Controlled growth of ZnO by adding H2O Wang, Huihu; Xie, Changsheng; Zeng, Dawen
Journal of crystal growth,
04/2005, Letnik:
277, Številka:
1-4
Journal Article
Recenzirano
The ZnO properties strongly depends on its shape and structure, thus it is significant to control the growth of ZnO. In this report, the wurtize ZnO particles were synthesized via Zn(CH3COO)2 ...hydrolyzing in methanol using chemical deposition method. The size and shape of ZnO particles were controlled well by adding H2O. Without adding H2O or with little volume ratio of adding H2O/methanol, the ZnO nanoparticle film was synthesized. On increasing volume ratio, the shape of ZnO particles varied from irregular particle, plate into regular cone with the size changing from nano-scale into micro-scale. Moreover, the height of the cone decreased as the volume of adding HO increased. These clearly demonstrate that HO could control the growth of ZnO particles.
•Scalable synthesis of 1–3 layers SnS2 with a typical size of 200–300 nm.•The 2D SnS2 based NH3 sensors exhibited high gas sensing at room temperature.•The sensing mechanism behind the largely ...enhanced sensitivity was also revealed.
Recently, tin sulfide (SnS2) with different structures has been widely used for NH3 detection. However, the low sensitivity and high operating temperatures severely limit its potential application. Here, we demonstrate enhanced room temperature NH3 sensing using scalable SnS2 nanosheets, which are facily synthesized by chemical exfoliation. Structural and morphological characterization revealed that the as-prepared two-dimensional (2D) SnS2 is composed of 1–3 layers (0.6 nm–1.8 nm). Compared with the bulk SnS2 that shows none response to NH3, the gas sensors based on the as-prepared 2D SnS2 exhibit excellent ammonia gas sensing performance at room temperature. When exposed to 500 ppm ammonia, the response time, i.e., 16 s, is the shortest among all the NH3 gas sensors based on transition metal dichalcogenides (TMDs). We attribute this enhanced sensitivity mainly to the effective NH3 gas adsorption is dominated by the high energy defect sulfur vacancies on the surface of 2D SnS2. The easily synthesized 2D SnS2 with sulfur vacancies are expected to find a vast application in gas sensing.
•ZIF-8 and ZIF-71 with the pore sizes of 0.34nm and 0.48nm were successfully coated on ZnO nanorods surface, respectively, which came from vertically oriented ZnO nanorod arrays.•It was found that ...the pore size is critical for enhancing the selectivity of the ZnO@ZIF nanorod array sensors for the detected gas whose molecular kinetic diameters are smaller than the pore size of ZIF.•Sensors based on ZnO@ZIF-71 NRs have a pre-concentrated role for ethanol and acetone, and obviously enhanced their response.
Recently, a metal-organic framework (MOF) coating method has been reported for improving the poor gas selectivity of metal oxide semiconductor (MOS) gas sensor. However, the correlation between MOF’s pore size and the size of gas molecule is not fully discussed, as well as gas-sensing properties to gases with similar molecular size. In this paper, two zeolitic imidazolate frameworks (ZIFs) with different pore sizes (∼3.4Å for ZIF-8, ∼4.8Å for ZIF-71) are synthesized on the surface of ZnO nanorod arrays to form a ZnO@ZIF core-shell structure, where ZIFs act as gas molecule sieve membrane that shields ZnO from gas molecules larger than the pore size of ZIFs. Hydrogen, ammonia, ethanol, acetone and benzene (molecular size in the range of 2.89–5.85Å) are selected as testing gases. The ZnO@ZIF-8 sensor exhibited a clear response to smaller molecules of hydrogen and ammonia rather than larger molecules of ethanol, acetone and benzene. While the ZnO@ZIF-71 sensor only exhibited inhibited response to benzene, which has the largest molecular size. These results indicate that the selectivity of ZnO gas sensor can be regulated by surface MOF coating with specific pore size. But this pore size depending selectivity regulation method is insufficient effective for targeting gases with similar molecular sizes, which may be improved by further modification on MOF materials for selective adsorption in our future work.
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•Ternary NiO-SnO2-rGO nanocomposites was successfully prepared for room-temperature NO2 sensing.•Largely enhanced response and fast recovery rate based on ternary nanocomposites were ...obtained.•The room-temperature sensing mechanism based on the ternary nanocomposites was proposed.•The potential application of ternary nanocomposites in room-temperature NO2 sensing was shown.
Recently, metal oxide semiconductors (MOS)-reduced graphene oxide (rGO) nanocomposites have attracted great attention for room-temperature gas sensing applications. Here, to further improve the room-temperature NO2 sensing properties of NiO-rGO, ternary NiO-SnO2-rGO nanocomposites was successfully prepared. The gas-sensing studies revealed that the ternary nanocomposites exhibited a remarkably higher response to NO2 at room temperature, and the response of the ternary nanocomposites to 60ppm NO2 is 10 times larger than that of the NiO-rGO under the circumstance of the equal specific surface area, indicating the important role of heterojunction. Significantly, the recovery rate of ternary nanocomposites was also accelerated compared to the bare NiO and the NiO-rGO. Here, we hope this work could provide a proper approach for further improvement of MOS-rGO based nanocomposites with even higher sensing performances.
Flexible pressure sensors as electronic skins have attracted wide attention to their potential applications for healthcare and intelligent robotics. However, the tradeoff between their sensitivity ...and pressure range restricts their practical applications in various healthcare fields. Herein, a cost‐effective flexible pressure sensor with an ultrahigh sensitivity over an ultrawide pressure‐range is developed by combining a sandpaper‐molded multilevel microstructured polydimethylsiloxane and a reduced oxide graphene film. The unique multilevel microstructure via a two‐step sandpaper‐molding method leads to an ultrahigh sensitivity (2.5–1051 kPa−1) and can detect subtle and large pressure over an ultrawide range (0.01–400 kPa), which covers the overall pressure regime in daily life. Sharp increases in the contact area and additional contact sites caused by the multilevel microstructures jointly contribute to such unprecedented performance, which is confirmed by in situ observation of the gap variations and the contact states of the sensor under different pressures. Examples of the flexible pressure sensors are shown in potential applications involving the detection of various human physiological signals, such as breathing rate, vocal‐cord vibration, heart rate, wrist pulse, and foot plantar pressure. Another object manipulation application is also demonstrated, where the material shows its great potential as electronic skin intelligent robotics and prosthetic limbs.
Compared with other microstructured flexible pressure sensors, this unique multilevel microstructure fabricated via a two‐step sandpaper‐molding method exhibits ultrahigh sensitivity and can detect subtle and large pressure over an ultrawide testing range, which can cover the entire expected pressure regime for practical applications. This sensor is promising for applications in wearable electronics and human health monitoring.
•The 2D WS2 nanosheets decorated with TiO2 QDs was prepared for the first time, which showed enhanced stability in the air.•The TiO2 QDs/WS2 nanohybrids based NH3 sensors exhibited the higher ...performance gas sensing, compared to the bare WS2.•The reason behind the largely enhanced sensitivity and the excellent stability of TiO2 QDs/WS2 nanohybrids was also revealed.
Recently, Tungsten disulfide (WS2) nanosheets are widely used for room-temperature NH3 sensing. However, the lower sensitivity and the microstructural instability severely limit its potential application. Here, few- or mono-layer WS2 nanosheets decorated with different amounts of TiO2 quantum dots (QDs) were successfully prepared for room-temperature NH3 sensing. The gas sensing studies revealed that the nanohybrids exhibited significantly enhanced sensitivity to NH3 at room temperature. The response of nanohybrids with the optimal molar ratio to 250ppm NH3 is nearly 17 times higher than that of the pristine WS2. Especially, the TiO2 QDs decorated WS2 nanohybrids showed almost no decline in sensitivity after several testing cycles, indicating the long-term stability of the nanohybrids-based sensing materials. The sensing mechanism based on the largely enhanced sensitivity and the long-term stability of nanohybrids also discussed in detail. It was believed that the largely enhanced sensitivity was attributed to the effective electron transfer between the WS2 and the TiO2 QDs through SOTi bonding, which was confirmed by XPS analysis. We hope that this work could help us to further understand the QDs sensitization mechanism and could provide a guideline to explore more transition metal dichalcogenides-based gas sensors with even higher sensing performances.
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•A novel flexible gas sensor based on 2D WS2 was reported for the first time.•The 2D WS2 with S defects can enhance NH3 gas sensitivity performance effectively.•Our devices can ...realize multifunctional sensing detection.
For the important applications of gas identification related to specific diseases in healthcare, flexible gas sensors have attracted more attention. Among them, two-dimensional transition metal dichalcogenides (2D TMDs) have been known as good promising flexible gas-sensitive materials. While how to tightly attach 2D materials on flexible substrates is still challenging. Here, we propose an enhanced room-temperature flexible paper-substrate sensors based on 2D tungsten disulfide (WS2) with S defects, which are facilely synthesized by chemical exfoliation and vacuum filtration method. Structure characterization shows that most of the as-prepared 2D WS2 are within 3 layers. Spectroscopic characterization proves the existence of S defects on the surface of 2D WS2 produced by chemical exfoliation. The room-temperature (25 °C) NH3 gas sensitivity results show that the response intensity of 2D WS2 with rich S defects is nearly three times higher than the highly crystalline 2D WS2. The results of the flexible gas sensitivity indicate the fast response and high stability of our devices in breathing detection and bending experiments. Furthermore, the devices can effectively distinguish bending stress changes and gas-sensitive response signals at the same time, realizing multifunctional sensing detection. Our work will be a reference for fabricating flexible sensors based on 2D materials.
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► Growth of BiOCl nanosheets in EG medium was experimentally revealed. ► Oriented attachment mechanism governed formation of single crystalline BiOCl. ► The exposed facets of BiOCl ...nanosheets were {110} planes. ► The samples could efficiently degrade MO irradiated either by UV or by Vis. ► The high efficiency was associated with the exposed {110} facets of BiOCl.
The formation mechanism of nanosheet assembled BiOCl nanostructures in non-aqueous solvothermal system was investigated through time series experiments. The products obtained at different reaction times were characterized by XRD, SEM and (HR)TEM techniques. The photocatalytic property of the samples was measured by decomposing the organic dye of methyl orange. The ability to generate hydroxyl radicals for the samples was also measured by photoluminescence method using coumarin as fluorescence probe molecules. It was revealed that oriented attachment was responsible for the slow transformation of BiOCl from polycrystalline nanoparticles to single crystalline nanosheets. The role of the solvent ethylene glycol and the interaction with the other species during the oriented attachment growth of the BiOCl nanosheets was discussed. The photocatalytic activity tests demonstrated that the BiOCl nanostructures could efficiently decompose methyl orange under either UV light irradiation or visible light irradiation. The high photodegradation efficiency was associated with the atomic arrangement of exposed {110} facets.
In this work, different sizes of α-Fe2O3 hollow cubic structures are prepared by calcination of Prussian blue templates with different sizes. Furthermore, the transformation mechanism is also ...investigated by applying different conversion temperatures to the same Prussian blue template. In specific, Prussian blue initially transformed into β-Fe2O3 and γ-Fe2O3, then transformed into α-Fe2O3 to reach the final thermodynamically stable stage. By aiming H2S as target gas, the gas-sensing performance of the pure phase α-Fe2O3 hollow cubes with different sizes was explored, which demonstrate high sensitivity to H2S gas at room temperature, as well as ideal stability and selectivity. Interestingly, the response value of four sizes of α-Fe2O3 to 5 ppm H2S are 1.17, 2.44, 4.67 and 1.15 respectively, which indicates that the gas-sensing response has a trend from rise to decline as the cube size increases. For α-Fe2O3 cube with size of 800 nm, it presents the optimized sensitivity. Finally, characterizations such as BET, XPS and PL reveal that with increment of α-Fe2O3 cube size, the specific surface area increases while the oxygen vacancy density decreases, whose joint influence is the mechanism for the optimized sensitivity of 800 nm α-Fe2O3 cube.
•Controllable synthesis of different sizes of α-Fe2O3 hollow.•Kinetic transformation of PB to β-Fe2O3 and γ-Fe2O3, then to the most thermodynamically stable α-Fe2O3.•Novel selectivity, repeatability and stability of α-Fe2O3 hollow cubes’ gas sensing performance to H2S at room-temperature.•Insight into the gas sensing mechanism of the joint effect of oxygen vacancies and specific surface area.
The desorption part of MOX's response curves to gases represents the dynamic information of gas desorption and oxide recovery on the sensitive layer. It contains abundance information and lacks to be ...well investigated. This paper proposes a feature extraction method from the desorption part of response curves in phase-space. The method extracts only one feature, min( dS t / dt )/max( S t ), which is found to be able to represent the recovery profile. This feature could be extracted in the front part of the recovery process. Besides, it is also found that this feature does not change with the reacting time (of the reaction between a sensor and a sample) changing. A dataset was used in the paper, which was consisted of 189 measurements of 9 VOCs by 5 TGS gas sensors at three concentrations. A common feature extraction method that extracted integral in phase-space was used as a comparison in sort classification with the proposed method. The correct recognition rates of Fisher Discriminant Analysis (FDA) with the proposed method and the phase-space integral extracting method were 91.5% and 79.9%, respectively. The results show that the proposed method is an efficient feature extraction method of the recovery profile of response curves.
