•ZnO/g-C3N4 composite was synthesized through ultrasonic mixing and subsequent calcination process.•10 wt% g-C3N4 loaded ZnO exhibits excellent NO2 sensing at room temperature under 460 nm light ...illumination.•The excellent sensing performance can be attributed to the absorbance of g-C3N4 and charge separation between ZnO and g-C3N4.
In this work, 2D/2D ZnO/g-C3N4 heterojunction composite was synthesized through an ultrasonic mixing and subsequent calcination process. The gas-sensing performance to NO2 was investigated at room temperature activated by visible/ultra-violet LED light sources. Noticeably, when ZnO/g-C3N4 composite is illuminated by 460 nm light, it exhibits the highest response of 44.8 to 7 ppm NO2, and the response and recovery time is 142 and 190 s, respectively. Furthermore, it possesses excellent repeatability and selectivity to NO2, and the limit of detection is 38 ppb. In addition, the effect of humidity on the sensing performance under visible light was also investigated. The excellent gas-sensing performance is attributed to the absorbance of g-C3N4 in the visible light region and the charge separation at the interface between ZnO and g-C3N4.
•A novel hierarchical litchi-like In2O3/Carbon dot hybrid was synthesised, and the preparation was environment friendly and simple.•The as-prepared sensors exhibited outstanding sensitivity and ...selectivity to NO2 with robust stability.•The fabricated sensors showed a low NO2 detection limit of 50 ppb.
Carbon dots, being one of the zero-dimensional carbonaceous nanomaterials, possess numerous fancy characteristics in physics and chemistry, such as quantum size, abundant edges and functional groups, and high electrical conductivity, which are beneficial to gas sensing properties. It also has the advantages of low-cost and environmental-friendly preparation. In this work, carbon dots were employed as dopants for modification of hierarchical litchi-like In2O3 nanospheres via a facile and environment-friendly hydrothermal approach to improve the gas sensing properties. As-obtained products were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, etc. Gas sensing properties of In2O3/carbon dots and pristine In2O3 were investigated systematically. As expected, the sensors based on the In2O3/carbon dots displayed enhanced response at working temperature of 50 °C, which was 4 times as high as the sensors based on the pristine In2O3. The sensors presented excellent selectivity. The enhancement of sensing properties should be mainly attributed to the heterojunctions constructed across the interface between the In2O3 and carbon quantum dots.
Early diagnosis and monitoring of SARS-CoV-2 virus is essential to control COVID-19 outbreak. In this study, we propose a promising surface enhanced Raman scattering (SERS)-based COVID-19 biosensor ...for ultrasensitive detection of SARS-CoV-2 virus in untreated saliva. The SERS-immune substrate was fabricated by a novel oil/water/oil (O/W/O) three-phase liquid-liquid interfaces self-assembly method, forming two layers of dense and uniform gold nanoparticle films to ensure the reproducibility and sensitivity of SERS immunoassay. The detection was performed by an immunoreaction between the SARS-CoV-2 spike antibody modified SERS-immune substrate, spike antigen protein and Raman reporter-labeled immuno-Ag nanoparticles. This SERS-based biosensor was able to detect the SARS-CoV-2 spike protein at concentrations of 0.77 fg mL−1 in phosphate-buffered saline and 6.07 fg mL−1 in untreated saliva. The designed SERS-based biosensor exhibited excellent specificity and sensitivity for SARS-CoV-2 virus without any sample pretreatment, providing a potential choice for the early diagnosis of COVID-19.
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•A new SERS-based COVID-19 biosensor was developed for ultrasensitive detection of SARS-CoV-2 virus.•A novel three-phase interfaces self-assembly method was applied for fabricating the SERS-immune substrate.•The SERS-immune substrate assembled by highly dense and uniform Au NPs can improve the reproductivity of SERS immunoassay.•The biosensor can detect the SARS-CoV-2 spike protein at ultra-low concentration of 6.07 fg mL−1 in untreated saliva.•The biosensor exhibits excellent specificity and sensitivity for SARS-CoV-2 virus without any sample pretreatment.
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NiO/ZnO composites were synthesized by decorating numerous NiO nanoparticles on the surfaces of well dispersed ZnO hollow spheres using a facile solvothermal method. Various kinds of ...characterization methods were utilized to investigate the structures and morphologies of the hybrid materials. The results revealed that the NiO nanoparticles with a size of ∼10nm were successfully distributed on the surfaces of ZnO hollow spheres in a discrete manner. As expected, the NiO/ZnO composites demonstrated dramatic improvements in sensing performances compared with pure ZnO hollow spheres. For example, the response of NiO/ZnO composites to 100ppm acetone was ∼29.8, which was nearly 4.6 times higher than that of primary ZnO at 275°C, and the response/recovery time were 1/20s, respectively. Meanwhile, the detection limit could extend down to ppb level. The likely reason for the improved gas sensing properties was also proposed.
•One-dimensional SnO2 and a series of Ru-doped SnO2 nanostructures were synthesized by electrospinning.•The grain size of the SnO2 nanocrystal were greatly decreased by Ru doping.•The sensors based ...on 2 mol% Ru-doped SnO2 nanofibers showed greatly enhanced gas sensing performance.•The detection limit for acetone gas of the SnO2 sensor was reduced after 2 mol% Ru doping.
We report the Ru doping effect on the gas-sensing properties of SnO2 nanofibers for acetone detection in this paper. For this purpose, pure and 1, 2, 3 mol% Ru-doped SnO2 nanofibers were prepared through electrospinning technique combined with calcination treatment. The fibrous microstructure of these nanofibers were maintained and the grain size of the SnO2 nanoparticals were decreased from 9.2 nm (pure) to 5.1 nm (3% Ru-doped) after Ru doping. In order to confirm that Ru doping is an effective way to improve the gas sensing properties of the SnO2-based gas sensor, the gas sensing properties of the sensors based on pure and Ru doped SnO2 nanofibers were investigated systematically. The results showed that the response to 100 ppm acetone of 2 mol% Ru-doped SnO2 nanofibers was 118.8, which was 12 times higher than that of pure SnO2 nanofibers. In the end, the role of Ru in the gas sensing mechanism of SnO2 nanofibers was analyzed according to the results of the X-ray photoelectron spectroscopy (XPS) and Ultraviolet photoelectron spectroscopy (UPS).
•Hollow Sn-doped NiO nanofibers are synthesized through a facile electrospinning approach.•The Sn-doped NiO sensor with suitable Sn content (6 at%) shows the highest gas response to triethylamine.•Sn ...doping concentrations can significantly influence the resistance of sensors in air and in target gas under different RH.•The resistances of the sensor change slightly in target gas under different RH with suitable Sn doping content (6 at%).
High stable triethylamine gas sensors under different relative humidity are highly desirable in order to correctly detect the concentrations of target gas. In this study, a series of Sn-doped NiO hollow nanofibers were prepared through a facile electrospinning process followed by heat treatment. Sn doping could inhibit the crystal growth, and the crystal sizes would decrease with the increase of Sn doping concentration. Gas sensing investigation indicates that Sn doping could significantly enhance the gas response towards triethylamine at a relative low temperature. Especially, the gas sensor exhibits the highest response to triethylamine when the doping content of Sn reaches to 6 at%. The response value is about 16.6–100 ppm triethylamine, and it is ∼9.2 times higher than that of pure NiO nanofibers at the same operating temperature. In addition, the resistances of the gas sensors with different doping contents of Sn would change differently in air or in target gas under variable relative humidity. The resistances in target gas are almost unchanged with the increase of relative humidity with the Sn doping content of 6 at%. It is reasonable to speculate that Sn doping can heavily alter the surface state of NiO nanofibers, which is beneficial for the improvement of the gas response and humidity dependence properties.
•Flower-liked ZnO architectures and Ce doped ZnO materials were successfully synthesized by a simple precipitation route.•Ce doping can improve the sensing performance of ZnO-based gas sensor by ...adjusting the proportion of oxygen species.•0.5 at% Ce/ZnO exhibited the highest response to ethanol and the response value was about 72.6 to 100 ppm ethanol.
Flower-liked ZnO architectures and Ce doped ZnO materials with different amounts (0.2, 0.5, 1.2 and 2 at% Ce) were successfully synthesized by a simple room-temperature precipitation route. As the gas sensing materials, their sensing performance were investigated systematically. The results indicate that Ce doping can improve the performance of ZnO sensor. The ZnO doped with 0.5 at% Ce exhibited the highest response to ethanol at the operating temperature of 300 °C, and the response value was about 72.6–100 ppm ethanol. With Ce doping, the proportions of oxygen vacancy and chemisorbed oxygen species were increased obviously, which could greatly promote the gas sensing properties of surface resistance-type metal oxide semiconductors. Thus, the doping of flower-liked ZnO with Ce should be a promising approach for designing and fabricating the high performance gas sensor.
•ZnO/SnO2 composites hollow spheres with uniform size were successfully synthesized through a three-step hydrothermal routine.•Such ZnO/SnO2 composites as sensing material presented excellent sensing ...properties to ethanol gases and the response to 30ppm ethanol was nearly 7-times higher than that of pristine SnO2.•The gas sensor showed a low detection limit to ethanol even to ppb-level.•The fabricated sensor showed commendable long-stability even after 200 cycle tests.
Heterostructure ZnO/SnO2 composites material with a hollow nanostructure was synthesized by solution method. The obtained products were characterized by X-ray diffraction (XRD), field-emission electron scanning microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results indicated that ZnO nanoparticles could be clearly observed on the surface of SnO2 hollow spheres and the surface oxygen chemisorbed ability of ZnO/SnO2 composites was much higher than that of single-component SnO2. The as-synthesized composites as sensing material was investigated and the results revealed that such composites had an excellent sensing performance to ethanol, and the response to 30ppm ethanol was nearly 7-times higher than that of pristine SnO2 at its optimum temperature. Moreover, it is noteworthy that such gas sensor showed a low detection limit (ppb-level). The enhanced sensing properties might be attributed to the formation of heterojunction and synergistic effect between SnO2 and ZnO.
•Polyaniline is composited with MoS2 nanosheet-coated electrospun SnO2 nanotubes.•A highly selective NH3 sensing platform is developed at room temperature.•Good sensing performance of excellent ...selectivity, high response, favorable repeatability and acceptable flexibility.•The mechanism connected with the enhancing properties was also investigated and presented.
In this work, we developed a NH3 gas sensor based on polyaniline (PANI) composited with MoS2 nanosheet-coated SnO2 nanotubes (PMS) via electrostatic spinning, hydrothermal route and in-situ polymerization technique. The morphologies, nanostructures and compositions of the materials were obtained from X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field emission scanning electron microscopy (FESEM), Transmission electron microscope (TEM) and Brunauer-Emmett-Teller method (BET). Thanks to nanostructure and the synergistic properties of PANI and MoS2/SnO2, the designed PMS gas sensor exhibited response signal of 10.9 towards 100 ppm NH3 at room temperature and a low detection limit of 200 ppb with good response-recovery time, good repeatability, acceptable flexibility and excellent selectivity. This study offers a versatile platform to modify PANI for highly selective detection of NH3 gas sensor at room temperature.
•We successfully introduce the ZIF-8 encapsulated noble metal Pt NPs into the 3DIO ZnO structure. The 3DIO Pt/ZnO materials obtained can be expanded to fabricate other kinds of small–sized and ...well–dispersed noble metal NPs modified 3DIO structures.•The 3DIO structure provides fast pathway for H2S molecules and large surface area for surface-related reactions, the Pt NPs act as high-performance catalyst. The as-prepared sensor effectively enhances the sensitivity as well as the recognition ability to trace-level H2S.•An optimized response of 11.2 can be achieved for 1 ppm H2S and a detection limit down to 25 ppb are achieved in ZIF-8 driven 3DIO Pt/ZnO sensor, which is 5.7-folds higher and 7.5 times lower than that of pristine 3DIO ZnO sensor, respectively.
The effective detection of trace-level H2S gas is not only necessary for personal safety but is also important for understanding various physical and pathological processes in human biological systems. In this work, three-dimensional inverse opal (3DIO) ZnO sensors modified with small and well-dispersed Pt nanoparticles (NPs) are presented for ultra-low concentration H2S detection. The 3DIO ZnO skeleton, which is prepared through a simple self-assembly template method, provides fast diffusion pathways for H2S molecules and a large surface area for surface-related reactions. The optimal metal–organic framework (MOF)-derived 3DIO Pt/ZnO sensor exhibits an excellent response to trace H2S (11.2 at 1 ppm), a low detection limit (25 ppb), superior selectivity, and stability. The enhanced gas sensing performance can be attributed to the size effect of the Pt NPs and the rational design of the MOF-derived 3DIO Pt/ZnO nanomaterial. These results indicate that the strategy of combining the MOF-derived small and well-dispersed noble metal NPs with the 3DIO structure can efficiently improve the gas sensing properties for trace-level target gas determination. This method can likely be extended to similar systems based on 3DIO materials.
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