Adsorption Of NO Molecules Research Articles

DFT study of the adsorption behavior of NO gas molecule on the Ga and As pair doped stanene nanosheets

Abstract The density functional theory computations were performed to examine the interaction between NO molecule and Ga–As codoped stanene nanosheets. The band structure calculations indicated that the Ga–As codoped stanene acts a semiconductor material with a band gap around the Fermi level. Thus, the NO adsorption mechanism is inspected on the Ga–As codoped stanene systems. The results suggested that the NO binding to the stanene via the N center is stronger than that via the O center. Besides, the adsorption on the Ga–As codoped system was found to be more favorable in energy than that on the pure one. Therefore, Ga–As codoped system can provide most stable adsorption configurations with the adsorbed NO molecule. While the adsorption happens, the charge densities were mostly accumulated over the adsorbed NO molecule, which implies the acceptor behavior of the NO molecule in reaction with stanene nanosheets.

First principle insights of NO2 detection via III-V nitride nanoribbons with armchair edges

The development of low-dimensional and robust nano-sensors is an area of potential research and development. In this direction, here, we investigated the sensing of NO2 gas molecules adsorbed on the edges of III-V nitride nanoribbons with armchair edges (AXNNR, X = B/Al/Ga). Five different adsorption sites are considered for the adsorption of NO2 molecules and the adsorption assisted modulation of electronic and transport properties has been observed for detection purpose. Interestingly, a semiconducting to metallic transition has been noticed in considered AXNNR due to NO2 interaction. The selectivity of NO2 with respect to N2 is found to be higher as compared to that of O2. Further, some of the selected structures exhibit an interesting negative differential resistance (NDR) phenomenon which suggest that NO2 adsorbed AXNNR could also be useful for designing of the fast switching devices and oscillators applications.

Unraveling the promoted nitrogen dioxide detection performance of N-doped SnO2 microspheres at low temperature

Abstract Nitrogen doping has been proven an efficient strategy to modulate the electronic structure of metal oxides to tune their properties. Herein, we report the synthesis of N-doped SnO2 microspheres through calcining the pristine SnO2 in NH3 atmosphere. Texture characterizations show that N–SnO2 microspheres exhibit 3D-porous architectures with a diameter of ca. 300–500 nm. After NH3 treatment, the SnO2 exhibits the formation of the N-doping and oxygen vacancies on the surface of the material, rich free-electrons and the narrow energy band. It is found that the as-prepared N-doped SnO2 microspheres at 200 °C (N–SnO2-200), show superior selectivity and high response (S = 155 to 5 ppm NO2) compared with its counterparts. DFT calculations and experimental results illustrate that N impurities and oxygen vacancies as N-induced active sites favor the adsorption of NO2 molecules; rich free-electrons increase the amount of adsorbed NO2 molecules; and the narrow energy band promotes the effectively electron transfer during the sensing reaction. Therefore, in this work we unravel the improved NO2 gas-sensing performances of the N-doped SnO2 and provide new guidance for the development of highly efficient metal oxide sensing materials for NO2 detection.

The impact of carrier gas on room-temperature trace nitrogen dioxide sensing of ZnO nanowire-integrated film under UV illumination

Chemiresistive gas sensors have been extensively explored for hazardous gas detection. Currently, an overwheming majority of previous attention was focused on the parameter improvement of sensor performance while the impact of carrier gas species on the performance was severely ignored. Aiming to a deep insight into this issue, in this work we prepared zinc oxide (ZnO) nanowire-network sensor and explored its UV-activated sensing performance toward trace nitrogen dioxide gas (NO2) at room temperature (25 °C) under two carrier gases, i.e., dry nitrogen (N2) and air. Within N2, the sensor exhibited a reversible response of 157 toward 50 ppb NO2 and a sensitivity of 7.8/ppb, which was not only among the best showcases of the existing work, but much larger than those within air (11 and 0.091/ppb, respectively). Moreover, decent selectivity and long-term stability were demonstrated. Far more UV irradiation-induced electrons which reacted with adsorbed NO2 molecules on ZnO surface as well as smaller baseline resistance under N2 than those under air jointly led to the superior response and sensitivity. After long-time UV exposure prior to gas-sensing tests within both carrier gas cases, the remaining oxygen ions (O2−) were weakly bonded on ZnO surface, contributing to the reversible behaviors at room temperature. The interconversion between physisorbed O2 molecules and ionic O2− on ZnO surface was proposed to rationalize the sensing phenomena especially when no continuous oxygen was supplied under N2 atmosphere, which enriched the current transduction mechanisms.

Capacitive Chemical Sensors Based on Two-Dimensional WSe2

We demonstrated capacitive-type chemical sensors (chemicapacitor sensors) based on two-dimensional (2D) tungsten diselenide (WSe2). The integration of 2D materials with high surface-to-volume ratios and a capacitor resulted in excellent chemical sensing with high selectivity, high sensitivity, and fast response. WSe2-based 2D chemicapacitors were fabricated by combining exfoliated WSe2 flakes with parallel-plate capacitors. The sensing ability of WSe2-based 2D chemicapacitors towards NO2 molecules was characterized by monitoring the changes in capacitance (ΔC/C0, ∼65%) and parallel resistance (ΔRp/Rp0, ∼−90%) due to the adsorption of NO2 molecules (200 ppm). Transient sensing characteristics with fast response and recovery were achieved with adequate reproducibility. Interestingly, ΔC/C0 and ΔRp/Rp0 exhibited different behaviors, which can be a useful value for distinguishing between different target gas molecules. Our novel approach provides a convenient and effective method for producing 2D chemicapacitor sensors at low cost and with low power consumption.

A DFT study of diesel exhaust NOxreduction over rare earth CeO2catalyst

Adsorption of NO on the CeO2(110) surface was investigated using RPBE approach of GGA within the framework of density functional theory (DFT) combined with periodic slab model. Two molecular orientations, N-end and O-end, over various adsorption sites, top, hollow, bridge and O site of CeO2(110) sur-face have been considered. Two molecular orientations under different coverage of CeO2(110) surface also have been considered. The optimized results indicate that the N-end adsorption models are more stable than the O-end ones. So N-end adsorption was more favourable than O-end. NO adsorption on a clean CeO2(110) surface was physisorption, while chemical adsorption occurred in the present of surface oxygen vacancy. Adsorption is stable when coverage was set to 0.25 monolayer. Researched on density of states of free NO molecule and adsorbed NO molecule, the results show that there is an interaction between NO molecule and the substrate . The population analysis indicates that the charges transfer from Ce atoms to NO molecule. The charges transfer of O-end is more than N-end.

Phase Separation of P3HT/PMMA Blend Film for Forming Semiconducting and Dielectric Layers in Organic Thin-Film Transistors for High-Sensitivity NO2 Detection.

Formation of the semiconductor/dielectric double-layered films via vertical phase separations from polymer blends is an effective method to fabricate organic thin-film transistors (OTFTs). Here, we introduce a simple one-step processing method for the vertical phase separation of poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(methyl methacrylate) (PMMA) blends in OTFTs and their applications for high-performance nitrogen dioxide (NO2) sensors. Compared to the conventional two-step coated OTFT sensors, one-step processed devices exhibit a great enhancement of the responsivity from 116 to 1481% for 30 ppm NO2 concentration and a limit of detection of ∼0.7 ppb. Studies of the microstructures of the blend films and the electrical properties of the sensors reveal that the devices formed by the one-step vertical phase separation have better capability for the adsorption of NO2 molecules. Moreover, a careful adjustment of the blend ratio between P3HT and PMMA can further improve the performance of the NO2 sensors, ranging from sensitivity to selectivity and to the ability of recovery. This simple one-step processing method demonstrates a potential possibility for developing high-performance, low-cost, and large-area OTFT gas sensors.

NOx Adsorption and Optical Detection in Rare Earth Metal-Organic Frameworks.

Acid gases (e.g., NOx and SOx), commonly found in complex chemical and petrochemical streams, require material development for their selective adsorption and removal. Here, we report the NOx adsorption properties in a family of rare earth (RE) metal-organic frameworks (MOFs) materials. Fundamental understanding of the structure-property relationship of NOx adsorption in the RE-DOBDC materials platform was sought via a combined experimental and molecular modeling study. No structural change was noted following humid NOx exposure. Density functional theory (DFT) simulations indicated that H2O has a stronger affinity to bind with the metal center than NO2, while NO2 preferentially binds with the DOBDC ligands. Further modeling results indicate no change in binding energy across the RE elements investigated. Also, stabilization of the NO2 and H2O molecules following adsorption was noted, predicted to be due to hydrogen bonding between the framework ligands and the molecules and nanoconfinement within the MOF structure. This interaction also caused distinct changes in emission spectra, identified experimentally. Calculations indicated that this is due to the adsorption of NO2 molecules onto the DOBDC ligand altering the electronic transitions and the resulting photoluminescent properties, a feature that has potential applications in future sensing technologies.

Creating oxygen vacancies on porous indium oxide nanospheres via metallic aluminum reduction for enhanced nitrogen dioxide detection at low temperature

Investigating the correlation between the electronic structure of indium oxide materials with oxygen vacancy defects and their sensing property to nitrogen dioxide is important for future development of high-efficient sensing materials. For the first time, the defective structure of porous In2O3 nanospheres was introduced in a two-zone tube furnace using metallic Al as reducing agent. Texture characterizations show that In2O3 and In2O3-x are porous nanospheres assembled by small particles with the size of ca. 10–20 nm. The surface oxygen vacancy defects and electronic structure of samples were characterized by X-ray power diffraction, X-ray photoelectron spectroscopy, electron paramagnetic resonance, photoluminescence, ultraviolet-visible spectrophotometer and Hall analysis, and the sensing performance of samples to NO2 gas was evaluated. The results display that the porous In2O3-x nanospheres prepared at the reducing temperature of 300 °C (Vo-In2O3-300) exhibits improved response of 130 to 3 ppm NO2 at 80 °C, which is almost 2.5-folds as high as the response (55) of the porous In2O3 nanospheres. The sensing mechanism study carried out using DFT indicates that oxygen vacancies on the surface of In2O3 as donor level optimize the electron structure and electrical properties of materials, such as supplying more free-electrons in the conduction band, narrowing the band gap and improving the mobility of electrons, which result in the low energy barrier for the adsorption of NO2 molecules on the surface and in turn enhance the gas-sensing performance of In2O3. Therefore, this work can provide some instructive thoughts for constructing In2O3-based sensing materials for high-efficient nitrogen dioxide detection.

Ab initio study of the adsorption and dissociation of NO2 on pristine and Cu decorated ZnO(0001)-3 × 3

Due to the importance of reducing environmental pollution, especially NO2, we have studied the adsorption of this contaminant to eliminate it from the atmosphere. We perform ab initio calculations of the NO2 adsorption on pristine and copper decorated zinc oxide (0001)-3 × 3 surface. Several high symmetry sites have been tested of the NO2 molecule adsorption. The structural and electronic properties of the most stable configurations are reported. The adsorption energies values show that the molecule is chemisorbed. The minimum energy pathways (MEP), to study the NO2 dissociation process, were calculated by the climbing image nudged elastic band (CI-NEB) method. The activation energy of the first stage NO2 dissociation on pristine ZnO surface is 0.14 eV, 1.83 eV lower than the 1.97 eV on the Cu decorated system. On the other hand, for the second dissociation process, the activation energy when Cu is present has a value of 1.16 eV which is 0.8 eV lower than the 1.96 eV needed on the pristine surface. Our results suggest that NO2 adsorption and first dissociation is possible on pristine ZnO(0001), but copper decoration allows a second dissociation stage providing a possible mechanism of the NO2 transformation into harmless substances.

Co-modulation of graphene by N hetero-doping &vacancy defects and the effect on NO2 adsorption and sensing: First-principles study

Abstract Modulation by hetero-doping or vacancy defect has been proved effective on gas-sensing response enhancement of intrinsic graphene. To explore the synergistic effect of hetero-doping and vacancy defects, in this work, the adsorption of NO2 molecule on the defective graphene co-modulated with N-doping and C-vacancy was studied using first-principles calculations. The doping&vacancy models of defective graphene were constructed by creating single/double C-vacancies with partial or total marginal C atoms around the defect substituted by N atoms. The calculations about band structure, DOS and atomic Mulliken population reveal that the sub-fully doped configurations achieve significant enhancement for NO2 adsorption and interaction with the defective surface in corresponding vacancy systems. Further analysis on geometry and charge density difference demonstrates that the sub-full doping of N atoms causes strong asymmetry in charge distribution around the vacancy, which is further correlative to the improved adsorption characteristic of the co-modulated graphene from the perspective of a local built-in electric field. In addition, the effect of pyrrolic and pyridinic nitrogen-doping on NO2 adsorption is also discussed. The present work provides theoretical understanding for the NO2 adsorption characteristic and mechanism of N-doping&vacancy co-modulated graphene. It is clearly demonstrated that the defective graphene with appropriate hetero-doping&vacancy co-modulation is attractive and promising for enhanced NO2 adsorption and NO2-sensing.

Hematite porous architectures as enhanced air purification photocatalyst

Different α-Fe2O3 porous architectures were obtained by electrospinning (nanotubes) or without electrospinning (flakes), and heating treatments using Fe(NO3)2/PVP (Polyvinylpyrrolidone) as a precursor. The particles constituting the nanotubes and flakes samples exhibited similar wall porosity and crystal size, while the existence of the micropore area was also a characteristic. The chemical identity was confirmed as hematite by XRD, Raman and XPS studies. The prepared samples were studied as photocatalytic materials in the removal of NOX gases from air, their De-NOX ability being superior to that previously reported for hematite photocatalysts. These porous hematite samples exhibited a high NO conversion efficiency and similar to that of TiO2 P25, this being the first report for α-Fe2O3 oxide. Additionally, the calculated De-NOX selectivity values were higher than that of TiO2 P25. The adsorption of NO2 molecules is facilitated on these porous architectures, assisting in the enhancement of the of the photochemical process selectivity.

Spin-Transport Tuning of Individual Magnetic Mn-Salophen Molecule via Chemical Adsorption.

Control over spin states at the single molecule level is a key issue in the emerging field of molecular spintronics. Here, we explore the chemical adsorption effect on the magnetic and spin-transport properties of individual magnetic molecule by performing extensive density functional theory calculations in combining with non-equilibrium Green’s function method. Theoretical results clearly reveal that the molecular magnetic moment of Mn-salophen can be effectively tuned by adsorbing F and CO on the central Mn cation, while the adsorbed NO molecule quenches the molecular magnetic moment. Without chemical adsorption, the currents through Mn-salophen molecular junction just show a little distinction for two spin channels, which agrees well with previous investigation. Remarkably, the conductive channel can be switched from the spin-up electrons to the spin-down electrons via adsorbing F and CO, respectively, and the corresponding two Mn-salophen molecular junctions with chemical modifications display nearly perfect spin-filtering effect. The observed spin switch and the predicted spin-filtering effect via chemical adsorption indicates that Mn-salophen holds potential applications in molecular spintronic devices.

TiO2/GRAPHENE OXIDE HETEROSTRUCTURES FOR GAS-SENSING: INTERACTION OF NITROGEN DIOXIDE WITH THE PRISTINE AND NITROGEN MODIFIED NANOSTRUCTURES INVESTIGATED BY DFT

The gas response of metal oxide-based sensors depends strongly on its adsorption properties. To explore the potential sensing capability of pristine and nitrogen modified TiO2/graphene oxide (GO) heterostructures, the adsorption of NO2 molecule on the N-doped nanocomposites was investigated using density functional theory (DFT) calculations. Six possible configurations were simulated based on the estimated adsorption energies. The binding sites were located over the oxygen, doped nitrogen and five-fold coordinated titanium atoms of TiO2. The electronic properties including atomic Mulliken population, projected density of states and molecular orbitals were investigated in detail. The N–O bonds of the NO2 molecule were significantly increased after the adsorption process. The adsorption of NO2 molecule on the N-doped nanocomposite is more energetically favorable than the adsorption on the undoped one. The results suggest that NO2 chemisorbs on the considered nanocomposites. Mulliken population analysis reveals a noticeable charge transfer from the nanocomposite to the molecule, which indicate that NO2 acts as a charge acceptor. Molecular orbital calculations show that the highest occupied molecular orbitals (HOMOs) of the studied systems were mainly localized on the adsorbed NO2 molecule. The significant overlaps in the projected density of states (PDOS) spectra of the interacting atoms confirm the formation of chemical bonds between them. There is a direct relationship between the results of charge transfer and sensing responses. N-doped nanocomposites have better sensing response than the undoped ones. The results highlight the possibility to develop innovative highly efficient NO2 sensors based on novel TiO2/GO nanocomposites.

Temperature- and pressure-dependent adsorption configuration of NO molecules on Rh(111) surface: A theoretical study

Understanding the behavior of NO molecules on Rh metal surfaces is necessary for gaining fundamental knowledge about catalytic chemistry and surface science. The present theoretical study details the configuration of NO molecules adsorbed on Rh(111) surface on the basis of density functional theory (DFT) calculations. The impact of coverage dependences on the adsorption/desorption energies is examined systematically: multiple configurations of NO adsorption structures are investigated with NO surface coverage from 0.06 to 0.75. A phase diagram for the various NO configurations with temperature and pressure is obtained by considering the adsorption equilibrium. Adsorption energies of NO molecules generally decrease with increasing surface coverage, reflecting the repulsive interactions between the adsorbed NO molecules. Microkinetic simulations for temperature-programmed desorption (TPD) spectra are performed. Simulated TPD spectra on the basis of the surface coverage-dependent desorption energies are in reasonable agreement with the experimental results.

Modulating the electronic structures and sensing properties of metal and non-metal atoms modified graphene sheets

This study is to explore different graphene supports effect on the stability of metal atoms and their adsorption characters of gas molecules by using the density functional theory (DFT) calculations. Based on the divacancy structure (555-777-) of graphene, three N, Si and P dopants within 555-777-graphene (3NM-graphene) can regulate the stability and activity of supported metal atoms (M = Co and Pt). Among the toxic gases, the 555-777-graphene-M exhibits high sensitivity for the adsorbed NO molecule. Besides, the isolated gas molecule on 3NM-graphene-M sheets is more stable than that on the 555-777-graphene-M sheets. The NO as specific gas molecule can be easily detected due to it has the largest adsorption energy. The NH3 and SO2 have larger adsorption energies than that of HCN molecule. Furthermore, the electronic and magnetic properties of gas molecules on 3NM-graphene-M sheets are comparatively investigated. It is found that the orbital hybridization between gas molecule and metal catalyst can well reveal the change in adsorption stability and magnetic properties by the transferred electrons. In comparison, the adsorbed gases on 3N-graphene-Co systems have larger magnetic moments than those on 3P-graphene-Pt and 3Si-graphene-Co sheets. These results can provide important information for designing the novel graphene-based materials as gas sensor devices.

High Turnover Frequency CO–NO Reactions over Rh Overlayer Catalysts: A Comparative Study Using Rh Nanoparticles

A comparative turnover frequency (TOF) study for structure-sensitive CO–NO reactions between overlayer (thin-film) and nanoparticle Rh catalysts was performed using a combined experimental and theoretical approach. Two types of honeycomb catalysts were prepared: one by the arc-plasma deposition of a 3 nm Rh overlayer having a (111) preferential orientation atop a 20-μm Fe–Cr–Al metal foil and the other by a conventional wet coating of Rh/ZrO2 powders comprised of Rh nanoparticles onto a cordierite honeycomb. The reaction rate of the overlayer was found to be more superior to the nanoparticles, despite a smaller surface area, as the TOF was 14-fold greater on the overlayer than on the nanoparticle. In situ infrared spectroscopy suggested that a hollow-site NO formed onto the overlayer in contrast to the bridge- and on-top-NO adsorptions on the nanoparticles. The energy barriers for surface reactions of adsorbed NO molecules were analyzed using a density functional theory based molecular dynamics approach f...

Catalysis of Cu Cluster for NO Reduction by CO: Theoretical Insight into the Reaction Mechanism.

Density functional theory calculations here elucidated that Cu38-catalyzed NO reduction by CO occurred not through NO dissociative adsorption but through NO dimerization. NO is adsorbed to two Cu atoms in a bridging manner. NO adsorption energy is much larger than that of CO. N–O bond cleavage of the adsorbed NO molecule needs a very large activation energy (ΔG°‡). On the other hand, dimerization of two NO molecules occurs on the Cu38 surface with small ΔG°‡ and very negative Gibbs reaction energy (ΔG°) to form ONNO species adsorbed to Cu38. Then, a CO molecule is adsorbed at the neighboring position to the ONNO species and reacts with the ONNO to induce N–O bond cleavage with small ΔG°‡ and very negative ΔG°, leading to the formation of N2O adsorbed on Cu38 and CO2 molecule in the gas phase. N2O dissociates from Cu38, and then it is readsorbed to Cu38 in the most stable adsorption structure. N–O bond cleavage of N2O easily occurs with small ΔG°‡ and significantly negative ΔG° to form the N2 molecule and the O atom adsorbed on Cu38. The O atom reacts with the CO molecule to afford CO2 and regenerate Cu38, which is rate-determining. N2O species was experimentally observed in Cu/γ-Al2O3-catalyzed NO reduction by CO, which is consistent with this reaction mechanism. This mechanism differs from that proposed for the Rh catalyst, which occurs via N–O bond cleavage of the NO molecule. Electronic processes in the NO dimerization and the CO oxidation with the O atom adsorbed to Cu38 are discussed in terms of the charge-transfer interaction with Cu38 and Frontier orbital energy of Cu38.

Design and implementation of a preconcentrator with Zeolite NaY for sensitivity enhancement of commercial gas sensors at low NO2 concentrations

Zeolite NaY was used to implement a NO2 preconcentrating system for the first time which provided the detection of ppb concentration levels of NO2 with high response level. NO2 gas is among air pollutants that significantly affect the quality of human health, even at low concentrations, which necessitates commercial NO2 sensors to attain low detection capability. In this work, we have reported responses of a commercial NO2 sensor to low concentration levels of NO2. Responses were improved by ∼44 times through using a designed and fabricated preconcentration system. The preconcentrator was composed of different sections in which the most important part was zeolite NaY as a NO2 adsorbent: it adsorbed NO2 molecules from the air polluted with 300 ppb NO2 during the adsorption cycle, then by applying a heating pulse, it was forced to release preadsorbed NO2 species into a smaller chamber in which a commercial gas sensor was placed to monitor the variations of NO2. In this process, the sensor response increased noticeably. System features such as durability and cross sensitivity, and preconcentrator working conditions, such as desorption temperature, duration of adsorption time, heating rate, and the air circulation flow were investigated. Results were described and it is shown that NO2 detection at ppb levels with high sensitivity is possible with such a low price preconcentration system.

Support vector regression and neural networks analytical models for gas sensor based on molybdenum disulfide

In this study, MoS2 gas sensor based on field effect transistor has been proposed and the adsorption of NO2 molecules on the channel surface can lead to significant changes on its electronic and transport properties. The analytical models have been developed for the NO2 gas sensors by making an initial assumption that the gate voltage is directly proportional to the gas concentration. The performance of this sensor, is predicted and investigated by support vector regression (SVR) and artificial neural network (ANN) algorithms. The MoS2 gas sensor displays current changes upon exposure to very low concentrations of NO2. The comparison between analytical model, ANN and SVR with the empirical data shows the successful model construction. However, ANN outperforms the SVR approach and gives more accurate results.