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In this study, we demonstrate the emergence of NO2 gas sensing capabilities in the typically non-active NiWO4, a strongly correlated electron system (SCES), by introducing substitutional Fe at the Ni site. NiWO4 typically exhibits strong Coulombic repulsion between Ni atoms, resulting in a large band gap of over 3.0 eV and insulating behavior. This correlated behavior is clearly reflected in the significant increase of band gap when considering the Hubbard U correction for the cations, bringing the theoretical value closer to the observed value. The single-phase Fe0.5Ni0.5WO4 displays a notable shift in the [NiO6] symmetric vibration mode and an increase in magnetization. Additionally, theoretical calculations confirm the preservation of the wide band gap, with the Fe and O levels generated within the band gap. These findings indicate that Fe located in the Ni sites modulate Coulombic repulsion in NiWO4 SCES insulators. Unlike the poor gas-sensing performance of intrinsic NiWO4, Fe0.5Ni0.5WO4 exhibits a significant NO2 response (Rg/Ra) of 11 at 200°C than other gases and a limit of detection (LOD) of 46.4 ppb. This study provides a pathway for realizing gas-sensing performance in strongly correlated electron insulators with large band gaps through the introduction of dopant levels at the cation sites. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide (NO 2) is a significant air pollutant with a notable environmental impact, necessitating precise monitoring. However, most existing NO 2 sensing materials exhibit low sensitivity and require high-temperature operation. In this study, we employed a hydrothermal and co-precipitation method to synthesize a novel ternary nanocomposite, In 2 O 3 /SnO 2 nanoparticles (NPs)/fluorine-doped carbon quantum dots (F-CDs). By varying the mass ratio of In 2 O 3 to SnO 2 NPs, we investigated the gas-sensing performance of the composite towards NO 2. The results demonstrate that when the ratio of SnO 2 and In 2 O 3 reaches to 1 : 2, the 2-In 2 O 3 /SnO 2 /F-CDs gas sensor exhibited the highest response, excellent selectivity, and remarkable stability under ultraviolet (UV) light irradiation at room temperature (∼25 °C). Furthermore, the response of the 2-In 2 O 3 /SnO 2 /F-CDs gas sensor displayed a strong linear relationship with the concentration of NO 2 gas. At a NO 2 gas concentration of 3 ppm, the sensitivity was 238, which is significantly higher than that of In 2 O 3 /SnO 2 NPs and In 2 O 3 sensors. The response time and recovery time were measured at 62 s and 33 s, respectively. Finally, based on experimental characterization results and band structure analysis, we confirmed the promising effects of ternary nanocomposite in enhancing gas sensing. [ABSTRACT FROM AUTHOR]

In this study, we have synthesized CuO, ZnO, and CuO@ZnO composites with different mole ratios of CuO and ZnO, like CZ11 (1:1), CZ21 (2:1), and CZ12 (1:2) for NO2 gas sensing. Furthermore, the synthesized CuO, ZnO, and CuO@ZnO composites have been mixed with 10 wt% rGO. For electrical measurements, thin films of the synthesized samples have been fabricated by drop casting method which is abbreviated as CuO/rGO, ZnO/rGO, CZG11, CZG21, and CZG12. The measured percentage response values of CuO/rGO, ZnO/rGO, CZG11, CZG21, and CZG12 for 10 ppm NO2 gas at room temperature are 30, 45, 56, 55 and 77, respectively. Thus, among these samples, CZG12 has the best percentage response, approximately 2.6 and 1.7 times greater than CuO/rGO and ZnO/rGO sensors, with a response time of 13 s. XPS results confirm that this sample has more oxygen vacancies as compared to bare CZ12. Moreover, we investigated the sensing behavior of the CZG12 sensor at different temperatures (27–100 °C) and relative humidity (RH) levels (20–95%). The sensor shows a better percentage response at room temperature and for intermediate humidity (∼50%) levels. Additionally, at room temperature, the sensor shows negligible response to other gases such as NH3, CO, H2S, and Cl2, proving its excellent selectivity towards NO2 gas. Moreover, it has been observed that after 100 days, the response is almost constant, suggesting the long-term stability of this sensor. The remarkable gas sensing capabilities of CZG12 sensor strongly imply its immense potential for environmental surveillance and regulation. [ABSTRACT FROM AUTHOR]

Highly sensitive p -MoS 2 /n-MoO 3 nanocomposite-based chemo-resistive gas sensors are synthesized by varying the reducing agents using hydrothermal synthesis followed by thermal annealing in an Ar environment for NH 3 and NO 2 detection at 50 °C. Structural characterizations confirmed the existence of MoS 2 nanoflakes and MoO 3 nanoplatelets and the appearance of abundant oxygen adsorption sites and sulfur vacancies in the nanocomposites. The MoS 2 :MoO 3 -based sensor (without any reducing agent) showed preferential detection of NH 3 with 52% sensor response for 5 ppm gas concentration having response/recovery times of 28 s/97 s with n-type sensing behavior dominated by MoO 3 charge carriers. On the contrary, NO 2 gas attracts electrons from the MoS 2 surface, exhibiting p-type sensing behavior with a sensor response of 42 % consisting of response/recovery times of 56 s/116 s with 5 ppm concentration at 50 °C. More interestingly, different adsorption sites and conductive channels play a huge role in the MoS 2 :MoO 3 nanocomposite for exhibiting opposite sensing behaviours upon exposure to NH 3 and NO 2 gases. Enhanced sensitivity is dedicated to synergistic effects appearing due to the construction of p-n heterojunction to strengthen carrier transport by enhancing the sensor response. The present work provides a unique methodology for constructing MoS 2 :MoO 3 -based sensors and the effect of reducing agents on various MoS 2 :MoO 3 -based sensors. Moreover, our study recommends the plausible use of the MoS 2 :MoO 3 composite-based heterojunctions to provide a constructive strategy for improving the performance of gas sensors. [ABSTRACT FROM AUTHOR]

The development of low-cost and low-power gas sensors for reliable NO2 gas detection is important due to the highly toxic nature of NO2 gas. Herein, initially, SnO2 nanowires (NWs) were synthesized through a simple vapor–liquid–solid growth mechanism. Subsequently, different amounts of SnO2 NWs were composited with MoS2 nanosheets (NSs) to fabricate SnO2 NWs/MoS2 NS nanocomposite gas sensors for NO2 gas sensing. The operation of the sensors in self-heating mode at 1–3.5 V showed that the sensor with 20 wt.% SnO2 (SM-20 nanocomposite) had the highest response of 13 to 1000 ppb NO2 under 3.2 V applied voltage. Furthermore, the SM-20 nanocomposite gas sensor exhibited high selectivity and excellent long-term stability. The enhanced NO2 gas response was ascribed to the formation of n-n heterojunctions between SnO2 NWs and MoS2, high surface area, and the presence of some voids in the SM-20 composite gas sensor due to having different morphologies of SnO2 NWs and MoS2 NSs. It is believed that the present strategy combining MoS2 and SnO2 with different morphologies and different sensing properties is a good approach to realize high-performance NO2 gas sensors with merits such as simple synthesis and fabrication procedures, low cost, and low power consumption, which are currently in demand in the gas sensor market. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate the emergence of NO2 gas sensing capabilities in the typically non-active NiWO4, a strongly correlated electron system (SCES), by introducing substitutional Fe at the Ni site. NiWO4 typically exhibits strong Coulombic repulsion between Ni atoms, resulting in a large band gap of over 3.0 eV and insulating behavior. This correlated behavior is clearly reflected in the significant increase of band gap when considering the Hubbard U correction for the cations, bringing the theoretical value closer to the observed value. The single-phase Fe0.5Ni0.5WO4 displays a notable shift in the [NiO6] symmetric vibration mode and an increase in magnetization. Additionally, theoretical calculations confirm the preservation of the wide band gap, with the Fe and O levels generated within the band gap. These findings indicate that Fe located in the Ni sites modulate Coulombic repulsion in NiWO4 SCES insulators. Unlike the poor gas-sensing performance of intrinsic NiWO4, Fe0.5Ni0.5WO4 exhibits a significant NO2 response (Rg/Ra) of 11 at 200°C than other gases and a limit of detection (LOD) of 46.4 ppb. This study provides a pathway for realizing gas-sensing performance in strongly correlated electron insulators with large band gaps through the introduction of dopant levels at the cation sites.

In this work, the impact of thiourea (TU) concentration (0.1, 0.15, and 0.2) M on the structure, surface topography, and morphology of CdS-PVA nanocomposites NCs thin film was investigated. Crystal structure (XRD) results revealed that all films had a polycrystalline structure of CdS phase with the presence of PVA wide peak at 2θ 22°. The crystallite size was increased (10–14) nm with an increase in the TU concentrations. The AFM results revealed that the film's roughness and the Root Mean Square (RMS) roughness was increased as TU concentrations increased. The FESEM results showed that the surface morphology of CdS-PVA films tends to be porous structures, and the pore size increases with the increase of TU concentration. The fabricated CdS-PVA nanocomposite gas sensors were tested at operating temperatures of (100, 200, and 300) °C. The results showed a high sensitivity for NO2 gas at an operating temperature of 200 °C for the TU concentration of 0.2 M and the sensitivity increased as the NO2 gas concentration increased. The novel results are connected with the fabrication of CdS-PVA nanocomposites as good nitrogen dioxide sensors.

In the presented work, the effect of nickel (Ni) and nickel oxide (NiO) nanoparticles on the sensing properties of multi-walled carbon nanotubes (MWCNTs) was studied. The sensor structure, developed on the basis of MWCNTs functionalized with oxygen containing groups, shows 10% sensitivity to nitrogen dioxide (NO2 gas) within 30 s, and the resistance increases under the influence of both oxidizing (NO2) and reducing (NH3) gases. However, after the decoration of the functionalized MWCNTs f-MWCNTs with Ni and NiO their sensing response to NO2 gas at room temperature were recorded 60% (within 20 s) and 107% (within 7 s), respectively and the selectivity was improved many times. The sensing mechanisms of the fabricated f-MWCNTs/Ni and f-MWCNTs/NiO-based sensor structures were explained from physical and chemical viewpoints. It was determined that both Ni and NiO play catalytic roles in the sensing processes of the fabricated f-MWCNTs/Ni and f-MWCNTs/NiO-based sensor structures. [ABSTRACT FROM AUTHOR]

The development of low-cost and low-power gas sensors for reliable NO2 gas detection is important due to the highly toxic nature of NO2 gas. Herein, initially, SnO2 nanowires (NWs) were synthesized through a simple vapor–liquid–solid growth mechanism. Subsequently, different amounts of SnO2 NWs were composited with MoS2 nanosheets (NSs) to fabricate SnO2 NWs/MoS2 NS nanocomposite gas sensors for NO2 gas sensing. The operation of the sensors in self-heating mode at 1–3.5 V showed that the sensor with 20 wt.% SnO2 (SM-20 nanocomposite) had the highest response of 13 to 1000 ppb NO2 under 3.2 V applied voltage. Furthermore, the SM-20 nanocomposite gas sensor exhibited high selectivity and excellent long-term stability. The enhanced NO2 gas response was ascribed to the formation of n-n heterojunctions between SnO2 NWs and MoS2, high surface area, and the presence of some voids in the SM-20 composite gas sensor due to having different morphologies of SnO2 NWs and MoS2 NSs. It is believed that the present strategy combining MoS2 and SnO2 with different morphologies and different sensing properties is a good approach to realize high-performance NO2 gas sensors with merits such as simple synthesis and fabrication procedures, low cost, and low power consumption, which are currently in demand in the gas sensor market.

Nitrogen dioxide (NO2) is part of the nitrogen oxides (NOX) groip, which comprises air pollitants generated by combistion activities. The primary soirces of NO2 are traffic, unvented heaters, and gas stoves among others. This compound poses significant risks to human health and the environment. Moreover, it plays a cricial role in the creation of Acid Rain. The cirrent work is carried oit to stidy the indigenoisly developed condicting polymerbased gas sensor for NO2 detection. The gas sensor fabricated ising condicting polymer sich as Polypyrrole (PPy) as the active layer on the cotton fabric sirface. The effects of washing on the composition and strictire of samples were investigated throigh the application of XRD and FTIR spectroscopy. XRD analysis revealed notable changes in crystal strictire. FTIR analysis provided insights into the molecilar bonds present, highlighting variations in the finctional groips before and after washing. We evaliated the electrical condictivities of samples before and after washing. The key findings shed light on the effects of washing on the chemical structure of gas sensing materials, which is critical for maintaining sensor performance. This paper discusses the gas sensing mechanism and configuration of the sensor. Its threshold limit value (TLV) is 25 ppm and hence detection at low ppm concentration has become the focus of research. [ABSTRACT FROM AUTHOR]

Hydrothermally synthesized In 2 O 3 nanocubes were sensitized with Au and gas sensing performance is analyzed. The Au sensitization was done using sputtering and gas sensing performance is studied as function of different sputtering time. The catalytic activity of Au particles on In 2 O 3 films increases with the sputtering time but acquires saturation at high sputtering time. The Au sensitization with sputtering time of 5 s was found to show improved sensor response (R g / R a) of 8435 than the sensor response of 6876 for pure In 2 O 3 film. The improved sensor response was attributed to the catalytic activity of Au particles on the In 2 O 3 film surface. In addition, Au sensitized In 2 O 3 also demonstrates the sensor response at 60 ppb. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (RGO) nanosheets wrapped around samarium oxide (Sm2O3) nanotubes were successfully synthesized using a facile and environmentally friendly hydrothermal method in this paper. X-ray diffraction, SEM, TEM, high resolution TEM, and X-ray photoelectron spectroscopy were used to characterize all of the prepared nanostructures. The purity of the material synthesized, which is made up of Sm2O3 nanotubes in a single cubic crystalline phase with a mean length of about 450 nm and a diameter of about 50 nm, were verified by additional tests. The synthesized samples were used to fabricate resistive sensors, which were then tested for NO2 and CO2 sensing properties at different concentrations (5–1000 ppm). In comparison to pure RGO and Sm2O3, the experimental results showed that the composite-based Sm2O3/RGO sensor has good sensing properties in terms of response (98.3%), fast response (15 s)/recovery time (12 s), and excellent response repeatability. The formations of p–p heterojunction in the Sm2O3/RGO composite were attributed for the improved sensing performance. [ABSTRACT FROM AUTHOR]

In the present work, pellet sensors of V2O5 nanoparticles and micro flower have been fabricated and electrical as well as NO2 gas sensing properties at the sensor surface were studied. The V2O5 nanostructures were synthesized by facile hydrothermal route using NH4VO3, C2H2O4, HNO3, and PEG precursors. The obtained structures were characterized by X-ray diffraction, Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Spectroscopy (EDX), and Brunauer–Emmett–Teller (BET) analysis. The XRD analysis showed the polycrystalline orthorhombic phase, while FESEM micrographs confirmed the nanoparticle and micro flower morphologies of V2O5. The EDX and elemental mapping analyses confirmed the presence of vanadium and oxygen atoms and their distributions. In addition, the BET analysis revealed a higher surface area of micro flowers (9.12 m2/g) compared to that of the nanoparticles (2.19 m2/g). The electrical and gas sensing measurements at the surface of the sensor showed excellent results and suggested that the pellet fabrication of V2O5 can be utilized for cost-effective, compact, and portable sensor development for environmental applications. [ABSTRACT FROM AUTHOR]

Herein, SnO 2 nanoparticles (NPs) were synthesized from a Sn-metal organic framework (MOF) through a hydrothermal synthesis approach for NO 2 sensing studies. The expected phase, morphology and composition of the SnO 2 NPs were demonstrated via different characterizations. The individual sizes of SnO 2 NPs were ∼20–30 nm, and they had a high surface area (185.31 m2/g). The sensing properties were measured at various temperatures towards NO 2 gas. It showed very high responses of 240.60 and 3984.98–10 and 100 ppm NO 2 , respectively, at 200°C. Also, it still displayed a high response of 47.11–100 ppm NO 2 gas at 25°C. Enhanced response of MOF-derived SnO 2 NPs gas sensor was owing to the high surface area of the SnO 2 NPs, the presence of oxygen vacancies, formation of plenty of SnO 2 -SnO 2 homojunctions and the creation of SnO/SnO 2 heterojunctions. The synthesis method employed in this study led to the preparation of high surface area SnO 2 NPs that can be used for preparing other metal oxides for the development of sensors. • Synthesis of MOF-derived SnO 2 NPs via a hydrothermal route. • The synthesized SnO 2 NPs reveals a high surface area of 185.31 m2/g. • The sensor showed high responses (R g /R a) of 240.6 and 3984.98–10 and 100 ppm NO 2 gas at 200°C, respectively. • The sensor showed a high response of 47.11–10 ppm NO 2 gas at room temperature. • Underlying sensing mechanism was explained in detail. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide (NO 2), a potential source for acid rain and photochemical smog, is known to harm human health, plant growth and crop yield, and the environment. Therefore, designing a room temperature operable NO 2 gas sensor with exceptional sensitivity and selectivity is extremely important. Herein, we report that Ti 3 C 2 T x MXene (T x = –OH, –O, –F, etc.) nanoribbons containing inbuilt anatase TiO 2 on their surfaces achieve highly sensitive detection of NO 2 gas at room temperature with negligible cross-responses to other gas analytes. The MXene nanoribbons' ability to form porous gas sensor film facilitates the efficient diffusion of gas molecules and the sufficient utilization of surface-active sites, leading to a high response of −87.5 % to 50 ppm NO 2 gas exposure with a response time of 9.2 s at room temperature. Signifying the low concentration NO 2 detection abilities, MXene nanoribbons displayed a response of −4.4 % towards 500 ppb NO 2 exposure. MXene nanoribbons' NO 2 gas sensing ability is carrier gas dependent and declines monotonically as operating temperature increases. In addition, the performance comparison experiments conducted at 50 ppm NO 2 gas exposure suggest that the MXene nanoribbons' response is 14.3, 1.6, and 45.3 times higher than the responses of multilayer MXene, MXene-TiO 2 nanoplate, and MXene-TiO 2 nanoparticle structures, respectively. The explicit selectivity and high sensitivity of MXene nanoribbons toward NO 2 gas are expected to provide exciting opportunities for personal safety and environmental monitoring. [Display omitted] [ABSTRACT FROM AUTHOR]

This study investigates the potential of Al-decorated ZnO nanomaterials as a sensing material for detecting noxious nitrogen dioxide (NO 2) gas. A series of samples with varying Al concentrations (0–6 mol%) were synthesized using a simple co-precipitation method. The structural, morphological, and spectral characteristics of the materials were thoroughly characterized using XRD, XPS, FESEM and EDX, HRTEM, BET, FTIR, and UV–Visible spectroscopy techniques. The prepared samples were investigated for the detection of NO 2 gas at various concentrations (1–20 ppm) and at different operating temperatures (140°C–220 °C). Notably, the 2 mol% Al-decorated ZnO nanomaterial exhibited the highest NO 2 gas sensing response, reaching a maximum value of 7.82 at 20 ppm concentration and 180 °C working temperature. The 2 mol% Al-decorated ZnO sensor demonstrated remarkable attributes, including rapid response and recovery times, consistent performance across a broad temperature range, excellent reproducibility, and stability. The study also investigated the mechanism underlying NO 2 gas sensing by Al-decorated ZnO sensors and discussed the findings. The results of this study suggest that Al-decorated ZnO nanorods, particularly the 2 mol% Al-decorated ZnO sensor, have potential for NO 2 gas detection in environmental monitoring and industrial applications. • A range of sensors were synthesized, including pure ZnO and ZnO decorated-aluminium. • The 2 mol% Al-decorated sensor exhibited exceptional performance in detecting hazardous NO 2 gas. • The study explored the sensing mechanism of Al-decorated ZnO sensors for NO 2 gas, offering detailed analysis and discussion. [ABSTRACT FROM AUTHOR]

Ternary systems are less studied for sensing applications due to complex synthesis procedures. However, they have more sources of resistance modulation, leading to an enhanced gas response. In this study, a ternary system, namely Au-decorated ZnO-polyaniline (PANI) composite nanofibers with different amounts of PANI (10, 25, and 50 wt.%) were synthesized for NO2 gas sensing studies. First, ZnO nanofibers were synthesized by electrospinning, and then an Au layer (9 nm) was coated on the ZnO nanofibers. Finally, PANI was coated onto the prepared Au-decorated ZnO nanofibers. NO2 gas sensing investigations indicated that the sensor with 25 wt.% PANI had the best response to NO2 gas at 300 °C. In addition, the optimized sensor exhibited high selectivity to NO2 gas. The improved performance of the optimal gas sensor was attributed to the role of Au, the formation of ZnO-PANI heterojunctions, and the optimal amount of PANI. The promising effect of this ternary system for NO2 sensing was demonstrated, and it can be extended to other similar systems. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate the emergence of NO 2 gas sensing capabilities in the typically non-active NiWO 4 , a strongly correlated electron system (SCES), by introducing substitutional Fe at the Ni site. NiWO 4 typically exhibits strong Coulombic repulsion between Ni atoms, resulting in a large band gap of over 3.0 eV and insulating behavior. This correlated behavior is clearly reflected in the significant increase of band gap when considering the Hubbard U correction for the cations, bringing the theoretical value closer to the observed value. The single-phase Fe 0.5 Ni 0.5 WO 4 displays a notable shift in the [NiO 6 ] symmetric vibration mode and an increase in magnetization. Additionally, theoretical calculations confirm the preservation of the wide band gap, with the Fe and O levels generated within the band gap. These findings indicate that Fe located in the Ni sites modulate Coulombic repulsion in NiWO 4 SCES insulators. Unlike the poor gas-sensing performance of intrinsic NiWO 4 , Fe 0.5 Ni 0.5 WO 4 exhibits a significant NO 2 response (R g /R a ) of 11 at 200°C than other gases and a limit of detection (LOD) of 46.4 ppb. This study provides a pathway for realizing gas-sensing performance in strongly correlated electron insulators with large band gaps through the introduction of dopant levels at the cation sites., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Lee, Kang, Park, Kim, Ji, Choa, Han, Hwang, Lee and Lee.)

The structure model of Al-doped ZnO (001) and (100) surface adsorbing NO2 is constructed. Based on the first-principles method of density functional theory, the energy band, adsorption energy and density of state are calculated using the Castep software package. The Al doping significantly increases the energy and adsorption energy of ZnO(001) and ZnO(100) crystal plane systems, and promotes the transfer of charge from NO2 to ZnO(001) and ZnO(100) surface, which promotes the Fermi energy level to move to the high energy potential, resulting in the decrease of the band gap width, thereby enhancing the adsorption capacity of NO2 gas molecules. [ABSTRACT FROM AUTHOR]

Layered-metal dichalcogenides with extraordinary characteristics of vast surface area, tunable bandgap and superior adsorption capability enable the potential for application in gas sensors. However, the synthesis of effective material for enhanced response performance remains a challenge. Herein, we exploited a fascinating sensitivity and selectivity towards NO 2 gas detection using SnS 2 nanoflakes prepared via the hydrothermal method. SnS 2 nanoflakes with a thickness of 25 nm and an average diameter of approximately 500 nm show the potential for the detection of NO 2 gas at low concentrations of ppb levels. The sensing properties of the SnS 2 sensors were investigated for different concentrations of NO 2 at various operating temperatures. The sensor exhibits the highest gas-sensing response of 161 at 250 οC upon exposure to 5 ppm of NO 2 gas with fast response and recovery times. In addition, the sensor shows excellent selectivity with a low detection limit of ppb level. The electronic structure and gas-sensing mechanism are elucidated via finding density of states, charge density, and band structure based on DFT study which is calculated by the Vienna ab-initio simulation package (VASP). The considerable small adsorption energy reveals a physisorption of the NO 2 molecules on the SnS 2 surface (-0.174 eV), indicating the SnS 2 nanoflakes are intriguing candidates for the speedy detection of NO 2 gas. [Display omitted] • SnS 2 sensor was fabricated via a one-step hydrothermal approach followed by the drop-casting method for NO 2 detection. • The ultrathin SnS 2 nanostructure sensors reach 161 times in response upon exposure to 5 ppm NO 2 at 250 οC. • The SnS 2 nanoflake sensor shows good NO 2 selectivity, stability, and ultra-low detection limit. • The DFT calculation of the adsorption behaviour of NO 2 gas molecules on the surface of SnS 2 was studied. [ABSTRACT FROM AUTHOR]

ZnO–Ti 3 C 2 T x MXene nanocomposites with varying MXene contents (0.5, 1, 2, and 5 wt%) were synthesized for NO 2 detection, and the impact of microwave (MW) irradiation time (1–8 min) on NO 2 response was explored. It was observed that the sensor containing 2 wt% Ti 3 C 2 T x MXene, irradiated for 5 min, indicated the best response of 42.65 to NO 2 (10 ppm) at 300°C. Additionally, the optimal gas sensor demonstrated long-term stability (over six months), and reproducibility. The boosted NO 2 response was ascribed to the creation of ZnO–MXene Schottky barriers, an increase in oxygen vacancies due to MW irradiation, a large surface area of the nanocomposite sensor, and the presence of surface groups on MXene. We confirmed the promising effects of MW irradiation in enhancing gas sensing, showcasing it as a cost-effective and readily available technique. • Synthesis of ZnO–Ti 3 C 2 Tx MXene nanocomposites with varying MXene contents. • MW irradiation of the synthesized composites for durations of 1, 3, 5, and 8 min. • 2 wt% MXene-sensor with 5-min MW exhibited an enhanced response to NO 2 gas. • Sensor demonstrated response of 42.65- 10 ppm NO 2 gas at 300°C, with excellent selectivity. • Enhanced response resulted from MW irradiation, formation of Schottky barriers, and functional groups. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of Au-decorated on NO 2 adsorption on ZnO NW was examined by DFT. • Theoretical mechanism of Au decoration in improving of NO 2 -response was considered. • Dissociation reaction and catalyzer of Au were clarified for NO 2 adsorption on Au. • Selectivity of Au-ZnO NW to NO 2 gas was investigated by Bader charge analysis. The adsorption of NO 2 on a pristine and Au-decorated ZnO nanowire (NW) was investigated using density functional theory (DFT) calculations to determine the role of Au-decoration on the gas sensing response of ZnO NW. Au decoration changed the electronic structure of ZnO NW, which could improve the NO 2 adsorption gas molecules on the surface of Au-decorated ZnO NW. Bader charge analysis showed that the enhanced response of Au-decorated ZnO NW gas sensor to NO 2 gas was related mainly to the gas adsorption on Au atoms. The NO 2 molecule adsorbed on the Au atom captures 0.54 e from the Au-decorated ZnO NW, which is higher than that of the pristine one. Calculations of the charge density difference and geometry revealed the catalytic role of Au for NO 2 adsorption. [ABSTRACT FROM AUTHOR]

1D rod shaped Zirconium (Zr) was decorated over spherical shaped Zinc (ZnO) nanostructures, using hydrothermal technique. The as-synthesized nanocomposites were discovered to be discriminatory in terms of sensing nitrogen dioxide (NO 2) gas. The impact of doping on structural parameters, optical properties, thermal stability, morphology, and shape were explored using HR-TEM, XRD, SAED, UV–Visible, FE-SEM, FT-IR, and EDS. The doping concentration was optimized for maximal reactivity with gas. ZZ@5 nanocomposites have the highest response (70.9 %) when compared to pure ZnO, ZZ@2, ZZ@7, ZZ@5, and ZZ@10 nanocomposites. NO 2 gas reaction and recovery times were 24.5 and 27.8 s, respectively. As the concentration of NO 2 gas climbs from 20 to 200 ppm, the reaction to gas sensors increases. NO 2 gas has higher selectivity for ZZ@5 nanocomposite than other gases (ethanol, ammonia, hydrogen, carbon monoxide, and liquefied petroleum gas). The repeatability of ZZ@5 nanocomposite was researched for 50 days and discovered to be impressive. • Optimization of Zirconium content for maximum sensor response. • Effect of doping on structural, thermal, optical and sensing behaviour. • After NO 2 gas sensing change in morphology. • High response NO 2 sensing. • Fast response and recovery time. [ABSTRACT FROM AUTHOR]

Ternary systems are less studied for sensing applications due to complex synthesis procedures. However, they have more sources of resistance modulation, leading to an enhanced gas response. In this study, a ternary system, namely Au-decorated ZnO-polyaniline (PANI) composite nanofibers with different amounts of PANI (10, 25, and 50 wt.%) were synthesized for NO2 gas sensing studies. First, ZnO nanofibers were synthesized by electrospinning, and then an Au layer (9 nm) was coated on the ZnO nanofibers. Finally, PANI was coated onto the prepared Au-decorated ZnO nanofibers. NO2 gas sensing investigations indicated that the sensor with 25 wt.% PANI had the best response to NO2 gas at 300 °C. In addition, the optimized sensor exhibited high selectivity to NO2 gas. The improved performance of the optimal gas sensor was attributed to the role of Au, the formation of ZnO-PANI heterojunctions, and the optimal amount of PANI. The promising effect of this ternary system for NO2 sensing was demonstrated, and it can be extended to other similar systems.

The response characteristics of a field-effect transistor (FET)-type gas sensor are compared with those of the resistor-type gas sensor fabricated on the same Si substrate. Both types of gas sensors have the same sensing material prepared by the same process. Indium oxide (In2O3) film is adopted as a sensing material to sense NO2 gas. The two types of gas sensors have different response characteristics depending on the operating condition. The resistor-type gas sensor shows relatively constant response at all operating currents, and the Si FET-type gas sensor shows high response in the subthreshold region. Both types of sensors have the highest response at 105 °C, and the current of the Si FET-type gas sensor can change up to ~ 3.8 × 104 times at 500 ppb of NO2 gas, which is ~8.15 times higher than that of the resistor-type gas sensor. In addition, when the pre-bias method (Vpre = −3 V) is applied to the Si FET-type gas sensor, the response of the Si FET-type sensor overwhelms that of the resistor-type sensor over the entire measurement temperature and concentration range. [ABSTRACT FROM AUTHOR]

In this paper, micro-flowers self-assembled by nanoplates were prepared by simple hydrothermal method for gas sensing application. The micro-flower-like morphology of the as-synthesized V2O5 sample has been confirmed by FESEM and TEM micrographs. The structural property investigation of the prepared V2O5 sample has been carried out by XRD and Raman studies. The XRD pattern of V2O5 micro-flower unveiled the pure and poly crystalline orthorhombic phase and Raman analysis revealed the layered like structure of V2O5 micro-flower. In addition, SAED pattern further confirmed the poly crystalline nature of the prepared sample. Further, the micro-flower structure was compressed into pellet form and the gas sensing behavior of these pellets has been tested for different target gases. The sensing results showed the better selectivity and sensitivity for trace amount of the NO2 gas at an optimum operating temperature of 200 °C [ABSTRACT FROM AUTHOR]

In this study, reduced graphene oxide (RGO) nanosheets were synthesized and then functionalized with Pt nanoparticles (NPs) for gas sensing studies at room temperature. Pt-functionalized RGOs (Pt-RGOs) were irradiated by a 2 MeV electron beam with different doses of 100 and 500 kGy (Pt-RGO-100 and Pt-RGO-500) to study the role of electron beam irradiation (EBI) on properties and NO 2 gas sensing characteristics. Different characterization techniques verified the generation of structural defects after EBI. Additionally, NO 2 sensing tests at room temperature revealed that the Pt-RGO-100 sensor had the highest response to NO 2 gas as well as the shortest response time. We surmise that the improved sensing signal with respect to NO 2 gas for Pt-RGO-100 sensor was related to the role of oxygen functional groups. However, decreases in the response for Pt-RGO-500 sensor were related to the creation of reactive oxygen gases that could be adsorbed on the active defects of the RGO by the interaction of electron beams with oxygen species in the ambient air, leading to a decrease of the effective defect sites and decreases of the sensing response. This work suggests progress towards an improved performance of RGO-based gas sensors that can work at low temperature, by using EBI as a clean tool applied at room temperature with Pt-functionalization. [ABSTRACT FROM AUTHOR]

• NO 2 gas enhances the degradation of the physical and chemical properties of PPS. • The molecular structure of PPS changes due to the oxidation of PPS by NO 2 gas. • The conversion of PPS by NO 2 exposure is predicted with the unreacted core model. • The proposed model can estimate the tensile strength of PPS filter to some extent. The degradation behavior of polyphenylene sulfide (PPS) fabric filter media by NO 2 gas at high temperatures was investigated in detail with a continuous-flow type exposure method, as specified in ISO16891:2016. An increase in the exposure time to NO 2 gas lessened the tensile strength and elongation of the PPS filter media in both machine and transverse directions. These reductions were observed in the transverse direction (TD) more markedly than in the machine direction (MD). Exposure to NO 2 gas enhanced the oxidation of sulfur, and introduced new oxygen-containing functional groups (e.g., SO and O S O) into the PPS molecular structure, which reduced the atomic ratio of carbon in the PPS filter media with increasing exposure time. These chemical degradations severely damaged the PPS fiber through cracking, splitting, and formation of protrusions on the surface. Furthermore, assuming that the chemical reaction between PPS and NO 2 gas is diffusion-controlled by NO 2 , a model to estimate the change in the conversion of PPS and the NO 2 concentration in the exhaust gas was proposed, based on an unreacted core model. It could successfully reproduce the experimental data. A model to evaluate the change in the tensile strength of the filter media was also proposed, which could express experimental data only in the MD. [ABSTRACT FROM AUTHOR]

Herein, we present the effect of electron-beam irradiation (EBI) on the gas-sensing properties of Pd-functionalized reduced graphene oxide (RGO). Scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were used to characterize the synthesized products. The samples were irradiated using electron beams at doses of 0 (Pd-RGO-0), 100 (Pd-RGO-100), and 500 kGy (Pd-RGO-500), and the NO2 gas-sensing properties were investigated. It was found that irradiation by electron beams has a critical effect on the gas-sensing properties of the samples, and the Pd-RGO-500 sensor showed the highest response to NO2 gas. In particular, the response of the unirradiated sensor and the sensor irradiated at doses of 100 and 500 kGy to 10 ppm NO2 were 1.027, 1.045, and 1.047, respectively. The response times of Pd-RGO-0, Pd-RGO-100, and Pd-RGO-500 to 10 ppm NO2 gas were 389, 335, and 345 s, respectively. The corresponding recovery times for these sensors were 808, 766, and 816 s, respectively. The increased numbers of oxygen functional groups and high-energy defects were the main reasons for the increased gas response. This study will eventually lead to increased performance levels of RGO-based sensors that use EBI, as this technology can introduce changes into materials in a non-contact, clean, and powerful manner.

We report the gas-sensing properties of pristine and SnS2 functionalized TeO2 nanowires (NWs). TeO2 NWs were synthesized by a vapor–liquid–solid growth method, and SnS2 functionalization was performed using an atomic layer deposition technique followed by thermal treatment. Structural and morphological analyses verified the formation of pristine and SnS2 functionalized TeO2 NWs with desired composition, phase, and morphology. Interestingly, sensing results showed that the pristine TeO2 NW gas sensor had better sensing properties relative to the SnS2 functionalized TeO2 NW gas sensor. An underlying sensing mechanism is explained in detail, and reasons for the decrease of sensing performance with the SnS2 functionalized TeO2 NW sensor was attributed to the coverage of TeO2 surface by the SnS2 nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract Aluminium doped ZnO (AZO) thin films have been synthesized by using a sol-gel spin coating method. The effect of Al-doping on physicochemical and NO 2 sensing properties of the AZO thin films were studied. The structural and compositional analysis confirms the phase formation of ZnO and substitution of aluminium atoms into zinc oxide lattice. The gas sensing performance of AZO thin films investigated at different operational temperatures towards NO 2 gas. The NO 2 sensing study reveals that the 2 at% AZO film sensor shows excellent gas sensing characteristics at 200 °C. Graphical abstract Image 1 Highlights • Effect of Al doping on NO 2 gas sensing properties of ZnO thin films is studied. • XPS study reveals the substitution of Al atoms into ZnO lattice. • The 2 at% AZO thin film detects 5 ppm NO 2 concentration at 200 °C. [ABSTRACT FROM AUTHOR]

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The demand for efficient gas sensors in detecting low ppb-level NO 2 gas is increasing rapidly for the human life and environmental protection. In this regard, surface acoustic wave (SAW) based gas sensor with selectively coated one dimensional (1D) graphitic carbon nitride (g-C 3 N 4 /GCN) nanostructure interface layer is a viable strategy for the sub-ppb level NO 2 gas detection at room temperature (RT∼30 °C). Here, we explore SAW gas sensor employed with 1D GCN nanoribbons (NRs) for NO 2 detection under UV-irradiation at RT. Intriguingly, the GCN NRs SAW sensor achieves an ultrahigh frequency response (Δ f ∼28.13 kHz), short response/recovery times (131 s/116 s), excellent selectivity to NO 2 (10 ppm) gas and also records a lowest detection limit (∼42 ppb) under UV activation at RT. The enhanced sensing performances were attributed to the high mass loading effect induced by the enhanced charge transfer between the 1D GCN NRs surface and NO 2 gas molecules, boosted by the photoexcited charge carriers, numerous surface sites, and improved specific surface area of 1D GCN NRs. The proposed GCN NRs SAW sensor demonstrates exceptional repeatability, good long-term stability with a minimal loss in its Δ f , and exhibited robust sensitivity towards NO 2 (10 ppm) under diverse relative humidity conditions (0–80%) at RT. The peculiar sensing results of GCN NRs SAW sensor was elucidates using energy band theory sensing mechanism assisted with resistive type gas sensor. Overall, this study offers significant insights into the development of cost-effective real-time RT based NO 2 sensor, paving the way for practical air quality monitoring. [Display omitted] • A novel 1D g-C 3 N 4 nanoribbons coated SAW sensor was developed for RT sub-ppb level NO 2 gas sensing. • The sensor's ability to detect NO 2 gas were significantly improved under UV (365 nm) irradiation. • The sensor's remarkable sensitivity and selectivity resulted from its plentiful functional groups and elevated surface area. • The SAW sensor demonstrated enduring stability, and rapid response/recovery times with low detection thresholds to NO 2 gas. • Mass loading effect is attributed to the exceptional frequency shifts to NO 2 gas. [ABSTRACT FROM AUTHOR]

Herein, the NO 2 gas sensing features of SnO 2 nanowires (NWs) and titanium-based metal–organic framework 901 (MOF-901)-coated SnO 2 NWs were investigated. Both gas sensors showed excellent selectivity to NO 2. At 200 °C, the responses of SnO 2 NWs and MOF-901-coated SnO 2 NWs to NO 2 (10 ppm) were 9.7 and 8.2, respectively. However, in a humid atmosphere, the latter nanowires showed better performance, mainly because of their hydrophobic nature and the metal–organic framework layer. At relative humidities (RHs) of 20% and higher, the MOF-901-coated sensor showed higher performance than the pristine sensor. In particular, at 80% RH, responses of 6.6 and 4.0 were obtained for these two sensors to 10 ppm NO 2 , respectively. Furthermore, the MOF-901-coated SnO 2 NWs showed better selectivity than the other sensor. We showed that MOF-901 behaved an important role in reducing the effects of water vapor and that it can be used as a molecular sieve for enhancing the NO 2 gas response of SnO 2 NWs in humid environments. • Synthesis of SnO 2 nanowires (NWs) and MOF-901 coated SnO 2 NWs for NO 2 gas sensing studies. • Superior NO 2 gas sensing of SnO 2 NWs in dry air atmosphere. • Superior NO 2 gas sensing of MOF-901 coated SnO 2 NWs gas sensor in the presence of humidity due to hydrophobic nature. • Excellent selectivity of both gas sensors to NO 2 gas. • Explanation of NO 2 gas sensing mechanism. [ABSTRACT FROM AUTHOR]

In this paper, pristine and Xe+ ion-irradiated sensors are studied for NO 2 sensing purposes. SnO 2 nanowires (NWs) were synthesized via a simple growth method and irradiated with Xe+ ions at different doses (1014, 1015, and 1016 ions/cm2). The gas sensors were fabricated after different characterizations of morphology, phase, and chemical composition. The NO 2 sensing experiments revealed that there was an optimal dose (1014 ions/cm2) for which the highest response to NO 2 was achieved. At 200 °C, the optimal sensor had a high response of 27.32–10 ppm of NO 2. Furthermore, the sensor demonstrated high selectivity to NO 2 gas. The boosted gas response of the optimized sensor was due to the formation of n-n homojunctions between the SnO 2 -SnO 2 NWs and the irradiation-induced formation of defects. This study confirms the usefulness of irradiation in boosting the sensing features of metal oxides. • Synthesis of SnO 2 nanowires using vapor-liquid-solid growth method. • Xe+-ion irradiation at different doses (1014, 1015 and 1016 ions/cm2). • NO 2 gas sensing at different temperatures and concentrations. • Enhanced response of the sensor irradiated with a dose of 1014 ions/cm2. • Explanation of the sensing mechanism to NO 2 gas. [ABSTRACT FROM AUTHOR]

A highly sensitive and selective NO2 gas sensor dependent on SnO2/ZnO heterostructures was fabricated using a sputtering process. The SnO2/ZnO heterostructure thin film samples were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Sensors fabricated with heterostructures attained higher gas response (S = 66.9) and quicker response-recovery (20 s, 45 s) characteristics at 100 °C operating temperature towards 100 ppm NO2 gas efficiently in comparison to sensors based on their mono-counterparts. The selectivity and stability of SnO2/ZnO heterostructures were studied. The more desirable sensing mechanism of SnO2/ZnO heterostructures towards NO2 was described in detail.

Functionalized-single wall carbon nanotubes (F-SWCNTs) were easily and efficiently decorated with Ag Nanoparticles. The sensor device consisted of a film of sensitive material (F-SWCNTs) and (F-SWCNTs/Ag NPs) deposited by drop coating on n-type porous silicon substrate. The two sensors show high sensitivity to NO2 gas at different temperatures. Test results demonstrated that the (F-SWCNTs/Ag NPs) have a better performance than (F-SWCNTs). The F-SWCNTs gas sensor shows high sensitivity (36 %) at RT with response time 11 sec, whereas F-SWCNTs/Ag NPs gas sensor shows better sensitivity (150.5 %) at RT with response time 8 sec. The device shows a very reproducible sensor performance, with high repeatability, full recovery and efficient response. The improvement in the detection of some specific gases (NO2) using Ag-functionalized nanotubes is explained. [ABSTRACT FROM AUTHOR]

[Display omitted] • Garcinia indica leaf extract was employed for optimized synthesis of ZnO NPs. • The structure and morphology of ZnO NPs were influenced by calcination temperatures. • The effect of calcination temperatures on the gas sensing potential of ZnO nanoparticles. • ZnO NPs calcined at 400 °C performed best as a gas sensing material. • ZnO NPs calcined at 400 °C demonstrated antibacterial activity. This study aimed to optimize Garcinia indica leaf extract mediated biogenic synthesis of antibacterial zinc oxide (ZnO) nanoparticles (NPs) and investigate how the calcination temperatures influence the structural and gas sensing properties of ZnO NPs. To study the effects of calcination temperatures, the optimally biosynthesized ZnO NPs were calcined at different temperatures in the range of 350–500 °C, used for the fabrication of thin films and characterized by various spectroscopic and imaging techniques. Characterization techniques confirmed that ZnO NPs were spherical with crystallite size in the range of 20–30 nm, mesoporous (with slit-shaped pores 1–10 nm), and had low band gap energy. Further, calcination temperatures were found to significantly influence the defect energy levels, porosity, surface roughness, and oxygen vacancies. In addition, the variation in calcination temperature was found to influence the gas response (R g /R a), relative response (%), sensitivity, response time, recovery time, and reproducibility. A higher gas response (231) was recorded for a thin film of ZnO NPs calcined at 400 °C than other tested temperatures. The average response and recovery time were 1 s and 218 s respectively for differently calcined ZnO NPs. ZnO NPs calcined at 400 °C were also found to exhibit remarkable antibacterial activity against E. coli and B. subtilis. [ABSTRACT FROM AUTHOR]

In this research, flexible and biodegradable NO 2 gas sensors were fabricated using dried mango peel, graphene, ZnO and carbon nanotubes. We fabricated two sensors, the first one used as sensitizing material ZnO with oxygen vacancy defects (V o x) and the second one employed ZnO with zinc interstitials (Zn i x) defects. The average gas response values (ΔR/R 0 value at 100 ppm and RH=35%) were 0.16 and 0.21 for the gas sensors fabricated with V o x and Zn i x, respectively. Moreover, the response/recovery times were 13.9/213.2 s and 11.4/145.5 s for the sensors fabricated with V o x and Zn i x, respectively. Interestingly, a reference sensor made without ZnO had 10–14 lower gas response values and 1.41 times higher response times than the sensors made with ZnO. This means that adding defective ZnO on the sensors' surface was key to enhance the detection of NO 2. Additionally, the performance of the sensors was studied for relative humidities (RH) in the range of 35–82% and found that the response times decreased from 11.4 to 13.9 s to 10.8–12.5 s after raising the RH from 35% to 57%. In general, the lowest response times were obtained in the sensors fabricated with Zn i x. Controlling the response/recovery times with ZnO-defects paves the way to improve the state-of-the-art ZnO based sensors. [Display omitted] • Biodegradable and flexible NO 2 sensors were fabricated using defective ZnO particles. • Sensors had on their surface ZnO particles with Vo or Zni defects. • Sensors made zni defects on the surface had the lowest response times of 9–12.5 s. • Sensors made with Zni defects had 55–63% higher gas response than these made with Vo. • Sensors operating at RH values of 35–57% had the lowest response times. [ABSTRACT FROM AUTHOR]

The elegant two-dimensional (2D) graphitic carbon nitride (GCN) holds great promise in the detection of hazardous toxic gases especially NO 2 , for environmental protection and public health safety. However, the poor sensitivity and low surface area of bulk 2D GCN restrains its practical applicability of room temperature (RT) NO 2 sensing. Herein, we present the fabrication of boron-doped GCN quantum dots (B@GCN QD) coated langasite (LGS) based surface acoustic wave (SAW) sensor for the RT NO 2 gas detection, and applied UV activation energy (365 nm) as an effective strategy to further enhance the NO 2 sensing. Fascinatingly, under UV light, the B@GCN QD/LGS SAW sensor showed an enhanced gas sensing performance to the NO 2 gas (500 ppb - 50 ppm) with high sensitivity (Δ f =35.97 kHz/50 ppm), good selectivity, ultra-low detection limit (DL∼7.9 ppb), fast response/recovery times (35 s/43 s), excellent long-term stability as compared to dark condition. This could be attributed to the generation of abundant photoinduced charge carriers under UV activation, which leads to the significant enhancement in conductivity and enlarged mass loading effect, also, the device showed robust sensitivity responses to NO 2 gas at various temperatures (RT-200 °C) and relative humidity (20–80%) conditions. Moreover, the effective doping of B to the GCN QD exhibited a typical p-type behavior which is good in agreement with density functional theory predictions that can induce structural defects, vacancies, and amine functional groups leading to a high specific surface area, which can remarkably enhance the sensitivity and selectivity of NO 2 gas. This work may provide insights into the design and development of 2D GCN nanostructure-based SAW RT gas sensors for environmental monitoring. [Display omitted] • A highly sensitive B@GCN QD/LGS SAW sensor was developed for RT NO 2 gas sensing. • The NO 2 gas sensing performances were greatly enhanced under UV illumination. • Enhanced surface area and functional groups were responsible for high sensitivity and selectivity. • The proposed device exhibited fast response/recovery times with low detection limit. • High ∆ f for NO 2 is ascribed to the enhanced mass loading and conductivity effect. [ABSTRACT FROM AUTHOR]

Thanks to their impact on gas sensing enhancement, irradiation techniques are being progressively employed in gas-sensing applications. Effects of Xe irradiation doses on the NO 2 -sensing features of ZnO nanoparticle (NP) was investigated in this study. In this regard, ZnO NPs were irradiated with Xe ions at doses of 1 × 1014, 1 × 1015, and 1 × 1016 ions/cm2. The NO 2 gas response of irradiated ZnO NPs was superior to that of the pristine one at the optimized sensing temperature of 200 ℃. Furthermore, irradiation with a dose of 1 × 1015 ions/cm2 brought about the highest response to NO 2 gas, with a response of approximately 88.5 toward 10 ppm-NO 2. Additionally, the optimized sensor exhibited outstanding NO 2 gas selectivity. The presence of high amounts of oxygen vacancies owing to irradiation at the optimized dosage mainly resulted in the high response. This study can be used as guidelines to conduct similar studies on other materials to enhance their gas-sensing characteristics. • ZnO NPs irradiated with high energy Xe ions with different doses were used for NO 2 gas sensing studies. • Irradiated gas sensors showed higher response to NO 2 gas relative to the pristine (un-irradiated) gas sensor. • The sensor irradiated with a dose of 1 × 1015 ions/cm2 showed the highest response to NO 2 gas among all gas sensors. • Optimized gas sensor also showed outstanding selectivity to NO 2 gas. • Gas sensing mechanism is discussed in detail. [ABSTRACT FROM AUTHOR]

Highly stretchable and disposable gas sensors were fabricated on household polyethylene (PE) wrap, employing rGO/Ti 3 C 2 T x MXene hybrid as gas-detecting medium. The fabrication procedure simply consisted of solution mixing of components and drop casting of the mixture. Furthermore, the PE wrap was cheap, stretchable, and sticky, well-fitting for one-time usable sensor applications. The rGO/Ti 3 C 2 T x hybrid particles were evenly distributed on PE, while rGO and Ti 3 C 2 T x MXene were in good contact in individual hybrid particles. The as-fabricated gas sensors could endure large strains of >100%, and responded to nitrogen dioxide (NO 2) and methane (CH 4) gases at room temperature. Notably, a stretchable gas sensor with optimal material combination retained good sensitivity to NO 2 even under large strains up to 100%. No response degradation was observed. The enhanced gas response and superb strain endurance were explained on the basis of the synergistic interplay of structural components. [Display omitted] • Stretchable, disposable gas sensors were fabricated by coating rGO/Ti 3 C 2 T x hybrid on household polyethylene wrap. • The specific surface area of the hybrid increased six times compared to pristine Ti 3 C 2 T x MXene. • The gas sensor could tolerate large strains of >100%. • The gas sensor normally responded to NO 2 gas even under large strains up to 100%. [ABSTRACT FROM AUTHOR]

A selective NO 2 gas sensor was fabricated using Au-decorated ZnO nanofibers. A layer of Au was sputter-deposited on the synthesized ZnO nanofibers. The thicknesses of the Au layers were varied as 3, 6, 9, 12, and 15 nm for optimization. Annealing of the samples at a high temperature converted the Au layer to isolated Au nanoparticle (NPs) dispersed on the ZnO nanofibers. Different characterizations including structural, chemical, and morphological confirmed that the composition and morphology of the Au-decorated ZnO nanofibers were appropriate for gas sensing. The sensor with an Au layer thickness of 9 nm demonstrated an optimal response at 350 °C. The enhanced sensing response stemmed from the optimal amount of Au, generation of Au–ZnO Schottky junctions, and catalytic effect of Au NPs. This study highlights the need for the optimization of the amount of Au NPs to achieve improved response to a target gas. • Electrospun ZnO nanofibers were decorated with different thicknesses (3,6,9,12 and 15 nm) of Au layers. • NO 2 gas sensing studies were performed for the different gas sensors. • ZnO nanofibers with 9 nm-thick Au layers exhibited the highest response to NO 2 gas. • The optimized gas sensor showed excellent selectivity to NO 2 gas. • The gas sensing mechanism is explained in terms of various determining factors. [ABSTRACT FROM AUTHOR]