NO Molecules Research Articles

Insight into the enhanced catalytic activity and H2O/SO2 resistance of MnFeOx/Defect-Engineered TiO2 for low-temperature selective catalytic reduction of NO with NH3

A series of Mn-Fe mixed oxide (MnFeOx) supported on high-surface-area TiO2 (Tiov) containing engineered Ti3+/oxygen vacancies was demonstrated for NH3-SCR of NO. The best catalyst MnFe/Tiov(0.05)-1 exhibited excellent NH3-SCR activity (>99 % conversion) over 60–260 °C and superior resistance to high H2O content (20 vol%), with NO conversion exceeding 90 % at temperatures lower than 150 °C. Furthermore, MnFe/Tiov(0.05)-1 exhibited outstanding durability over 70 h of sustained operation in the co-presence of H2O and SO2, whereas catalytic deactivation was observed for the conventional TiO2-supported catalyst (MnFe/Ti). The combined results of various characterization techniques confirmed that the interactions between the MnFeOx and Tiov supports were strengthened. The defect-rich surface of the Tiov support promoted the dispersion of MnFeOx and facilitated the redox cycle Mn4+ + Ti3+ ↔ Mn3+ + Ti4+, thus facilitating the adsorption and activation of NH3 and NO molecules. Moreover, the in situ diffuse reflectance infrared Fourier transform results indicated that H2O strongly suppressed the adsorption/activation of NH3 and NOx and the reactions between NH3 and NOx through the Langmuir–Hinshelwood pathway on MnFe/Ti, while such adverse effects were significantly reduced when using MnFe/Tiov(0.05)-1, in which the Eley–Rideal mechanism was dominant.

Dispersion of Molecular Patterns Written in Turbulent Air.

We study the dispersion of tiny molecular clouds in turbulence by writing patterns in turbulent air and following their deformation in time. The writing is done by fusing O_{2} and N_{2} molecules into NO in the focus of a strong ultraviolet laser beam. By crossing several of these laser beams, patterns that have both small and large scales can be painted. The patterns are visualized a while later by inducing fluorescence of the NO molecules with a second UV laser and registering the image. The width of the lines that make the pattern is approximately 50 μm, a few times the Kolmogorov length η, the smallest length scale in turbulence, while the overall size of the patterns (≈4 mm) is inside the inertial range of the used turbulent jet flow. At small scales molecular clouds disperse under the joint action of molecular diffusion and turbulence. The experiments reveal for the first time this subtle, yet very important interaction. At macroscales (≈200 η) we verify the Batchelor dispersion of objects whose size is inside the inertial range; however, the expected influence of molecular diffusion is smaller than the accuracy of the experiments.

The promoting effect of Pt loaded with different redox supports on NO[sbnd]NO2 cycle-assisted soot combustion

Supports with different redox properties (Al2O3, Ce0.5Zr0.5O2-Al2O3, Ce0.5Zr0.5O2) and their corresponding Pt-based catalysts were prepared to investigate the effect of the suitability between Pt and different supports and the promotion of the NONO2 cycle on the catalytic activity of soot combustion. It is interesting that Pt-loaded nonredox support Al2O3 exhibited a poor catalytic activity for soot combustion in the absence of NO but an excellent catalytic activity in the presence of NO. However, unlike the Al2O3 support, Pt loaded Ce0.5Zr0.5O2-Al2O3 and Ce0.5Zr0.5O2 as redox supports showed an opposite result. N2 adsorption-desorption and XRD results indicated that Pt loading had no obvious effect on the texture properties of the supports. More zero-valent Pt (Pt0) on Pt/Al2O3 revealed by XRD, CO chemisorption and XPS was suggested as a major factor for promoting NO oxidizing cycles. Therefore, an amount of NO2 molecules produced on Pt0 is key to accelerate soot combustion under loose contact. The weak interaction between Pt and Al2O3 kept more Pt in the lower valence state. The Pt from Pt/Ce0.5Zr0.5O2-Al2O3 and Pt/Ce0.5Zr0.5O2 reduced the number of NONO2 cycles and further limited the assistance of NO2 in soot combustion due to a high-valence state of most of Pt. However, the preferable reducibility of the redox supports benefit soot combustion in O2/N2 because of the presence of active oxygen. This work would provide a new understanding for the further improvement of soot oxidation with the catalysts.

Adsorption behavior of small molecule on monolayered SiAs and sensing application for NO2 toxic gas

Owing to the ultrahigh surface-to-volume ratio and excellent carrier transport property, two-dimensional (2D) materials are regarded as most promising candidates for gas sensor with high sensitivity. Using the first principles calculations, we have examined the adsorption behavior of typical gas molecules on the 2D SiAs monolayer. The monolayered SiAs could sensitively response physical absorption of SO2, O2, NO, and NO2 molecule due to substantial charge transfer, and these molecules have introduced various defective states around the Fermi level. Most importantly, the quantum transport calculations have shown that the I–Vb behavior is substantially enhanced due to the toxic gas absorption. Specifically, striking improvement on transport performance is induced by NO2 absorption due to remarkable charge transfer, making the SiAs monolayer a promising candidate to selectively and sensitively detect NO2 molecule. Furthermore, we have shown that the work function and the charge transfer can be manipulated by strain, allowing potential application for anisotropic electronics. Our findings could be helpful to the potential application of the NO2 toxic detection in future.

Simultaneous Monitoring of Atmospheric CH4, N2O, and H2O Using a Single Gas Sensor Based on Mid-IR Quartz-Enhanced Photoacoustic Spectroscopy.

An optical sensor based on external-cavity quantum cascade laser (EC-QCL) was developed for simultaneous triple-species monitoring of CH4, N2O, and H2O vapor using off-beam quartz-enhanced photoacoustic spectroscopy (OB-QEPAS). The EC-QCL wavelength was scanned over three neighboring absorption lines of CH4 (1260.81 cm-1), N2O (1261.06 cm-1), and H2O vapor (1261.58 cm-1) by tuning the grating of the EC-QCL with a piezoelectric actuator. Molecular relaxation effects impacting the generation of the QEPAS signals resulting from light absorption by CH4 and N2O molecules were investigated in the mid-infrared region near 8 μm. A theoretical model was introduced for the mid-infrared region, including the beneficial influence of water vapor. An enhancement of the QEPAS signals by a factor of 3 for CH4 in air and of 20% for N2O in air was observed in humidified samples compared to that in dry samples. The QEPAS measurement was scaled by the calibrated reference spectrometers; detection limits of 98 ppbv for CH4, 12 ppbv for N2O, and 750 ppmv for H2O vapor were obtained with a 1σ signal-to-noise ratio (SNR = 1) in humidified gas mixtures. Real-time Kalman filtering was applied to improve the measurement precision by a factor of approximately 4 while keeping the same temporal resolution, leading to measurement precisions of 60 ppbv for CH4, 10 ppbv for N2O, and 0.07% for H2O in the measurements of 1.99 ppmv CH4 and 312 ppbv N2O humidified with 2.8% H2O vapor, with a 1 s lock-in amplifier time constant and an equivalent bandwidth of 0.1 Hz.

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.

2-D Be2C as Multitime Reversible Environmental Oxygen- and Nitrogen-Containing Gases Sensor Material Under First Principle Investigations

A combined density functional theory and nonequilibrium Green’s function (DFT-NEGF) approach has been conducted to examine the potential of monolayer Be2C nanosheet as a promising sensor for various environmentally toxic/nontoxic nitrogen- and oxygen-containing multigases (NCGs and OCGs). A total of eight gases comprising four OCGs (O2, CO, CO2, and H2O) and four NCGs (NO, NO2, N2O, and NH3) are investigated on the surface of monolayer Be2C to identify its gas sensing potential. The nontoxic O2, CO2, and H2O are also included in the study considering their obvious presence in the environment. Our investigation suggests that at room temperature, larger adsorption energy of NO, NH3, and O2 gas molecules on the surface of Be2C reflects a more significant recovery time as 1016, 105, and 1012 s, respectively. The positive higher adsorption energy of NO2 gas molecules as 0.91 eV adsorbed on the Be2C nanosheet at room temperature results in a very short recovery time of 10−29 s. The adsorption energy of the NO2 gas molecule is positive, making it unsuitable for gas sensors. In all cases, notable variation is observed in electronic and adsorption properties, charge transfer, recovery time, work function, and transport characteristics of OCGs and NCGs on Be2C surface. OCGs and NCGs show electron acceptor nature during interaction with Be2C nanosheet. The electronic transport of Be2C sheet shows its highly selective and sensitive nature toward OCGs and NCGs. Overall, monolayer Be2C reveals as an excellent multitime reversible multigas sensor material for four gases, viz. CO, CO2, H2O, and N2O with their significantly low recovery time, whereas it appears to be one-time disposable sensor material for O2, NO, and NH3 gases with higher adsorption energy and relatively long recovery time.

Study of the NH3-SCR Mechanism on LaMnO3 Surfaces Based on the DFT Method

LaMnO3 with perovskite structure is a SCR de-NOx catalyst with good performance at low temperatures. In this paper, the SCR reaction process on the 010 surface of LaMnO3 catalyst was studied by DFT method, to guide the development of catalysts and their effective application. The results obtained through research indicate that both E-R and L-H mechanisms exist on the catalyst surface. The NH3 molecule can be absorbed on L acid and then oxidized by lattice oxygen to form NH2. Then, NH2 can react with the NO molecule to form NH2NO and decompose to N2 and H2O. The NH3 can also be absorbed with hydroxyl to form NH4+, it can also react with NO to form NH2NO and then decompose. The NH4+ also can react with NO3− which is formed by NO oxidized when O2 is present, to participate in the rapid SCR process.

Adsorption and electronic properties of pristine and Al-doped C60 fullerenes using N2O molecule: A theoretical study

The adsorption behaviors of N2O on the geometric and the electronic characteristics of C60 and Al@C59 fullerenes have been studied through density functional theory (DFT). In this research, the adsorption of N2O on the structural and electronic properties of pristine and Al@C59 fullerenes has been evaluated to examine its feasibility as an N2O absorbent nanomaterial as a novel idea. Electronic properties of the adsorption complexes such as binding energies, dipole moments and global indices were determined. Interaction between N2O and C60 and Al@C59 fullerenes illustrate binding energies in the range of 0.2–41.2 kJ/mol. Al@C59 fullerene has been considered for the adsorption of N2O due to the effect of that on the of sensitivity of N2O molecule that is improved significantly. Density of state (DOS) analysis indicates that there is a strong interaction between adsorbate and adsorbent as evidenced by the occurrence of orbital hybridization between adsorbate and adsorbent during adsorption. Herein, the low binding energy and large electronic charge transfer between Al@C59 fullerene and N2O show the potential of Al@C59 as a suitable sensor for N2O gas.

Adsorption behaviors of the Sc2C(OH)2 monolayer for small gas molecules: A first-principles study

We investigated the Sc2C(OH)2 monolayer adsorption properties for small gas molecules using the first-principles calculations. The nature of interactions is elucidated based on the calculated adsorption energies, charge transfer, band structure, densities of states, and charge density differences of the adsorption configurations. The adsorption stability on the Sc2C(OH)2 monolayer increases in the order: H2< N2< CO2< CO < H2O < NO < N2O < C2N2< BBr3< SO2< O2< NO2. AsF5 and Br2 molecules are spontaneously dissociated into the Sc2C(OH)2 monolayer. Moreover, the electronic transport of the Sc2C(OH)2 monolayer has been computed based on the nonequilibrium Green’s function formalism. Our results predicted that Sc2C(OH)2 monolayer-based sensor can detect NO2 gas with sensitivity to a NO2 molecule of up to 20% at the bias voltage of 0.5 V. However, oxygen is the interfering gas, which leads to the low selectivity of the NO2 sensor. In addition, Sc2C(OH)2 monolayer-based sensor is significantly affected by humidity, with a conductivity decrease of about 3% after H2O molecule adsorption.

Ab-initio characterization of iron-embedded nitrogen-doped graphene as a toxic gas sensor

Special binding sites in graphene are beneficial for near-surface interaction. These binding sites, which are supplied by single-atom catalysts, change the electronic characteristics of graphene and its derivatives, greatly expanding its potential use as gas sensors. Iron–nitrogen–carbon is reflected as one of the most effective substitutes for platinum in oxygen reduction reactions. The selection for carbon-enclosed FeN4 moieties, which serve as catalytically active centers, is among the top priorities. Current research focuses heavily on carbon-enclosed FeN4 moieties from a gas sensing perspective. In the present work, transition metal atom iron supported on nitrogen-doped graphene (FeN/G) was analyzed by density functional theory. The effect of gas adsorption on the structural and electronic properties was investigated with adsorption energy, charge transfer, work function, and band structure. The results indicate the chemisorption nature of carbon monoxide (CO), nitrogen oxide (NO), and nitrogen dioxide (NO2) with strong adsorption energies of − 1.641 eV, − 2.081 eV, and − 1.345 eV. They induced spin polarization when adsorbed on the graphene support, which drastically modulated the electronic characteristics of the substrate. While other gas molecules of carbon dioxide, hydrogen disulfide, and ammonia (CO2, H2S, and NH3) with adsorption energies of − 0.154 eV, − 0.371 eV, and − 0.460 eV were physisorbed and served as electron donors, sulfur dioxide (SO2) exhibited weak chemisorption at a value of − 0.620 eV. Nitrogen-containing gas molecules of NO, NO2, and NH3 showed band gap shortening with increasing conductivity as compared to bare iron embedded graphene supported structure. Based on the investigation, the structure has potential application for the detection of NO and NO2 and other gases.

Influence of the metal - support and metal - metal interactions on Pd nucleation and NO adsorption in a Pd4/γ-Al2O3 (110D) model.

The role played by the metal - support (MSI) and metal - metal (MMI) interactions on two important processes in controlling the catalyst performance - nucleation and molecular adsorption - has been investigated using density functional theory (DFT), by means of B3LYP functional, combined with localized molecular orbital energy decomposition analysis (LMOEDA), and natural bond orbital (NBO) calculations, with aid of a Pd4/γ-alumina (110D) model (Pd4/Al13O23H7). Our results indicate the occurrence of an electronic metal - support interaction (EMSI) which induces a most intense charge transfer in the Pd4 → γ-alumina backdonation direction, most expressive in Pd → Al, promoting an electronic redistribution within the units and attenuating the MMI. Nevertheless, the MSI/MMI synergistic effect seems to favor slightly the nucleation of a fifth palladium atom, leading to a distorted square pyramidal arrangement for Pd5. The LMOEDA analysis points to a mostly covalent character in the Pd - Al bonds, whereas the Pd - O bonds are mainly electrostatic in nature. The palladium atoms deposited on oxygen anions are the acid centers, where both NO molecule and an additional palladium atom anchor more strongly. In addition, the MSI/MMI effect, through the electronic and geometric contributions, drives the adsorption of the NO molecule to the mode which most favors the Pd → NO (4dz2 → 2π*) backdonation (bridge mode). MSI and MMI effects on the nature of the Pd - O (electrostatic) and Pd - Al (covalent) bonds, charge transfer into Pd4/γ-Al2O3 (110D) interface (back donation) and preferential site for adsorption of a single NO molecule and an additional Pd atom (Pd - O).

Transition metal disulfide (MoTe2, MoSe2 and MoS2) were modified to improve NO2 gas sensitivity sensing

For the detection of the more hazardous nitrogen oxides (NO2), there is a need to find a readily fabricated, low-cost, high-performance two-dimensional material. This paper selected three transition metal disulphides (TMDs), MoTe2, MoSe2 and MoS2, as materials for detecting NO2 molecules by density flooding theory (DFT). The results show that the pure Mo(Te/Se/S)2 monolayer has a poor detection effect on NO2 molecules, and the modified monolayer exhibits better performance than its natural counterpart due to the significant electron hybridization between the dopant and the gas molecules after the introduction of metal atoms on the surface. It also leads to significant changes in electronic properties and work functions. The charge transfer mechanism based on Hirshfeld analysis shows that the charge transfer from the modified substrate to the NO2 molecule improves the binding characteristics. And by discussing the adsorption structure, adsorption energy, local electron density, density of states, and frontier orbit theory, we show that MoTe2 is a promising material for gas detection and removal, which will provide experimentalists with theoretical guidance for the application of Mo(Te/Se/S)2 based sensing materials. Our work is important for predicting novel monosulfide sensing materials and extending the application of TMDs as chemical gas sensors in the field of environmental monitoring.

Catalytic NO Reduction by NO Pre-Adsorbed RhCeO2 NO- Clusters.

A fundamental understanding on the dynamically structural evolution of catalysts induced by reactant gases under working conditions is challenging but pivotal in catalyst design. Herein, in combination with state-of-the-art mass spectrometry for cluster reactions, cryogenic photoelectron imaging spectroscopy, and quantum-chemical calculations, we identified that NO adsorption on rhodium-cerium bimetallic oxide cluster RhCeO2 - can create a Ce3+ ion in product RhCeO2 NO- that serves as the starting point to trigger the catalysis of NO reduction by CO. Theoretical calculations substantiated that the reduction of another two NO molecules into N2 O takes place exclusively on the Ce3+ ion while Rh behaves like a promoter to buffer electrons and cooperates with Ce3+ to drive NO reduction. Our finding demonstrates the importance of NO in regulating the catalytic behavior of Rh under reaction conditions and provides much-needed insights into the essence of NO reduction over Rh/CeO2 , one of the most efficient components in three-way catalysts for NOx removal.

Moisture-Insensitive and Highly Selective Detection of NO2 by Ion-in-Conjugation Covalent Organic Frameworks.

As a common toxic gas, nitrogen dioxide (NO2) seriously threatens the environment and human respiratory system even at part per billion (ppb) level. Covalent organic frameworks (COFs) have gained widespread attention in sensing applications because of the benefits of designability, environmental stability, and a large number of active sites. However, the competitive adsorption of water molecules and the target gas molecules at room temperature as well as the weak interaction between COFs and gas molecules hinder their practical applications. Here, we introduce ion-in-conjugation (IIC) into a covalent organic framework (COF) by preparing a condensate of squaraine (SA) with 1,3,5-tris(4-aminophenyl)benzene (TAPB) to form a mesoporous macrocyclic material (SA-TAPB). Layers of SA-TAPB, drop cast onto interdigitated Ag-Pd alloy electrodes, show a statistically significant conductivity response to NO2 at concentrations as low as 30 ppb and a theoretical detection limit of 10.9 ppb. The sensor displays a lower sensitivity to variations in humidity when operated at 80 °C compared to room temperature. The density functional theory (DFT) calculations indicated that the main adsorption site of NO2 is dual hydrogen bonds formed between two amide hydrogen atoms of SA-TAPB and the NO2 molecule. Gas adsorption experiments revealed that SA-TAPB has the largest adsorption capacity of NO2 versus other interference gases, which were responsible for the excellent selectivity toward NO2.

Atomically dispersed Co catalyst for electrocatalytic NO reduction to NH3

Electrocatalytic NO reduction to NH3 (NORR) represents an energy-efficient and eco-friendly route to simultaneously remedy NO pollution and produce valuable NH3. Herein, we design atomically dispersed Co anchored on MoS2 (Co1/MoS2) as a highly active and durable NORR catalyst. Detailed characterizations and theoretical calculations unveil the creation of active Co1-S3 moieties on Co1/MoS2, which can selectively absorb NO molecules and promote the hydrogenation energetics of NORR process. As a result, Co1/MoS2 exhibits an excellent NORR performance with an NH3 yield of 217.6 μmol h−1 cm−2 and an NH3-Faradaic efficiency of 87.7 % at −0.5 V vs RHE, substantially outperforming pristine MoS2 and most reported NORR catalysts.

Exploring the potential use of Fe-decorated B40 borospherene as a prospective catalyst for oxidation of methane to methanol

First-principles calculations based on density functional theory were utilized to evaluate whether an iron atom decorated B40 borospherene can be employed as a catalyst for converting methane (CH4) to methanol (CH3OH) in the presence of N2O or O2 molecule. Geometry optimizations indicated that N2O and O2 are both chemisorbed on the Fe atom of the catalyst, whereas CH4 is physisorbed. Using N2O as the oxidant, the oxidation of CH4 begins with N2O decomposition on the catalyst, which has an activation barrier of 0.50 eV. The CH4 molecule then combines with the activated O atom remained on the Fe to form the CH3OH molecule. However, the oxidation of CH4 with O2 requires an activation barrier as high as 1.91 eV, implying that this process is unlikely to occur under normal conditions. These novel results are anticipated to help in the design and modeling of noble-metal free catalysts for CH4 oxidation.

Multifunctional 2D g-C4N3/MoS2 vdW Heterostructure-Based Nanodevices: Spin Filtering and Gas Sensing Properties.

Two-dimensional (2D) magnetic materials are the key to the development of the new generation in spintronics technology and engineering multifunctional devices. Herein, the electronic, spin-resolved transmission, and gas sensing properties of the 2D g-C4N3/MoS2 van der Waals (vdW) heterostructure have been investigated by using density functional theory with non-equilibrium Green's function method. First, the g-C4N3/MoS2 vdW heterostructure demonstrates ferromagnetic half-metallicity and superior adsorption capacity for gas molecules. The spin-dependent electronic transport of the g-C4N3/MoS2-based nanodevice is obviously regulated by parallel or anti-parallel spin configuration in electrodes, leading to perfect single-spin conduction behavior with a nearly 100% spin filtering efficiency, a negative differential resistance effect, and other interesting electrical transport phenomena. Moreover, g-C4N3/MoS2 exhibits directional dependency and strong transport anisotropic behavior under bias windows, indicating that the electric current propagates more easily through the vertical direction than the horizontal direction. The physical mechanisms are revealed and analyzed by presenting the bias-dependent transmission spectra in combination with the projected local device density of states. Finally, the g-C4N3/MoS2-based gas sensor is more sensitive to CO, NO, NO2, and NH3 molecules with the chemisorption type. The strong chemical adsorption leads to the formation of electrons on the local scattering center and ultimately affects the transport properties, resulting in the maximum gas sensitivity reaching 6.45 for NO at the bias of 0.8 V. This work not only reveals that the g-C4N3/MoS2 vdW heterostructure with high anisotropy, perfect spin filtering, and outstanding gas sensitivity is a promising 2D material but also provides an insight into the further application in futuristic electronic nanodevices.

The adsorption characteristics of MoS2–CuO heterojunction to polar gas molecules (CO, NO and NO2): A first–principle study

Some polar gas molecules (CO, NO and NO2) have serious influences on the atmospheric environment and human respiratory system, so it is important to design effective gas sensors for detecting the toxic gas molecules and then removing them. In this paper, the MoS2–CuO heterojunction model was established and the potential gas adsorption sites were explored. The electronic property and the adsorption characteristics of MoS2–CuO heterojunction on CO, NO and NO2 gas molecules were calculated based on the first-principle. The results show that among them, the NO adsorption system has the highest adsorption energy (3.678 eV) and charge transfer (0.126e), with its adsorption distance of 3.088 Å. MoS2–CuO heterojunction is more sensitive to NO polar molecules than CO and NO2 gas molecules. Furthermore, the hybridization of N–2p, Cu–3d and O–2p orbits and the charge transfer in the adsorption process are revealed by the partial density of states (PDOS) and the deformation charge density (DCD). It is the main reason why the heterojunction is more sensitive to NO molecules. Therefore, MoS2–CuO heterojunction is a promising combination of gas sensor materials, which can be used for the adsorption and detection of polar molecules.

Adsorption of NO gas molecule on the vacancy defected and transition metal doped antimonene: A first-principles study

The adsorption behaviors of single vacancy defected and transition metal (TM) atoms (Sc, Ti) doped antimonene for NO molecule have been systematically investigated using the first-principles calculations based on the density functional theory (DFT-D2 method). The results show that the NO molecule is physisorbed on pure antimonene with the low adsorption energy. While the NO molecule is chemisorption on single vacancy defected antimonene (SV-antimonene), TM doped antimonene (Sc-antimonene, Ti-antimonene) and TM doped single vacancy defected antimonene (Sc-SV-antimonene, Ti-SV-antimonene). The introduction of vacancy defects and TM atoms can effectively enhance the interaction between the NO molecule and the antimonene by analyzing the density of states (DOS), charge density difference (CDD) and the electron localization function (ELF). In addition, the significant changes in work function (WF) after NO adsorption indicate that defected and doped antimonene are sensitive to NO molecule. The optical properties suggest that the increase in absorption coefficients of all adsorption systems can be observed in the visible region. Therefore, these results provide theoretical guidance for the design of high-sensitive gas sensors based on antimonene.