Display omitted
•Pt quantum dots catalyze the generation of massive reactive oxygen species.•The nanocomposites exhibited the higher gas-sensing performance of ammonia compared with WS2 NSs.•The PtS ...interface bonds play the pivotal role of promoting electrons transfer.•The inherent mechanism behind the largely enhanced sensitivity was also revealed.
As a typical two-dimensional (2D) layered transition metal dichalcogenides (TMDs), tungsten disulfide (WS2) has been considered as a promising sensing material for room-temperature NH3 detection. However, the bulk WS2-based room-temperature NH3 sensors can hardly recover to its initial state after turning off gas. Although the recovery rate of bulk WS2 was accelerated by thinning method, the response of few- or monolayer WS2 nanosheets (NSs) to NH3 was sharply decreased. Here, in premise of keeping fast recovery rate, few- or monolayer WS2 NSs modified with Pt quantum dots (QDs) were prepared for room-temperature NH3 detection, which exhibited significantly enhanced sensing properties with fast recovery speeds. Especially, the response of nanocomposite to 250 ppm NH3 is nearly 10 times than that of WS2 NSs, which could be attributed to the significantly decreased initial conductivity caused by electrons flowing from higher Fermi level of Pt QDs to that of WS2 NSs and the higher catalytic activity. Furthermore, the PtS bonds confirmed by XPS results could benefit electrons transfer between the interface. We hope that the 0D/2D heterostructure system in this work could provide a direction to improve sensing properties of 2D TMDs-based room-temperature sensors.
We studied plain TiO
2
and CdS/TiO
2
nanocomposite photoelectrode by testing their photocurrent response in gas phase. The CdS/TiO
2
nanocomposite photoelectrode was prepared by the technology of ...screen printing and the successive ionic layer adsorption and reaction process. In comparison with the plain TiO
2
photoelectrode, the CdS/TiO
2
nanocomposite photoelectrode showed an extraordinary enhancement on the photocurrent amplitude. Under the irradiation of UV light and under 1, 5, and 10 V bias, respectively, the photocurrent amplitude of CdS/TiO
2
nanocomposite photoelectrode was 37, 95, and 151 times higher than that of the plain TiO
2
. To explain these distinctive phenomenon, we conclude that CdS not only acts as a sensitizer in the CdS/TiO
2
nanocomposite, but also acts as a hole capturer. This conclusion was clearly demonstrated by the subsequent reproducible photocurrent response experiments of the on–off cycles of illumination.
It is well known that the metal atoms of metal oxide semiconductor (MOS) exhibit significant activity in gas sensing. However, limited by the shielding effect of the outer oxygen atom layer, layered ...MoO3 is often difficult to show ideal gas adsorption activity. Hence, the MoO3 microporous nanoflowers (MPNFs) assembled by porous two-dimensional nanosheets were successfully synthesized and exhibited excellent gas sensing performance to H2S, and the response was 7.2 times higher than that of simple MoO3 nanosheets. The abundant pores of MoO3 MPNFs were due to the influence of the crystal cell shrinkage effect on the atomic arrangement, while the significantly enhanced gas sensing performance was attributed to the positive effect of the microporous structure on gas diffusion and the exposed edge Mo atoms. This was confirmed by DFT calculation results that, compared to the Mo atoms on the surface of MoO3 nanosheets, the Mo atoms around the pores were exposed because they broke through the shielding effect of the oxygen atom layer and exhibited higher adsorption activity for H2S and O2 molecules. Therefore, this work can shed a light on the design of high-performance gas sensors based on metal oxides.
Display omitted
•The MoO3 microporous nanoflowers (MPNFs) were successfully synthesized and used for H2S gas sensing.•The crystal cell shrinkage effect was used to explain the formation mechanism of pores.•The shielding effect of oxygen atoms was used to explain the sensing enhancement mechanism of MoO3 MPNFs.•DFT calculations revealed that Mo atoms at the edges exhibit significantly enhanced gas adsorption activity.
Hierarchical porous (HP) nanostructures of metal oxide have been attracting increasing attention due to its fast response and high sensitivity in sensors application. However, the controllable ...synthesis of HP structures is rather complex and these fragile structures can be easily destroyed during fabrication process of sensors. To solve this problem, a novel integration of materials synthesis and sensors manufacture was successfully realized by introducing the topological transformation approach (TTF) on basis of a facile, low-cost, conventional process including screen printing and calcination. By employing this method, HP-SnO2 micro-rods assembled by nanoparticles were prepared in situ on the co-planar sensors’ surface. The formation mechanism of HP-SnO2 was mainly attributed to a decomposition reaction followed by gas escaping process. As expected, the as-prepared HP-SnO2 sensor exhibited not only fast response (∼4.3s), which was one-tenth of response time of the gas sensor based on SnO2 nanoparticles, but also high sensitivity (Ra/Rg=3.86) to formaldehyde at 1ppm. The excellent gas-sensing properties can be indeed ascribed to the HP structure which was favorable for gas diffusion and sensing reactions. This work renders great potential in the fabrication process of gas sensor with HP structure simply by a TTF method which can be further applied in indoor pollution detection.
SnS2 has been widely studied as a gas sensing material due to its special layer stacking structure. However, high baseline resistance and poor sensitivity at low operating temperatures remain a ...challenge. Herein, substitute doped Ce–SnS2 was effectively prepared by a facile solvothermal method, the interlayer spacing of Ce–SnS2 was significantly enlarged compared with that of pristine SnS2 and demonstrated outstanding gas sensing performance for NO2. At a low temperature of 100 °C, it exhibited a significant gas sensing response to 500 ppb NO2, with a response value of 1.67, while pristine SnS2 showed no gas sensing response. The gas sensing enhancement mechanism was revealed by DFT, the synergistic effect of the introduction of highly active Ce sites and interlayer engineering caused by the doping of Ce improved the gas sensing performance of Ce–SnS2. This study not only provides a potent means for enhancing the gas sensing capabilities of SnS2 sensors, but also opens up new horizons for the interlayer engineering of transition metal dichalcogenides (TMDs) material.
•The Ce–SnS2 nanoflowers with controllable interlayer spacing were synthesized to detect ppb–level NO2.•Ce doping into SnS2 becomes a highly active site, enhancing the adsorption capacity of NO2.•The expanded interlayer spacing promotes the diffusion of NO2 molecules between the interlayers.•The synergistic effect of highly active Ce sites and interlayer engineering enhances the gas sensing performance of NO2.
ZnO nanorod-bundle thin films have been synthesized by a simple self-assembly method with the aid of F
127 (EO
106–PO
70–EO
106) triblock copolymer. Their morphologies and crystal structures were ...characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM). SEM results showed that films were composed of a lot of bundles, which comprised nanorods with the diameter of about 10 nm. The possible formation mechanism of ZnO nanorod-bundle structures is proposed. Gas-sensing property of thin films, to alcohol, was also detected. It was also found that the sensitivity, to 100 ppm alcohol, of ZnO nanorod-bundle thin films was higher than that of ZnO nanoparticle thin films. The results showed that the triblock copolymer, served as the surfactants, could effectively control the morphologies and the aspect ratio of nano-ZnO, and then improve its gas-sensing property.
High sensitivity and selectivity of C-doped WO 3 gas sensors are reported in this paper. C-doped WO 3 is synthesized by a facile infiltration and calcination process using the cotton fibers as ...templates. The response of C-doped WO 3 sensor toward toluene (50 ppm) and xylene (50 ppm) reach 91 and 199, respectively. By comparing the response of C-doped WO 3 sensor toward various indoor noxious gases (toluene, formaldehyde, ethanol, methane, benzene, and xylene), distinctive selectivity toward toluene and xylene is found. In addition, C-doped WO 3 exhibits relative hygro-stability, differing from traditional gas sensor material. The results indicate that C-doped WO 3 has good potential in practical applications, due to its remarkable performance and facile synthesized methods.
•Reasons for room-temperature difficult recovery of WS2 sensors for NH3 detection.•The excellent recovery within 271.9s was observed for single-layer WS2 sensor.•The recovery time of WS2 sensor has a ...anti-linear relation with number of layer.
Display omitted
Tungsten disulfide (WS2), as a representative layered transition metal dichalcogenides (TMDs), is expected as a promising candidate for high-performance NH3 sensor at room temperature. Unfortunately, the common WS2 based NH3 sensors are difficult to recovery at room temperature, which severely limits its application. Hence, how to improve recovery has become an urgent problem to be solved. Herein, we prepare five types of WS2 nanosheets with different layer numbers from bulk to monolayer, and find that the recovery time of NH3 gas sensor is rapidly linear shorten as the number of layers decreasing. Through the first-principles calculation of the interaction between NH3 and WS2 substance, the different binding energy between ammonia and the surface (−0.179eV) and interlayer (−0.356eV) of layered WS2, as well as the different electron transfer way, should be responsible for the difficult recovery rate of various WS2 samples. Therefore, reducing the number of layer of WS2 is a promising approach to speed up recovery. Based on this conclusion, we successfully prepare a fast recoverable ammonia gas sensor based on single layer WS2, which exhibits exciting fast recovery within 271.9s at room temperature without any condition. Moreover, our work also can act as a reference for other gas detection of TMDs based gas sensor to improve the gas performance at room-temperature.
Zijie Yan 1 and Yu Wang 2 and Dawen Zeng 3 and Douglas B. Chrisey 4 and Min Liu 5 1, Department of Chemical & Biomolecular Engineering, Clarkson University, Potsdam, NY 13699, USA 2, School of ...Materials Science and Engineering, Nanchang University, Nanchang 330029, China 3, Department of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China 4, Department of Physics and Engineering Physics, Tulane University, New Orleans, LA 70118, USA 5, Department of Electrical and Computer Engineering, The University of Toronto, Toronto, ON, M5S 3G4, Canada Received 16 September 2015; Accepted 16 September 2015; 4 November 2015 This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Core-shell heterostructures of metal oxide semiconductor (MOS) and metal organic framework (MOF) improve gas-sensing properties due to the MOF's molecular sieving effects. However, the selection of ...MOF is limited by the requirement of identical metal element in MOF to that in MOS, which is crucial for valid interface adhesion. In this paper, WO3@ZIF-71 (zeolitic imidazolate framework) structure with different metal elemental components (W and Zn) was fabricated by a step-by-step (SBS) approach. As a result, ZIF-71 was uniformly coated on the surface of WO3. In order to explore the influence of ZIF-71 (pore size: 4.8 Å), the gas sensitivity of WO3 and WO3@ZIF-71 were tested. Different kinetic diameters gases: H2S (3.62 Å), CH3COCH3 (4.6 Å), CH3CH2OH (4.53 Å), NO2 (5.8 Å) were selected as testing gas. Gases with small molecules (H2S, CH3COCH3 and CH3CH2OH) can pass through the membrane of ZIF-71 and contact with WO3, while larger ones (NO2) were blocked outside the membrane. Excitingly, the response of WO3@ZIF-71 toward H2S gas was significantly improved, which soars from 2.24 of 20 ppm for pure WO3 to 19.12 for H2S at 250 °C, increased about 9 times. These results indicate that the MOS@MOF core-shell structure can be synthesized by the SBS method without the restriction of the same metal elements in MOS and MOF, which is also an effective approach to regulate the selectivity and sensitivity of the MOS@MOF gas sensor.
Display omitted
•Flower-like WO3@ZIF-71 is successfully synthesized.•ZIF-71 was uniformly coated on the surface of WO3 with different metal elemental components via a step-by-step approach.•The WO3@ZIF-71 nanorod gas sensor showed 9 times enhanced response toward H2S at 250 °C.
PDF
