Highly selective and sensitive response of 30.5 % of sprayed molybdenum trioxide (MoO 3 ) nanobelts for nitrogen dioxide (NO 2 ) gas detection

Hierarchically porous ZnO derived from zeolitic imidazolate frameworks for high-sensitive MEMS NO2 sensor

Three-dimensional (3D) porous metal oxide nanomaterials with controllable morphology and well-defined pore size have attracted extensive attention in the field of gas sensing. Herein, hierarchically porous ZnO-450 was obtained simply by annealing Zeolitic Imidazolate Frameworks (ZIF-90) microcrystals at an optimal temperature of 450 °C, and the effect of annealing temperature on the formation of porous nanostructure was discussed. Then the as-obtained ZnO-450 was employed as sensing materials to construct a Micro-Electro-Mechanical System (MEMS) gas sensor for detecting NO2. The MEMS sensor based on ZnO-450 displays the excellent gas-sensing performances at a lower working temperature (190 °C), such as high response value (242.18% @ 10 ppm), fast response/recovery time (9/26 s) and ultralow limit of detection (35 ppb). The ZnO-450 sensor shows better sensing performance for NO2 detection than ZnO-based composites materials or commercial ZnO nanoparticles (NPs), which are attributed to its unique hierarchically structures with high porosity and larger surface area. This ZIFs driven strategy can be expected to pave a new pathway for the design of high-performance NO2 sensors.

Conductometric Gas Sensor Based on MoO3 Nanoribbon Modified with rGO Nanosheets for Ethylenediamine Detection at Room Temperature

An ethylenediamine (EDA) gas sensor based on a composite of MoO3 nanoribbon and reduced graphene oxide (rGO) was fabricated in this work. MoO3 nanoribbon/rGO composites were synthesized using a hydrothermal process. The crystal structure, morphology, and elemental composition of MoO3/rGO were analyzed via XRD, FT-IR, Raman, TEM, SEM, XPS, and EPR characterization. The response value of MoO3/rGO to 100 ppm ethylenediamine was 843.7 at room temperature, 1.9 times higher than that of MoO3 nanoribbons. The MoO3/rGO sensor has a low detection limit (LOD) of 0.235 ppm, short response time (8 s), good selectivity, and long-term stability. The improved gas-sensitive performance of MoO3/rGO composites is mainly due to the excellent electron transport properties of graphene, the generation of heterojunctions, the higher content of oxygen vacancies, and the large specific surface area in the composites. This study presents a new approach to efficiently and selectively detect ethylenediamine vapor with low power.

Octahedral Molybdenum Iodide Clusters Supported on Graphene for Resistive and Optical Gas Sensing

This paper reports for the first time a gas-sensitive nanohybrid based on octahedral molybdenum iodide clusters supported on graphene flakes (Mo₆@Graphene). The possibility of integrating this material into two different transducing schemes for gas sensing is proposed since the nanomaterial changes both its electrical resistivity and optical properties when exposed to gases and at room temperature. Particularly, when implemented in a chemoresistive device, the Mo₆@Graphene hybrid showed an outstanding sensing performance toward NO₂, revealing a limit of quantification of about 10 ppb and excellent response repeatability (0.9% of relative error). While the Mo₆@Graphene chemoresistor was almost insensitive to NH₃, the use of an optical transduction scheme (changes in photoluminescence) provided an outstanding detection of NH₃ even for a low loading of Mo₆. Nevertheless, the photoluminescence was not affected by the presence of NO₂. In addition, the hybrid material revealed high stability of its gas sensing properties over time and under ambient moisture. Computational chemistry calculations were performed to better understand these results, and plausible sensing mechanisms were presented accordingly. These results pave the way to develop a new generation of multi-parameter sensors in which electronic and optical interrogation techniques can be implemented simultaneously, advancing toward the realization of highly selective and orthogonal gas sensing.

Room-temperature triethylamine sensing of a chemiresistive sensor based on Sm-doped SnS2/ZnS hierarchical microspheres

An Sm-doped SnS2/ZnS sensor shows excellent gas-sensing performance towards triethylamine at room temperature.

Controllable Insertion Mechanism of Expanded Graphite Anodes Employing Conversion Reaction Pillars for Sodium-Ion Batteries

Controlling the structural and reaction characteristics of carbonaceous anode materials is essential to realizing alternative alkali-ion batteries. In this study, we report on expanded graphite material employing MoS_x conversion reaction pillars (EG-MoS_x) inserted into the interlayers and assess them as potential anode candidates for Na-ion batteries. We succeed in a tailored control of the insertion characteristics between one-phase reaction and two-phase reaction by modifying the crystal structure of EG-MoS_x under different thermal treatment conditions. EG-MoS_x-900 anode with an enlarged interlayer of ∼5.38 Å delivers an exceptionally high capacity of 501 mAh g^-1. We successfully solve the irreversible capacity issues of the expanded graphite materials by forming chemical preformation of the solid electrolyte interface (SEI) layer on the electrode surface, thereby significantly increasing coulombic efficiencies of thermally tuned EG-MoS_x (52.20 → 97.25%). We elucidate the electrochemical mechanism and structural properties of the EG-MoS_x anode materials by ex situ characterizations. Inserting active sulfide pillars enables us to overcome the performance limitations of existing Na-ion battery technologies, and we expect that this strategy will be applied to realize another family of alkali-ion batteries.

A highly sensitive ppb-level H2S gas sensor based on fluorophenoxy-substituted phthalocyanine cobalt/rGO hybrids at room temperature

The peripheral and non-peripheral substitution of 4-trifluoromethylphenoxy groups in the design of gas sensing phthalocyanine cobalt/reduced graphene oxide (rGO) hybrids with two different positions of the substituents was realized. Tetra-α(β)-(4-trifluoromethylphenoxy)phthalocyanine cobalt/reduced graphene oxide (3(4)-cF3poPcCo/rGO) hybrids were prepared through noncovalent interaction, and were analyzed by FT-IR, UV-vis, TGA and SEM. The gas sensing performance of the cF3poPcCo/rGO hybrid gas sensors towards ppb hydrogen sulfide (H2S) was measured at room temperature. The results show that the 4-cF3poPcCo/rGO sensor has better sensitivity, selectivity and reproducibility than the 3-cF3poPcCo/rGO sensor, as well as a perfect linear response to the concentration of H2S. For the 4-cF3poPcCo/rGO sensor, the response sensitivity to 1 ppm H2S is as high as 46.58, the response and recovery times are 600 s and 50 s for 1 ppm H2S, and the detection limit is as low as 11.6 ppb. This is mainly due to the loose and porous structure of the cF3poPcCo/rGO hybrids, the fact that graphene is an excellent conductive agent, and the fact that the electron-withdrawing capability of the trifluoromethyl group can increase the holes of rGO and PcCo. In addition, through electrochemical impedance spectroscopy (EIS) and I-V curves, and density functional theory, the influence of different positions of the substituents of cF3poPcCo/rGO on the sensing performance and the sensing mechanism for improving sensitivity were discussed and confirmed in detail.

Fabrication and characterization of cellulose acetate-based nanofibers and nanofilms for H2S gas sensing application

Electrospun nanofibers and solution-casting nanofilms were produced from an environmentally friendly cellulose acetate (CA) blended with glycerol (as an ionic liquid (IL)), mixed with polypyrrole (PPy, a conducting polymer) and doped with tungsten oxide (WO₃) nanoparticles. The sensing membranes fabricated were used to detect H₂S gas at room temperature and shown to exhibit high performance. The results revealed that the lowest operating temperature of both nanofiber and nanofilm sensors was 20 °C, with a minimum gas detection limit of 1 ppm. Moreover, the sensor exhibits a reasonably fast response, with a minimum average response time of 22.8 and 31.7 s for the proposed nanofiber and nanofilm based sensors, respectively. Furthermore, the results obtained indicated an excellent reproducibility, long-term stability, and low humidity dependence. Such distinctive properties coupled with an easy fabrication technique provide a promising potential to achieve a precise monitoring of harmful H₂S gas in both indoor and outdoor atmospheres.

Layered α-MoO3 nanoplates for gas sensing applications

A versatile chemical route to produce rectangular layered α-MoO₃ nanoplates with enhanced NO₂ gas sensing response.

Synthesis and gas sensing properties of membrane template-grown hollow ZnO nanowires

One-dimensional, hollow nanostructured materials are among the most promising materials for sensing applications owing to their high surface area that facilitates the adsorption of target gases. Accordingly, for gas sensing studies, hollow ZnO nanowires (NWs) with different surface areas were successfully synthesized herein by using polycarbonate membranes with different pore sizes as templates, and deposition of ZnO via the atomic layer deposition technique. The sensing properties of the synthesized hollow ZnO NWs were examined for CO and NO₂, revealing their comparative sensing performances with ZnO nanomaterials-based sensors reported in literature. This study highlights a novel way of synthesizing hollow ZnO NWs by using membrane template and their promising sensing properties as well.

Superior selectivity and enhanced response characteristics of palladium sensitized vanadium pentoxide nanorods for detection of nitrogen dioxide gas

Vanadium pentoxide (V₂O₅) nanorods have been deposited onto the glass substrates by spraying 75ml of 30mM vanadium trichloride (VCl₃) solution at optimized substrate temperature of 400°C. The XRD study confirms the formation of orthorhombic crystal structure of V₂O₅ nanorods. The FE-SEM micrograph shows the nanorods-like morphology of V₂O₅. The presence of palladium (Pd) in the Pd-sensitized V₂O₅ nanorods is confirmed using EDAX study. The gas sensing measurements show that the Pd-sensitized V₂O₅ sensing material is an outstanding candidate for nitrogen dioxide (NO₂) gas detection. Obtained results demonstrate that the Pd-sensitized V₂O₅ nanorods show the superior selectivity for NO₂ gas in comparison with other gases such as NH₃, H₂S, CO, CO₂ and SO₂ at an operating temperature of 200°C. It shows the 75% response for 100ppm NO₂ gas concentration with response and recovery times of 22s and 126s, respectively. Finally, the gas sensing mechanism based on chemisorption process is proposed to illustrate how Pd nanoparticles affect the gas sensing characteristics (response and response-recovery times).