Improved Gas-sensing Performance Research Articles

Gas-phase synthesis of MoO3 nanoclusters with helium-induced high energy (060) crystal facet: Enhancing oxygen adsorption for improved gas-sensing

Adsorbed oxygen species on the surface of metal oxide semiconductors (MOS) play an important role in the field of gas-sensing. However, considering the large number of possible MOS, manipulating surface oxygen species by exposing high-energy crystal facets often requires strict experimental conditions and may not be efficiently repeated for nano MOS. This poses a huge challenge to the rational design of advanced gas-sensing materials. This study explores the fabrication of MoO3 nanocluster (NC) film by cluster beam deposition. Helium (He) is co-fed with argon (Ar) into the aggregation chamber to influence the nucleation and growth of Mo NCs. This unique process facilitated the exposure of the high-energy (060) crystal facet in MoO3 during the aging phase. This exposed crystal facet greatly reduces the oxygen adsorption energy barrier and increases the adsorbed oxygen content, resulting in a significant improvement in gas-sensing performance. The study examined the impact of energetic facets on gas sensor sensitivity by using ethanol, ammonia, and toluene as target gases. The results indicate that exposing high-energy crystal facets significantly enhances sensor performance. This approach to creating NCs with high-energy crystal facets has broad potential for advancing MOS nanostructure-based gas sensors.

Unveiling the synergistic effects of hydrogen annealing on CeO2 nanofibers for highly sensitive acetone gas detection: Role of Ce3+ ions and oxygen vacancies

Acetone, a toxic and widespread gas, necessitates continuous monitoring. Cerium oxide (CeO2), an n-type rare earth semiconductor metal oxide with unique oxygen storage capabilities, has garnered significant interest in gas detection. In this study, hydrogenated CeO2 nanofibers were obtained by electrospinning and subsequent annealing in hydrogen gas. XRD results reveal that hydrogen annealing does not alter the original cubic fluorite phase structures of CeO2. SEM results also indicate that hydrogen annealing did not alter the nanofiber structures of CeO2. XPS analysis confirms the reduction of Ce4+ to Ce3+ ions, resulting in an increased concentration of Ce3+ ions and oxygen vacancies with increasing annealing temperature. The hydrogenated CeO2 sensor (CeO2-H-680) exhibits a response of 5.45 to 100 ppm acetone at 200 ℃, 4.2 times higher than that of the pure CeO2 sensor, as well as good selectivity, repeatability, and long-term stability. The improved gas-sensing performance achieved through hydrogen annealing is attributed to the increased concentration of Ce3+ ions and oxygen vacancies. Overall, hydrogen annealing of metal oxides effectively regulates oxygen vacancies for enhanced gas sensing performance.

High sensitivity and selectivity of formaldehyde sensor based on Nd2O3 @In2O3 heterojunction rod-like composites

The rare-earth material Nd2O3, which has abundant oxygen vacancy defects and unique structural property of 4f‐4f electron leap, shows its great potential for chemical sensing applications. However, the difficulty in selecting suitable Nd-precursor complexes has limited the synthesis and further applications of Nd2O3 materials. Herein, we synthesized Nd(OH)3 using a simple solvent method, followed by calcination by mixing it with the precursor MIL-68(In) to generate Nd2O3 surface-modified In2O3 composites. After that, its gas-sensitive performance was investigated. It was observed that the response of 5 wt% Nd2O3 @In2O3 to formaldehyde (100 ppm) is the highest (850.3), which is 25 times higher than that of In2O3. Compared with In2O3, Nd2O3-decorated In2O3 not only exhibited higher sensitivity and better selectivity but also reduced response time. The improved gas-sensing performance could be attributed to the formation of heterojunctions between Nd2O3 and In2O3 as well as the increase of adsorbed oxygen and defective oxygen. This kind of gas sensor based on Nd2O3-decorated In2O3 has more obvious advantages for fast and high-response detection of formaldehyde.

Hollow ZnWO4/In2O3 Nanotubes for Ultrasensitive and Rapid Trace Detection of Triethylamine

The directional modulation of metal oxide semiconductors (MOSs) can be effective in developing high-performance gas-sensing materials. Herein, we propose an efficient strategy by modifying ZnWO4 on In2O3 to achieve controllable modulation of oxygen vacancies and energy band structures in ZnWO4/In2O3 heterostructures. The sensor based on optimized ZnWO4/In2O3 exhibits significantly enhanced performance to detect triethylamine, including a lower operating temperature (100 °C), a higher responsivity (Ra/Rg = 221.2 for 100 ppm), and a lower detection limit (500 ppb). In addition, the fabricated sensor exhibits faster response and good selectivity. The improved gas-sensing performance could be attributed to the acid–base interaction between triethylamine gas and ZnWO4, the formation of heterojunctions, and the increase of oxygen vacancies to achieve a synergistic modulation of the chemical and energy band structures. It is anticipated that our current investigation could offer insights and a useful strategy for triethylamine detection.

Snowball flower-like g-C3N4/ZnFe2O4 mesoporous hollow microspheres with enhanced triethylamine sensing properties

Herein, the snowball flower-like g-C3N4/ZnFe2O4 mesoporous hollow microspheres, in which two-dimensional (2D) g-C3N4 nanolayers were loaded onto the surface of ZnFe2O4 hollow microspheres, were constructed by a simple solid phase reaction. The effect of the g-C3N4 concentration on the structure, morphology and gas-sensing performance of the g-C3N4/ZnFe2O4 composites had been explored. On the basis of gas sensitivity test results, the composites owned lower working temperature (160 ℃) and better selectivity toward TEA in comparison with pure ZnFe2O4. Notably, the sensor based on the g-C3N4/ZnFe2O4-15 hollow microspheres (adding 15 ml of g-C3N4 aqueous solution) exhibited outstanding sensing properties, including superior response (18.3) toward 100 ppm TEA at optimum work temperature of 160 ℃, speedy response-recovery time (33, 30 s) and outstanding stability. And the sensor maintained high response of 4.3 to low concentration TEA (5 ppm). The improved gas-sensing performance of the composites could be attributed to the porous ZnFe2O4 hollow microspheres loaded by 2D g-C3N4 nanolayers with large specific surface area and the heterostructure formed between them. Hence, a potential application of the g-C3N4/ZnFe2O4 microspheres might be achieved in detecting TEA at a low optimum work temperature.

Preparation of a hierarchical 3D structure composed of Co-doped SnO2 nanosheets with excellent gas sensitivity to acetic acid

In this article, we used a simple one-step hydrothermal method to successfully synthesize Co-doped SnO2 and tested its gas sensitivity performance. The material was characterized by a variety of technical methods. The results show that the prepared material is a flower-like hierarchical structure assembled by porous nanosheets, and the thickness of the nanosheets is about 20 nm. Materials with different doping ratios were tested for gas sensitivity. The results show that the material with a doping ratio of 3 mol% exhibits an excellent gas-sensitive response to acetic acid at 300 °C, while also having good stability and selectivity. Therefore, Co-SnO2 shows great potential in the detection of acetic acid. The improvement of gas-sensing performance is attributed to the formation of many oxygen vacancy defects on the surface of the material caused by Co doping, which is more conducive to the adsorption of oxygen molecules on the surface of the material.

Metal-Organic-Framework-Decorated Carbon Nanofibers with Enhanced Gas Sensitivity When Incorporated into an Organic Semiconductor-Based Gas Sensor.

Because of their high porosity, metal-organic framework (MOF) materials have attracted much attention for use in gas-sensing applications. However, problems with the processability of MOFs for use in reliable gas-sensing electronics remain unsolved. Herein, combination of the strong gas-adsorbing properties of MOF nanomaterials and organic thin-film transistor-type chemical sensors is proposed and experimentally demonstrated. The hybrid blend system with inorganic MOF nanomaterials and organic semiconductors likely exhibits thermodynamic instability because of each phase's self-aggregation, which is difficult to settle without surface functionalization. We propose a novel method to produce an inorganic-organic hybrid sensor by introducing carbon nanofibers as a scaffold. We demonstrate that the carbon nanofibers perform dual functions: enabling the attachment of MOF nanoparticles at the fiber surface, which stabilizes the nanoparticle-embedded polymer layer, and maintaining reliable conductivity for improved gas-sensing performance. On the basis of our characterization of their nanomorphology and nanocrystal structure, the MOF nanoparticles and carbon nanofibers are shown to render a hybrid core-shell structure in the conjugated polymer matrix. This organic-inorganic hybrid system was incorporated into a field-effect transistor device to detect hazardous NO2 gas analytes, operating in real-time with high responsivity. The prototype chemical sensor holds enormous promise for other chemical sensors.

Preparation of porous sea-urchin-like CuO/ZnO composite nanostructure consisting of numerous nanowires with improved gas-sensing performance

Preparation of porous sea-urchin-like CuO/ZnO composite nanostructure consisting of numerous nanowires with improved gas-sensing performance

Hydrothermal synthesis of ZnSnO3/rGO composite material and highly gas sensing performance to acetone

This study used the hydrothermal method to synthesize ZnSnO3 and ZnSnO3/rGO composite material with hierarchical and porous structure. ZnSnO3 was attached on the surface of rGO or between the lamellar layers to form a physically boned heterojunction semiconductor composite material. The ZnSnO3/rGO sensing material shows better gas-sensing properties than ZnSnO3 sensor to acetone. Compared with the operating temperature of ZnSnO3 sensor (425 °C), the optimal operating temperature of ZnSnO3/rGO sensor was only 350 °C, the sensitivity to 50 ppm acetone gas was 80.371, and the response/recovery time was only 4 /27 s. The improved gas-sensing performance of ZnSnO3/rGO sensing material can be ascribed to the large specific surface area, hierarchical, porous structure, and unique heterojunction of the composite material. The high sensitivity, fast response/recovery characteristics, excellent selectivity and stability of ZnSnO3/rGO make it an ideal sensing material for detecting acetone.

Sensing mechanism of Ag/α-MoO3 nanobelts for H2S gas sensor

Sensing mechanism is still a big problem in the field of gas sensor. In-depth study of the sensing mechanism can provide better ideas for the design of sensing materials, and it is also more conducive to the improvement in gas-sensing performance. In this work, Ag/α-MoO3 material was obtained by loading Ag in α-MoO3 nanobelts prepared by hydrothermal method. The material was characterized by field electron scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Comparing the gas sensing properties of α-MoO3 and Ag/α-MoO3, it is found that Ag effectively improves the selectivity of the material to H2S at 133 °C. The response of the 5 wt% Ag/α-MoO3 sensor to 100 × 10−6 hydrogen sulfide (H2S) is 225 and the detection limit is 100 × 10−9. The sensing mechanism was verified by gas chromatography and mass spectrometer (GC–MS), XPS and Fourier transform infrared spectroscopy (FTIR).

Design of Hydrothermally Derived Fe2O3 Rods with Enhanced Dual Functionality Via Sputtering Decoration of a Thin ZnO Coverage Layer.

The Fe2O3–ZnO composite rods were successfully synthesized by combining hydrothermal growth of Fe2O3 rods and sputtering deposition of a thin ZnO coverage layer. Two types of the Fe2O3 rods with round and rectangular cross-sectional morphologies grown via control of the urea content in hydrothermal growth processes were used as rod templates to fabricate the Fe2O3–ZnO composite rods. The Fe2O3–ZnO composite rods exhibited an improved photoelectric conversion efficiency in the Fe2O3 rods via a construction of a heterogeneous structure. The photocatalytic degradation performance of rhodamine B dyes with Fe2O3 rods was substantially increased via sputtering decoration of a thin ZnO coverage layer on the Fe2O3 rods. Moreover, the Fe2O3–ZnO composite rods exhibited superior acetone vapor-sensing responses than the pristine Fe2O3 rods herein. The extended optical absorption ability together with the enhanced photoinduced charge separation efficiency via construction of the Fe2O3–ZnO heterogeneous system explained the improved photoactivity of the composite rods. Furthermore, the formation of a heterojunction between the Fe2O3 and ZnO increased the interfacial potential barrier height and enhanced the sensor resistance variation size upon exposure to the acetone vapor. This accounted for the improved gas-sensing performance of the Fe2O3–ZnO composite rods. The experimental results herein provide a promising approach to design Fe2O3-based composite rods with desirable photocatalytic and gas-sensing functionalities.

Fabrication of oxygen-doped MoSe2 hierarchical nanosheets for highly sensitive and selective detection of trace trimethylamine at room temperature in air

Intelligent gas sensors based on the layered transition metal dichalcogenides (TMDs) have attracted great interest in the field of gas sensing due to their multiple active sites, fast electron, mass transfer capability and large surface-to-volume ratio. However, conventional TMDs-based sensors typically work at elevated temperature in inert atmosphere, which would largely limit the corresponding practical applications. Herein, novel oxygen-doped MoSe2 hierarchical nanostructures composed of ultrathin nanosheets with large specific surface area have been designed and generated typically at 200 °C in air for fast and facile gas sensing of trimethylamine (TMA), effectively. Benefited from the gas-accessible hierarchical morphology and high surface area with abundant nanochannels, highly sensitive and selective detection of trace TMA has been achieved under ambient condition, and as detected the theoretical limit of detection (LOD) is 8 ppb, which is the lowest for TMA detection under ambient condition among the reported studies. The mechanism of oxygen doping on the improved gas-sensing performance has been investigated, revealing that the oxygen doping could greatly optimize the electronic structure, thus regulate the Fermi level of MoSe2 as well as the affinity between TMA molecule and sensor surface. It is expected that the oxygen doping strategy developed for the highly efficient gas sensors based on TMDs in present work may also be applicable to other types of gas-sensing semiconductors, which could open up a new direction for the rational design of high-performance gas sensors working under ambient condition.

Ultrasensitive ppb-level H2S gas sensor at room temperature based on WO3/rGO hybrids

Gas sensors with high performance and low energy consumption are necessary for system integration in the environment monitoring of explosives. High-performance room-temperature hydrogen sulfide (H2S) gas sensors were fabricated based on the hybrids of tungsten oxide (WO3)/reduced graphene oxide (rGO). WO3 nanocubes modified with different contents of rGO were synthesized by acid-based hydrothermal method. The optimal amount of rGO in the composite is 5 wt%, at which the room-temperature operating sensor presents the highest sensitivity of approximately 32.7 to 500 ppb H2S, a fast recovery time of ~ 180 s, as well as an excellent sensing selectivity. The overall improvement in sensing performances demonstrated an important progress made in H2S sensor fabrication for portable and real-time gas detection. The improved gas-sensing performance is attributed to the large specific surface area of the WO3 nanocubes, the formation of WO3/rGO heterojunctions, and the enhanced electron transfer efficiency.

The highly improved gas-sensing performance of α-Fe2O3-decorated NiO nanowires and the interfacial effect of p–n heterojunctions

Mesoporous n-type α-Fe2O3-decorated p-type NiO NWs were synthesized by two-step nanocasting method, and the influence of the heterogeneous α-Fe2O3 decoration on the components, microstructure and gas-sensing performance of NiO NWs was discussed.

Investigation of Reduced Graphene Oxide and a Nb-Doped TiO2 Nanotube Hybrid Structure To Improve the Gas-Sensing Response and Selectivity

The precise detection of flammable and explosive gases and vapors remains an important issue because of the increasing demand for renewable energy sources and safety requirements in industrial processes. Metal oxides (TiO2, SnO2, ZnO, etc.) are very attractive materials for the manufacturing of chemical gas sensors. However, their gas selectivity issues and further improvement in the sensing response remain a significant challenge. The incorporation of metal oxides with two-dimensional (2D) graphene oxide (GO) is considered to be a promising approach to obtaining hybrid structures with improved gas-sensing performance. Herein, we report the development of GO and niobium-doped titanium dioxide nanotube (NT) hybrid structures with a tunable selectivity and sensing response against hydrogen gas, achieved by properly controlling the degree of reduction and concentration of GO. The effects of these parameters are systematically studied in terms of the response amplitude and selectivity. It was found that, compared to undoped titanium dioxide nanotubes, the hybrid material with an optimal concentration of reduced-GO and the introduction of niobium shows an increase in hydrogen response of about an order of magnitude and a simultaneous reduction of the response to possible interfering compounds such as carbon monoxide and acetone, thus providing enhanced selectivity. This research may provide an efficient way to enhance the chemical sensing performance of metal oxide nanomaterials.

Synthesis and enhanced NO2-sensing properties of ZnO-decorated SnO2 microspheres

In this work, ZnO was decorated onto SnO2 microspheres via a facile solvothermal method, and the gas sensing characteristics of the ZnO/SnO2 composites was systematically studied. Results showed that the ZnO/SnO2 composites was highly responsive to NO2, with much lower response to interfering gases such as ethanol and acetone. At the optimum temperature (200 °C), the response of the ZnO/SnO2 composite to 100 ppm NO2 was about 3 times higher than that of pristine SnO2 microspheres. Furthermore, ZnO decoration on SnO2 microspheres led to significant reduction in the response time. The improvement of gas-sensing performance may be ascribed to the formation of more surface adsorption sites on the ZnO/SnO2 composite.

Improved Gas Sensing Performance of ALD AZO 3-D Coated ZnO Nanorods

This paper reports an enhancement on the sensing performance of ZnO nanorod ethanol sensors with a new approach by utilizing nested coatings of Aluminum doped ZnO (AZO) thin films by Atomic Layer Deposition (ALD) technology. ZnO nanorods were grown by the hydrothermal method with the ZnO seed layer synthesized on Silicon wafers by ALD. To enhance the sensing performance of ZnO nanorod ethanol sensors, multiple coated AZO thin film 3-D coatings were deposited on the surface of the intrinsic ZnO nanorods by ALD. To investigate the sensing performance of the ZnO nanorods sensor for the detection of ethanol vapor, a gas sensor testing system was designed and built with a sealed reaction chamber and a temperature controller. The demonstrated sensing performance results include the sensing response comparison between ZnO nanorods before and after ALD coatings with AZO films at different temperatures and with various concentrations of input ethanol vapor. The response times and recovery times of ZnO nanorods before and after ALD coatings with AZO thin films were analyzed to investigate the sensing enhancement. The sensing response improvement peaks at 25°C room temperature with approximately 200% enhancement. However, the sensing response improvement decreases as a function of increasing operating temperature.

Improved formaldehyde-sensing performance of SnO2/Zn2SnO4 nanocomposites by structural evolution

SnO2/Zn2SnO4 hollow microspheres with porous shell (HPMSs) were successfully prepared by using ZnSn(OH)6 (ZHS) hollow microspheres (HMSs) as sacrificial templates, which were pre-synthesized via a fast solid-state grinding method combined with subsequent chemical etching process. The obtained samples were characterized by XRD, SEM, TEM, and N2 adsorption-desorption, respectively. Results indicated that the diameter of the prepared SnO2/Zn2SnO4 HPMSs were around 300–700nm and their shell-thickness was about 50nm. On the shell of the composite HPMSs, a large number of 5–20nm pores were in situ created. In comparison with the SnO2/Zn2SnO4 porous microspheres (PMSs) that prepared directly from solid ZHS microspheres, the SnO2/Zn2SnO4 HPMSs exhibited much higher sensitivity to formaldehyde, demonstrating the improved gas-sensing performance through structural evolution from PMS to HPMS.

Enhancing ethanol detection by heterostructural silver nanoparticles decorated polycrystalline zinc oxide nanosheets

Noble metals decorated two-dimensional nanostructures with a large surface-to-volume ratio raise substantial promise for many technological applications particularly for high-performance chemical sensing. Here, we design and synthesize a hierarchical heterojunction comprising ultrathin two-dimensional polycrystalline ZnO nanosheets on a large scale, which serve as reaction positions for reduced gases, and uniformly dispersed Ag nanoparticles to enhance reaction activity. We find that the Ag nanoparticles in the heterostructural system act as strong electron acceptors, inducing remarkable surface space charge layers. As a result, the heterostructural system shows significantly improved gas-sensing performance to ethanol as compared to pure ZnO. Such metal nanoparticles decorated two-dimensional polycrystalline ZnO nanosheets can be applied in not only as gas-sensing but also catalytic and photocatalytic fields.

Sensor for volatile organic compounds using an interdigitated gold electrode modified with a nanocomposite made from poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) and ultra-large graphene oxide

A highly efficient gas sensor is described based on the use of a nanocomposite fabricated from poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) and ultra-large graphene oxide (UL-GO). The nanocomposite was placed by drop casting in high uniformity on interdigitated gold electrodes over a large area of silicon substrate and investigated for its response to volatile organic compounds (VOCs) at room temperature. Monolayers of UL-GOs were synthesized based on a novel solution-phase method involving pre-exfoliation of graphite flakes. The nanocomposite was optimized in terms of composition, and the resulting vapor sensor (containing 0.04 wt% of UL-GO) exhibits strong response to various VOC vapors. The improved gas-sensing performance is attributed to several effects, viz. (a) an enhanced transport of charge carriers, probably a result of the weakening of columbic attraction between PEDOT and PSS by the functional groups on the UL-GO sheets; (b) the increase in the specific surface area on adding UL-GO sheets; and (c) enhanced interactions between the sensing film and VOC molecules via the network of π-electrons. The sensitivity, response and recovery times of the PEDOT-PSS/UL-GO nanocomposite gas sensor with 0.04 wt% of UL-GO are 11.3 %, 3.2 s, and 16 s, respectively. At a methanol vapor concentration as low as 35 ppm, this is an improvement by factors of 110, 10, and 6 respectively, compared to a PEDOT-PSS reference gas sensor without UL-GO.