototypical 2D transition-metal tellurides.

Adsorption and sensing performance of air pollutants on a β-TeO2 monolayer: a first-principles study

Two-dimensional (2D) β-TeO2 is a novel semiconductor with potential applications in electronic circuits due to its air-stability and ultra-high carrier mobility. In this study, we explore the possibility of using a 2D β-TeO2 monolayer for the detection of gaseous pollutants including SO2, NO2, H2S, CO2, CO, and NH3 gas molecules based on first-principles calculations. The adsorption properties including the adsorption energy, adsorption distance and charge transfer indicate that the interaction between 2D β-TeO2 and the six gases is via a physisorption mechanism. Among the six gas adsorption systems, the SO2 adsorption system has the most negative adsorption energy and the largest charge transfer. In addition, the adsorption of SO2 obviously changes the electrical conductivity of the β-TeO2 monolayer because the band gap decreases from 2.727 eV to 1.897 eV after adsorbing SO2. Our results suggest that the 2D β-TeO2 should be an eminently promising SO2 sensing material.

Adsorption of CH4, CO, and H2S on a MoTe2 Monolayer Doped with Metal Atoms (Au and Ru): An Ab Initio Study

Detecting toxic gases, such as CH4, CO, and H2S, in everyday life holds great significance. This research article focuses on investigating the adsorption characteristics of CH4, CO, and H2S on MoTe2 and MoTe2 doped with Au and Ru using the density functional theory. The study examines various aspects, including adsorption energy, charge transfer, density of states, and charge density difference of the adsorption configuration. The findings demonstrate that the adsorption properties of Ru-doped MoTe2 exhibit a significant enhancement for all three gases, with CO displaying the highest adsorption performance. Through comparative analysis, it is evident that the adsorption affinity between MoTe2-Ru and the three gases is robust, thus indicating improved gas detection capabilities.

Three-Dimensional Assemblies of Edge-Enriched WSe2 Nanoflowers for Selectively Detecting Ammonia or Nitrogen Dioxide

Herein, we present, for the first time, a chemoresistive-type gas sensor composed of two-dimensional WSe₂, fabricated by a simple selenization of tungsten trioxide (WO₃) nanowires at atmospheric pressure. The morphological, structural, and chemical composition investigation shows the growth of vertically oriented three-dimensional (3D) assemblies of edge-enriched WSe₂ nanoplatelets arrayed in a nanoflower shape. The gas sensing properties of flowered nanoplatelets (2H-WSe₂) are investigated thoroughly toward specific gases (NH₃ and NO₂) at different operating temperatures. The integration of 3D WSe₂ with unique structural arrangements resulted in exceptional gas sensing characteristics with dual selectivity toward NH₃ and NO₂ gases. Selectivity can be tuned by selecting its operating temperature (150 °C for NH₃ and 100 °C for NO₂). For instance, the sensor has shown stable and reproducible responses (24.5%) toward 40 ppm NH₃ vapor detection with an experimental LoD < 2 ppm at moderate temperatures. The gas detecting capabilities for CO, H₂, C₆H₆, and NO₂ were also investigated to better comprehend the selectivity of the nanoflower sensor. Sensors showed repeatable responses with high sensitivity to NO₂ molecules at a substantially lower operating temperature (100 °C) (even at room temperature) and LoD < 0.1 ppm. However, the gas sensing properties reveal high selectivity toward NH₃ gas at moderate operating temperatures. Moreover, the sensor demonstrated high resilience against ambient humidity (Rh = 50%), demonstrating its remarkable stability toward NH₃ gas detection. Considering the detection of NO₂ in a humid ambient atmosphere, there was a modest increase in the sensor response (5.5%). Furthermore, four-month long-term stability assessments were also taken toward NH₃ gas detection, and sensors showed excellent response stability. Therefore, this study highlights the practical application of the 2H variant of WSe₂ nanoflower gas sensors for NH₃ vapor detection.

Research status of gas sensing performance of MoTe2-based gas sensors: A mini review

Transition metal dichalcogenides (TMDs) have been widely explored for their excellent gas sensing properties, especially high sensitivity and stability at room temperature. MoTe2 exhibits good sensitivity and selectivity to some nitrogen-containing gases (i.e., NO2, NH3) and has received extensive attention in gas sensing. In addition, increasingly complex production environments place demands on high-quality gas sensors. Therefore, worldwide efforts are devoted to designing and manufacturing MoTe2-based gas sensors with faster response and recovery speed. This paper summarizes the research progress of MoTe2-based gas sensing, focuses on the practical measures to improve the response and recovery speed of MoTe2-based sensors, and discusses the mechanism. This provides guidance for exploring higher performance MoTe2 sensors.

P-block atom modified Sn(200) surface as a promising electrocatalyst for two-electron CO2 reduction: a first-principles study

The P-block atom can effectively regulate the activity of two-electron CO2 reduction on Sn(200) surface.