Gas Sensitive Performance Research Articles

ZIF-67 MOF-derived Co3O4/NiCo2O4/CC unique layered structure with excellent gas performances

In this work, the synthesized Co3O4/NiCo2O4/CC is a layered structure, which was prepared by a feasible method of hydrothermal reaction, thermal annealing of ZIF-67 template and other thermal treatment. This novel structure is based on carbon cloth, and Co3O4 hollow nanocubes as semiconductor material grow in situ on nanowire arrays. Under the condition of different temperatures and different concentrations of ethanol, the response of the gas sensor based on Co3O4/NiCo2O4 was studied. The result shows high sensitivity, good linear relationship and excellent response-recovery properties. And its high sensitivity is demonstrated with a maximum response up to 35 at 180 °C and 200 ppm. The sensor performs well in gas sensitivity thanks to the structure of the material. Large specific surface area, high porosity and fast electronic transport channel between Co3O4 and CC are all important reasons. Accordingly, this method of preparing the novel hierarchical structure can improve the gas sensitive performance. This work would provide a reference for further research on the application of Co3O4 MOF-derived structure in gas sensitive.

New nano-composite based on carbon dots (CDots) decorated magnesium oxide (MgO) nano-particles (CDots@MgO) sensor for high H2S gas sensitivity performance

Schottky device based on carbon dots (CDots) decorated magnesium oxide (MgO) nano-particles (CDots@MgO) has been engineered for H2S gas sensing applications. TEM microscope proves the decoration of CDots on the surface of MgO nano-particles. The sensor device has been tested for various reducing gases. However, CDots@MgO device displays high response against H2S gas, as a resultof reducing the barrier height between CDots@MgO crystals. I–V behavior of the engineered sensor device is examined under both open air and H2S gas environments. The parameters (series resistance Rs, effective barrier height ϕB, and ideality factor n) of the schottky diode are determined for the CDots@MgO and MgO based sensors. Interestingly, under the exposure of 120 ppm of H2S, CDots@MgO sensor has shown response current value 11 times higher than MgO sensor at external biasing voltage = −0.7 V. The reduction of barrier height can be observed with increasing the (Tapplied) up to 200 °C and then increases. The obtained results prove that both device response and sensitivity are strongly influenced by the change in the barrier height. Finally, this effort introduces an invaluable methodology aiming at sensing the harmful gases by engineering a new gas sensor based on Schottky device of metal oxides decorated with CDots for high response, low power-consumption, high repeatability and high stability.

Controllable gas sensitive performance of 1T’ WS2 monolayer instructed by strain: First-principles simulations

With the development of gas sensor technology, higher requirements are put forward for element sensitivity and controllable gas adsorption strength. Here, the adjustment effect of uniaxial or biaxial strains on 1T’ WS2 is discussed to achieve the controllable adsorption performance of NO2. Results suggested that the adsorption strength can be controlled by the applied tensile strain when the strain was between 1% and 10%, and it increases with the increase of strain. The biaxial strain was more conducive to generate the orbital mixing between NO2 and 1T’ WS2. The mechanism of strain affecting gas adsorption strength is clarified.

Microwave-assisted hydrothermal synthesis of copper oxide-based gas-sensitive nanostructures

Hydrothermal methods are widely used in chemical synthesis of target products with specific morphology and nanostructure. Those methods are very efficient for the preparation of well-controlled structures but the reaction time is usually long. The assistance of microwave makes the reaction system heat up faster, more uniformly and reactions are accelerated, it also can be utilized to change the morphology or structure of materials, which improves the physic-chemical properties of synthesized products and influences its gas-sensing performance. Copper oxide (CuO) is widely applied in semiconductor gas sensors because of its good reactivity and stability. This review article briefly introduces the principle, mechanism and recent development of CuO nanostructures obtained by microwave-assisted hydrothermal synthesis (MWHS) process. It also discussed the relation between endopathic factors of material and its gas-sensitive performance. The technical challenges and prospective solutions for high-performance CuO-based gas-sensitive materials with unique nanostructure are proposed. It is pointed out that the hierarchical CuO-based nanostructures and their composite materials prepared by MWHS process are efficacious methods to improve the gas-sensitive performance of the materials. On the basis of the morphology, the materials are divided into nanorods, nanoflowers, nanosheets, nanospheres and other nanostructures. The influence of microwave parameters on the properties of synthetic products is analyzed. The influence followed by metal element loading on the structure and properties of CuO-based materials by MWHS process is further discussed. Then this review summarizes the research progress of graphene-CuO and metal oxide-CuO composites prepared by MWHS process in recent years.

3D flower-like NiCo-LDH composites for a high-performance NO2 gas sensor at room temperature

Excellent response with a fast response/recovery time, as well as good repeatability and longtime stability, are considered to be advantageous features of an ideal gas sensor. To this purpose, in this paper, uniform 3D flower-like layered nickel-cobalt layered double hydroxide (NiCo-LDH) composites were prepared by a simple hydrothermal method. The gas sensing performance of the NiCo-LDH NO2 gas sensors was investigated at room temperature (RT). Among the composites, Ni1Co1 (Ni/Co molar ratio = 1:1) shows a high response of 31.22 at 100 ppm with fast response and recovery times equal to 1.6 s and 11.6 s, respectively. Similarly, the Ni1Co1 sensor indicates a low detection limit of only 0.01 ppm (10 ppb) and shows excellent stability (60 days) and high selectivity to NO2. The NiCo-LDH sensor has excellent NO2 gas sensitivity performance due to its a high specific surface area or Co(OH)2 and Ni(OH)2 synergy. Therefore, we believe that Ni/Co-LDH sensors can be widely used in the field at RT and have good development prospects.

Investigation on Gas Sensing Properties and SVM Training of Perovskite Metal Oxide LaFeO3 Microsphere

Perovskite oxides have attracted extensive attention due to their excellent photoelectric properties in recent years. In this paper, LaFeO3 (LFO) perovskite microsphere were synthesized by simple hydrothermal synthesis with iron nitrate and lanthanum nitrate as metal sources and citric acid as complexing agent. The microstructure and crystal structure of perovskite nanomaterials were characterized by SEM and XRD. The LaFeO3 perovskite type gas sensor was manufactured and its gas-sensitive characteristics were studied. The results show that LaFeO3 sensor has good gas-sensitive performance to ethanol whose response reaches about 15 at 250℃, and has excellent selectivity and recovery ability. In addition, in the concentration gradient test, the support vector machine in mathematical theory was used for training and recognition, and the result shows that the recognition rate could reach 100%. Figure 1

Modulation of TEA and methanol gas sensing by ion-exchange based on a sacrificial template 3D diamond-shaped MOF

This paper introduces a facile and simple method to synthesize ZnO and modulate ZnO to change into CuO/ZnO for realizing gas sensitive performance transformation from triethylamine (TEA) to methanol (CH3OH) without altering the original morphology of ZnO. ZnO with diamond-shape was prepared simply by calcining a three-dimensional (3D) Metal Organic Framework (MOF) {[Zn5(L)2(H2O)5]·7(DMA)·10(H2O)}n (HPU-15) as template. When HPU-15 was immersed in solutions containing Cu(II) cations, Zn2+ in HPU-15 could be exchanged by Cu2+ rapidly. Then, CuO/ZnO was derived from the ion-exchanged product Cu@HPU-15. Unlike ZnO shows the selective responses to TEA, CuO/ZnO shows the highest sensing performance to CH3OH. First principles calculations showed that the gas sensitive performance transformation is mainly attributed to the changes of adsorption energy of materials, which gives rise to the transformation of sensing performance. Besides, the unique p-n junction is also beneficial for CH3OH gas sensing performance. Therefore, such post-synthetic metal ion exchange approach provides a novel strategy for the development of functional sacrificial template MOF materials for the application in the modulation of the sensitive performance of sensor.

Enhanced gas sensing performance of perovskite YFe1-x Mn x O3 by doping manganese ions.

Perovskite YFe1−xMnxO3 with a hierarchical structure were prepared by a simple hydrothermal method and used as gas sensing materials. The structure, morphology and composition of YFe1−xMnxO3 were investigated using X-ray diffraction, transmission electron microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The gas sensing test showed that all YFe1−xMnxO3 perovskites with different Mn doping concentrations displayed fast response and recovery characteristics to multiple analytes as well as good stability and recoverability. With the increase of Mn doping concentration, the response of YFe1−xMnxO3 to four kinds of target atmospheres first increases, then decreases. The sensing performance of YFe1−xMnxO3 is best when x = 0.05. Compared with pure YFeO3, the responses of YFe0.95Mn0.05O3 to 1000 ppm of CH2O, C2H6O, H2O2 and 100% relative humidity were increased by 835%, 1462%, 812% and 801%, respectively. The theoretical detection limit of YFe0.95Mn0.05O3 for H2O2 and CH2O is 1.75 and 2.55 ppb, respectively. Furthermore, the possibility of buildings a sensor array based on YFe1−xMnxO3 with different doping concentrations was evaluated by principal component analysis and radar chart analysis. It is feasible to realize the visual and discriminative detection of the target analyte by constructing sensor arrays through radar chart analysis and database construction.

Enhanced room-temperature NO2 sensing properties of biomorphic hierarchical mixed phase WO3.

WO3 with a mixed phase (m-WO3 and h-WO3) was synthesized by facile hydrothermal and annealing methods using biomass carbon (Hemp stems) as a sacrificial template. The biomorphic hierarchical structure effectively enhanced the dispersion of WO3 microspheres, which increased the contact area for the target gas molecule. The control of the mixed phase compositions was achieved by space confinement of biomass carbon and heat treatments. The synergistic effect of the mixed phase increased the mobility of carriers and promoted the separation and transport of electrons and holes. Thus, it improved the adsorption-diffusion capacity of NO2 molecules and enhanced the sensor performance at lower operating temperature effectively. The B-WO3-04 (450 °C, 4 h) exhibited an ultra-high response (Ra/Rg = 71.07) towards 100 ppm NO2 gas with excellent repeatability and appreciable long-term stability at room temperature. The significant improvement of B-WO3-04 gas sensing performance was mainly due to its unique hierarchical structure and the optimal proportion of the mixed phase composition.

Synthesis and gas sensitivity properties of novel metallocorroles and functionalized graphene oxide

Corrole compounds with the 18-[Formula: see text] electron marcrocycle display unique electrochemical properties and show potential value in sensor fields. In this paper, a novel 10-(4-Chlorophenyl)-5,15-di(4-methylphenyl)-Corrole (Cl-Cor 1) and its metal complex 10-(4-Chlorophenyl)-5,15-di(4-methylphenyl)-Corrole-Co (Cl-Cor-Co 2) were synthesized. Then corrole compounds were introduced onto graphene oxide (GO). UV-Vis spectroscopy, fourier-transform infrared spectroscopy (FTIR), and mass spectrometry were used to determine synthesized compounds. Capacity gas sensing analysis system was also examined to evaluate the gas sensitivity toward NO2 of Cl-Cor 1, Cl-Cor-Co 2, Cl-Cor+GO 3, Cl-Cor-Co+GO 4 and GO 5 at room temperature. It can be found that Cl-Cor-Co 2 has gas-sensing property for nitrogen dioxide (NO)2, but recovery performance is low. It is interesting that the gas sensitivity and recovery performance could be evidently improved when the GO is grafted onto Cl-Corrole-Co, which is ascribed to the [Formula: see text]-[Formula: see text] interaction between Corrole and GO. The gas respond at room temperature enormously indicating that covalently Cl-Cor-Co+GO 4 can be used as gas sensors candidate.

Porous ZnO cubes derived from metal–organic frameworks with excellent sensing performance triethylamine

Recently, the metal organic frameworks (MOFs) structure is concerned by its unique porous structure and regular morphology. In this paper, ZnO has been prepared by calcining MOF-5 precursors which obtained via a solvothermal method. For a better comparison, the reaction time needs to be appropriately changed to control the sizes of samples. The obtained samples were analyzed for composition and morphology by a series of characterization methods, and the results showed that particle size of MOF-5 precursors increased with reaction time. The ZnO particles formed after calcination are composed of crystal grains of 20–30 nm and thus have a porous structure. Gas-sensitive performance tests show that the sensor based on MOF-5-derived ZnO has good gas sensitivity. Among them, the responsiveness of MOF-5-derived ZnO prepared by solvothermal reaction for 4 h was the highest at 300 °C, and the response value to 100 ppm triethylamine (TEA) was 120.6. In addition, MOF-5-derived ZnO has better selectivity and repeatability than ZnO which is prepared using other methods.

Ethylamine gas sensing properties of SnO2/rGO nanocomposite materials

Ethylamine has been widely used in production and life, but it needs to be monitored in real-time because of its important harm to human health. In this study, an SnO2/rGO nanocomposite gas sensitive material was synthesized by hydrothermal method, and the gas-sensing properties of ethylamine were tested by a self-made gas sensitivity test platform. The results show that the SnO2/rGO nanocomposite materials have good gas-sensitive performance of ethylamine and low detection limit (up to 1 ppm). Finally, the mechanism of gas sensitivity is proposed.

TiO₂-Based Nanoheterostructures for Promoting Gas Sensitivity Performance: Designs, Developments, and Prospects.

Gas sensors based on titanium dioxide (TiO2) have attracted much public attention during the past decades due to their excellent potential for applications in environmental pollution remediation, transportation industries, personal safety, biology, and medicine. Numerous efforts have therefore been devoted to improving the sensing performance of TiO2. In those effects, the construct of nanoheterostructures is a promising tactic in gas sensing modification, which shows superior sensing performance to that of the single component-based sensors. In this review, we briefly summarize and highlight the development of TiO2-based heterostructure gas sensing materials with diverse models, including semiconductor/semiconductor nanoheterostructures, noble metal/semiconductor nanoheterostructures, carbon-group-materials/semiconductor nano- heterostructures, and organic/inorganic nanoheterostructures, which have been investigated for effective enhancement of gas sensing properties through the increase of sensitivity, selectivity, and stability, decrease of optimal work temperature and response/recovery time, and minimization of detectable levels.

Influence of discharge voltage on the sensitivity of the resultant sputtered NiO thin films toward hydrogen gas

Nickel oxide thin films were deposited on glass substrates as the main gas sensor for H2 by the DC sputtering technique at various discharge voltages within the range of 1.8–2.5kV. Their structural, optical and gas sensing properties were investigated by XRD, AFM, SEM, ultraviolet visible spectroscopy and home-made gas sensing measurement units. A diffraction peak in the direction of NiO (200) was observed for the sputtered films, thereby indicating that these films were polycrystalline in nature. The optical band gap of the films decreased from 3.8 to 3.5eV when the thickness of the films was increased from 83.5 to 164.4nm in relation to an increase in the sputtering discharge voltage from 1.8 to 2.5kV, respectively. The gas sensitivity performance of the NiO films that were formed was studied and the electrical responses of the NiO-based sensors toward different H2 concentrations were also considered. The sensitivity of the gas sensor increased with the working temperature and H2 gas concentration. The thickness of the NiO thin films was also an important parameter in determining the properties of the NiO films as H2 sensors. It was shown in this study that NiO films have the capability to detect H2 concentrations below 3% in wet air, a feature that allows this material to be used directly for the monitoring of the environment.

Efficient exfoliation of g-C3N4 and NO2 sensing behavior of graphene/g-C3N4 nanocomposite

In this work, graphitic carbon nitride (g-C3N4) nanosheets were prepared and employed to improve the gas sensitivity performance of graphene. g-C3N4 nanosheets (NS-CN) were exfoliated from bulk powder using a proton-enhanced liquid-phase exfoliation method, where the co-ordinate bonds between nitrogen of g-C3N4 and proton H+ of HCl benefit the swelling of bulk and improve the delamination process. The thickness and size of the exfoliated nanosheets were about ∼4nm and 1–2μm, respectively. A slight increment of the bandgap of g-C3N4 was observed after exfoliation. It was found that the proton functionalization of g-C3N4 powder before exfoliation facilitates the production of uniform nanosheets. A certain amount ranging from 0% to 90% of as-prepared g-C3N4 was added to a graphene solution and ultrasonically mixed to prepare a graphene/g-C3N4 nanocomposite (G/NS-CN). The performances of pure graphene-based and nanocomposite-based sensors in sensing NO2 gas were systematically investigated and compared. We found compositing g-C3N4 with graphene significantly enhanced the sensing performance of the graphene sensor. A trade-off effect on sensing response was observed as the weight ratio of NS-CN to graphene in the nanocomposite sensor was changed, suggesting the specific roles of g-C3N4 and graphene in sensing behavior. It was found that the nanocomposite sensor with 15wt% of NS-CN exhibited the best sensing response. The sensor in this optimized composition presented a linear and stable response as well as good recovery toward NO2 gas. The sensing mechanism of the nanocomposite sensor was also proposed.

Synthesis of mesoporous K2O-In2O3 nanowires and NOx gas sensitive performance study in room temperature

In this work, highly crystalline mesoporous In2O3 nanowires (NWs) doped with K2O, ZnCl2 or CaCl2 were synthesized by template-calcined method using SBA-16 as template. The mesoporous K2O-In2O3NWs (INW-K2), which was synthesized by mixing 0.2 mol L−1 In(NO3)3 solution with 0.02 g KNO3 so that In(NO3)3 and KNO3 mass ratio was 30:1, has high density of chemisorbed oxygen. Its diameter is about 4–8 nm and pore size is 3–5 nm. For INW-K2, K2O doped on its surfaces serves as alkaline center and benefits the adsorption and diffusion of acidic NOx. Meanwhile, the INW-K2 provides large number of active centers for gaseous reactions on the surface of the nanowires. Therefore, the gas sensing property of INW-K2 is significantly improved, the response of NOx to 97 ppm is about 151.78 and response time is only 12 s, the detection limitation decreased to 48.5 ppb at room temperature (RT). The highly crystalline mesoporous K2O-In2O3 nanowires might offer a new opportunity for synthesizing multifunctional sensing materials in future.

Gas sensitivity and photocatalytic performance of cuprous oxide with novel morphologies

In this work, Cu2O nanoparticles (NPs) with quasi-spherical and bookmark-like morphologies were successfully synthesized via a new facile solution method. The morphologies of products were characterized to show porous surfaces and the size is as small as approximately 20–50nm. Given the special morphology, Cu2O NPs exhibited superior gas sensitivity to either ethanol or acetone vapors and strong adsorption abilities and high degradation activities for methyl orange under visible-light irradiation. The investigation provided not only a way of synthesizing Cu2O particles with dozens of nanoscale, but also a way of improving its gas sensitivity and catalytic degradation ability.

Enhanced BTEX gas-sensing performance of CuO/SnO2 composite

Series CuO/SnO2 composites for selectively sensing BTEX (benzene, toluene, ethylbenzene, and xylol) designed by a principle of catalytic oxidation were synthesized. The sensing materials were prepared by a facile microwave-assisted approach. The composites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). TEM results reveal that the as-prepared SnO2 are nanoscaled porous particles. For 3mol% CuO/SnO2 composite, the existence of CuO nanoparticles is proved by EDS and HRTEM. Gas sensing results of side-heating sensors display that the CuO/SnO2 composites sensors compared with pristine SnO2 sensor have much better responses to BTEX rather than other VOCs such as ethanol, acetone, methanol, formaldehyde and ammonia. Among these CuO/SnO2 composites, the sensor based on 3mol% CuO/SnO2 composite has the best selectivity and sensitivity for BTEX. At the optimal working temperature of 280°C, the response value of the sensor to 50ppm BTEX are more than 6 times. Excellent gas sensitive performance of 3mol% CuO/SnO2 based sensor to BTEX belongs to the addition of catalyst CuO.

Synthesis of α-Fe2O3 with the aid of graphene and its gas-sensing property to ethanol

The design and synthesis of nanomaterials with high gas sensing property have been given extensive attention to satisfy future societal and environmental needs. Herein, a facile hydrothermal method is developed to prepare the Fe2O3 nanoparticles in the presence of graphene sheets; afterwards, a heat treatment process is performed for producing well-dispersed Fe2O3 nanoparticles along with the elimination of graphene sheets. The investigation on the evolution process reveals that the presence of graphene is critical for not only preventing agglomeration of Fe2O3 nanoparticles but also keeping Fe2O3 nanoparticles in small sizes. The obtained Fe2O3 nanoparticles with the aid of graphene present excellent gas sensitive performance (more than 4.0 times to 1000ppm of ethanol than that of pure Fe2O3 obtained without graphene) toward ethanol, indicating the potential applications as sensor material towards ethanol detection.

Preparation of In<sub>2</sub>O<sub>3</sub>/MWCNTs Nanocomposites and their Gas-Sensing Property to Ethanol

In2O3/multi-walled carbon nanotube (MWCNT) nanocomposites containing different MWCNT contents were synthesized via direct growth of In2O3 nanoparticles on the functionalized MWCNTs. The nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results exhibited that In2O3 nanoparticles with a diameter of approximate 10 nm were densely decorated on the surface of the MWCNTs. The gas sensitive performance of the nanocomposites to ethanol was also investigated. It was found that In2O3/MWCNTs sensor showed much higher response than that of the pure In2O3 sensor. Moreover, the sensing mechanism was discussed.