Phosgene Gas Sensing of Ti 2 CT 2 (T = F − , O − , OH − ) MXenes

Unlocking the sensing and scavenging potential of Sc2CO2 and Sc2CO2/TMD heterostructures for phosgene detection

The detection of phosgene is critically important owing to its extreme toxicity and potential use as a chemical warfare agent to ensure public safety and security. Two-dimensional (2D) scandium carbide MXenes (Sc2CTx; T = O-, x = 2) stand out as promising materials for gas sensing applications owing to their unique electronic and adsorption properties. In this study, first-principles calculations based on the GGA-PBE functional were employed to investigate the structural, electronic, and mechanical characteristics of Sc2CO2 with different surface termination positions. The adsorption behavior of Sc2CO2 was systematically explored for various gas molecules, including N2, O2, CO, NO, CH4, H2S, and, notably, phosgene (COCl2). Specifically, phosgene exhibited a high adsorption energy, highlighting the selectivity of Sc2CO2 towards this toxic gas. Furthermore, the impact of gas adsorption on the electronic structure of Sc2CO2 was investigated. Strategies such as increasing the operating temperatures and forming heterostructures with transition metal di-chalcogenides (MoSe2 and WSe2) proved to be highly effective to mitigate the challenges related to slow recovery time. Thus, this work underscores the potential of Sc2CO2 MXenes as highly sensitive and selective gas sensors, particularly for phosgene sensing.

DFT Study on the Janus ZrSSe Monolayer for Its Potential Application in NO Gas Sensing

The growth of industry has resulted in increased global air pollution, necessitating the urgent development of highly sensitive gas detectors. In this work, the adsorption of the Janus ZrSSe monolayer for CO, CO2, NH3, NO, NO2, and O2 was studied by first-principles calculations. First, the stability of the ZrSSe monolayer is confirmed through calculations of cohesive energy and AIMD simulations. Furthermore, the calculations indicate that the Se layer exhibits higher selectivity and sensitivity toward gas molecules compared to the S layer. Specifically, among the gases adsorbed on the Se layer, NO has the shortest adsorption distance (1.804 Å), the lowest adsorption energy (-0.424 eV), and the greatest electron transfer (0.098 e). Additionally, density of states analysis reveals that adsorption of NO, NO2, and O2 on the Janus ZrSSe monolayer can induce a transition from a nonmagnetic to a magnetic state. The adsorption of NO not only alters the magnetic state but also induces a transition from a semiconductor to metal, which is highly advantageous for gas sensing applications. There results suggest that the Janus ZrSSe monolayer has the potential to serve as a highly sensitive detector for NO gas.

Efficient exploration of transition-metal decorated MXene for carbon monoxide sensing using integrated active learning and density functional theory

The urgent demand for chemical safety necessitates the real-time detection of carbon monoxide (CO), a highly toxic gas. MXene, a 2D material, has shown potential for gas sensing applications (e.g., NH3, NO, SO2, CO2) due to its high surface accessibility, electrical conductivity, stability, and flexibility in surface functionalization. However, the pristine MXene generally exhibits poor interaction with CO; still, transition metal decoration can strengthen the interaction between CO and MXene. This study presents a high-throughput screening of 450 combinations of transition-metal (TM) decorated MXene (TM@MXene) for CO sensing applications using an integrated active learning (AL) and density functional theory (DFT) screening pipeline. Our AL pipeline, adopting a crystal graph convolutional neural network (CGCNN) as a surrogate model, successfully accelerates the screening of CO sensor candidates with minimal computational resources. This study identifies Sc@Zr3C2O2 and Y@Zr3C2O2 as the optimal TM@MXene candidates with promising CO sensing performance regarding the screening criteria of recovery time, surface stability, charge transfer, and sensitivity to CO. The proposed AL framework can be extended for property finetuning in the combinatorial chemical space.

MXene-based Ti2C/Ta2C lateral heterostructure: an intrinsic room temperature ferromagnetic material with large magnetic anisotropy

Two-dimensional (2D) lateral heterostructures (LH) combining Ti₂C and Ta₂C MXenes were investigated by means of first-principles calculations. Our structural and elastic properties calculations show that the lateral Ti₂C/Ta₂C heterostructure results in a 2D material that is stronger than the original isolated MXenes and other 2D monolayers such as germanene or MoS₂. The analysis of the evolution of the charge distribution with the size of the LH shows that, for small systems, it tends to distribute homogeneously between the two monolayers, whereas for larger systems electrons tend to accumulate in a region of ∼6 Å around the interface. The work function of the heterostructure, one crucial parameter in the design of electronic nanodevices, is found to be lower than that of some conventional 2D LH. Remarkably, all the heterostructures studied show a very high Curie temperature (between 696 K and 1082 K), high magnetic moments and high magnetic anisotropy energies. These features make (Ti₂C)/(Ta₂C) lateral heterostructures very suitable candidates for spintronic, photocatalysis, and data storage applications based upon 2D magnetic materials.

Machine learning and DFT investigation of CO, CO2 and CH4 adsorption on pristine and defective two-dimensional magnesene

Adsorption study of environmentally toxic small gas molecules on two-dimensional (2D) materials plays a significant role in analyzing the performance of sensors. In this work, density functional theory (DFT) and machine learning (ML) techniques have been employed to systematically study the adsorption properties of CO, CO₂, and CH₄ gas molecules on the pristine and defective planar magnesium monolayer, known as magnesene (2D-Mg). The DFT analysis showed that mechanically robust 2D-Mg retains its metallicity in the presence of both mono and di-vacancy defects. Our observations have shown that 2D-Mg, whether defective or pristine, exhibits distinct adsorption behaviors towards CO, CO₂, and CH₄ gas molecules, including varying chemisorption and physisorption, charge transfer, and distance from the gas molecules. When analyzing the recovery time of gas molecules at room temperature, it is clear that adsorption energy has a direct correlation with the adsorption-desorption cycles, and CH₄ possesses an ultra-low recovery time (15.27 ps) compared to CO₂ (1.04 ns) and CO (0.90 μs) molecules. The analysis showed that defects do not have a significant impact on the work function of 2D-Mg. However, the work function decreased upon adsorption of CH₄, resulting in improved sensitivity due to changes in the electronic properties. Additionally, we explored supervised ML regression models to evaluate their ability to act as a surrogate for the DFT-based adsorption energy calculation. Using both system statistics and smooth overlap of atomic position (SOAP)-based featurization, we observed that adsorption energies can be predicted with a mean absolute error of 0.10 eV.

Application of Titanium Carbide MXenes in Chemiresistive Gas Sensors

The titanium carbide MXenes currently attract an extreme amount of interest from the material science community due to their promising functional properties arising from the two-dimensionality of these layered structures. In particular, the interaction between MXene and gaseous molecules, even at the physisorption level, yields a substantial shift in electrical parameters, which makes it possible to design gas sensors working at RT as a prerequisite to low-powered detection units. Herein, we consider to review such sensors, primarily based on Ti3C2Tx and Ti2CTx crystals as the most studied ones to date, delivering a chemiresistive type of signal. We analyze the ways reported in the literature to modify these 2D nanomaterials for (i) detecting various analyte gases, (ii) improving stability and sensitivity, (iii) reducing response/recovery times, and (iv) advancing a sensitivity to atmospheric humidity. The most powerful approach based on designing hetero-layers of MXenes with other crystals is discussed with regard to employing semiconductor metal oxides and chalcogenides, noble metal nanoparticles, carbon materials (graphene and nanotubes), and polymeric components. The current concepts on the detection mechanisms of MXenes and their hetero-composites are considered, and the background reasons for improving gas-sensing functionality in the hetero-composite when compared with pristine MXenes are classified. We formulate state-of-the-art advances and challenges in the field while proposing some possible solutions, in particular via employing a multisensor array paradigm.

A Family of 2D-MXenes: Synthesis, Properties, and Gas Sensing Applications

Gas sensors, capable of detecting and monitoring trace amounts of gas molecules or volatile organic compounds (VOCs), are in great demand for numerous applications including diagnosing diseases through breath analysis, environmental and personal safety, food and agriculture, and other fields. The continuous emergence of new materials is one of the driving forces for the development of gas sensors. Recently, 2D materials have been gaining huge attention for gas sensing applications, owing to their superior electrical, optical, and mechanical characteristics. Especially for 2D MXenes, high specific area and their rich surface functionalities with tunable electronic structure make them compelling for sensing applications. This Review discusses the latest advancements in the 2D MXenes for gas sensing applications. It starts by briefly explaining the family of MXenes, their synthesis methods, and delamination procedures. Subsequently, it outlines the properties of MXenes. Then it describes the theoretical and experimental aspects of the MXenes-based gas sensors. Discussion is also extended to the relation between sensing performance and the structure, electronic properties, and surface chemistry. Moreover, it highlights the promising potential of these materials in the current gas sensing applications and finally it concludes with the limitations, challenges, and future prospects of 2D MXenes in gas sensing applications.

Rational design of selenium inserted 1T/2H mixed-phase molybdenum disulfide for energy storage and pollutant degradation applications

MoS₂based materials are recognized as the promising candidate for multifunctional applications due to its unique physicochemical properties. But presence of lower number of active sites, poor electrical conductivity, and less stability of 2H and 1T MoS₂inherits its practical applications. Herein, we synthesized the Se inserted mixed-phase 2H/1T MoS₂nanosheets with abundant defects sites to achieve improved overall electrochemical activity. Moreover, the chalcogen insertion induces the recombination of photogenerated excitons and enhances the life of carriers. The bifunctional energy storage and photocatalytic pollutant degradation studies of the prepare materials are carried out. Fabricated symmetric solid-state supercapacitor showed an exceptional capacitance of 178 mF cm^-2with an excellent energy density of 8μWh cm^-2and power density of 137 mW cm^-2, with remarkable capacitance retention of 86.34% after successive 8000 charge-discharge cycles. The photocatalytic dye degradation experiments demonstrate that the prepared Se incorporated 1T/2H MoS₂is a promising candidate for dye degradation applications. Further, the DFT studies confirmed that the Se inserted MoS₂is a promising electrode material for supercapacitor applications with higherC_Qdue to a larger density of states near Fermi level as compared to pristine MoS₂.

From Fundamental to CO2 and COCl2 Gas Sensing Properties of Pristine and Defective Si2BN Monolayer

The capability of Si2BN monolayer (Si2BN-ML) in sensing CO2 and COCl2 molecules is investigated by analyzing the structural, electronic, mechanical and gas sensing properties of defect-free and defective Si2BN-ML. Electronic...

A theoretical study of allopurinol drug sensing by carbon and boron nitride nanostructures: DFT, QTAIM, RDG, NBO and PCM insights

The application of low-dimensional nanomaterials in clinical practice as efficient sensors has been increasing day by day due to progress in the field of nanoscience. In this research work, we have conducted a theoretical investigation to nominate a potential electrochemical sensor for the allopurinol (APN) drug molecule via studying the fundamental interactions of the drug molecule with two nanocages (carbon nanocage/CNC - C24 and boron nitride nanocage/BNNC - B12N12) and two nanosheets (graphene - C54H18 and boron nitride - B27N27H18) by means of the DFT B3LYP/6-31G(d,p) level of theory in both gas and water phases. The adsorption energies of APN-BNNC conjugated structures are in the range of -20.90 kcal mol-1 to -22.33 kcal mol-1, which indicates that weak chemisorption has occurred. This type of interaction happened due to charge transfer from the APN molecule to BNNC, which was validated and characterized based on the quantum theory of atoms in molecules, natural bond analysis, and reduced density gradient analysis. The highest decreases in energy gap (36.22% in gas and 26.79% in water) and maximum dipole moment (10.48 Debye in gas and 13.88 Debye in water) were perceived for the APN-BNNC conjugated structure, which was also verified via frontier molecular orbital (FMO) and MEP analysis. Also, the highest sensitivity (BNNC > BNNS > CNC > GNS) and favorable short recovery time (in the millisecond range) of BNNC can make it an efficient detector for the APN drug molecule.