Adsorption Of NO Molecules Research Articles

Highly selective sensing of toxic NOx gases for environmental monitoring using Ru-doped single walled TiO2 nanotube: A density functional theory study

Applying density functional theory simulations, in this study, we examine the sensing properties of Ru-TNT surface towards NOx molecules such as NO and NO2. The obtained results show that Ru doping creates a large-spin density over the Ru-TNT surface, which hints at an increase in the adsorption energy of NOx molecules. The electronic properties of the Ru-TNT surface are significantly altered after NO and NO2 molecule adsorption, as proven by the larger change in the energy gap values. Moreover, the selectivity study indicates that the Ru-TNT is capable of selectively sensing the NOx molecules in the presence of other gases, e.g., CO2, CO, NH3 and H2O. Using an external positive electric field can resist the strong anchoring of NOx molecules over the Ru-TNT surface, suggesting that material recovery is feasible. Thus, the Ru-TNT structure can be applied as a selective, sensitive, and promising ambient temperature gas sensor for NOx molecules.

Selective reduction of NO by CO using copper-aluminum oxides from hydrotalcite-type precursors: Study of chemical species and thermal stability

The objective of this work was to analyze the influence of Al on copper catalysts, regarding thermal stability and performance during NO reduction by CO. Two copper-based catalysts were prepared by precipitation and subsequent calcination at 600 °C, with and without aluminum in their composition (CuAl-HT-c and Cu-p). The precursor CuAl-HT was synthesized to obtain a hydrotalcite structure. The catalysts obtained after calcination of the precursors were characterized by N2 physisorption, TPR, N2O titration, in situ XRD and in situ XANES. They showed good catalytic performance, however with Cu-p being the most active but with larger formation of N2O (important greenhouse gas). In this catalyst, the interaction between the adsorbed NO molecules is facilitated, probably due to the higher concentration of Cu+.Regarding the aged catalysts, Cu-p was deactivated due to sintering, which is attributed to the lack of aluminum. CuAl-HT-c-900 had its performance improved during aging, either because the reduction of NO by CO is a structure-sensitive reaction for this catalyst (and the increase in particle size after aging is related to larger activity), or because of the presence of copper aluminate, which can also improve activity and selectivity.

VBF MBenes as promising gas sensor and adsorbent toward CO, CO2, NO, and NO2

MBenes have attracted wide interest because of their potential value the materials, chemistry, and physics domains. In this study, we investigated an VBF material, a member of the MBene family, for gas-sensing applications. The adsorption behavior of CO, CO2, NO, and NO2 molecules on perfect and transition metals (TM; Mn, Fe, Co, Ni)-doped VBF structures was examined using density-functional theory (DFT) calculations. The calculation results indicated that the pristine VBF structure has a weak adsorption capacity toward CO, CO2, NO, and NO2. Thus, introducing TM impurities significantly improved the sensitivity of the VBF substrate to CO, NO, and NO2 gases. Electron localization function (ELF) diagrams showed that the adsorption behaviors at this point are chemisorption. Moreover, the I-V curves showed that the Mn-doped VBF has a good sensitivity to the adsorption of NO molecules. The good sensitivity, suitable recovery time, and high stability indicate that the Mn-doped VBF is an ideal reusable gas sensor for NO molecules. In addition, after seven NO molecules were adsorbed on VBF-Fe and VBF-Co substrates, the systems still maintained a good adsorption capacity. Thus, Fe- and Co-doped VBF can be used to capture the toxic NO gas.

Mesoporous and Encapsulated In2O3/Ti3C2Tx Schottky Heterojunctions for Rapid and ppb-Level NO2 Detection at Room Temperature.

Rapid and ultrasensitive detection of toxic gases at room temperature is highly desired in health protection but presents grand challenges in the sensing materials reported so far. Here, we present a gas sensor based on novel zero dimensional (0D)/two dimensional (2D) indium oxide (In2O3)/titanium carbide (Ti3C2Tx) Schottky heterostructures with a high surface area and rich oxygen vacancies for parts per billion (ppb) level nitrogen dioxide (NO2) detection at room temperature. The In2O3/Ti3C2Tx gas sensor exhibits a fast response time (4 s), good response (193.45% to 250 ppb NO2), high selectivity, and excellent cycling stability. The rich surface oxygen vacancies play the role of active sites for the adsorption of NO2 molecules, and the Schottky junctions effectively adjust the charge-transfer behavior through the conduction tunnel in the sensing material. Furthermore, In2O3 nanoparticles almost fully cover the Ti3C2Tx nanosheets which can avoid the oxidation of Ti3C2Tx, thus contributing to the good cycling stability of the sensing materials. This work sheds light on the sensing mechanism of heterojunction nanostructures and provides an efficient pathway to construct high-performance gas sensors through the rational design of active sites.

Theoretical study of adsorption properties and electrical transport performance of toxic gas molecules on novel orthorhombic BN monolayer semiconductor

The adsorption properties of toxic gases on the surface of low-dimensional nanomaterials are a research hot topic and key issue for developing semiconductor sensors to detect toxic gas molecules. Recently, a novel orthorhombic BN monolayer has attracted extensive attention from researchers. Using first principles calculations, we investigate the adsorption properties of typical toxic gas molecules, such as CO, H<sub>2</sub>S, NH<sub>3</sub>, NO, NO<sub>2</sub>, and SO<sub>2</sub> molecules, on the surface of two-dimensional (2D) orthorhombic BN monolayer adsorption. The calculated adsorption energy show that the adsorptions of the above six molecules on the surface of BN monolayer are energy-favorable exothermic processes. It is found that NO<sub>2</sub> and NH<sub>3</sub> molecules are of chemical adsorption, while other systems are of physical adsorption, and NO adsorbing system exhibits a spin-polarized electronic band structure. The calculated density of states reveals that the adsorption of NO molecule and SO<sub>2</sub> molecule have significant influences on the electronic structure near the Fermi level. Moreover, the adsorption of the NO<sub>2</sub> molecule on the substrate exhibits remarkable variation of the work function, suggesting that the o-BN monolayer possesses excellent selectivity and sensitivity to NO<sub>2</sub> molecule. In addition, we use first principles combined with non-equilibrium Green’s function to simulate the electrical transport properties of monolayered o-BN semiconductor based nanodevice with adsorption of typical toxic gas molecules. The <i>I-V</i><sub>b</sub> curve shows that the current through the nanodevice is 6500 nA for the NO<sub>2</sub> molecule adsorbing system under 1 V bias voltage. The calculation results reveal that the adsorption of NO<sub>2</sub> molecule on the o-BN monolayer can significantly enhance its electrical transport performance, and the o-BN monolayer possesses excellent sensitivity and selectivity to the NO<sub>2</sub> gas molecule. The work function and the charge transfer can be effectively manipulated by tensile strain, indicating its potential application in anisotropic electronics. Our results indicate that the o-BN monolayer has excellent adsorption performance to toxic gases, showing its practical application in capturing toxic gas molecules as a gas sensor in future.

Microscopic Mechanism of Fe2O3-Catalyzed NO Reduction during Sludge Combustion: A Density Functional Theory Study

Systematic studies on the mechanism underlying Fe2O3-catalyzed NO reduction in a reducing atmosphere during sludge combustion remain limited. In this study, density functional theory was employed to investigate the adsorption properties of NH3, CO, and NO on the α-Fe2O3(001) surface, and the mechanisms underlying the NH3 and CO reduction of NO during the adsorption process. The results demonstrated that NH3, CO, and NO chemically adsorbed on the surface Fe top site, thereby generating distinctly high adsorption energies. NO exhibited the highest adsorption energy. With regard to the catalytic mechanisms of NH3 and CO during NO reduction, the α-Fe2O3(001) surface exhibited different characteristics. NH3 reduction of NO tended to follow the Eley–Rideal (E-R) mechanism. The dissociation of -NH2NO is the rate-determining step for the NH3 reduction of NO. The presence of α-Fe2O3(001) reduced the dissociation energy barriers of NH3 and NH2NO, thereby catalyzing the reduction reaction. In contrast, NO dissociation was more challenging during the CO reduction of NO. The α-Fe2O3(001) surface reduced the dissociation barrier of the NO-NO dimer from 2.04 to 1.53 eV. Two adsorbed NO molecules first formed NO-NO dimers; these then dissociated into N2O and atomic oxygen, thereby catalyzing the reduction reaction.

Unveiling Pseudo‐Inert Basal Plane for Electrocatalysis in 2D Semiconductors: Critical Role of Reversal‐Activation Mechanism

AbstractPartially occupied orbitals play a pivotal role in enhancing the performance of electrocatalyst by facilitating electron acceptance and donation, thus enabling the activation of molecular bonds. According to this principle, the basal plane of most 2D semiconductors is inert for electrocatalysis because of the fully occupied orbitals at the surface. Here, taking monolayer CrX (X = P, As, Sb) and Cr2PY (Y = As, Sb) as examples and through first‐principles calculations, it is revealed that even with fully occupied surface orbitals, the basal planes exhibit remarkable catalytic activity for the nitrogen oxide reduction reaction (NORR). This leads to the concept of the pseudo‐inert electrocatalyst. The underlying physics behind such pseudo‐inert character can be attributed to the reversal‐activation mechanism: contrary to conventional expectations, the adsorbed NO molecule reversely triggers the activity of the inert basal plane first, and then the basal plane activates NO molecules, forming the intriguing “Reversal Activation‐Transfer‐Donation‐Backdonation” process. This study further predicts that such pseudo‐inert character can demonstrate many distinctive properties, for example, it can introduce a novel type of surface catalysis, one that selectively targets radicals possessing an inherent dipole moment such as NO. The explored phenomena and insights greatly enrich the realms of electrocatalysis and 2D materials.

Ce-doped ZnO nanostructures: A promising platform for NO2 gas sensing

In this comprehensive study, Ce-doped ZnO nanostructures were hydrothermally synthesized with varying Ce concentrations (0.5%, 1.0%, 1.5%, and 2.0%) to explore their gas-sensing capabilities, particularly towards NO2. Structural characterization revealed that as Ce doping increased, crystal size exhibited a slight increment while band gap energies decreased. Notably, the 0.5% Ce-doped ZnO nanostructure demonstrated the highest NO2 gas response of 8.6, underscoring the significance of a delicate balance between crystal size and band gap energy for optimal sensing performance. The selectivity of the 0.5% Ce-doped ZnO nanostructures to NO2 over other gases like H2, acetone, NH3, and CO at a concentration of 100 ppm and an optimized temperature of 250 °C was exceptional, highlighting its discriminatory prowess even in the presence of potential interfering gases. Furthermore, the sensor displayed reliability and reversibility during five consecutive tests, showcasing consistent performance. Long-term stability testing over 30 days revealed that the gas response remained almost constant, indicating the sensor's remarkable durability. In addition to its robustness against humidity variations, maintaining effectiveness even at 41% humidity, the sensor exhibited impressive response and recovery times. While the response time was swift at 11.8 s, the recovery time was slightly prolonged at 56.3 s due to the strong adsorption of NO2 molecules onto the sensing material hindering the desorption process. The study revealed the intricate connection between Ce-doping levels, structure, and gas-sensing. It highlighted the 0.5% Ce-doped ZnO nanostructure as a highly selective, reliable, and durable NO2 gas sensor, with implications for future environmental monitoring and safety.

Theoretical evaluation of gas sensing and capturing characteristics on the point defective diboron dinitride monolayer

Defects can significantly alter the properties of 2D material surfaces, thereby affecting the application results. In this work, the adsorption behaviors of H2S, SO2, NH3, and NO2 gas molecules on rationally defective diboron dinitride (n-BN) monolayers in the presence and absence of an external electric field and moisture condition are studied by the first-principles calculation approach. The results demonstrate that the boron and nitrogen defects are more likely to be generated and both defective monolayers have strong absorption effects on SO2 and NO2 gas molecules with absolute values of adsorption energy above 2.5 eV. And the conductivity change after adsorption of NO2 molecule is particularly pronounced in nitrogen defect monolayer, thus greatly increasing the sensitivity to the gas molecule. Based on the high sensitivity, the defective monolayer could be an ideal one-time scavenger for SO2 and NO2 gas molecules. While the H2S and NH3 molecules could obtain the appropriate adsorption energy and the adjustable recovery time on the defective monolayer under the dry or existent external electric field environment. These results make it possible to design a useable gas device with good gas sensing and capturing characteristics on the defective n-BN monolayer.

Effect of metal (Zn and Co) doped/co-doped on Ti3C2O2 MXene to NO gas sensing capability: A DFT study

The gas-sensitivity of ammonia, nitric oxide, nitrogen dioxide, methane, and formaldehyde on pristine Ti3C2O2 and transition metal-doped Ti3C2O2 were studied systematically by density functional theory (DFT). The electron density and density of states of the adsorption systems were further analyzed to study the sensing performance. The obtained results reveal that doping with transition metals (TM = Co, Zn) to pristine Ti3C2O2 could significantly enhance the adsorption abilities of Ti3C2O2, leading to a stronger interaction between gas molecules and Ti3C2O2. Among all systems, the adsorption of NO molecule by Zn–Co co-doped Ti3C2O2 is significantly improved. The results of the density of states and charge density difference certify the charge of the surface charge distribution of Zn and Co modified Ti3C2O2. Calculated electronic properties for studied systems indicate that Zn–Co co-doped Ti3C2O2 presents high sensitivity to NO molecules. The results showed that Zn–Co co-doped Ti3C2O2 MXene is an excellent material for NO sensors.

First‐Principles Investigation of NO Molecule Adsorption on As6/Sb6 and Sb6/Bi6 Lateral Heterostructures

Predicting and designing highly gas‐sensitive semiconductors is crucial for solving growing environmental problems. Herein, four lateral heterostructures (LHSs), As6/Sb6 AC‐/ZZ‐LHSs and Sb6/Bi6 AC‐/ZZ‐LHSs, are constructed. The adsorption of NO molecule on these LHSs is investigated using first‐principle calculations. The results indicate that the adsorption of NO molecule on As6/Sb6 LHS with armchair (AC) interface is physisorption, whereas NO molecule is chemically adsorbed on As6/Sb6 LHS with zigzag (ZZ) interface and Sb6/Bi6 AC‐/ZZ‐LHSs, with strong adsorption energy and large charge transfer. All LHSs act as charge donors for the NO molecule. Meanwhile, the adsorption of NO molecule causes a significant change in the electronic properties of As6/Sb6 ZZ‐LHS and Sb6/Bi6 AC‐/ZZ‐LHSs, which shows that these LHSs have great potential for application in NO gas sensors.

Modulation of Uptake and Reactivity of Nitrogen Dioxide in Metal-Organic Framework Materials.

We report the modulation of reactivity of nitrogen dioxide (NO2 ) in a charged metal-organic framework (MOF) material, MFM-305-CH3 in which unbound N-centres are methylated and the cationic charge counter-balanced by Cl- ions in the pores. Uptake of NO2 into MFM-305-CH3 leads to reaction between NO2 and Cl- to give nitrosyl chloride (NOCl) and NO3 - anions. A high dynamic uptake of 6.58 mmol g-1 at 298 K is observed for MFM-305-CH3 as measured using a flow of 500 ppm NO2 in He. In contrast, the analogous neutral material, MFM-305, shows a much lower uptake of 2.38 mmol g-1 . The binding domains and reactivity of adsorbed NO2 molecules within MFM-305-CH3 and MFM-305 have been probed using in situ synchrotron X-ray diffraction, inelastic neutron scattering and by electron paramagnetic resonance, high-field solid-state nuclear magnetic resonance and UV/Vis spectroscopies. The design of charged porous sorbents provides a new platform to control the reactivity of corrosive air pollutants.

Modulation of Uptake and Reactivity of Nitrogen Dioxide in Metal‐Organic Framework Materials

AbstractWe report the modulation of reactivity of nitrogen dioxide (NO2) in a charged metal–organic framework (MOF) material, MFM‐305‐CH3 in which unbound N‐centres are methylated and the cationic charge counter‐balanced by Cl− ions in the pores. Uptake of NO2 into MFM‐305‐CH3 leads to reaction between NO2 and Cl− to give nitrosyl chloride (NOCl) and NO3− anions. A high dynamic uptake of 6.58 mmol g−1 at 298 K is observed for MFM‐305‐CH3 as measured using a flow of 500 ppm NO2 in He. In contrast, the analogous neutral material, MFM‐305, shows a much lower uptake of 2.38 mmol g−1. The binding domains and reactivity of adsorbed NO2 molecules within MFM‐305‐CH3 and MFM‐305 have been probed using in situ synchrotron X‐ray diffraction, inelastic neutron scattering and by electron paramagnetic resonance, high‐field solid‐state nuclear magnetic resonance and UV/Vis spectroscopies. The design of charged porous sorbents provides a new platform to control the reactivity of corrosive air pollutants.

Reaction mechanism of selective catalytic reduction of NO with NH3 on Fe3O4 (1 1 1) surface: Experimental and DFT studies

Iron-based catalysts have vast potential for application prospect in selective catalytic reduction of NOx with NH3 (NH3-SCR). These catalysts offer excellent SCR activity at medium and high temperatures, N2 selectivity and environmental performance. Among these catalysts, Fe3O4 catalyst is highly active and significant in the denitration reaction due to the presence of both ferrous and ferric ions. This study utilized density functional theory (DFT) in combination with experimental measurements to investigate the reaction pathway of NH3-SCR on the Fe3O4(111) surface. The research found that the surface was favorable for the adsorption of NO molecules and followed the NO activation mechanism. Upon activation of NO at the Feoct site, it reacted with NH3 to form NH2NO, This compound then underwent decomposition into N2 and H2O. The presence of O2 on the catalyst facilitated the surface dehydrogenation reaction and completed the SCR cycle reaction. Based on the DFT results, the formation of NH2NO intermediate was the rate-determining step of SCR reaction. The Fe3O4(111) surface followed the L-H mechanism, which was in line with the experimental results. This study provided novel insights into the SCR reaction process and can be useful in developing new iron-based SCR catalysts.

Nanocomposites of Quasicrystal Nanosheets and MoS2 Nanoflakes for NO2 Gas Sensors

Nitrogen dioxide (NO2) is one of the air pollutant gases that harms the environment, human health, and the world ecosystem. The main source of NO2 emission is the combustion engine, and therefore, it requires a gas-sensing device to monitor the emission. Herein, we report a highly sensitive and selective NO2 sensor by low-cost and scalable fabrication methods using a hybrid nanocomposite of two-dimensional (2D) Al70Co10Fe5Ni10Cu5 quasicrystal (QC) nanosheets and MoS2 nanoflakes. The 2D-QC nanosheets combined with MoS2 nanoflakes form a heterostructure, which improves the gas sensor’s performance. The Al70Co10Fe5Ni10Cu5/MoS2 heterostructure showed an excellent gas-sensing response (ΔR/Ra %) of ∼66%, which is about 2.27 times higher than that of the pristine MoS2 nanoflakes-based sensor for 100 ppm NO2 at 100 °C. In addition, the hybrid nanocomposite gas sensor device also exhibited high selectivity and good sensitivity. The improvement in the gas sensor performance is explained using the density functional theory analysis, which illustrates that the 2D-QC provides a lot of active sites for the adsorption of NO2 molecules, explained using the adsorption energy, charge difference density, and Bader charges analysis. These gas-sensing results emphasize the significance of the integration of the 2D Al70Co10Fe5Ni10Cu5 QC with MoS2 nanoflakes, being useful to the design and development of NO2-based gas-sensing technology and holding great promise in environmental protection.

In situ formation of cocatalytic sites boosts single-atom catalysts for nitrogen oxide reduction

Nitrogen oxide (NOx) pollution presents a severe threat to the environment and human health. Catalytic reduction of NOx with H2 using single-atom catalysts poses considerable potential in the remediation of air pollution; however, the unfavorable process of H2 dissociation limits its practical application. Herein, we report that the insitu formation of PtTi cocatalytic sites (which are stabilized by Pt-Ti bonds) over Pt1/TiO2 significantly increases NOx conversion by reducing the energy barrier of H2 activation. We demonstrate that two H atoms of H2 molecule are absorbed by adjacent Pt atoms in Pt-O and Pt-Ti, respectively, which can promote the cleave of H-H bonds. Besides, PtTi sites facilitate the adsorption of NO molecules and further lower the activation barrier of the whole de-NOx reaction. Extending the concept to Pt1/Nb2O5 and Pd1/TiO2 systems also sees enhanced catalytic activities, demonstrating that engineering the cocatalytic sites can be a general strategy for the design of high-efficiency catalysts that can benefit environmental sustainability.

A theoretical insight into the mechanism of NO heterogeneous reduction on char surface: The catalytic effect of potassium

In this paper, the catalytic effect of K on the NO heterogeneous reduction over char surface was investigated using the quantum chemistry calculation. The adsorption performance and the detailed reaction pathways were obtained via density function theory before and after potassium decorating. Additionally, the mayer bond order, thermodynamic and kinetic analysis were studied to further clarify the effect of K on the NO-char reaction. The calculation results showed that K can promote the adsorption of NO molecules on char surface. It was found that the reaction energy barriers were reduced with the decoration of K, indicating that K can promote the chemical reaction. Four reaction pathways were obtained based on Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms, and the order of reaction activity was as follows: L-H@K > L-H > E-R@K > E-R. Moreover, thermodynamic analysis showed that the reaction equilibrium constants increased with the addition of K, suggesting that the reaction was more complete and irreversible. From kinetic analysis, the reaction rate constants increased with temperature, and the rate of reactions were more faster in the presence of K, which indicated that K can accelerate the NO heterogeneous reduction. Based on the thermodynamic and kinetic performances, it is concluded that K has a significant promotion on the NO heterogeneous reduction by char. The theoretical results systematically reveal the catalytic mechanism of K on the NO reduction by char, which can make contributions to the clean and efficient utilization of the potassium-containing fuels.

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).

Adsorption of NH3 and NO2 Molecules on Sn-Doped and Undoped ZnO (101) Surfaces Using Density Functional Theory

The adsorption and interaction mechanisms of gaseous molecules on ZnO surfaces have received considerable attention because of their technological applications in gas sensing. The adsorption behavior of NH3 and NO2 molecules on undoped and Sn-doped ZnO (101) surfaces was investigated using density functional theory. The current findings revealed that both molecules adsorb via chemisorption rather than physisorption, with all the adsorption energy values found to be negative. The calculated adsorption energy revealed that the adsorption of the NH3 molecule on the bare ZnO surface is more energetically favorable than the adsorption of the NO2 molecule. However, a stable adsorption configuration was discovered for the NO2 molecule on the surface of the Sn-doped ZnO surface. Furthermore, the adsorption on the undoped surface increased the work function, while the adsorption on the doped surface decreased. The charge density redistribution showed charge accumulation and depletion on both adsorbent and adsorbate. In addition, the density of states and band structures were studied to investigate the electronic behavior of NH3 and NO2 molecules adsorbed on undoped and Sn-doped ZnO (101) surfaces.

Urchin-like Bi2S3 nanostructures with rich sulfur vacancies for ppb-level NO2 sensing

The unique features of Bi2S3 enable it to be a promising candidate for preparing high-performance NO2 gas sensors. However, pristine Bi2S3 is usually inert for effective detection of ppb-level NO2 at room temperature owing to the lack of active sites. Herein, urchin-like Bi2S3 nanostructures with rich-defects were designed and prepared by a one-step hydrothermal method to realize ppb-level NO2 detection at room temperature. The optimal sensor based on urchin-like Bi2S3 with sulfur defects demonstrated an ultrahigh sensing response of 21.7 (almost 13 times higher than that of pristine Bi2S3) and a short response/recovery time of 42/36 s to 1 ppm NO2. In addition, an ultralow theoretical detection limit of 3 ppb was achieved for the sensor. The improved sensing performance could be ascribed to the numerous sulfur vacancies and the distinctive hierarchical structures, which promote the adsorption of NO2 molecules and boost charge transfer between NO2 and Bi2S3. This study would provide a new perspective on nanostructured materials for NO2 sensing at room temperature.