Desorption Of NO Research Articles

Plasmonic Au-enabled photoenhanced room temperature NO2 sensing of 2D SnS2-heterostructure via single-step mechanochemical synthesis

The development of high-performance gas sensors for NO2 detection is critical due to its harmful effects on human health and environment. Tin disulfide (SnS2), with its layered structure akin to transition metal dichalcogenides (TMDs), shows potential for NO2 sensing. However, SnS2-based sensors typically exhibit weak response and incomplete recovery at room temperature. In this study, we propose 2D SnS2 nanosheets modified with gold nanoparticles (Au-NPs) by a single-step mechanochemical synthesis, in which photoelectric sensors depend on the light absorption properties of the sensitive material, thus Au-NPs with LSPR effect coupled with SnS2 can enhance the absorption capacity of the composite in the UV light band. The higher light absorption efficiency means that more electrons and holes can be produced under light excitation, and the holes can react with the NO2 adsorbed on the surface of the material, speeding up the desorption of NO2. As compared to the unmodified SnS2 sensor, the response values of Au/SnS2 sensor to 10 ppm NO2 at room temperature increased from 7.74 to 16.01, while the response/recovery time reduced from 169/201 s to 98/154 s. Moreover, the Au/SnS2 sensor can detect low concentrations of NO2 (50 ppb) with excellent repeatability, selectivity, and long-term stability at room temperature. This study demonstrates that integrating Au-NPs modification with UV photo-assistance is a viable strategy for developing high-performance room temperature gas sensors.

Electrodeposition of dense spherical Ni3P on nickel foam cathode enhance nitrate electrochemical reduction via promoting nitrate adsorption

Electrochemical nitrate reduction to nitrogen gas is considered as an alternative strategy to address water pollution problem, but the high cost and poor product selectivity of electrode limit its application. Here, Ni3P loaded nickel foam was fabricated via one-step eletrodeposition as cathode for electrochemical nitrate reduction. Due to the improvement of electron transfer rate and electrochemically active surface area, current efficiency and reaction rate constant enhanced 20.4-flod and 40-fold, respectively. Batch experiments revealed the remarkable nitrate reduction performance (∼97.53 %) after the optimization of potential, initial NO3- concentration and pH. Presence of chlorine induced electrochlorination will tune N2 (selectivity up to ∼100 %) to become the dominant products. Mechanism study suggested that the atomic H*-mediated indirect reduction, meanwhile properties of Ni3P to strengthen NO3- adsorption and prevent desorption of NO and NO2 are responsible for the enhancement of nitrate reduction. This work is meaningful for water environment protection and energy sustainable development.

Enhancing Compatibility of Two-Step Tandem Catalytic Nitrate Reduction to Ammonia Over P-Cu/Co(OH)2.

Electrochemical nitrate reduction reaction (NO3RR) is a promising approach to realize ammonia generation and wastewater treatment. However, the transformation from NO3 - to NH3 involves multiple proton-coupled electron transfer processes and by-products (NO2 -, H2, etc.), making high ammonia selectivity a challenge. Herein, a two-phase nanoflower P-Cu/Co(OH)2 electrocatalyst consisting of P-Cu clusters and P-Co(OH)2 nanosheets is designed to match the two-step tandem process (NO3 - to NO2 - and NO2 - to NH3) more compatible, avoiding excessive NO2 - accumulation and optimizing the whole tandem reaction. Focusing on the initial 2e- process, the inhibited *NO2 desorption on Cu sites in P-Cu gives rise to the more appropriate NO2 - released in electrolyte. Subsequently, P-Co(OH)2 exhibits a superior capacity for trapping and transforming the desorbed NO2 - during the latter 6e- process due to the thermodynamic advantage and contributions of active hydrogen. In 1m KOH + 0.1m NO3 -, P-Cu/Co(OH)2 leads to superior NH3 yield rate of 42.63mgh- 1cm- 2 and NH3 Faradaic efficiency of 97.04% at -0.4V versus the reversible hydrogen electrode. Such a well-matched two-step process achieves remarkable NH3 synthesis performance from the perspective of optimizing the tandem catalytic reaction, offering a novel guideline for the design of NO3RR electrocatalysts.

Selective passivation of 2D MoS2 nanosheets surface defects by spontaneous growth of Au nanoparticles for full response-recovery NO2 detection at room temperature

Full recovery at room temperature (RT) is quite challengng for two dimensional transition metal dichalcogenides chemiresistive gas sensors. The main reason for the incomplete recovery is the strong bonding of gas molecules onto sensing layer defects. Here, we show that the recovery rate of MoS2 chemiresistive NO2 sensors can be improved by selective passivation of MoS2 nanosheets (NSs) defects with Au nanoparticles (NPs) via a simple spontaneous reduction method. MoS2 NSs were produced by liquid shear exfoliation. Pristine and Au NPs functionalized MoS2 were characterized using ς-potential, UV–Visible spectroscopy, TEM, SEM, AFM, EDS, XRD, XPS and Raman spectroscopy. The analyses confirm the presence of Au NPs on the edges of MoS2 NSs at defective sites with NP sizes of 1–4 nm and 5–30 nm. Both pristine MoS2 and Au-decorated MoS2 NSs were employed to fabricate NO2 chemiresistive devices. Au-decorated MoS2 sensors showed an improved performance (for 1 ppm NO2, Au-MoS2 sensor exhibited a response of 5.6 % instead of 2.2 % for MoS2 sensor), and gave faster response and better recovery time. Concurrently, the functionalization is independent of the adsorption and desorption of NO2. Most importantly, the functionalization of MoS2 NSs helps to full response-recovery within one hour, without either thermal or UV irradiation treatment.

Exploring the dynamic evolution of lattice oxygen on exsolved-Mn2O3@SmMn2O5 interfaces for NO Oxidation

Lattice oxygen in metal oxides plays an important role in the reaction of diesel oxidation catalysts, but the atomic-level understanding of structural evolution during the catalytic process remains elusive. Here, we develop a Mn2O3/SmMn2O5 catalyst using a non-stoichiometric exsolution method to explore the roles of lattice oxygen in NO oxidation. The enhanced covalency of Mn–O bond and increased electron density at Mn3+ sites, induced by the interface between exsolved Mn2O3 and mullite, lead to the formation of highly active lattice oxygen adjacent to Mn3+ sites. Near-ambient pressure X-ray photoelectron and absorption spectroscopies show that the activated lattice oxygen enables reversible changes in Mn valence states and Mn-O bond covalency during redox cycles, reducing energy barriers for NO oxidation and promoting NO2 desorption via the cooperative Mars-van Krevelen mechanism. Therefore, the Mn2O3/SmMn2O5 exhibits higher NO oxidation activity and better resistance to hydrothermal aging compared to a commercial Pt/Al2O3 catalyst.

Role of graphene substrate in the formation of MoS2-based nanoparticles with improved sensitivity to NO2 gas

MoS2 coatings were formed on surface-oxidized silicon, chemical vapor deposition (CVD)-grown graphene, and reduced fluorinated graphene (rFG) from ammonium tetrathiomolybdate. The samples were annealed under ultra-high vacuum conditions at a temperature of 1000 °C. Analysis of X-ray photoelectron and X-ray absorption spectra revealed a bonding between MoS2 and the supporting material that was particularly strong for CVD-graphene. Uniform covering of the flat CVD-graphene surface with MoS2 nanoparticles and numerous contacts between them promoted the removal of sulfur and the formation of exposed molybdenum edges. A cracked MoS2 coating consisting of dense domains was formed on the wrinkled rFG surface. The study of samples as NO2 gas sensors revealed the best performance of MoS2/CVD-graphene. The sensor detected NO2 in air below 50 ppb at room temperature, had good response and recovery, operated in humid air, and demonstrated excellent NO2 selectivity. The other two sensors gave signals at elevated temperatures. The advantage of MoS2/CVD-graphene is due to improved electron transport in the hybrid, accessibility of small MoS2 nanoparticles to the analyte, and passivation of high-energy molybdenum sites by oxygen, which improves NO2 desorption.

Effect of the introduction of Zn on the electronic state of copper species in Cu-exchanged mordenite

This work evaluated the effect of Zn on the electronic state of copper in the Cu-Zn-mordenite binary system. The samples were prepared in two stages by sequential ion exchange of the initial sodium mordenite, using aqueous solutions of sulfate salts of these two metals, and changing the order of introduction of each of the cations, first Cu2+ and then Zn2+, or in the inverse order. The content of Zn and Cu changed within the 0.02–3.14 wt% interval at various Zn/Cu ratios. The prepared samples were characterized with UV–Vis spectroscopy in situ during temperature-programed oxidation (TPO) in oxygen, temperature-programed reduction (TPR) in hydrogen, and temperature-programed adsorption and desorption of NO (TPD). Cu and Zn have different affinities to mordenite, resulting in competition between them for zeolites sites, their redistribution, and formation of bimetallic Cu-O-Zn species. The order of ion-exchange makes it possible to modify the nature and the relative content of these metal species. Electronic properties of the resulting copper species strongly depend on both the Zn/Cu ratio and the order of exchange of metal ions. The knowledge we have obtained will be useful for designing of new effective catalysts based on copper-exchanged zeolites.

Angle-resolved X-ray photoelectron spectroscopy intensity modeling of SiNx ultrathin layer grown on Si (100) and Si (111) substrates by N2 plasma treatment

In this work, we investigate the silicon nitridation process using a N2 plasma Glow Discharge Source (GDS) in an ultra-high vacuum chamber. In situ Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS) measurements were performed to determine various chemical environments of the surface species. The main goals of this study are determination of the film chemical composition, to estimate its thickness and identify various phenomena taking place during the nitridation process under different experimental conditions. To achieve these objectives, we developed an ARXPS intensity model for an ultrathin SiNx overlayer. Based on the ARXPS results, which indicate that the silicon nitride film is not homogenous, we adopted a bi-layer model composed of two SixNyOz layers with varying thickness and chemical composition. The model is built from analysis of photoelectron intensities, considering a comparison between experimental and theoretical data. This bi-layer model revealed that the silicon nitride layer consists of a surface layer composed of approximately equal amounts of silicon and nitrogen (50% each), and an interfacial layer containing varying amounts of oxygen depending on experimental parameters. The presence of oxygen is due to residual air contamination in the vacuum chamber and/or to Si native oxide. The estimated thickness of silicon nitride film is less than 9 nm, depending on the nitridation time and temperature.The model developed in this work enabled us to study the effects of initial surface state (as received or chemically cleaned), Si substrate crystallographic orientation (such as (100) and (111)), and the nitridation temperature (room temperature and 500°C). The diffusing species (N+, N2+, O+), which play a crucial role during nitridation, were found to be influenced by temperature, treatment time, and substrate orientation. The diffusion phenomenon competed with other processes such as NO desorption, leading to a significant impact on formation of the SiNx film. Furthermore, we compared the thickness obtained from the ARXPS model using cross-sectional High-Resolution Transmission Electron Microscopy (HR-TEM) images. Additional Low-Energy Electron Diffraction (LEED) measurements indicated that the SiNx film was amorphous.

Theoretical insights into the structural, electronic and gas-sensing properties of Sc-decorated black phosphorus via strain engineering

Structural and electronic properties of Sc-decorated black phosphorus (SP) and its gas sensing for NO molecule were investigated using density functional theory with the emphasis on the response to applied strain. It found that SP transformed into indirect bandgap semiconductor, and converted into a metal characteristic under strain. SP showed strong interaction with the NO with a high adsorption energy of −2.92 eV since the orbital hybridization and extensive charge transfer, and exhibited 3.3-fold sensitivity compared to black phosphorus, suggesting that SP was a potential NO sensor. Furthermore, strain engineering provided an effective route to facilitate the desorption of NO.

Spin modulation of single Fe atoms with thiolate‐poisoned Pd nanoclusters for highly efficient ammonia synthesis

AbstractNitrate reduction toward ammonia is pivotal in energy and environmental domains but faces challenges in achieving simultaneous high selectivity and activity. Manipulating interactions between intermediates and metal species is deemed effective for catalytic enhancement. In this study, a uniformly configured Fe1‐N4 single‐atom catalyst with four‐coordination was synthesized. Subsequent deposition of thiol‐poisoned Pd nanoclusters provided a platform to investigate the neighboring effect of Pd nanoclusters, excluding activity influences from Pd catalysts. Through this neighbor engineering, the Fe 3d electron spin configuration shifted from low spin to medium spin (MS). Experimental and theoretical analyses affirmed that MS Fe species optimized nitrate reduction by enhancing the *NO desorption process. This spin‐modulated Fe single‐atom catalyst demonstrated superior activity (392.16 mmol−1 gcat−1 h−1, ~40 mol−1 gFe−1 h−1) and a Faraday efficiency of 98.6% at −0.5 V vs. RHE, surpassing reported values. This study presents a promising strategy for nitrogen‐chemistry transition metal catalysts.

A DFT study on Cu-ZSM-5 as a catalyst for NO decomposition: Possible activity of a Cu(I) pair located at the T3 tetrahedral sites

The decomposition of NO catalysed by Cu+ pairs coordinated at the Al-substituted T3 sites of the 10-membered rings of Cu-ZSM-5 was studied by means of DFT/ONIOM calculations. Three mechanisms for NO decomposition were defined on the active site, all based on the formation and further decomposition of an hyponitrite anion, which gives the N2O molecule and a [Cu‒O‒Cu]2+ bridge, where both copper ions are oxidized. N2O can react with the oxidized active site according to two different spin-allowed mechanisms which give immediately the products, N2 + O2. Otherwise, N2O reacts with a new reduced site according to a spin-forbidden mechanism which gives N2 and a second [Cu‒O‒Cu]2+ bridge. When the latter mechanism occurs, reduced sites are restored by further reaction of [Cu‒O‒Cu]2+ with NO and desorption of NO2, which is finally decomposed on a second [Cu‒O‒Cu]2+ site, giving O2 + NO. Turnover frequencies (TOFs) calculated by means of the Energetic Span model showed that one of the spin-allowed mechanisms should be relatively fast, whereas the spin-forbidden one is expected to be extremely slow. Computational results were discussed with reference to experimental data available in the literature.

Unveiling the roles of distinct active sites over Pd/SSZ-13 for low-temperature NOx adsorption

Pd-based zeolites are attractive candidates for passive NOx adsorbers to reduce NOx emission from vehicle exhausts at low temperature. However, it is not well understood the NO adsorption/desorption mechanism in the presence of H2O and CO, which are constant components in diesel exhaust. In this study, an initial Pd/SSZ-13 sample was treated by reduction in H2 and then oxidation in NO to obtain a hydrophilic Pd/SSZ-13 with mostly Z[Pd2+(OH)] sites, or by thermal aging at 750 °C to prepare a hydrophobic Pd/SSZ-13 dominated by Z2Pd2+ and Z[Pd2+(OH)] sites. The two distinct Pd/SSZ-13 catalysts were characterized by XRD, H2-TPR, 27Al MAS NMR, and in situ DRIFTS spectra of CO adsorption, etc. Furthermore, the NOx adsorption/desorption reaction experiments and in situ DRIFTS studies were carried out on the two Pd/SSZ-13 catalysts under various conditions to explore the role of Z2Pd2+ and Z[Pd2+(OH)] sites in NO adsorption in the presence of H2O or co-existence of H2O and CO. Additionally, the recovery of active Pd sites after NO desorption was studied.

The fabrication of Mn single atoms/clusters on Al2O3 for enhanced catalytic NO oxidation

The exploitation of transitional metal catalysts for high-efficient conversion of NO to NO2 still persists as an imperative issue due to the high cost of currently used Pt–based catalysts. Herein, we report a TEA-modification strategy to anchor Mn single atoms/clusters on Al2O3 (Mn/Al2O3-T) for NO oxidation. Activity tests show that Mn/Al2O3-T (T83 = 275 °C) displays a superior NO-to-NO2 capacity compared with the unmodified Mn nanoparticle on Al2O3 (Mn/Al2O3-B, T66 = 300 °C) and Pt/Al2O3 (T43 = 350 °C) counterparts. Comprehensive characterization and DFT calculations discover that the effective adjustment of TEA can promote the generation of coordination unsaturated Mn sites with elongated Mn-O bonds, which can improve the mobility of surface lattice oxygen and facilitate the activation of molecular oxygen. Additionally, reducing Mn size from nanoparticles to single atoms/clusters favors the formation of labile nitrate species and facile desorption of NO2, thereby regenerating active sites and accelerating overall NO oxidation reaction.

NO2 gas response and recovery properties of ambipolar CNT-FETs with various CNT/CNT junctions

Gas sensors based on ambipolar carbon nanotube (CNT) field-effect transistors with various amounts of CNTs were fabricated by dielectrophoretic assembly. The nitrogen dioxide (NO2) gas response and recovery properties of the transistors were measured to investigate the effect of CNT amount on gas response. For the device with a small amount of CNTs, responses from the CNT bulk and CNT/electrode contacts were observed. For devices with a large amount of CNTs, in which a network-like structure of CNTs was observed near the electrodes, an increased current in both electron and hole conduction regions was observed compared with that for the device with a small amount of CNTs. The increased current in the electron conduction region rapidly decreased during recovery. This response is consistent with that of CNT/CNT X-type contacts, which have a high resistance before NO2 adsorption. Equivalent circuits of CNT channels with CNT/CNT contacts were developed, allowing the transistor behavior to be qualitatively discussed. Evaluation of time constants revealed that CNT/electrode contacts and CNT/CNT X-type contacts exhibited high NO2 adsorption and desorption rates, respectively.

A simple redox model of low-T NO + CO adsorption onto Pd-CHA as effective Passive NOx Adsorbers

Pd-exchanged chabazite (Pd-CHA) catalysts show NO adsorption and desorption features which comply well with the requirements for low-T Passive NOx Adsorber (PNA) applications. An earlier work based on transient adsorption...

Comparative study on gas-sensing properties of amorphous MoS2 nanoparticles and crystalline MoS2 nanoflowers

High-performance gas sensors for the field of gas sensing have drawn a lot of attention to molybdenum sulfide materials, but there is little research on the influence of crystallization state of MoS2 on gas sensitivity performance. In this study, amorphous MoS2 and crystalline MoS2 were prepared by the hydrothermal method. Then, the gas-sensing characteristics of the as-synthesized amorphous MoS2 and crystalline MoS2 toward NO2 gas were thoroughly investigated and compared. According to the results, with an excellent response value of 1.99 toward 5 ppm NO2 at room temperature, the crystalline MoS2 gas sensor outperformed the amorphous one, while that of the amorphous MoS2 under the same condition was 1.25. However, Four times faster recovery periods were observed in the amorphous MoS2 sample compared to the crystalline MoS2 sample. At the same time, the recovery level of amorphous MoS2 is high and can be fully restored. We discovered that the primary cause of the strong recovery performance of amorphous MoS2 is the presence of localized states that facilitate the easy transition of electrons from the conduction band to the valence band, allowing for effective recombination with the holes. Additionally, the surface of the material absorbs a significant amount of oxygen, which will occupy more of the NO2 adsorption site and hasten the desorption of NO2. This work may aid in the development of gas sensors based on amorphous molybdenum sulfide.

Electrification-Enhanced Low-Temperature NOx Storage-Reduction on Pt and K Co-Supported Antimony-Doped Tin Oxides.

NOx storage-reduction (NSR), a promising approach for removing NOx pollutants from diesel vehicles, remains elusive to cope with the increasingly lower exhaust temperatures (especially below 250 °C). Here, we develop a conceptual electrified NSR strategy, where electricity with a low input power (0.5-4 W) is applied to conductive Pt and K co-supported antimony-doped tin oxides (Pt-K/ATO), with C3H6 as a reductant. The ignition temperature for 10% NOx conversion is nearly 100 °C lower than that of the traditional thermal counterpart. Furthermore, reducing the power in the fuel-lean period relative to that in the fuel-rich period increases the maximum energy efficiency by 23%. Electrically driven release of lattice oxygen is revealed to play vital roles in multiple steps in NSR, including NO adsorption, desorption, and reduction, for improved NSR activity. This work provides an electrification strategy for developing high-activity NSR catalysis utilizing electricity onboard hybrid vehicles.

Pd, Ag decorated MoSi2N4 monolayer: A potential material for reusable CO and NO gas-sensitive material with high sensitivity

Recently, a novel MoSi2N4 monolayer has been successfully synthesized (Science 369, 670, 2020) and exhibits excellent photoelectric property. Motivated by this, the adsorption characteristics and sensing properties of four toxic gases (CO, NO, NO2, SO2) on the Pd and Ag doped MoSi2N4 (Pd-MSN and Ag-MSN) monolayers were systematically investigated by DFT computations, which aims to explore their feasibility as a potential gas-sensitive material. The studied results show that the Pd-MSN and Ag-MSN monolayers possess high stability due to the large binding strength. The SO2 molecule is physically adsorbed on the Pd-MSN and Ag-MSN surface with Eads of −0.43 and −0.45 eV. However, the chemisorption of CO, NO, NO2 on the surface can be found with the Eads of −0.73 eV ∼ −1.24 eV, and the strong surface bonding force is mainly contributed by the significant hybridizations between N-p orbital of Pd/Ag-MSN and p orbitals of CO, NO, NO2. Moreover, the Pd-MSN and Ag-MSN monolayers are highly sensitive to CO and NO molecules due to their great change in electrical conductivity and work function. Additionally, the recovery time of NO and CO in Pd-MSN system is respectively predicted to be 0.03 and 0.12 s at room temperature, whereas the rapid desorption of NO and CO from Ag-MSN surface requires the help of high temperature. Therefore, the Pd-MSN monolayer can be a promising gas-sensitive material with excellent sensitivity for the detection of CO and NO. Those studied results can provide a theoretical guidance for the designing of MoSi2N4 based gas sensors.

An Assessment of Zeolite Framework Effect for Low-Temperature NOX Adsorbers

Pd-promoted zeolites (Y, ZSM-5, FER, SSZ-13) were prepared and characterized to analyze their properties as low-temperature NOx adsorbers. The samples were investigated by BET and XRD and by in situ FT-IR spectroscopy of CO and NO adsorption to probe the Pd sites and the nature of the adsorbed NOx species. The NOx adsorption/desorption performances at low temperatures were examined by microreactor measurements upon NO/O2 adsorption followed by TPD in the presence of water and carbon dioxide. It was enlightened that: (i) the zeolite framework influences the Pd dispersion: the smaller the zeolite cage, the higher the Pd dispersion, irrespective of the Si/Al ratio. Accordingly, the following Pd dispersion order has been observed, inversely to the zeolite cage size: Pd/SSZ-13 > Pd/ZSM-5 ~ Pd/FER >> Pd/Y; (ii) Pd is present as isolated Pdn+ species and in PdOx particles; (iii) the Pd dispersion governs the NOx storage capacity: the smaller the zeolite cage, the higher the Pd dispersion and the storage capacity; (iv) NO adsorbs mainly in the form of Pd nitrosyls and nitrates; (v) NO desorption occurs both at a temperature below 200 °C and in a high-temperature range (near 350 °C).

Quantitative Analysis of SO2 and NO2 Adsorption and Desorption on Quartz Crystal Microbalance Coated with Cobalt Gallate Metal-Organic Framework

Quantitative Analysis of SO2 and NO2 Adsorption and Desorption on Quartz Crystal Microbalance Coated with Cobalt Gallate Metal-Organic Framework